October 2019 Volume 97 | Issue 10
Optimisation-driven conceptual design
Balancing act
Health and safety interventions
Fiona Cobb, author of the Structural Engineer’s Engineer’ s Pocket Book , talks life, work
and her approach to conservation projects
Designing for health and wellbeing
Upfront 5 Editorial 6
News
Features 8
8
Next-generation buildings: wired for health and wellbeing
Professional guidance 16 Business Practice Note No. 28: Making a health and safety intervention 18 Why it pays to be able to demonstrate
your understanding of structural behaviour
Technical 20 Optimisation-driven conceptual
design: case study of a large transfer truss
Project focus 28 Design of the world’s world’s first sprayed-net,
hyperboloid, lattice ice structure
Opinion 32 Profile: Fiona Cobb 34 Viewpoint: Computational design:
embedding sustainability 38 Verulam
28
At the 42 Diary datesback 9 1 0 2 r e b o t c O
44 Spotlight on Structures 46 Produ Products cts & Services 47 Services Directory 48 TheStructuralEngineer Jobs 50 And finally…
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Y M A L A : r e v o c t n o r F
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Editorial
Upfront
PRESIDENT Joe Kindregan
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Welcome to the new-look The Structural Engineer
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Warners Midlands plc The Maltings, Manor Lane Bourne, Lincolnshire PE10 9PH United Kingdom © The Institution of Structural Engineers. The Structural Engineer (ISSN 1466-5123) is published by IStructE Ltd, a wholly owned subsidiary of The Institution of Structural Engineers. It is available both in print and online. Contributions published in The Structural Contributions Engineer are published on the understanding that the author/s is/are solely responsible for the statements made, for the opinions expressed and/or for the accuracy of the contents. Publication does not imply that any statement or opinion expressed by the author/s reflects the views of the Institution of Structural Engineers’ Board; Council; committees; members or employees. No liability is accepted by such persons or by the Institution for any loss or damage, whether caused through reliance on any statement, opinion or omission (textual or otherwise) in The Structural Engineer , or otherwise. The Institution of Structural Engineers International Internation al HQ 47–58 Bastwick Street London EC1V 3PS United Kingdom t: +44 (0)20 7235 4535 e: mail@istructe.
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MANY OF YOU WILL BE AWARE that AWARE that the Institution has been rolling out a new, modern brand over the course of the year, commencing with the launch of its new website in May. Well, it’s now the turn of The Structural Engineer to to undergo a makeover. ‘Evolution not revolution’ has been our approach so, while we hope you’ll agree that the magazine looks fresh and modern, it also shouldn’t feel too diff erent erent from what you are used to. We’ve also taken this opportunity to consider some of the feedback from
issue. Do have a browse as, with an ever-expanding portfolio of courses, there is likely to be something of interest to most of you. Innovations for 2020 include the launch of an online preparation course for the Chartered Membership Exam. This is the first step of a wider ambition to bring more online training opportunities to members all around the world. Look out for further developments. There is also a range of courses aimed specifically at smaller practices, including: ‘Design of
our most recent survey. You told reader us that you value the ‘Professional guidance’ and ‘Technical’ sections most of all, so we’ve prioritised these by bringing them forward in the magazine. Do let us know what you think of the new look – either on the Institution’s social media channels or by emailing
[email protected] [email protected].. As usual, we bring bring you a wide range range of conten contentt this month, but if there’s a thread running through the issue, it’s one of concern for our future. On page 34, 34, we learn how computational tools have the potential to embed sustainability in everyday projects. This idea of material effi ciency through computational approaches continues in a case study y of optimisation-driven conceptual design (page 20). 20) ).. ) Lastly, Pai Lin Li Travel Award winner, Amy Brander,, considers how engineers can design for the health
retaining walls small practitioners’ and ‘Foundation design forfor small practitioners’. To T o find out more about the Institution’s CPD courses, visit www.istructe.org/cpd-2020 www.istructe.org/cpd-2020..
WE HOPE YOU’LL AGRE AG REE E TH THAT AT TH THE E MAGAZINE LOOKS FRESH AND MODERN
and wellbeing of a building’s occupants (page 8). 8). I hope you enjoy the issue. CPD COURSES Members in the UK and Ireland will have received the Institution’s 2020 CPD course brochure with this his
5 October 2019 | thestructuralengineer.org
AND FINALLY… Due to a production error, the solutions given to September’s September’ s ‘And ‘A nd finally…’ problem were not correct. See page 41 for the correct solutions to the 41 for question.
News
Upfront
Industry news
New RAE report addresses UK engineering priorities
Industry news KICKER:
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A new report from from the National Engineering Policy Centre at the Royal Academy of Engineering – Engineering priorities for our future economy and society – provides advice from the engineering community on critical strategic challenges to the UK’s prosperity and wellbeing. The report is designed to inform the recently announced spending review, and comes in the context of the UK’s impending exit from the EU and potential for a general election. It calls on the government to work with the engineering profession to invest in skills, innovation, digital and traditional infrastructure, and clean energy technologies.
New technical handbooks for Scottish Building Regulations New technical handbooks which explain how to achieve
2017/18 grant-winner Emily Pepper received a best poster prize at the Young Researchers’ Researchers’ Conference 2019
Institution news
Apply now Apply now for an MSc MSc Research Grant
Read the report in full at www.raeng.org.uk/ priorities.. priorities
THE INSTITUTION’S ANNUAL MSc ANNUAL MSc Research Grant scheme is open to applications. Up to five grants of £800 each are available. The gran grants ts by the Inst Instituti itution’s on’s Resear Research ch Fund Fund supp support ort postgr postgradua aduate te resea research rch projects carried out as part of a full-time or part-time MSc degree programme within a department of civil or structural engineering. Applicati cations ons shoul should be made by academ academic ic projec projectt supervis supervisors ors on on behalf behalf of students. The deadline for applications is 19 November. November. To apply for a grant, or find out more about the scheme, visit www. istructe.org/training-and-development/apply-for-grants/mscresearch-grants/ .
Industry news begins with the history of fibrous plaster
historic brous plaster
and then explains forms ofmethods deterioration, current survey standards, of repair and, finally nally,, management of buildings with the material. Fibrous plaster is a form of decorative plasterwork composed of plaster of Paris, reinforced with layers of hessian and secured within a timber framework. It was used to imitate more expensive and time-consuming traditional limebased, hand-modelled plaster pl aster.. Although fibrous plaster is often associated with the Victorian and Edwardian theatre and music hall, it was fitted in a wide range of buildings in the UK. However However,, it is often unrecognised, and has been ignored in technical research and conservation guidance over recent
Historic England has published interim guidance for conservation professionals and building managers responsible for buildings with fibrous plaster in the UK. Historic Fibrous Plaster in the UK: Guidance on its Care and Management was was prepared by Historic England in association with Historic Environment Scotland, Cadw, the Welsh Government, and the Historic Environment Division of Northern Ireland. The guidance focuses on fibrous plaster ceilings, since they present a potential risk of collapse if neglected. It
Find out more at www.gov.scot/ policies/buildingstandards/monitoringimproving-buildingregulations/ .
Industry news
New guidance available on fi
the requirements set out in the Building (Scotland) Regulations 2004 come into force on 1 October. Published by the Scottish Government, the updated versions of the technical handbooks apply to a building warrant submitted on or after 1 October 2019 and to building work which does not require a warrant commenced from that date. The new hand handbook books s include revisions throughout Section 2 (fire) covering fire performance of external cladding systems in high-rise domestic buildings and certain higher-risk non-domestic buildings; provision for means of escape, evacuation alert and signage in high-rise domestic buildings.
CROSS-AUS marks fi rst anniversary Confidential Reporting on Structural Safety – Australasia (CROSS-AUS) was launched on 26 September 2018 by Institution President Faith Wainwright to capture and share lessons learned from structural safety issues which might not otherwise get public recognition. It builds on the success of the long-running CROSS scheme in the UK. Find out more about CROSS-AUS, including how to submit a report, at www.cross-aus.org.au www.cross-aus.org.au.. CROSS-AUS newsletter 2 features the first reports submitted since the launch of the scheme. These cover a range of issues, including competency, communications, documentation, application of Australian Standar Standards, ds, site inspection inspections, s, quality
decades.
control, the influence of parties other than engineers, temporary works and excavation hazards.
Download the guidance at https:// historicengland.org.uk/imagesbooks/publications/historic- fibrousplaster/ .
6 October 2019 | thestructuralengineer.org
Read the newsletter at http://bit.ly/CROSS AUS_NL_ AUS _NL_2 2.
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Pai Lin Li Travel Award 2018
AMY BRA BRANDE NDER R MEng MEn g
Engineer, Building Structures, Engineer, WSP, London, UK
Next-generation buildings: wired for health and wellbeing
SYNOPSIS Amy Bra Amy Brand nder er,, winner of the Institution’s Pai Lin Li Travel Award in 2018, discusses her research into the WELL Building Standard and the potential to design buildings that prioritise the health and wellbeing of their occupants. Using examples from Sweden and Canada, Amy outlines design features that will impact on structural engineers and considers the challenges that these impose.
Biophilic design
Over the past year, the construction industry has witnessed a rise in structural design that prioritises the health and wellbeing of a building’s occupants. Although Althoug h architects architects and engineers engineers have worked together for years, creating spaces within buildings where they believe occupants’ needs can be met, the WELL Building Standard has recently gained momentum. This standard can be used as a scienti fic tool to work out exactly how building design aff ects ects occupants’ health, wellbeing and performance. There are numerou numerous s reasons reasons why a focus on health and wellbeing in structural design is important. First, humans now spend on average 90% of their time inside buildings1. As engineers, we have the opportunity to build an environment
The Internatio International nal WELL Buildin Building g Institute Institute has developed the WELL Building Standard, which is a rating system used to score a building based on how it impacts an occupant’s health and wellness. WELL has been developed using ‘scientific and medical research and literature on environmental health, behavioural factors, health outcomes and demographic risk factors that aff ect ect health’ due to our built environment 3. It is an intelligent system, used in building design to enhance a person’s experience
Biophilia is a love of living things, a need to be surrounded by nature. According to E.O. Wilson, ‘People have an innate and genetically determined affi nity … with the natural world’4. Biophilic design uses these principals to design a building and restore nature into the built environment. In 2016, an estimated 54.5% of the world’s population lived in urban settlements. By 2030, this is projecte projected d to rise to 60%, while one in three people will live in cities with at least half a million inhabitants5. Despite these statistics, most of the globe’s cities have been designed without enough consideration for the environment and alienate us from nature. Recent trends and practices have led to ‘green building design and construction’. However, this focuses on the environmental impact of a building, with little attention to the social and economic sides of sustainability. We need nature in our cities. Biophilic design has huge economic, health, social and environmental benefits. When a building is designed to incorporate biophilia, the health benefits include decreases in blood pressure and heart rate, reduced stress, enhanced concentration and improved memory6.
in which willhave spend most of their to time. Wepeople therefore a responsibility ensure such spaces enable them to live a happy and healthy lifestyle. Second, there is a direct link between chronic health problems and the built environment2. Physical health problems commonly seen in the workplace include back pain, arthritis and obesity, which can be caused by sitting in a chair for the majority of the working day. Common mental health problems caused by a typical work environment include stress and social anxiety. I wanted to focus my study on sustainable building design, looking at the three pillars of sustainable design (social, environmental, economic) and
and make life better. WELL provides Silver, Goldtheir or Platinum certi fication, similar to other building standards (e.g. BREEAM and LEED). WELL is used to measure a building against seven key criteria: air, water, nourishment, light, fitness, comfort and mind. The certification is strict, and every building attempting to achieve WELL certification must employ a WELL Accredited Accred ited Profession Professional al who support supports s accreditation. The WELL standard can be used to certify core and shell projects or interiors. The projects that aff ect ect design and construction, and therefore structural engineering, are those trying to achieve core and shell certification. Like all building standards, WELL
These benewellbeing, bene ts tie intowhere designing health and one for of the key focuses is to reduce common chronic health problems caused by the built environment. Economic benefits tie into health and social benefits: in an offi ce there is less absenteeism and better staff retention; retention; in a classroom there are improved learning rates and higher cognitive function; in retail spaces people stay longer and are willing to pay more 6. Google is known for being one of the first companies to design its offi ces with a specific focus on human health and wellbeing, providing a workplace that is comfortable and improves its employees’ working lifestyle. Google claims to have attracted a larger number of applicants
WELL certification. I hoped to learn how chronic health problems can be reduced or eliminated with a new outlook on structural design. Evidence shows that productivity is improved in a healthier
is continuously being improved and updated. WELL Version 2 is the most current; however, several buildings certified today were designed to previous standards.
and a more skilled workforce by doing this, and has also generated positive publicity7. Biophilic design can be implemented in many ways. At University Avenue,
Introduction
work environment. Many companies are now prioritising health and wellbeing when designing their offi ces, and in doing so claim to attract a more talented workforce.
WELL Building Standard
8 October 2019 | thestructuralengineer.org
fi
Pai Lin Li Travel Award 2018
Figure 1:
Biophilic street design at University Avenue, Ave nue, Toronto
9 thestructuralengineer.org | October 2019
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Pai Lin Li Travel Award 2018
Toronto, Canada, Toronto, Canada, large large breaks breaks where trees, grasses and shrubs have been planted separate the roads from pedestrians (Figure 1). 1). At WSP’s offi ces in Stockholm, Sweden, internal green space has been used to connect people to nature (Figure 2). 2).
are within the basement of a building. In cities, it has become common practice for structural engineers to design buildings with complex basements that maximise the use of space available on site. Physical activity spaces are advised in a building trying to achieve WELL certification. Gyms are becoming common in offi ce buildings, but designing for a gym within an o ffi ce
Study objectives Within the built environment, clients are becoming increasingly interested in this more holistic approach to construction. Structural engineers could benefit hugely by educating themselves in this area. It is a modern outlook on design, and certainly has become a talking point within the industry. Despite this, I believe most structural engineers know little about the concept, and how it aff ects ects structural design. This study took took place in two countries: countries: Sweden and Canada. I visited several cities with the intention to learn more about designing for health and wellbeing. My aims were to: learn how to design sustainably with a focus on WELL and biophilic design learn how this type of design will change current engineering practice learn how this practice varies by project, region, country, changes in the natural environment, working culture and current engineering methods understand the pros and cons of designing to WELL and how it plays a part in future-ready design.
building imposes a huge challenge on the structural engineer. Gyms bring increased vibration and loud noises. Acoustic isolation, isolation, such as as box-in-box box-in-box construction, is an example of a solution which challenges the structural engineer.
Impact on structural engineering Designing buildings wired for health and wellbeing changes the practice of structural engineering. Solutions that would have been adequate before may not work when trying to achieve WELL certification and incorporate biophilic design. here are divided intoExamples some of presented the seven categories under which WELL is assessed.
Light Allowing as much much natural natural light into the the building as possible is important for a person’s cognitive function, and views can stimulate productivity5. Atriums are a typical solution used to allow natural light into a building, and to allow visual, physical and psychological connection between floors in a building. An atrium within within a building building changes changes the whole dynamic of structural design. The challenges challenges that come with atrium design include designing for brittle finishes, which, in turn, impact deflection limits as well as complex connection detailing. Buildings the energy. future may be equipped to in store At present, a building’s generated energy is lost if it is not used, and energy is used at varying rates depending on the weather or the time of day, e.g. on a cloudy day, more energy will be used to light the building, whereas little energy is used at night when the building is empty. Energy generated at night could be stored and used in the daytime. The space needed to store this energy will be a new and complex challenge for engineers.
Air Air can have a detrimental detrimental impact on on human health, particularly in large cities where air pollution is a problem. Structural engineers now consider ‘greening’’ our cities with a biodiverse ‘greening range of plant life as a method of reducing the impact construction has on clean air. Structural solutions include landscaping, green walls and green roofs. These solutions solutions introduce introduce trees trees and green spaces into building design, absorbing CO2 and helping to reduce
Fitness A simple step to improving improving occupants’ occupants’ health and wellbeing is exercise. Offi ce buildings, more often than not, are
air pollution. The challenges that come with these solutions include designing for heavy soil and drainage loading. This can aff ect ect the size of the entire structure, particularly if the plants are at roof level.
built with bike storage facilities, which promotes cycling to work. This not only encourages exercise on the way to and from work, but reduces the company’s carbon footprint. Often, these facilities
2: Biophilic design at WSP offi ces, Globen, Stockholm Figure
Figure
3:
Canteen-style collaboration spaces, WSP, Stockholm
10 October 2019 | thestructuralengineer.org
Comfort Being able to control one’s environment makes people feel more comfortable. A simple example example of this is opening a window, something people do to control their body temperature and feel comfortable. Comfort also varies with gender. On average, women feel the cold more readily than men and enjoy a warmer environment8. A building with varying temperature temperature zones and openable windows will require a more complex mechanical, electrical and public health (MEP) solution. This can result in larger openings/ducts due to the nature of the temperatures and air flows in the building. A typical feature of a WELL building is having an advanced air purification system. Filtering CO2 out of the air enables people to focus more clearly and feel more awake at work. This facility also also requires requires larger pipes pipes and ducts, often increasing the services zones in a building. Larger services zones and increased openings alter the building design. The structural structural engineer engineer will require require information on larger openings earlier in the design process. Larger services zones aff ect ect the floor-to-floor height of a building, dictating the overall height. This will impact impact on the structural structural engineer considerably. More design team
Pai Lin Li Travel Travel Award 2018
meetings and increased coordination between the MEP and structural engineers are typical for a WELL build.
Skanska has only recently developed the in-house knowledge to become involved in developing a WELL-certified building. Design and construction for WELL certification is still a relatively new field, and is costly in consultancy and research fees. The majority of Skanska’s buildings in Sweden are LEED certi fied, so it was a natural progression progression to start certifying with WELL. Epic is a six-storey o ffi ce block under
Mind Wellbeing is important. Offi ces are now becoming flexible spaces, with the mental and physical health of occupants at their core. Within the workspace, we are starting to see areas where people can interact more easily: comfortable seating areas, drawing boards and meeting spaces. Buildings are now being built with large, open-plan spaces, promoting social interaction within the workplace. This aff ects ects structural engineers, who are now designing to reduce the number of columns, which obstruct open spaces within the building. This means that engineers design floors that will span further, pushing materials and construction to the limit. Designs will now be flexible and future ready. Changes in use will be possible in the future. This adds complexity to structural design. A structure will have to be designed for various scenarios: commercial, residential or offi ce use, all of which come with varying load, vibration and accessibility requirements.
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4: Typical offi ce waste recycling facilities, Stockholm Figure
Project Epic Skanska is a Swedish company known for its creativity and sustainable solutions to construction. It is the lead developer on Epic, a pioneer project for WELL in the city of Malmö. Around 80% of Epic’s offi ce space was rented out one year in advance of completion, which is unusual in the city.
construction near the central station in the heart of Malmö. The project has a very large plan area (15 000m2) and is made up of two buildings connected by a large atrium. The atrium is full height, with sky pedestrian bridges connecting one side to the other (Figure 5). 5). Fullheight, six-storey-tall six-storey-tall trees will be planted within the atrium’s ground floor, providing habitats for a variety of plant and tree species to exist inside the building. At the centre centre of the the building, constructed in steel, is a large staircase (Figure 6). 6). It will be a focal point on entering the building, while the lifts will
Case study: Sweden Sweden is a country that is already well equipped to design for WELL certification. The culture in the country is set up for improving people’s health and wellbeing. It is typical in Sweden to have large canteen spaces (Figure 3) where 3) where everyone in the o ffi ce eats lunch together, encouraging social interaction. In Sweden, the concept of multidisciplinary teams has taken off and and offi ce spaces are adjusted for collaboration among disciplines. The recycling recycling cultuand culture re inoSweden Swede n is very strict. In homes ffi ces, waste is separated into categories (Figure 4). 4). Water quality in Sweden is excellent. The majority majority of buildings buildings trying to achieve WELL certification have to do very little to pass the water criteria. Finally, people in Sweden are typically forward thinking and sustainability conscious. New trends and practices, such as WELL, are quickly adopted in the country. Large companies are competitive over sustainabilityy and want to be the first sustainabilit to house their employees in a WELLcertified building. People are choosing to work for one company over another based on ethics and WELL rating. Companies like E.ON and Castellum have rebranded themselves around health and wellbeing to attract a better workforce, retain staff , and promote themselves.
5: Central atrium, Epic, Malmö Figure
BOTH THE STAIRCASE ST AIRCASE AND A ATRIUM TRIUM ADD TO COMPLEXITY THE DESIGN OF THE STRUCTURE
6: Central staircase, Epic, Malmö Figure
11 thestructuralengineer.org | October 2019
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Pai Lin Li Travel Award 2018
Figure 7: External finishes, Epic, Malmö
be hidden from view. This will encourage people to use the stairs rather than the lift, focusing on the fitness requirement of WELL certification. Both the staircase and atrium add complexity to the design of the structure. The atrium presents a problem with brittle finishes, while the stairs are bespoke, spanning signi ficant heights from floor to floor. The atrium connects the two sides sides of the building. This was very important to the architect as one side is a road and the other a calm harbour. Two tempers meet using this atrium, allowing a visual, physical and psychological connection between floors. Multiple features withinrating the building helped Epickey achieve a WELL of Platinum core and shell. The facade is made from prefabricated brick produced in Poland (Figure 7). 7). The bricks are broken in half, reducing the weight of the facade. The half-brick not used on the facade is crushed and made into tiles. The interior wood finish is made of old window frames – a simple but sustainable solution (Figure 8). 8). Finally, Skanska has focused on the impact people will have on climate change once the building is in use. The bike storage in the the building is integrated: there will be storage by the reception inside the building, and by people’s desks. Bike security encourages
Project Eminent Eminent was the first core and shell WELL-certi fied building to finish construction in Scandinavia, in late 2018. It is an offi ce building in Hyllie, Malmö with over 9600m2 of offi ce space. The client was Castellum and the architect was Kanozi. Architects have always tried to design design for value, not cost. Kanozi described WELL certification as an opportunity to
and blue light is proven to calm people, adjusting the mood inside the building. There are are large steel steel trusses at at ground floor, exposing the structure (Figure 9). 9). This helps passers-by passers-by feel feel connected connected to the building’s construction/history. Eminent was designed for biophilia. There will will be a green green roof made of Biotoptak 9. This type of green roof works better than sedum, attracting a biodiverse range of insects. Hanging
push value, even if it costs more. Ideas that add value to the project and improve people’s lives might have been scrapped in the past. Now they are included, as removing them may reduce WELL points, which drive lettable value. Eminent has deliberately been built at the end of a row of buildings, rather than standalone. This looks better, is well planned and integrated. Heritage and community are a major consideration in design. The building’s facade is made of the old brick which is typical of Malmö’s industrial heritage. A community feel is attractive to the public, so the entirety of Eminent’s ground floor is public space (except for a gym). The building is giving something back to the city. Eminent was designed with people’s health and wellbeing at its focus. It is a large building on plan area, but only seven storeys tall. The floors are a very tall 2.9m and open plan. The whole space feels light and airy. There is a gym at ground floor for occupants to exercise in. The space on each floor is easily adaptable. There can be up to four small offi ces on each floor. It is future ready. A large courtyard in the centre of the triangular building not only provides outdoor space, but allows light to reach the rest of the building. Windows have some grey and blue glass panels. Grey
gardens in the central stairwell avert the eye away from computer screens. Green walls are to be used on the facade, adding nature, texture and colour. The structural structural engineering engineering solution solution is typical of Sweden. Precast posttensioned concrete slabs are used throughout. Each slab panel is one-way spanning between steel beams. Columns are either steel or composite steel and concrete. Composite columns are used at ground floor to minimise size. Figure 10 shows 10 shows bracing between columns used for lateral stability in addition to a single concrete core. There are two types of facade on this building. One is a brick stud wall in traditional construction and the other is a solid concrete wall.
fi
Figure 8: Internal nishes, Epic, Malmö
people to cycle. Every tenant will also be provided with membership of a car-sharing scheme. This allows them to cycle to work, but drive to meetings during the day.
12
Case study: Canada Canada is also prominent in the health and wellbeing sector, with several interesting buildings achieving WELL standardisation. The majority majority of new builds builds in major cities are designed to LEED10, a certification that shares criteria with WELL. If a building has a high LEED score, it is easier to achieve WELL certification. Fitwel 11 has also become popular for offi ce spaces in Canada. It is another, more flexible system used to measure fl
Figure 9: Large steel truss at ground oor, Eminent, Malmö
October 2019 | thestructuralengineer.org
Pai Lin Li Travel Travel Award 2018
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THE SPACE ON EACH FLOOR IS EASILY ADAPTABLE. ADAPT ABLE. THERE CAN BE UP TO FOUR SMALL OFFICES ON EACH FLOOR a building for health and wellbeing. Fitwel strategies that are adopted can shape the building’s WELL profile. It is commonly used in existing buildings/ refurbishments. Offi ce spaces can easily transition from Fitwel to WELL certification if the client wishes. CBRE HQ CBRE is a sustainability-focused realestate company which was the first in Canada to announce a zero-carbon work plan in 2010. Its new headquarters (HQ) are on the 11th and 12th floors of King Street West, a 42-storey tower in central Toronto. T oronto. The The offi ce interior is designed to WELL Platinum certification and was completed in 2016 (Figures 11–13). 11–13). A number of innovative measures were adopted to improve employee health and wellbeing in the building: | Circadian rhythm lighting is used to mimic changes in sunlight during the day – from a warmer red colour in the morning and evening to a bright blue colour at midday. Blue light makes people more alert, while red increases the amount of melatonin we produce, encouraging us to sleep. Artificial light is often dangerous for our health because it does not follow the sun’s natural cycle12. | MERV-13 filters in pipes mean the highest-quality highest-qu ality air is supplied to the offi ce. The CO2 level in the offi ces is kept to a maximum of 80 parts per million using these filters. As a consequence, people feel healthier when inside the space. | White noise is used in the offi ce spaces to reduce distractions. As white noise fractures sound, it is possible to tell someone is talking near you, but not be able to hear what they are saying. In contrast, silence is used in the meeting rooms where voices need to be heard. desks and meeting rooms are within 25 feet (approx. 8m) of a window and natural light. | All desks have smooth surfaces and curved edges to prevent wrist pain.
10: Bracing needed for lateral stability, made into feature, Eminent, Malmö Figure
Figure
11:
Lunch hall, CBRE HQ, Toronto 13: Glass technology walls in meeting room, CBRE HQ, Toronto Figure
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Breakout spaces, CBRE HQ, Toronto
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Pai Lin Li Travel Award 2018
CBRE HQ provides evidence of how to successfully execute a design wired for health and wellbeing. The feedback from employees is outstanding outstanding.. Employees filed 82–94% satisfaction in the postoccupancy offi ce survey relating directly to WELL. People working in the o ffi ces have specifically mentioned they feel less tired, and that this is due to the air and lighting in the offi ce. They have also said they are more productive during their time at work. Finally, people have enjoyed having more opportunity to control their health. CIRS building The Centre Centre for Interactive Interactive Research Research on on Sustainability (CIRS) at the University of British Columbia runs green building tours all year round. The CIRS building (Figure 14), 14), famous for its state-of-theart technology, is a unique example of sustainable building design. As soon as you you walk into the building, building, you notice the large timber stairway (Figure 15), 15), while the lifts are hidden from view. The atrium in the centre of the building connects floors for social interaction and floods the building with light. The building building is formed of concrete concrete and structural glued laminated (glulam) timber. The structural timber in the lecture theatre is made from wood aff ected ected by mountain pine beetle infection (Figure 16). 16). The mountain pine beetle is an invasive species that dries out trees by sucking out their moisture. This is a huge problem in Canada, as dry wood can lead to forest fires, and needs to be removed. Rather than allowing the timber to go to waste and inevitably be caught in a forest fire, it is increasingly being used in construction construction.. Air and temperature temperature in the CIRS CIRS building is controlled for occupant comfort and wellbeing. There are 3000 sensors in the building, which measure CO2, motion and temperature. If the temperature levels within the building are too high, windows in corridor spaces automatically open and the heating automatically automatica lly turns off . To heat the building, energy is generated from solar panels (Figure 17). 17). These panels serve a dual purpose of providing shade and generating energy. Biophilic design features throughout the building. A green roof houses a large variety of native plant species which have been selected for their ability to absorb large amounts of CO 2 (Figure 18). 18). The MEP system pumps air in at roof level, which is cleaner that at lower levels. The tiles on the green green roof are are raised, with water collected underneath. This water is transported to an 83 000l tank underneath the building and used for
14: CIRS building, University of British Columbia Figure
15: Central timber stairway stairway,, CIRS building Figure
THE ATRIUM ATRIUM IN THE CENTRE OF THE BUILDING CONNECTS FLOORS FOR SOCIAL INTERACTION AND FLOODS THE BUILDING WITH LIGHT 14
plant irrigation and to flush toilets. There is a green wall on the western face of the building, made up of climbing plants called chocolate vine Akebia (Akebia quinate). This species was selected because it is lush with thick leaves in the summer, shading the building, but bare in the winter, allowing light in to heat the building. Conclusion Designing a building with the occupants’ health and wellbeing as the focal point is a new concept, brought about by
October 2019 | thestructuralengineer.org
Pai Lin Li Travel Travel Award 2018
Figure 16: Timber
recent developments in societal needs and advancing technology. It started as a trend, but has now become common in many countries. I believe adopting the principles explained in this report will ensure a building is future ready. This paper has has made many many observations based on successful projects, whether that is designing to WELL, for health and wellbeing, or
affected by mountain pine beetle infection, CIRS building
REFERENCES 1) Bessoudo M. (2017) Health, Health, wellness and experience in the built
incorporating biophilic design; however, there are still changes that need to be made for the concept to become common practice. WELL is expensive. Projects that would hugely benefit from adopting these principles may choose not to due to the additional cost to the client. It is the engineer’s job to explain to the client the benefits of this type of design, and how they outweigh the high capital cost. Costs can be mitigated throughout a building’s lifespan. CBRE HQ saw very little additional cost due to WELL being incorporated at such an early stage and adopted into the conceptual design. The largest cost to the client comes comes from consultancy fees. With very few buildings designed to WELL, a lot of hours are spent researching how it can be achieved. Skanska claims that, with every new building it designs and constructs to WELL, the lower the consultancy fees and the faster it becomes. Another problem problem with WELL WELL standardisation is maintenance costs, particularly concerning biophilic design. Green walls and roof gardens must be implemented and maintained correctly, or plants will die. This paper lists sts the benefits that designing for health and wellbeing has on the occupants of the building, and also on the building’s owner/employees. It is a design outlook that bene fits everyone involved if implemented correctly; however, the challenge that comes with this type of design is awareness. Often responsibility is passed to the sustainability consultant, but to become successful it needs a multidisciplina multidisciplinary ry approach. It aff ects ects every aspect of a project’s lifecycle and design. A truly sustainable sustainable engineering engineering solution on must be environmentally, socially and economically sustainable. I believe WELL can be used as a tool to create a truly sustainable building design.
Feature
environment: From green buildings to Conscious Cities [Online] Available
at: www.ccities.org/health-wellnessexperience-built-environment-greenbuildings-conscious-cities/ (Accessed: September 2019) 2) Bessoudo M. (2017) Promoting health and wellness wellness for buildings buildings Figure 17: Solar
panels, CIRS building
[Online] Available at: www.wsp.com/ en-GL/news/2017/wsp-championhealth-and-wellness-across-propertybuildings (Accessed: September 2019) 3) International WELL Building Institute (2019) About (2019) About WELL [Online]
Available at: Available at: www.wellc www.wellcerti ertified.com/ about-iwbi (Accessed: September 2019) 4) Wilson E.O. (1986) Biophilia,
Cambridge, MA: Harvard University Press 5) United Nations Department of Economic and Social A ffairs (2016) The World’s Cities in 2016
(Data Booklet) [Online] Available at: www.un.org/en/development/ desa/population/publications/pdf/ urbanization/the_worlds_cities_ in_2016_data_booklet.pdf (Accessed: September 2019) 6) Kellert S.R. and Wilson E.O. (1995) The Biophilia Hypothesis, Washington
DC: Island Press 7) The Globe and Mail (2018) Take a tour of Google’ Google’s s new Toronto of fi fice c e [Online] Available at: www.
theglobeandmail.com/report-onbusiness/careers/take-a-tourof-googles-new-toronto-offi ce/ article5220954/ (Accessed: September 2019)
Figure 18: Biodiverse green roof, CIRS building
8) Kim H., Richardson C., Roberts J., Gren L. and Lyon J.L. (1998) ‘ Cold Cold hands, warm heart’, Lancet, 351 (9144),
p.1491, DOI: https://doi.org/10.1016/ S0140-6736(05)78875-9
HAVE YOUR YO UR SAY SA Y
9) Veg Veg Tech (2019) (2019) Biotoptak [in [in
Swedish] [Online] Available at: www. vegtech.se/sedumtak---grona-tak/ biotoptak/ (Accessed: September 2019) 10) US Green Building Council (2019) LEED [Online] Available at: https://new. usgbc.org/leed (Accessed: September
Watch the lecture
[email protected]
Amy will present present her Pai Lin Li Travel Travel Award Award research at a lecture at Institution HQ on 17 October. To attend the lecture or register for the livestream, visit www.istructe.org/events/hq/moving-toward-asustainable-future/ .. sustainable-future/
15
2019) 11) Center for Active Design (2019) Fitwel [Online] Available at: https:// fitwel.org/
@IStructE
#TheStructuralEngineer
(Accessed: September 2019)
12) Panda S. (2018) The Circadian Code, London: Vermilion
thestructuralengineer.org | October 2019
Professional guidance
Business Practice Note | No. 28
BUSINESS PRACTICE NOTE This series has been developed by the Institution’s Business Practice and Regulatory Control Committee to provide guidance on aspects of running a practice and project management.
Introduction In the UK, health and safety awareness on building sites has improved substantially in the past 10–15 years. However,, we can all still do more to However ensure that everyone goes home safely at the end of their working day and that we do not adversely aff ect ect the environment in which we are working. A key tool in improving health and safety outcomes is intervention. This Busine Business ss Practic Practice e Note Note presents presents guidance and tools that can be used to intervene eff ectively ectively to stop unsafe behaviours, hopefully preventing injuries, fatalities and environmental damage. Within the off shore shore oil and gas sector (and others, such as nuclear and rail), it is common to have clear written policies on intervention, which are backed up by a ‘top-down’ culture. The advice in this note is based on a system used by existing oil and gas operators. There are many other policies and systems in use, but the following gives a good example of a working intervention strategy that could be successfully adopted in most construction environments.
How to make a successful intervention If you become aware of a potentially unsafe act or procedure, the key to successful intervention is to be helpful and considerate. Start by introducing yourself and saying that you would like to discuss health and safety safety.. Be polite and show genuine interest and concern. Giving consideration to the person’s feelings will help to put them at ease. If, in your opinion, there is an immediate danger, request that work is stopped until you have had a chance to discuss the situation, consider the potential outcomes, and fully resolve the issues that concern you. Ask the person person what they have done to manage their health and safety risks
No. 28
Making a health and saf safet ety y intervention Matt Byatt offers advice on how to intervene successfully when witnessing an unsafe act or procedure. Use open questions when intervening, e.g.: |What are the hazards and risks of the work being carried out? | How could you (or others) be hurt? | What steps have been taken to prevent injury to you and your colleagues? | What additional steps could be taken and how could things be improved? For an intervention to have a successful outcome, the focus must be on behaviour and situations that can be changed. Try to focus on positives, rather than dwelling on negatives. Look to the future and how things can be improved. It is important to be specific, clear and talk about what you see (not what you think or believe). Ask questions, ons, look for for common common ground, and define the problem but ask for solutions. Try to diff use use any tension, not add to it. Where required, try to agree with the individual a safer way of doing things and agree on ownership if there are actions to be taken. Thank the individual for their time. If you have agreed a follow-up action, make sure you complete it.
today. This allows them to explain all the good things they have done, and for you to recognise their eff orts orts and give positive feedback.
Remember,, if it doesn’t ‘feel’ right, it Remember probably isn’t!
What if you can’t intervene directly? There are occasions ons when when direct direct perso personal nal intervention is diffi cult to achieve, e.g. when passing a project or site to which you don’t have access. In such an instance, you can either try to make direct contact with the site’s health and safety management team by telephone, if a contact number is available, or report the concern to the appropriate regulator – in the UK this is the Health and Safety Executive (HSE).
Following up an intervention Following an intervention, it is good practice to discuss the issue with the site or project’s health and safety management team. It is particularly important that the situation is reported and recorded if you are not going to be there in person to check that the agreed follow-up actions are fully and correctly instigated. Structural safety issues can (and should!) be submitted confidentially to the Confidential Reporting on Structural Safety (CROSS) scheme so that a wider
A
successful success ful intervention will focus on changing behaviours or situations
K C O T S I
16
October 2019 | thestructuralengineer.org
Business Practice Note | No. 28
audience can learn lessons from the safety issue. See See www.structuralsafety www.structuralsafety.org .org for for information on how to do this. If your concerns are for the longerterm safety of the building or structure, rather than the immediate safety of the construction team and/or public, CROSS Report 726 gives guidance on reporting options1.
Reporting to HSE
If your intervention is not well received and you are not happy with the outcome, you should report the situation to the regulator – the HSE in the UK. Clear guidance and contact details for reporting concerns are provided at www.hse.gov.uk/contact/ concerns.htm.. concerns.htm
Potential challenges Intervention takes practice. Keep practising until you become comfortable intervening. It is about keeping people safe, not point scoring or being awkward. Nonetheless, interventions can be viewed by some as a threat or unwanted interference, which can make intervening more challenging. However, we all have a moral obligation and duty of care to prevent health and safety issues if it is within our power to do so. Ask you yourse rself: lf: if you walk walked ed by and
said nothing, how would you feel if the behaviours that you witnessed subsequently resulted in a fatality?
Conclusions The aut author hor’’s pers persona onall expe experie rience nces s sugg suggest est that, in general, the construction sector in the UK still has much to learn from the oil and gas sector with respect to its health and safety culture. Having both intervened in health and safety matters, and been on the receiving end of interventions by others, it is comforting to know that other people are genuinely looking out for one’ one’s s safety. However, not everyone considers this approach beneficial. So, if we are to make construction safer, cultures must continue to change and individuals or companies that do not currently see the full value of improving safety need to be re-educated. Following the Grenfell Tower disaster in the UK, one of the recommendations of the Hackitt Review2 was to create a mandatory occurrence reporting mechanism. The Ministry of Housing, Communities and Local Government is currently running a trial of this reporting mechanism, and it is likely that it will be formally launched across the industry in late 2019 or early 2020.
Professional guidance
This note has been prepared by EUR ING Matthew Byatt CEng, FIStructE on behalf of the Institution of Structural Engineers’ Business Practice and Regulatory Control Committee. Members are reminded that they should always comply with the legislation of the region in which they are working and should be aware of any jurisdictions specific to that region. Business Practice Notes are provided as guidance to members, but do not form part of the Regulations and/or Laws of the Institution. All members are obliged to abide by the Institution’s Code of Conduct.
REFERENCES
1) Structural-Safety (2018) Report ID 726: Combustible insulation in rainsc insulation rainscreen reen claddin cladding g [Online] Available
at: www.structural-safety www.structural-safety.org/publications/view.org/publications/viewreport/?report=10222 (Accessed: September 2019) 2) Hackitt J. (2018) Independent Review of Building Regulations and Fire Safety: fi nal report report [Online] Available
at: www.gov www.gov.uk/government/publications/independent.uk/government/publications/independentreview-of-building-regulations-and-fire-safety-final-report (Accessed: September 2019)
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thestructuralengineer.org thestructuralengineer .org | October 2019
Professional guidance
Certificate in Structural Behaviour
Why it pays to be able to demonstrate demonstrate your understanding of structural behaviour Tim Ibell introduces Ibell introduces the Institution’s new Certificate in Structural Behaviour and explains the value of being able to demonstrate one’s understanding. There is nothing nothing more fundam fundamental ental to the skill set of a structural engineer than an understanding of structural behaviour behaviour.. It is like an actor knowing their lines or a pilot understanding aeronautics. Understanding structural behaviour binds together structural engineers across the world, regardless of their chosen structural speciality speciality.. About a decade decade ago, ago, the the Instituti Institution on embarked on an ambitious education programme to enhance understanding of structural behaviour among its members, particularly Student and Graduate Members. The single most impactful initiative was the development and launch of the Structural Behaviour Course and its recent companion, the Certi ficate in Structural Behaviour Behaviour.. The questio questions ns in the course course help early-career engineers, and students in particular, to develop confidence in simple statically determinate structures. It’s a flexible online test, with a bank of
moment diagram without numbers, and to be able to determine the sense (compression or tension) in a truss, again without knowing specific numbers. Some concepts in structural behaviour are diffi cult to grasp when first met. For example, changing the stiff ness ness of structural elements within a statically indeterminate structure will lead to changes in bending moment distributions. Coupled with this, it is often stated that the lower-bound theorem allows structural engineers to sleep at night, so understanding its power is rather important. In a highly redundant building structure, we cannot possibly know what the bending moment distribution really is, because foundations move, for instance. These concepts must be understood before an engineer can hope to achieve a robust design. Having easy access to an online resource that embraces the idea of ‘having a go as often as you like’ in a
hundreds of questions, which can be taken repeatedly in one’s own time and space. As the the course course progr progresses esses,, questions questions start to cover approximation of statically indeterminate structures, by linking deflected shapes to feasible bending moment diagrams via estimates of points of contraflexure. Such approximation is an essential skill of a structural engineer, not least to quickly assess the accuracy, accuracy, or otherwise, of computer output. Coupled with approximation is the skill of being able to sketch a bending
supportive atmosphere is exactly what’ what’s s needed to embed understanding and increase confidence. Of course, when this skill has been developed, there is nothing quite like demonstrating this advance in your abilities to others, which is where the certi ficate off ers ers a great opportunity. From my own academic point of view, the course and certificate hold many advantages to embed core understanding. One option is to use the course as part of coursework, with the highest score achieved by the students,
THE CERTIFICA CERTIFICATE TE DEMONSTRATES TO EMPLOYERS A HIGH LEVEL OF UNDERST UNDE RSTANDING ANDING across as many attempts as desired, being the final coursework mark. This represents assessment-led learning, something which leads to profound understanding and confidence. Following this, the certificate is a fantastic way for students to kickstart their career. The certificate demonstrates to employers a high level of understanding, and that the young engineer will be better at avoiding technical errors and able to ‘sense check’ errors in software output. Thus, the Institution’s Institution’ s two resources on structural behaviour are a perfect combination for preparing students for the workplace. Increasing numbers of employers are also supporting their graduates in developing their understanding of structural behaviour through both the course and the certificate. In doing so, they are improving their employees’ chances of passing their Professional Review. Professor Tim Ibell FREng , FIStructE is a Past President of the Institution and Professor of Structural Engineering at the University of Bath.
FIND OUT MORE... | Find
out more about the Certificate in Structural Behaviour at www.istructe.org/sbcertificate www.istructe.org/sbcertificate..
The course is based on a bank of hundreds of questions with multiple-choice answers
18
October 2019 | thestructuralengineer.org
Certificate in Structural Behaviour
Professional guidance
The employer’s view
The graduate’s view
The student’s view
Ian Craig, Director, Evolve Nadia Perkins, Delivery Leader, Evolve
Hemant Gor, Graduate Member
Tarun Mittal, Student Member
An engineer engineer drawing a bending moment diagram for a structure is analogous to a doctor checking a patient’s patient’ s heartbeat. Diagrams like these provide insight into the load distribution of a structure, and eff ective ective
During my early-car early-career eer development, it was hard to demonstrate my skills formally, e.g. in the form of qualifications. However, this was possible through the Certificate in Structural Behaviour because it doesn’t require
them to gainimproving the certi cate a positive step in bettering themselves, theirisskills, and pursuing a path towards becoming a chartered structural engineer. We have a strong IStructE chartership programme within the company,, into which all our graduates are enrolled. This gives company them personal guidance in achieving the Initial Professional Development (IPD) core objectives. One of the most significant IPD objectives is 2.2, where the candidate must demonstrate the ability to solve structural engineering problems. While it can be diffi cult to gain good experience in a wide range of topics, achieving the certificate demonstrates that the candidate has already accomplished this and possesses essential understanding of structures. To T o assist assist our our graduate graduate engine engineers, ers, the Evolve Evolve team hosts internal lunchtime sessions to go through practice questions for the course and certificate, aided and assisted by chartered engineers and associates. Our career development process gives Evolve’s clients
utilisation of section and failure mechanisms. The exam for the Certificate in Structural Behaviour tested my ability to calculate load paths, perform approximate analysis, and understand how they will de flect, without the use of a computer. This is importan importantt because, because, during the detail engineering stage of a project, these skills help to review the design and identify possible errors in 2D/3D computer modelling. Practising for the certificate improved my skills in drawing bending moment and force diagrams, as well as approximate analysis. As a result, I was given the opportunity to work on new multibillion-dollar projects. I
industrial experience, just strong basics and a sound understanding understandin g of structural analysis. This is the only quali fication that gives students the opportunity to achieve professionall goals during their higher professiona education. Practising for the certificate, using the Structural Behaviour Course, helped me determine whether I would be able to handle designs responsibly in the professional world, as many lives depend on our designs. I’ve also taken my first step towards chartered status, as the certificate contributes to my Initial Professional Development objectives. Finally, the certificate gave me confidence in my skills and an extra edge over other candidates, which helped me
confidence that all the engineers working on their projects, even if not yet chartered, have strong engineering knowledge and capability. This can be formally demonstrated with the certificate, which is an internationally recognised mark of competence.
recommend the certificate to anyone who wants to put themselves forward for challenging new projects, improve their bid-winning skills or take the next steps towards chartered membership.
get a new job. I would recommend to every structural engineering student that they take advantage of the the course and attain the certificate to prove their skills to employers.
At Evolve, Evolve, people are the foundati foundation on of everything we do. Our key message is to inspire and develop great people who share our passion for engineering excellence. We believe that guiding our young engineers through the Structural Behaviour Course and encouraging fi
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thestructuralengineer.org | October 2019
Technical
Optimisation-driven conceptual design
Optimisation-driven conceptual design: case study of a large transfer truss HELEN FAIRCLOUGH MEng MEng Research Engineer, Expedition Engineering, London; and University of Sheffi eld, UK MATTHEW GILBERT BEng, PhD, BEng, PhD, CEn CEng, g, MICE MICE,, MASCE MASCE Professor, University of Sheffi eld, UK CLEMENT THIRION MEng, MSc, MEng, MSc, CEn CEng, g, MICE MICE Senior Associate, Passage Projects, London, UK (formerly Expedition Engineering, London)
SYNOPSIS
This article describes the use of structural optimisation at the conceptual design stage to identify materially effi cient solutions that incorporate buildability considerations. In the proposed approach, a minimum-weight solution is first identified, providing a benchmark against which other designs can be judged. However, as this solution will often be complex in form (and effectively impossible to construct in practice), additional constraints are then gradually introduced to rationalise it, and to explore the regions of the solution space which separate it from simpler, more familiar solutions. This enables the designer to balance material effi ciency and complexity in a more informed manner. The effi cacy of the approach is demonstrated via application to a case study of a transfer truss design.
ANDY TYAS ANDY TYAS BEng, BEn g, PhD PhD Professor, University of Sheffi eld, UK PETE WINSLOW MEng, MEn g, MA, MA, PhD, PhD, CEn CEng, g, MIStr MIStruct uctE E Associate, Expedition Associate, Expedition Engine Engineering, ering, London, UK
Introduction Recent advances in aff ordable ordable computing power mean that optimisation techniques, once primarily the preserve of aerospace and high-end automotive designers, are becoming accessible to the wider structural design community. The most general forms of structural optimisation are topology optimisation or, for frameworks, layout optimisation. Both of these involve starting with a blank space, the design domain, and generating a geometry for the structure based on mathematical rules. These techniques have the potential to achieve the most
for a range of materials, including concrete2 and steel joints3. Alternatively, steel joints cast using 3D printed moulds can provide a means of avoiding issues with scale and certi fication. The use of 3D printing in the production of joints for a truss may reduce the costs associated with unusual joint configurations and may ultimately allow more tailored designs to be considered. It is also possible to rationalise optimum forms to make them easier to fabricate. Previous studies have shown that simplified structures that are similar in form to the optimal layout have the
materially effi cient designs possible, but are not currently commonly used in structural engineering practice, partly due to the complexity of the forms they generate. For example, consider the 50m span basement transfer truss required for a hotel development project (Figure 1). 1). A range of designs for the problem are presented in Figure 2. 2. Fig. 2a shows 2a shows the basic truss structure derived manually, manually, which resembles a Warren truss. In contrast, the solution shown in Fig. 2c, 2c, obtained using numerical layout optimisation, would in theory consume much less material. However, this comprises many thin members, each of diff erent erent length and crosssection. This is a close approximation to the true theoretical solution for this problem, which can be obtained based on the principles set out by Michell in 19041, and which includes an in finite number of
potential to retain a signi ficant level of 4material effi ciency with much lower complexity . This is explored here. One such simpli fied structure is shown in Fig. 2b; 2b; this has a weight which is little higher than the identified optimum form, and less than half that of the manually derived truss (Fig. 2a). 2a). Based on this observation, the method described here involves first finding a minimum-weight structure without imposing limits on complexity, complexity, and then gradually rationalising the design by accounting for practical considerations. Here, the term ‘structural complexity’ is used to refer to a range of features; considering minimumweight structures, the number of members and the number of diff erent erent cross-sections are both commonly identified as major issues. Therefore, the method progressively removes members and/or standardises cross-sections, to lead to a gallery of
infinitely thin members. Application of new manufacturing manufacturing methods has the potential to remove some barriers to fabrication. For example, additive manufacturing, or ‘3D printing’, techniques are being developed
candidate designs. However,, it is unlikely to be possible to find forms However that are both very simple and very l ightweight. Instead, a choice will need to be made concerning the trade-off between between material effi ciency and
20
October 2019 | thestructuralengineer.org
Optimisation-driven conceptual design
complexity (Figure 3). 3). A demonstration of this will be provided, using the hotel basement transfer structure problem already referred to, from a project by Expedition Engineering. To T o achieve this, a number number of numerical layout optimisation methods developed at the University of Sheffi eld are employed. These methods are implemented in the commercially available LimitState:FORM5 design optimisation software. A feature of the software is that the user can manually remove or modify individual structural members during the optimisation process. The study demonstrates the potential to achieve greater material e ffi ciency through exploration of the solution space, the set of all possible feasible solutions to a problem. It is found that a wide range of possibilities lie between the mathematically optimal, but impractical, forms at one extreme, and the forms typically used in practice today at the other extreme. This allows the design team to make informed decisions on the implications of using a less conventional layout and to indicate where an investment in more complex detailing may be justi fied. Conversely, it will also indicate when benefits are marginal, and therefore when a more standardised design is likely to provide the most economical choice.
Technical
FIGURE 1: Basement
transfer truss: configuration and applied load magnitudes M_1
L_1
L_-1
L_-2
L_-3
M_2
M_3
8700
2500
M_4
M_ 5
9200
9200
M_6
8700
9200
2500
0 0 0 3 0 0 0 4 0 0 0 3
3000
7600
7200
7400
7400
7200
7600
3000
L_-4 L _ B_2
B_3
B_4
B_5
B_6
B_1
1.5MN
LOADING FROM COLUMNS OF SUPERSTRUCTURE
B_7
4.9MN
VERTICAL SUPPORT AT DIAPHRAGM WALLS
3.4MN
3.4MN
29MN 0.5MN
0.7MN
4.9MN
1.5MN
OUT OF PLANE RESTRAINT AT FLOOR SLABS
29MN 0.6MN
DESIGN DOMAIN - AREA WHERE TRUSS MEMBERS ARE PERMITTED
0.7MN
LOADING FROM BASEMENT VIA COLUMNS FROM L_-1 TO L_-3
0.5MN LOADING FROM TRANSVERSE TRUSSES
Available Avai lable optimisati optimisation on techniques techniques Heuristic optimisation methods, such as genetic algorithms, have proved popular in recent years, largely due to the ease with which a non-specialist user can include real-world constraints; a description of several such approaches and their application has been given by Debney6. However,, these methods have severe However drawbacks. For example, the starting points for these methods are usually randomly generated, or based on intuition, but will often influence the final output, likely leading to a suboptimal design being obtained (i.e. corresponding to a ‘local hollow’, which may be much higher than the ‘valley bottom’ shown in Figure 4). 4). Additionally,, with these methods, there Additionally there is no way of knowing how much further bene fit is possible once a solution has been found. This may lead either to unnecessarily unnecessarily ineffi cient designs being accepted, or alternatively to substantial eff ort ort being wasted attempting to improve on a design which is already optimal or near-optimal. Here, an alternative two-step optimisation approach is proposed. In the first step, the problem is simplified so that only the essential physics is modelled; in this case, meaning that only equilibrium and stress limit considerations remain. This allows a reference solution to be obtained, providing a lower bound on the structural volume (or weight). The second step is to apply various methods to move through the solution space to locate promising solutions, if possible in close proximity to the reference solution (Fig. 4b). 4b). For the identification of minimum-weight structures, continuum-based topology optimisation methods are commonly used. These routines are are now included in many many
FIGURE 2: Basement transfer truss: sample discrete designs for problem shown in Fig. 1
COMPLICATED
FIGURE 3: Example of trade-off between
material usage and structural complexity
Y T I X E L P M O C
POSSIBLE DESIGNS
PARETO FRONT SIMPLE LIGHT
HEAVY
MATERIAL MATER IAL USAGE
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thestructuralengineer.org thestructuralengineer .org | October 2019
Technical
Optimisation-driven conceptual design
a) Heuristic method
b) Proposed two-step approach
(e.g. genetic algorithm)
e m u l o V Local optimum
e m u l o V
2. Near Near-global -global optima of realistic problem
Global optimum
1. Glob Global al optimum optimum of simplied problem
Structural Form 4: Methods of treating real-world, non-convex design problems FIGURE
general-purpose finite-element software packages, and are widely used i n the aerospace and automotive industries. However,, they are less obviously useful in the However design of building structures. This is because a typical building structure comprises a sparse assembly of discrete elements, with a very low associated volume fraction (the proportion of original design domain which is occupied by structure after the optimisation), beyond the normal working range of continuum topology optimisation routines. Figure 5 shows 5 shows an example continuum optimisation result for the present case study, produced using the freely available MATLAB script developed by Sigmund7. For building frames, it is more appropriate to instead work with discrete structural elements, as is proposed here. In this case, numerical layout optimisation employing a
Structural Form ground structure8 can be used, in which the design domain is populated with nodes, then interconnected by potential members (Figure 6). 6). Mathematical routines can then be used to identify the subset of members which form, for example, the structure which consumes the minimum amount of material. In the low-resolution example shown in Fig. 6, 6, this resembles a deep Warren truss; at higher resolutions, the minimum-weight solution closely resembles half a bicycle wheel, with a semi-circular compression member and many radial ties. This demonstrates key characteristics of minimum-weight structures: members are axially stressed and bending is eliminated; furthermore, compression and tension members are approximately orthogonal and lie along lines of principal virtual strain. Here, the optimisation problem considered throughout is to minimise the volume of material consumed, subject to equilibrium and strength constraints, using a plastic multiple-load-case formulation9. The mathematical optimisation
THE AVAILABILITY OF EFFICIENT SOL SOLVERS VERS ALLOWS PROBLEMS P ROBLEMS WITH MILLIONS OF POTENTIAL MEMBERS TO BE SOLVED IN SECONDS
problem is linear linear,, which ensures that the global optimum for the given problem can be found, and the availability of effi cient solvers allows problems with millions of potential members to be solved in seconds on an ordinary desktop computer. A Python script implementing the ground structure-based layout optimisation method is freely available10.
Case study: basement transfer truss The case study concerns concerns the conceptual design of a steel transfer truss providing a 50m clear span between the retaining walls on opposite sides of a deep basement (Fig. 1). 1). This carries the loads from a five-storey building and a garden at ground level. It also supports a pair of 50m span transverse trusses which apply a substantial load at the bottom of the design domain. The permitted structural depth is 10m, covering three levels below ground-floor level. The intermediate floors can be used to provide out-of-plane bracing against buckling of the truss elements. This provides an ideal application application for optimisation methods. The combination of loading from the transverse trusses and the building above provides a speci fic and unusual configuration, meaning that the minimum-volume solution may not be familiar or immediately intuitive. Also, because the basement levels through which the truss passes are primarily plant and ‘back of house’ spaces, there are far fewer constraints on the locations of structural members than in more visible areas of the project – although the approach described is equally applicable to arbitrary design domains. Finally, the structure is to be constructed using fabricated hollow square sections, constructed from S355 steel plate. The LimitState:FORM software software was used to undertake the optimisation study described; this implements the ground structure-based layout optimisation procedure described in the previous section. The software also allows deflection limits to be specified and irregularly shaped design domains to be de fined, as well as permitting some further basic structural analysis internally and allowing export to external software (e.g. Oasys GSA 11) to enable more detailed analysis and design to be undertaken.
5: Basement transfer truss: continuum topology optimisation solution FIGURE
22
October 2019 | thestructuralengineer.org
Optimisation-driven conceptual design
Technical
optimisation method FIGURE 6: Stages in numerical layout optimisation
For the purposes of this exploratory study, study, the permissible strength in compression was reduced to approximate the e ff ect ect of member buckling; the value of limiting compressive strength varied from 95% of the yield strength
Design domain withDOMAIN loads and supports a)(A) DESIGN WITH
LOADS
AND SUPPORTS
c) Potential members forming ground structure
(C) POTENTIAL MEMBERS FORMING THE GROUND STRUCTURE
Step 1: Identification of global optimum for simplified problem
Potential nodes b) (B) POTENTIAL
NODES
d) Resulting optimised (minimum volume) layout
(D) RESULTING OPTIMISED
Output from step 1:
Numerical ground structure-based layout optimisation method used to find minimum volume, considering stress and equilibrium constraints
Step 2: Move to identify practical solution, applicable to real-world problem Manual rationalisation used to take account of complexity constraints, including: reducing number of members/ nodes removing complex joints (number of, or angles of, connected members) standardising cross-sections moving towards more common or understandable layouts
Output from step 2:
FIGURE 7: Proposed two-step process (where step 2 may involve several iterations)
23
in the shortest members, to zero in members unrestrained for over 19m. Both uniform and pattern loading (with the transverse truss on one side only factored favourably) cases were considered, resulting in three load cases in the optimisation problem. Using layout optimisation, the structure is usually modelled as a pin-jointed truss; therefore, any node which is not supported out-of-plane by a floor plate or support will be unrestrained against buckling. It would be possible to resist this form of buckling by using nodes/joints with moment capacity. However, in order to ensure all designs were comparable, in this study, joints were permitted to lie only on floor levels and up the sides of the design domain. Although deflections are often critical in the design of long-span structures, for the sake of simplicity,, in the present study, simplicity study, only the ultimate limit state was considered initially (i.e. stress constraints). However, However, the software used can also account for deflections, and deflectiongoverned problems actually off er er greater potential savings with the use of optimisation methods; this is discussed later in the article.
Interactive rationalisation of structure The LimitState:FORM software software allows the engineer to interactively edit an optimised solution, e.g. to make it easier to build. This forms the second step of the two-step process outlined in Fig. 4, 4, i.e. moving from the solution of the simplified problem to a design that is a feasible solution for the real-world problem (Figure 7). 7). Following a manual edit, a secondary optimisation problem is solved to ensure the edited structure is both stable and as lightweight as possible. This uses the same volume-minimising objective function and equilibrium/stress constraints as the initial problem; however, the reduced ground structure used in the manual editing stage allows simpler structures to be produced. This process can be repeated a number of times if desired. Each secondary optimisation problem includes linear size optimisation and non-linear geometry optimisation steps, where the latter allows joint positions to be adjusted. Each of these optimisation problems can be solved very quickly,, in just a few seconds for the problems quickly shown here, permitting rapid exploration of the solution space. In the interactive step, the designer can individually choose members to add or remove from the structure (Figure 8), 8), with the influence
thestructuralengineer.org thestructuralengineer .org | October 2019
Technical
Optimisation-driven conceptual design
FIGURE 8: User interface – red members
of such edits on the required volume of material to form the structure clear at all times. The designer can choose their modifications based on any potential criteria, such as minimum angles between members, total numbers of joints, etc., but is free to break rules if they they wish. This allows for a flexible definition of complexity complexity,, which may be specific to the problem at hand or vary as the designer reacts to solutions identified by the optimiser optimiser..
manually marked for deletion
Fig 9j shows 9j shows the results of layout optimisation where nodes are only permitted to lie at loading points and at the top and bottom of the supports; Fig. 9k shows 9k shows the case where these members are not restrained from buckling in the outof-plane direction by the floor plates that they pass through. In Fig. 9l, 9l, the number of diff erent erent cross-sections used in this case is limited to four. The manual rationalisation method can be used to force the structure
Results The results of the proposed approach approach are presented in Figure 9 with 9 with an increasing number of constraints applied to the structure. The output of the layout layout optimisation technique is shown in Fig. 9a. 9a. These results use a grid of nodes at 0.25m spacing, which results in 32 million possible members. This provides a numerical approximation to the Michell truss for this problem. While this structure would clearly be challenging to construct, it provides a close approximation of the lower-bou lower-bound nd reference solution, which uses the minimum possible amount of material to carry the applied load. In Fig. 9b, 9b, the nodes are restricted to lie only on the slab lines where lateral restraint is provided; in Fig. 9c, 9c, the permitted compressive strength is reduced to account for member buckling. At this point, the structure can be said to be physically possible – although unlikely to be buildable using currently available technology. Fig. 9d shows 9d shows the result when the pattern loading cases are considered. Fig. 9e shows the results of automatic rationalisation using the joint-length method 12. A series of designs following manual rationalisation steps are shown in Figs. 9f–h. 9f–h. After this,
FIGURE 9: Basement transfer truss: derived concept designs
forms using a limited number of di ff erent erent cross-sections are found; the result with four cross-sections is shown in Fig. 9i. 9i. This is currently performed as a post-processing step with the node locations and layout remaining unchanged.
24
to take on easily recognisable forms, such as the Warren truss like form shown in Fig. 9m. 9m. For cases where the number of diff erent erent cross-sections is further limited, the outcomes are shown in Figs. 9n–p, 9n–p, with the design in Fig. 9n allowing 9n allowing four cross-sections in any configuration, the design in in Fig. 9o having 9o having equal cross-sections along the top and bottom chords, and the design in Fig. 9p also 9p also having a single cross-section for all diagonals. The options presented presented in Fig. in Fig. 9 9 provide the designer with the information needed to quickly appraise the trade-off between between complexity of form and weight of steel required for this particular design problem. Another way of thinking about the journey through the solution space is to consider the outcome at each step following a given design
October 2019 | thestructuralengineer.org
Optimisation-driven conceptual design
decision; this is illustrated in Figure 10 for 10 for the basement transfer truss case study. This means that the engineer can take an informed view on the consequence of each design decision. For example, moving to a familiar Warren-like truss layout leads to a significant increase in the required steel tonnage, even when compared with other solutions with the same number of joints (e.g. the structure structure shown directly below has the same number of joints).
Commentary The proposed method method provides a quick way of finding a number of possible design concepts. This allows the impact of di diff erent erent design decisions on the overall structure to be evaluated, informing the decisionmaking process. As with all optimisation methods, it is important that the problem passed to the optimiser accurately represents the real demands on the design. For example, a structure optimised only for a uniformly distributed loading may not be able to resist pattern loading
FIGURE 10: Basement transfer truss: volume increases
due to imposed design constraints
of that load, and as external and internal work must be equal, the layout of the l owest-volume design with stress limits will correspond to the layout with the lowest deflection (when all members are subjected to a given stress). To T o move between the stress-based solution and the deflection-based one, all cross-section areas in the solution can be scaled by an appropriate factor. factor. As the minimum volume layout has both the least material and the highest stiff ness, ness, it produces the minimum volume result for a given de flection when scaled
higher steel tonnage than the optimal value. The volume penalty on the rationalised form also increases slightly; however, however, it still off ers ers an increased saving compared with the Warren-like truss. This shows that the potential advantages of layout optimisation are further magnified when the design is governed by deflections. Seeking the minimum volume of material is a clear quantifiable goal for use in the optimisation process. This value can potentially be used as a surrogate for other quantities, such as embodied carbon or material cost, although in reality both of these will also be influenced by other factors, including the complexity of the structure. In addition to complexity complexity,, the manual rationalisation method also allows concerns such as construction sequence and aesthetic considerations to be addressed intuitively. Therefore, Therefore, it may be necessary to maintain some element of manual control even when more automated methods are used. This also provides the designer designer with more freedom to explore the design
IT IS IMPORTANT THAT THE PROBLEM PASSED TO THE OPTIMISER ACCURATELY REPRESENTS THE REAL DEMANDS ON THE DESIGN
cases, if these are not also included in the problem specification at the outset. While post-optimisation checks can identify such issues, better solutions will generally be obtained if these are included in the initial model. As a relatively long-span structure, structure, deflections are also likely to be important. Therefore, an understanding of how the sti ff ness ness of the optimised designs compares to more traditional layouts is of interest. It has been previously demonstrated that for single-loadcase problems, the optimal truss layout will be the same irrespective of whether the design is governed by stress limits or deflection limits13. This is based on a minimum-weight minimum-weight truss structure for a single load case being statically determinate and fully stressed. This means that the constituent truss members will be uniformly strained and, therefore, that the internal strain energy will be proportional to the volume of material used. Since the external work done by an applied load is proportional to the de flection
(this can be interpreted as the sti ff est est structure for a given volume). As rationalisation moves a design further from the optimum, its volume increases and also its sti ff ness ness reduces. For deflection-governed designs, these e ff ects ects compound and cause even greater di ff erences erences in volume. However,, this is not generally the case in However multiple-load-case problems. While this study does have multiple load cases, the fully l oaded case dominates the design. The top row of Figure 11 shows 11 shows stress-based designs; the Warren-like Warren-lik e truss (right) has both a 40% higher volume than the optimised structure (left) and also a 32% higher deflection. If a range of mid-span de flections are imposed in the fully loaded case (Fig. 11), 11), for each of the deflection-governed cases, the Warren-like Warren-lik e truss now requires around 64%
25
Technical
landscape than when using traditional optimisation methods, which output only a single design solution. The truss-based nature nature of the layout optimisation method means that interaction with solutions should be fairly intuitive to anyone familiar with more conventional frame analysis programs. Developing a feel for the best members to add or remove comes with practice. This intuition may be obtained through experience, although it will be informed by knowledge of the fundamental features of minimum-weight structures (such as preferring the use of purely axially loaded members, and noting that tension and compression members should ideally intersect at close to 90° in problems dominated by a single load case). In our increasingly resource-conscious resource-conscious society,, the training of future structural engineers society should foster a culture of inquisitiveness around optimisation and a desire to improve the effi ciency of our structures, making use of eff ective ective software tools to facilitate this.
thestructuralengineer.org thestructuralengineer .org | October 2019
Technical
Optimisation-driven conceptual design
Conclusions Structural optimisation techniques have the potential to help structural engineering designers to realise significant savings in material usage, embodied carbon and/or cost. While it is important that care is taken in formulating a design problem, and in performing detailed checks on the design solutions generated, the case study described here, of a 50m span hotel basement transfer truss, clearly demonstrates the usefulness of optimisation, and that available tools are now becoming suffi ciently mature for use in engineering practice at the conceptual design stage. The two-step optimisation approach presented addresses some of the major concerns that have previously limited uptake of optimisation in practice. Using this approach, a wide range of structural options can be generated, helping the design team to make informed decisions on the balance to be struck between complexity and material effi ciency. The results show the potential for signi ficant material savings, even once fabrication constraints are accounted for. for. This provides an opportunity for designers to explore options derived from highly effi cient structural forms, which may not initially be obvious.
Acknowledgements Acknowl edgements This paper is based on a poster poster prepared by Helen Fairclough that was awarded 1st Prize at the 2017 IStructE Young Researchers’ Conference. The authors acknowledge acknowledge the financial support of Expedition Engineering and the EPSRC under grant reference EP/N023471/1. LimitState, a Sheffi eld University spinout
company cofounded by Matthew Gilbert, Andy Tyas T yas and two other academics, academics, provided access access to its LimitState:FORM design optimisation software for the purposes of this study.
11: Basement transfer truss: effect of limiting mid-span deflection FIGURE
REFERENCES
1) Michell A.G.M. (1904) ‘The limits of economy of material in frame-structures’, Philosophical Magazine, 8 (47), pp. 589–597 2) Richardson V. (2017) ‘3D printing becomes
concrete: exploring the structural potential of concrete 3D printing’, The Structural Engineer , 95 (10), pp. 10–17 3) Galjaard S. (2019) Additive Additive Manufactur Manufacturing, ing, Design method for critical structural steel elements [Online] Available at: www.arup.com/
projects/additive-manufacturing (Accessed: June 2019) 4) Prager W. (1978) ‘Optimal layout of trusses with finite numbers of joints’, J. Mech. Phys. Solids, 26 (4), pp. 241–250 5) LimitState Ltd (2017) LimitState:FORM (2017) LimitState:FORM
[Online] Available at: https://limitstate3d.com/ (Accessed: August 2018) 6) Debney P. (2016) ‘An introduction to engineering optimisation methods’, The Structural Engineer , 94 (3), pp. 34–41 7) Sigmund O. (2001) ‘A 99 line topology optimization code written in Matlab’, Struct. Multidisc. Optim., 21 (2), pp. 120–127
scale frameworks subject to multiple load cases, member self-weight and with joint length penalties’, Proc. 6th World Congress of Structural and Multidisciplinary Optimization,
Rio de Janeiro, Brazil 10) He L., Gilbert M. and Song X. (2019) ‘A
Python script for adaptive layout optimization of trusses’, Struct. Multidisc. Optim., 60 (2), pp. 835–847 11) Oasys (2019) GSA – Structural Design & Analysis Software Analysis Software [Online] Available at: www.
oasys-software.com/products/structural/gsa/ (Accessed: September 2019) 12) Parkes E.W. (1975) ‘Joints in optimum frameworks’, Int. J. Solid Struct ., ., 11 (9), pp.
1017–1022 13) Nagtegaal J.C. and Prager W. (1973)
‘Optimal layout of a truss for alternative loads’, Int. J. Mech. Sci ., ., 15 (7), pp. 583–592
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8) Dorn W.S., Gomory R.E. and Greenberg H.J. (1964) ‘Automatic design of optimal structures’, Journal de Mecanique, 3, pp. 25–52 9) Pritchard T.J., Gilbert M. and Tyas A. (2005) ‘Plastic layout optimization of large-
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Project focus
Hyperboloid lattice ice structure
1: Installations at Harbin International Ice and Snow Sculpture Festival FIGURE
fi
Design of the thehyperboloid, world’s world’ s rst sprayed-net, lattice ice structur structure e CAMERON MILLAR
SYNOPSIS
Engineering student, University of Cambridge, UK
In December 2018, a team of student engineers and architects from the University of Cambridge took part in the Harbin Institute of Technology’s second annual International Ice and Snow Innovation Construction Competition. With average winter temperatures being a chilly –15°C, Harbin is an ideal environment for ice structures. The Cambridge design – the world’s first sprayed-net, hyperboloid, lattice ice structure – won the Best Design and Construction Works Award in the competition. 28
October 2019 | thestructuralengineer.org
Hyperboloid lattice ice structure
Introduction
but this never got beyond scale modelling. One supposed advantage was the ability of the pykrete to self-heal if holed in an attack. In more recent years, an ice hotel industry has developed, with countries such as Canada, Norway and Finland off ering ering rooms sculpted from snow and ice. As a construc construction tion material, material, ice is ‘free’ and is most sensibly used in compression. This can be achieved by building with blocks, or by casting, spraying or extruding water over an appropriately shaped mould.
The city city of Harbin Harbin in China has has hosted hosted an International Ice and Snow Sculpture Festival annually since 1985. It is now the world’s largest ice and snow sculpture festival, attracting up to 15M visitors annually between December and February. Sculptures created during the festival can be up to 50m tall and are erected by a team of 10 000 workers using 120 000m3 of snow and 110 000m3 of ice harvested from the Songhua River (Figure 1). 1). The Harbin Harbin Institute Institute of Technology echnology’’s (HIT) International Ice and Snow Innovation Construction Competition was launched to complement the main festival, and in 2018, teams from the University of Cambridge, TU Eindhoven, Tsinghua T singhua Univers University ity and Kent State State Universit Universityy travelled to Harbin to learn from the experience of constructing using ice and snow.
Hyperboloid design The HIT competit competition ion proposed proposed a simple brief: brief: erect a sculpture within a 5m × 5m × 5m cube that showcases innovation in design and construction. Accordingly, the Cambridge team designed a 5m tall, hyperboloid, lattice structure, formed of two hexagons (5m diameter at the top and 2.5m diameter at the base) joined by inclined columns of approximately linearly varying diameter (150mm at the base to 75mm at the top) (Figure 2). 2). The team’ team’s s design design ambition on was to erect erect a rope-net hyperboloid to act as falsework, around which the construction material would be sprayed. During construction, the ropes were suspended from a crane, keeping them in tension (Figure 3); 3); upon completion of the spraying, the crane would be released, giving a compression-only structure. Compression-only was desirable due to the limited tensile capacity of ice, and is why many ice structures are created as shells. However, these can require inflatable moulds onto which water is sprayed, or tensioned fabric formwork. Both of these are expensive to produce as they must be made uniquely for each structure. In comparison, a rope-net is easy to produce in a few hours from materials commonly found in any hardware store.
Ice construction Ice has been used in construction for thousands of years. Early Inuit travelled across what is now Alaska,, Canada and Greenland, Alaska Greenland, building ice and snow houses for shelter. Igloos were built of blocks of snow or ice in a circular form and were good at retaining heat and protecting occupants against wind in harsh conditions. During World War II, Geoff rey rey Pyke developed ‘pykrete’, a composite material of water and wood pulp (sawdust, paper or cellulose) that can be up to three times as strong in compression, has a fracture toughness up to 20 times that of freshwater ice, and is more durable. The original composition included 14% sawdust by weight; the dust provided insulation and slowed the melting rate. In 1943, Project Habakkuk proposed using pykrete in the construction of an aircraft carrier,
FIGURE 2: Completed ice structure from Cambridge team
FIGURE 3: Prestressed hemp rope-net before spraying
Project focus
The beauty beauty of the the design gn was how the formwork became part of the final structure. Ice construction is usually diffi cult because the formwork required is large and technically challenging, as it must hold the water while it freezes (and expands). Through the use of a net, the formwork was easy to design, cheap to produce, and very sustainable. Moreover, the formwork itself helped prestress the ice, increasing the overall structural stability. Very few forms allow a tension tension-only -only lattice lattice to to form a compression-only structure upon release of the loading mechanism. The hyperboloid lattice did this well. At the same time, the structural form was elegant and effi cient; and as a compression only structure, it had a short load path, so transferred the loads applied to it effi ciently to the ice foundations.
Construction To construct To construct the the hyperboloid, hyperboloid, two two timber timber hexagons were fabricated for the top and bottom sections. Hemp rope was assembled between the two hexagons in the pattern required for hyperboloid geometry. Then, three blocks of river ice, each with a mass of roughly 600kg, were placed atop the bottom hexagon to act as ballast and the top hexagonal frame was lifted using a mobile crane (Fig. 3). 3). A 1t load was applied by the crane to the structure to pretension the hemp rope. The tensioned tensioned ropes ropes were were then wetted and and wrapped in toilet roll, a technique that would increase the speed of subsequent construction. The natural natural fibres in hemp are thought to allow a strong bond between the ice and rope to form, preventing pull-out and maintaining the prestress applied. Where the ropes crossed, they were secured together using cable ties to keep the lines of force action in the final structure as close together as possible. The tensioned tensioned rope-net rope-net was then then sprayed sprayed with water mixed with cellulose (0.6% by weight) continuously for three days using a fireman’s hose (Figure 4). 4). The mix design for spraying was selected to maintain a balance between the viscosity required for spraying and the strength required for the final structure. During spraying, the geometry was monitored to give approximately equal build-up of ice around the whole structure (Figure 5). 5). A second second ice mixtur mixture e with a larger cellulos cellulose e content was then mixed separately and used to reinforce the structural nodes, which were not achieving suffi cient thickness through primary spraying alone. This second mixture had pastelike qualities and could be easily placed by hand onto areas needing to be thicker. A ‘cherry picker’ (or mobile elevating work platform) was used to access parts which could not be reached from the ground. Once spraying was completed, the crane hook was lowered and disconnected from the top of the hyperboloid (Fig. 2). 2). It was estimated that the release of the prestress put an axial load in the ice columns of 0.14MPa, which was intended to help prevent the ice from cracking. The release of the crane demonstrated the success of the design,
29 thestructuralengineer.org | October 2019
Project focus
Hyperboloid lattice ice structure
FIGURE 5: Continual
growth of ice over spraying process
FIGURE 4: Spraying
as the structure stood in place for the remaining duration of the competition without any noticeable defects. Conclusion The team team from the Universit Universityy of Cambridge Cambridge successfully designed and constructed the world’s first hyperboloid lattice ice structure in Harbin, China, using an innovative sprayed-net technique. The properties properties of ice encourage encouraged d the use use of a form that produced a purely tensile support structure during construction, yet transformed into a purely compressive structure upon release.
structure with pykrete
By tension prestressing the supporting rope-net, a compressive prestress was created in the ice struts which reduced the structural eff ects ects of imperfections. Hemp rope was used throughout to improve the bonding with the ice, and the water–cellulose mixture gave the material the required strength. Most ice structures require large and complex single-use formwork. By incorporating the formwork into the final structure, the method used in the erection of the hyperboloid was cheap, sustainable and fast.
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Opinion
Profile
Fiona Cobb Fiona Cobb has surprised herself throughout her career, from going to university to be an engineer, to working for a top London consultant, consulta nt, to writing a book that’s in the Science Museum. Her latest adventure is to start her own practice,
IF YOU HAVE EVER owned or borrowed a copy of the Structural Engineer’s Pocket Book , you will know the name of its author, Fiona Cobb. That’s at least 40 000 of you according to the print run, but it’s likely to be a lot, lot more. Cobb drafted out the potential headings for the publication in a vaporetto vaporetto water water taxi while working briefly in Venice, approached a publisher directly and was commissioned to put the handbook together. It’s now in its third edition, is an approved text for 66 university courses in 16 countries and is included in the structural engineering exhibit in London’s Science Museum. So, for everyone who has ever used the tables, data, facts, formulae and rules of thumb to source job-simplifying job-simplifyin g and time-saving time-saving information, information, or who has worked with Cobb during her two-decade career at
ply panels made by a gondola maker. That started a real interest in how trades make their mark and became very relevant to the conservation work I do, where we are very reliant on the skills of the craftspeople. ‘I also started working at the Grade I and II listed Westminster School with Ptolemy Dean Architects. Ptolemy won a competition for a new building on one of the school yards; his solution was to reverse the 20th century additions and restore the historic pattern of the buildings. That led to five projects to reorder the accommodation in Busby’s Yard, which unlocked the heritage aspects and the internal circulation routes, but we were allowed to provide new accommodation by adding storeys in a sensitive setting in the middle of a UNESCO World Heritage Site. ‘That’s where I saw that if you understand the context of a historic structure and do something subtle,
she tells Jackie Whitelaw.
Price & Myers, here’s what she is up to next.
sensible andyou useneed. good I’m materials, you will get the permissions also always aware of people 300 years in the future looking at what I’ve done and judging me.’ me.’
Going it alone At 46, Cobb has just left left the security security of employment employment at one of the UK’s leading practices, where she became an expert in conservation and heritage work, to start her own business of Cobb & Company. The firm opened its doors in early October and the signs are that it will be just as successful successful as her her other ventures, ventures, including including the pocket book. ‘From the moment I left Price & Myers, I’ve been approached about a job every day,’ she says. ‘That better work–life balance I had planned may have to wait, but it’s very gratifying to be in demand. ‘I’ve worked with a lot of people for a long time, I suppose – grown up with them, eff ectively,’ ectively,’ she says. ‘We’ve gone through the various life stages at the same time, so there’s a bond. And I’ve helped out others who started their own business ahead of me. Now they are returning the favour – they understand how di ffi cult it is to take that first step and they appreciate the entrepreneurial urial nature of what I’m doing.’
Heritage values values Cobb can divide ivide her 22-year 22-year career at Price r ce & Myers yers into nto two halves, diff erent erent experiences that led subliminally nally to the conclusion that her own n business was the right next step. tep. ‘My first 10 or or 11 years from rom 1997 were fant fantastic fantastic. astic.. I was under un er founding partner artner Sam Price’s wing, became me chartered in four years, was made an associate, did a master’s, r’s, wrote the book and worked on some some gre great at projects, including cluding clud ing the the one in n Venice Ven ice with Sam Sam to convert convert a brewery into o flat ats. s. Thiss had a some some som e gorgeous sculptural culptural touches such as doubly curved, urved, stressed-skin,
Changing priorities During this time, Cobb had settled with her partner and had children. That has defined the last 10 or 11 years of her working, as well as personal, life. ‘I was working part time, juggling life and there were many days when I felt I was failing. There were moments when I lost confidence – when I felt I wasn’t doing as good a job as before because I had to get up and leave the o ffi ce at 5pm and nor was I doing as good a job as thought I ought at home. Six hours at work, six more at home, it was exhausting. I could see why women dropped out or their careers stalled. And there were no women role models ahead of me to guide me. ‘Someone described those years as the survival years for a working mother, and I was lucky because my husband is a freelance osteopath and adjusted his hours to make mine work. We’ve been properly 50:50.’ Cobb could have given up, but now, with w t the t e children c ren eight e g t and an ten and more mor mo re self-su se -s -su uffi cient, c en ent, t, sshe e iss glad that she didn’t. What did happen tthough was that latterly she had more time to think, and particularly to think ab about what she really wanted wanted to do with th the next 20 years year ye ars so of her er wo wor working r ng life. e. ‘II asked myself what I rreally enjoyed, and the answer answer was projects. pro e I like making beautiful buildings and the world a nicer place. As Pri Price & Myers got bigger, I found I was more involved in management or admini administration. It was ttime me to make make the leap. leap leap ‘Sam ‘S m Price Price and Robert Myers had established e t s e the t e company company in their mid40s, 0s, and there are a lot of of people I know who began their ow own businesses
32 October 2019 | thestructuralengineer.org
Profile
Opinion
A CAREER IN FIVE FIVE PROJECTS PROJECTS
QUEEN’S SCHOOL, ETON COLLEGE, WINDSOR
A £12M refurbishment refurbishment with CSK Architects of a complex of science buildings including a Victorian Grade II listed building, a 1960s block and 1980s building by Sir Philip Dowson.
THAT STARTED A REAL INTEREST IN HOW TRADES MAKE THEIR MARK at a similar age. A spate of my projects was coming to completion and there was a company reorganisation under way. It was the right time for me.’
Accidental Accide ntal engineer engineer If there seems inevitability about the move, Cobb was as surprised as anyone when the time came. ‘I like to think I have a plan, but in my career, all the good stuff has has been luckily accidental,’ she says. ‘I wasn’t supposed to go to university, I wasn’t supposed to be an engineer, I wasn’t expecting to write a book and I arrived at a top practice like Price & Myers by chance. It certainly never occurred to me that I’d set up my own business, but here I am.’ At school, although although no one in her her family had ever
E N L I M O D I D
WESTON TOWER, WESTMINSTER ABBEY, LONDON
Project for the Dean and Chapter of Westminster Abbey with Ptolemy Ptolemy Dean Archite Architects: cts: a new stair stair and lift tower tucked into the narrow Poets’ Yard between the Grade I listed abbey and scheduled monument of the Chapter House and next to the site of Caxton’s printing press. The core of the tower is reinforced concrete with a steel exoskeleton which is stabilised by the oak stair and landings.
T N A R U D R E T E P
MAGGIE’S CENTRE, CHELTENHAM
A new-build new-build ‘home ‘home from home’ home’ for cancer cancer patients patients with with MJP Architects: timber, steel frame and a sedum roof.
Y D E N N E K N O M I S
S M A I L L I W N A L A
BUSBY’S YARD, WESTMINSTER SCHOOL, LONDON Five phases of reordering of accommodation with Ptolemy Dean Architects.
PARABOLA ARTS CENTRE, CHELTENHAM LADIES’ COLLEGE
Conversion and extension with Foster Wilson Architects of a Grade II* listed Victorian villa to create a performing arts theatre.
been to university, her physics teacher asked her why she wasn’twhen considering it, Cobb thought why not, and went for it. ‘I was at an enormous comprehensive in Dundee and I’d just assumed I’d leave and get a job. But, instead, I studied Civil Engineering with European Studies at Heriott Watt University in Edinburgh. ‘The final year in France was daunting but great fun – it definitely made me braver and I learned that a few words and a smile can get you a long way as long as you have a go at the language, rather than try to form the perfect phrase. I think it gave me confidence to put myself forward for things even though I don’t know everything there is to know.’ But being abroad meant she missed the ‘milk round’ (or graduate recruitment process) and had to find a job for herself, which she did at a small practice in Edinburgh. ‘They were great, but everyone I knew had left the city so there was nothing to hold me there. I went through the job adverts in a professional magazine and applied to three not knowing too much about the companies. ‘Price & Myers were the only one that replied. I went down to London for the interview and it was clearly a brilliant place to work. I was desperate for an o ff er.’ er.’ ‘I thought I’d work down in London for five years and go home, but instead I found a lot of nice people and lovely projects and I’ve stayed.’ Now it’s time for Fiona Cobb and Cobb & Company to make their own mark.
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33 thestructuralengineer.org | October 2019
Opinion Viewpoint
Viewpoint
Computational Computat ional design: embedding embeddin g sustainability
The Institution’s Digital Institution’s Digital Work flows and Computational Design Panel calls Panel calls for a rethink of what computational design offers the industry for more sustainable design.
Press coverage of computational design is dominated by otherworldly architectural geometry and innovative (read: expensive) materials and techniques. The Institution’s Digital Work flows and Computational Design (DWCD) Panel is working to bring these tools down to earth and into the everyday vernacular of structural engineers at all stages in their career. ‘Computationally designed’ buildings,
materials will endeavour to use materials and techniques to reduce the embodied carbon, or make the structure fit better with local skills and traditions. However, not only is this again a niche filled with ‘sustainability specialists’, it is also seen as a bolt-on to a practice’s day-to-day work. This is, is, of course, course, a generalisation, sation, but not too distant from the reality of sustainable design – at least within the
often polished style, are allwith too a often seen parametric as expensive exploratory works into the use of these advanced tools to create innovative architecture. Rightly so. These complex structures are striking, impressive and evidence of personal and corporate technical prowess in high-performance structural design. However, the side eff ects ects of these sorts of advertisements should not be underestimated. Often, this perceived glamour of complex digital work flows obscures much of the potential benefit of using these tools and, perhaps more importantly, of computational design thinking. The panel panel encourages encourages you you to put put
UK. Given theas impact of our on the planet a whole, thisindustry is not the attitude our profession should be taking.
aside these types of grand, complex and expensive structures and instead to consider something else entirely: the vast potential of computational design to embed sustainable practice in our design work regardless of tooling. While sustainability is an increasingly important topic, it often takes one of two distinct forms within our industry. The first is a cynical view of sustainability – essentially as an afterthought to construction projects. A metric metric by which which to score brownie points with the local government, or somehow bring attention to the project internationally – playing on the ‘green’ qualities of the building. The second, second, on the opposite opposite side side of the spectrum, is ‘sustainable’ design practices oriented directly towards improving the sustainability of projects. Engineers with a passion for sustainable
Material use The constructio construction n industry industry uses uses nearly half of the 1.3–1.5bn tonnes of steel produced globally: 750M metric tonnes of steel contribute in the region of 1250M tonnes of CO2 per year1, carving out pit mines for iron ore and coal, the runo ff from which can seep into groundwater. It is quite clear that that even a singledigit percentage reduction would considerably reduce anthropogenic impact on the planet. A similar lar situation situation is found with concrete. Neglecting the relatively recent adoption of ground granulated blastfurnace slag (GGBS) and pulverised fuel ash (PFA) as concrete additives, the production of Portland cement has considerable impact on the planet. Annually, 8% of global CO CO2 emissions come from the production of structural concrete alone2. Reducing emissions from construction activities, and related impacts, could
THERE ARE MANY TOOLS NOW REACHING LEVELS OF MATURITY MATURITY WHERE WHE RE WE CAN SEE REAL-WORLD ADVANTAGES ADVANT AGES AND USE CASES
go a considerable way to reducing the environmental impact in areas that are likely to feel the brunt of climate change. Africa, South America, India and Southeast Asia are particularly at risk.
Material gains So, the question posed is twofold: 1) What 1) What sort of savings can be achieved? 2) By 2) By what means can we reduce material usage or use alternatives materials and techniques? A third third question question would usually be: ‘Is it worth undertaking?’ However, this can be answered by the first two, and with the increasingly dire state of the climate, it is unlikely that we will have the luxury of maintaining unsustainable practices for much longer. The library library of computat computational ional methods methods is ever increasing, and it is generally quite diffi cult for those constrained by delivery schedules to have the time or funding available to put research methods or new techniques into practice. This eff ectively ectively requires iconic projects to fund the use of these tools in their quest for interesting forms and solutions to design challenges. Reaching the level of development seen in, for example, the automotive industry is slow without widespread investment in research and development. There are are many many tools now reaching reaching levels of maturity where we can see real-world advantages and use cases. At the Institut Institution’ ion’s s Digital Digital Design gn and Computation Conference in March 2019, several projects were showcased. Delegates were inducted into the world of construction issue management via new database-driven building information modelling platforms, computational links with popular analysis software and, in particular, an EPSRC research project based around layout optimisation. This project project has has developed developed tools tools and methods for quickly experimenting with structural forms for concept design. The plug-in plug-in for the the popular ar visual visual
34 October 2019 | thestructuralengineer.org
Viewpoint Opinion
programming tool Grasshopper quickly places elements and joints to resist a set of user-defined loads – minimising material volume by tracing the optimum load path down to supports3. Used mindfully, tools like this that allow for visual interrogation of structural behaviour could be the key to a more sustainable built environment, even without alteration of traditional design techniques.
Design through to delivery With the advancement of software tools within the structural engineering profession, there is huge potential for savings. How much does the structure of a building contribute to its whole-life carbon? As always with these sorts of questions, the answer is, ‘it varies’. Over a 30-year lifespan, the embodied carbon will comprise 40%, a signi ficant proportion 4, but one that will generally reduce as the building is in service for longer (neglecting any sequestration or increase in renewable energy sources). Furthermore, as weemissions see a reduction operational carbon duringin service, the proportion of whole-life carbon taken up by the structure will creep up. Of course, we needn’t wait for this to happen to begin carefully considering material use, nor should we. There are two two types of saving ng that can be off ered ered by computational design: time and material resources. Time can be subdivided vided into into design design time and construction time. The designer’s time has the potential to be saved (along with the electricity used to run their analysis models!) using computational design methods to automate calculations and generate scheme designs in a more agile fashion,
robustness of our structures often benefits from alternative load paths through elements that are imperfectly manufactured. However, optimisation techniques applied to beam systems, or on a more granular level at connection/ component design, can still off er er significant savings – if the associated design procedures become easier to use.
Computational design is about more than just experimental architecture. The
sustainability as one of its main guiding principles. If instead, a multi-objective optimisation of initial scheme designs could be undertaken, the industry could eff ortlessly ortlessly embed sustainable choices from the very beginning while maintaining a more measured conservative design. Takin T aking g an info informed rmed decision sion base based d on the output of the design tool is something the engineer has done for decades. This should be no diff erent. erent. But what does this mean in real terms? What are the processes by which computational design could drive down
responding quickly to changing briefs or requirements. Design time is cheaper than time on site; thinking more carefully during the design stage can reap dividends later during construction. On site, detailing of connections and using methods to quickly rationalise large numbers of connections (for example) can help in fabrication and assembly time. Coordination using digital design tools more generally can not only reduce the time taken for manufacture, but can better avoid clashes and prevent late design changes that often result in waste. Material usage, however, comes as a trade-off between between effi ciency and redundancy. Optimisation of material usage reduces the number of redundant load paths through an element. Thus, the lower bound of material usage will likely never be achieved. The inherent
aim is to remove the burden of detailed iterative calculation to allow engineers to concentrate on designing innovative solutions to new problems, and better solutions to old problems. The view of the the struc structura turall engine engineer er as the stalwart of the design team isn’t unusual, and perhaps it isn’t unfounded either. Many of us have known the pressure of tight design deadlines looming towards the end of the day and the need to specify critical members far earlier, and to a higher level of detail, than should be required at any given stage. With the watchful eyes of the quantity surveyor and the client monitoring every gram of steel or cubic centimetre of concrete above the initial estimate, the tendency is to over-specify. A conse conserva rvative tive appr approach oach (per (perhaps haps), ), a risk-averse approach (surely), but an approach that seldom considers
material usage? The answ answers ers come in the the form form of common engineering choices that often take too much time to answer during a project. | Could a select number of steel columns or transfer beams of higher strength significantly reduce the overall tonnage? | Can we benchmark our structure against the minimum possible amount of material given the most effi cient grid? | What is the trade-off between between more groundworks against a lighter, higherstrength structure? | How does designing a highly effi cient structure limit change of use? | What is the optimum truss-member layout for a given set of load cases? | Can we use a local, more renewable source (e.g. rammed earth or bamboo) for certain applications instead of
Optimising for strength(s)
The perceived
glamour of complex digital work flows can obscure the potential benefit of these tools
35 thestructuralengineer.org | October 2019
Opinion Viewpoint
importing steel or assuming low-strength concrete? There are There are many many such ques question tions s that, that, if addressed, could provide a significant reduction in embodied carbon and improve our design work. Computational methods and automation of such design studies have the potential to quickly and e ffi ciently resolve these questions. Conclusions The use of analy analysis sis tools to to optim optimise ise framing arrangements, components, etc. involves the design of algorithms, as does undertaking studies to investigate strategic use of diff erent erent materials or diff erent erent strengths of the same material. Structural engineers should be leading in the design of these algorithms, the software that will retool our industry. Yet, there’s little to no requirement for structural engineers to learn to program in modern university curricula, and not all universities o ff er er dedicated programming courses for students wishing to take them as electives. There Ther e are are curre currently ntly relatively atively few tools (if any)sustainability that optimisecriteria. structural systems using However, the semblance of the tools required is beginning to coalesce (a process that the panel urges engineers to get involved with).
Unfortunately, computational design tools have not yet reached critical mass, nor do they have suffi cient gravity to begin the self-sustaining reactions that will one day lead to ubiquitous use across the engineering world. The intention of this article is to expose more engineers to the use of computational tools in areas far more diverse than they may have previously considered. The pane panell believ believes es that that a speed speedyy uptak uptake e and enthusiastic adoption of computational techniques, through automation of the mundane via scripts or spreadsheet, via pre-packaged solutions or through fully developed software packages, coupled with the ability of structural engineers to build the tools they need themselves, will have considerable advantages for project coff ers, ers, our planet and our consciences. Ashley Kacha MEng Ashley is the Institution’s Senior Engineer for Computational Design and specialises in the development and application of digital tools. His work supports the DWCD Panel and coordination of the Institution’s direction in this rapidly evolving field.
REFERENCES REFERENCES
1) Carbon Trust (2011) International (2011) International Carbon Flows [Online] Available at:
www.carbontrust.com/resources/ reports/advice/international-carbonflows/ (Accessed: September 2019) 2) Lehne J. and Preston F. (2018) Making Concrete Change: Innovation in Low-carbon Cement and Concret Concrete e [Online] Available
at: www.chathamhouse.org/sites/ default/ files/publications/201806-13-making-concrete-changecement-lehne-preston-final.pdf (Accessed: September 2019) 3) Computational Design Optimization of Building Structures website (2019) [Online] Available
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at: www.build-opt.org/ (Accessed: September 2019) 4) UK Green Building Council (2015) Tackling embodied carbon
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in buildings buildings [Online] Available at:
www.ukgbc.org/sites/default/ files/Tackling%20embodied%20 carbon%20in%20buildings.pdf (Accessed: September 2019)
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Opinion
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Readers’ letters, comments and queries
Building safety regulations DANIEL MUNDAY I refer to Alasdair Beal’s letter (August 2019) regarding the UK government’s proposed changes to the Building Regulations following the Grenfell Towerr fire, and Verulam’s response. One of the most important statements he made was in his concluding paragraph, in which he suggested some ‘obvious first’ changes in legislation. It is a pity that Verulam did not pick up on these suggestions – this would have helped to highlight them. It has long been a contention mine that Alasdair’s ‘(iii) bring back all of building control functions under local authority control’ should be carried out. The building control function respects matters of public health and safety and should therefore be in the public domain and administered by publicly accountable bodies. Of course, this means better resources, as Alasdair points out, but as it is a service that developers have to pay for, surely it could be priced to break even; after all, the private companies are making profits out of providing the service. Surely a thorough review of the existing building control system, looking at past triumphs and failures, with a view to improving and enhancing the system, is the way forward. Daniel is a senior building control surveyor and there are many who would support his views. As Verulam urged after Alasdair’s letter, there was an opportunity to respond to the public consultation on the future of the Building Regulations. That consultation has just ended: we will see what the outcome will be.
Baku–Tbilisi– Kars snowfall protection structure PAUL TAYLOR Having read the article on the snowfall protection structure for the Baku–Tbilisi–
Send letters to… All contributions to Verulam Verulam should be submitted via email to: to:
[email protected] Contributions may be edited on the grounds of style and/or length by the Institution's publishing department.
Kars ars rail corridor (August 2019) it is clear that the original proposal a) pro on page 17 and the alternative proposal b) on the same ame am e page page pa ge are are both ot flaw awed, awe e , for diff erent erent rreasons.. This project project cried cried out for for a solution solution of precast arch sections built of reinforced concrete. The rail access makes the arch sections easy to transport and place and they will not have the disadvantages of the corrugated steel alternative. This is a case where a fundamental decision
The manufacturer of the corrugated sections was not involved in development of the initial scheme, which was done years prior to construction. The manufacturer manufact urer was was only invited to to propose propose an alternative. alternative. This This alternative alternative was was selected by the lead contractor due to the benefi ts ts it off ered ered in the circumstances of a construction construction market market that that is otherwise otherwise reliant on concrete concrete construction. construction. In other words, it appears that the reader has misunderstood misunders tood the organisat organisation ion and management side of the project. project. Regarding the comments made concerning design life, beyond doubt – given similar conditions conditions – reinforced reinforced concrete structures generally perform
was wrong, and no doubt led by the manufacturer of the corrugated steel arch sections. The design life of 100 years plus without maintenance for the steel sections is optimistic in the extreme and the cost and disruption to replace them at the end of their life makes the alternative option too expensive and disruptive. Precast reinforced concrete arch sections have been used very successfully in the UK and are a far more sustainable solution than the steel alternative. They would not need the geogrid etc., so overall would have been a
better andarequire and requir e lessassessment maintenance. maintenan ce. However, durability of the steel solution was done in accordance with ISO 12944:2001, ISO 9223:1992 and ISO 9224:1992, all of which are are well recognised recognis ed and probably probably used used in many many parts of the world. d. The results of this assessment may appear appear optimistic, optimistic, yet yet dry and and mountainous mountainou s regions regions provide de an entirely entirely di ff e fferent rent environment to that in the UK. That said, given the rare nature of these projects,, only time projects time will reveal reveal the bene benefi ts, ts, as well as shortcomings, shortcomings, of the completed completed structure.
THIS PROJECT CRIED OUT FOR A SOLUTION OF PRECAST ARCH SECTIONS BUILT OF REINFORCED CONCRETE
much better solution. Shame it wasn’t built this way.
AUTHORS’ RESPONSE AUTHORS’ RESPONSE (MIKUS (MIKUS CIRULIS AND MARIS CIRULIS) Mr Taylor provides interesting views and we felt that some clari fi c fication ation would benefi t the overall appreciation of the project. Modernisat Modernisation ion and retro retrofi tting tting of this railway line also included track upgrades along some parts of the line and construction of new bridge structures at others. In essence, construction of the snowfall protection protect ion structure structure had had to be executed without railway transportation being available. Given the circumstance circumstances, s, the steel arch solution was tailored to overcome existing challenges at the time and not the the idealised sed scenario scenario that could have made made a precast precast arch arch solution solution more favourable.
As always, always, engin engineers eers have their own strong views on ‘the best solution’, but as always, there is variety! There are advantages to concrete but some disadvantages: it’s heavier, might equally struggle to last 100 years and local markets will affect cost. If something does break under the diffi cult-to-quantify loading, it’s not hard to see how a patch of sheeting could be rapidly applied. Transporting Transporting and placing concrete in adverse conditions might be harder.
Engineering in the domestic sector GARY SMITH I write in support of Andy Greenwood’s letter in August. We often meet with clients who have been advised by architects that it would be in the best interests of
38 thestructuralengineer.org thestructuralengineer .org | October 2019
Letters
the project to ‘remove the entire rear of the dwelling’ in the name of open-plan aesthetics. Thereafter, we are often met with the response, ‘we did it on the last project and didn’t need a sway frame’. To T o further further exacerbate exacerbate issues, issues, engineers engineers are sometimes not allowed the depth to insert a sway frame in the overhead structure, and any protrusions in the ends of the structure are met with refusal. It is possible to ‘hide’ such a portal in the fabric of the structure if it is detailed correctly, but the two most important issues are i) the sway sensitivity and ii) the foundations. On the first matter, we have assessed portals from other projects that have insuffi cient lateral stiff ness ness and move in excess of 200mm when analysed with the actual column and connection sti ff ness. ness. Anything with a result resulting ing lateral lateral deflection of greater than height/500 is likely to be problematic. On the second issue, the foundations to these portals are likely to be large pads, sometimes extending over the boundary line in closely positioned domestic dwellings! Such frames cannot be seated on the original footing and be deemed acceptable. We are sometimes commissioned on projects after the architect has submitted the plans to building control! Our design solutions are very rarely shown on the original drawings and are never received favourably. Introduction of these solutions at such a late stage in the project is never good news to the client or to the building control checking team. Removing large sections of domestic dwellings is becoming very common, and the design of the aforementioned sway frames should be reviewed by the engineer representative supporting the appointed building control team, be it private or local authority. Gary’s experience certainly echoes those of previous letters.
JOHN CARR Further to Andy Greenwood’s comments on the topic of ‘Engineering in the domestic sector’ in the August issue, I would like to off er er some additional guidance to designers of steel portal frames which are intended replace the lateral load resistance along the lines of ‘missing walls’. Firstly, Note 1 of Diagram 14 in Building Regulations Approved Document A (which relates to residential buildings of traditional masonry construction) states that the total extent of openings should not exceed two-thirds of the length of the wall in question. The implication from clause 2C28 is that, if this rule is contravened, then an alternative method of providing lateral stability (such as a steel portal
frame) should be provided. It is therefore of some concern that projects not complying with this rule are obtaining building control approval. Secondly, the illustration used in Andy’s letter is misleading, since it suggests that the centroid of the applied wind load is at the top of the steel portal frame (i.e. at firstfloor level). In fact, this would only be the case for a singlestorey building with a flat roof (given that the wind load on the bottom half of the wall from ground to first floor goes down to the ground). In all other cases, including the two-storey house with a pitched roof used in the illustration, the centroid will be some distance above the top of the portal frame/ first-floor level. Hence, there is a resulting moment which needs to be considered. Unless it can be demonstrated that this moment can be safely transferred down to foundation level by the remaining masonry walls (which is unlikely, in my experience), then the steel
APPROVED APPROVED DOCUMENT A COULD ADDRESS ADDR ESS THIS THIS COMMON PROBLEM BY GIVING SOME SIMPLE RULES
portal frame (and its be designed to resist thefoundations) moment in must question (as well as the pure horizontal load, of course). This can often result in a net uplift force on the frame’s foundations. Finally, the provision of discreet pad foundations to the columns of a steel portal frame is often impractical for both semi-detached and terraced properties (which I see a lot of in south Yorkshire and northeast Derbyshire), which is exacerbated when the ‘missing wall’ sits on an existing cellar wall. A practical practical solution solution in such such situations situations is to provide a reinforced concrete beam for the full length of the frame, with the columns located at either end of the beam. This solution avoids the issues with trying to form large pad foundations which extend beyond the property’s boundary, as well as helping to spread the point loads from the columns reasonably uniformly over the full length of the beam. The self-weight self-weight of the reinforc reinforced ed concrete concrete beam also helps to resist any net uplift at
Opinion
the column bases (strapping the beam down to a cellar wall, if present, can give further uplift resistance). Also note that using a reinforced concrete beam eff ectively ectively cancels out the equal and opposite horizontal reactions (which have been generated by vertical loads) at the column bases. As always, always, ther there e is techni technical cal intere interest st in everything.
CHRIS VAUGHAN In response to Andy Greenwood’s letter to Verulam (August 2019), I can comment as follows: As a structural structural engineer running an approved inspector, we often see rear extensions which include the removal of the rear wall to provide an open-plan arrangement at ground floor. Often the designer, who is usually an ‘engineer’, specifies two beams on padstones to carry the cavity wall/ floors/roof above firstfloor level with no consideration of lateral stability. A goal-post frame, as suggested by Andy, is a good solution, but often the foundations for these frames are not adequately thought about or detailed.that We too have heard the statement ‘my neighbour didn’t provide a frame’ or ‘we didn’t get asked to do that on our last project’. I agree with Andy that too many so-called ‘engineers’ don’t think about lateral stability. Our stance is to replace the stiff ness ness lost when more than two-thirds of the length of the rear wall is removed, as a building control body will not accept a scheme that has not considered lateral stability. Approved Document A could address this common problem by giving some simple rules for dealing with this scenario. Chris writes for and on behalf of Approved Inspe Approved Inspectors ctors Ltd. It It looks looks unlikely that his will be the last word on this topic.
Safety factors for overturning STUART MARCHAND
Andy Gree Greenwood’ nwood’s
sway frame
Barry Franchi (Verulam, May 2019), Yul Tammo and Alastair Hughes (Verulam, Tammo (Verulam, July 2019) raise interesting questions on safety factors and how they are calculated. When writing the new CIRIA guide C761, Tower crane foundation and tie design, eff ort ort was put into understanding what the code writers understood by the equilibrium limit state and discussions were held with one of the people involved. All structural structural analysis is based on a model, and it is a question of whether the model is suffi ciently accurate for the task in hand. Overturning taken about the edge of the foundation, when combined
39 thestructuralengineer.org thestructuralengineer October 2019 | thestructuralengineer.org .org | September 2019
Opinion
Letters
with the other design criteria of bearing capacity and serviceability, is deemed to be accurate enough. Unfortunately, it is not possible for a geotechnical engineer to give a value of stress on a (rectangular) stress block because the value depends on the shape of the block, as well as on the type of ground. Because the shape changes as the tower crane rotates, this becomes a complex issue to resolve, which has resulted in the simplification being retained. It is also interesting to note that the worst case for ground failure is neither with the jib at right angles nor over a corner, but several degrees less away from the corner situation. As ever ever,, our read readers ers are are fascin fascinated ated by ‘structural puzzles’. Verulam’s Verulam’s previous ruminations were to the effect that all manner of interpretations are possible depending on assumptions. Stuart’s comments reinforce that view and he returns to the crucial question of: ‘is the model good enough for the task in hand’. Readers might like to consider the topic of ‘sensitivity’. On a decentsized base on rock, the mythical point of rotation can’t be far from the edge and if it were slightly inboard, the computed safety factor would not reduce much. Conversely, for a narrow base on soft ground, if the rotation point moved inboard (due to edge pressure weakness) there might be disproportionate reduction in the overturning safety factor.. Safe structures are ones that factor are insensitive to small errors in assumptions.
Ali Alista stair ir Day Day and dynamic relaxation GABRIELE DEL MESE The two-part two-part paper in recent issues (June and July 2019) on Alistair Day’s ‘dynamic relaxation method’ reads like a good novel. So, I congratulate the authors for drawing attention to the considerable contribution made by
Alistair to the the general general theory of structure structures. s. In our contempora contemporary ry world, where designers venture more and more along untrodden paths, I believe Day’s method is taking the place that Hardy Cross’ ‘moment distribution method’ once enjoyed for framed structures after its introduction in 1930. After H. Cross, several other ‘working’ engineers produced improved approximate hand methods for the analysis of framed structures structure s and for plates and shells. All their ‘methods’ have gone into history defined by their author’s name. Having been involved in several projects which required diffi cult structural analysis, I can honestly say that my teams and I have bene fited enormously from using ‘Day’s method’. Hence, I propose that the ‘dynamic relaxation method’ should be renamed after its inventor, i.e. after Alistair Day, and invite all colleagues to end its ‘unnamed’ status. One of the projects mentioned by the authors in the second part of their paper was the design of the Padre Pio Church in southern Italy. I inherited this interesting project from Peter Rice, who sadly died in 1992. Peter developed a preliminary scheme in 1990, which then lay dormant, ready to start again in 1995, when I was the engineer. Since several design conditions had changed, I developed a new structural scheme and was privileged to work with several colleagues in Arup whose contribution was exemplary. We handed that scheme over to an Italian engineer in 1997 (not 1995 as mentioned in the paper). The Italian engineers changed it yet again – sadly. I will end my contribution by congratulating again the authors on their eff ort ort to highlight Day’s contribution to our profession and by asking a simple question: Probably, circumstances, rather than planned strategy, pushed Alistair Day to develop his method while he was at Arup. As Arup is constantly involved in unusual projects, how much e ff ort ort and funding is the company devoting to some kind of ‘engineering research’ not just as incidental encouragement, but as a proper strategic philosophy ‘to build a better world’? Wouldn’t it be nice if this became a task feature of some ‘Engineering Council’ with everybody’s contribution finalised to everybody’s benefit? I attach a couple of extracts from my Padre Pio sketchbook, signed and dated: these were part of a preparatory study for some lab tests on global stability. This is pleasant feedback from Gabriele. It’s always nice to see readers enjoying the magazine.
THIS PUBLICATION HAS LONG BEEN AND WILL CONTINUE TO BE THE MOST USEFUL GUIDE TO SUBSIDENCE AND RECTIFICATION PROCESSES. John Patch
COULDN’T AGREE MORE. A FANT FANTASTIC ASTIC TECHNICAL GUIDE FROM THE GRAND MASTER HIMSELF ON THIS SPECIALIST AREA WHICH WHICH CONTINUES TO IMPACT MANY MAN Y. WELL SAID, BRIAN. Martyn Headley
Nervi and Portsmouth Cathedral ANDREW NEW As an aside from Professor Professor Leslie’s Leslie’s excellent account of Pier Luigi Nervi’s Nervi’s work in the August issue, I think it may be of interest to look back at an English example which never ‘got o ff the ground’. Portsmouth Cathedral, a succession of 13th, 17th and 20th century building phases, was left unfinished at the outbreak of war in 1939, with three bays of a new aisled nave sealed off by by a blank brick west wall. In the 1960s, Lord Mottistone, the design partner of the architectural firm of Seely and Paget, proposed an innovative westward continuation by a light glazed structure spanning the whole width of the nave and aisles and terminating with a semi-dome. Intended as a memorial to D-Day D-Day,, its foundation stone was optimistically laid by Lord Montgomery. After Lord Mottistone’s death in 1963, the scheme was rejected by the Royal Fine Art Commission, which suggested bringing in a structural engineer of repute. As his former chief assistant, and newly quali fied as an engineer myself, I felt able to put forward the name of Nervi. In due course, four of us (including a client representative) flew to Rome, where we were made very welcome by him and his sons, and taken to see the drawing offi ce, the Palazetto and the workshop
40 thestructuralengineer.org thestructuralengineer .org | October 2019
Letters
where the ‘boat’ units were cast. To our surprise, he even gave us the use of his car, with chauff eur, eur, to make an afternoon excursion to the water gardens at Tivoli. Naturally,, he came to Portsmouth to Naturally assess the problem we were posing, and I remember that when we took him to visit the dockyard, he stood on the deck of HMS Victory and and was clearly fascinated by the geometry of the rigging. Back in London, he and his equally modest and charming wife were entertained by Paul Paget at his City home, and all seemed set for an impressive collaboration. After nearly half a century century,, I cannot trace any better than the accompanying illustrations of Nervi’ Nervi’s s proposal, with its obvious affi nity to the Turin exhibition hall. Suffi ce it now to say that events at the cathedral, coupled with an inadequate response to the public appeal for funds, caused the project to be put on hold for many years. The urge to make a stridently contrasting appendage to the already disparate building gave way to a realisation that it was more appropriate to try to continue what the architect Sir Charles Nicholson had built in the 1930s, notwithstanding fundamental changes in the building industry in the meantime. That aim was indeed skilfully achieved in the rather less ambitious western addition by Michael Drury that can be seen today, today, and so we are left with a ‘might have been’ to
add to the Nervi catalogue. It’s always great to learn from the giants of the past. Plus, we can look back wistfully to the days when key engineers could employ a chauffeur.
Checking the drawings ALLAN MANN
Opinion
John Lawson’s reminiscences of draughting in his early days. In my first job, the boss also also prowled around the the offi ce after work. Knowing this, our ace draughtsman would regularly buy the local evening paper, circle suitable job adverts and just tuck the page under his drawing board where it could be spotted by the prowling eyes. The e ff ects ects were wondrous to behold!
What fun! Keeps morale up!
In last month’s Verulam pages, I read
Correction Regrettably, a production error meant that the solutions given to September’s ‘And finally…’ question were not correct: 1) For Situation A, the bending moment diagram was drawn incorrectly.
SITUA SIT UA ION A
SITUA SIT UA ION B
BENDING MOMENTS
w x
1.53
6
=
10 x 1.5 3
= 5.6kNm
W L
8
2) For Situation B, the calculation for the shear force incorrectly gave the denominator as 6, instead of 2. We apologise to author, Brian Pyle, and present the corrected solutions here (right).
10 x 2) x 2 8 = 10kNm =
3 wL
6
10 x 2 3 6 = 13.3kNm =
SHEAR FORCES
20kN
ZERO SHEAR
2
=
22 x 10 2
= 20kN
2 w L
2
=
10 x 2 2
= 20kN
. n o i t a n a l p x e r e l l u f a r o f e n i l n o r e w s n a e h t w e i V . s t n e m e l e D 2 g n i s u d e l l e d o m e r o c e h t h t i w , t c e j o r p l a e r a m o r f s t l u s e r e h t s e h c t a m s i h T . s n m u l o c e r o c e h t h t i w d e r a p m o c s s e n ff i t s e v i t a l e r g n i s a e r c n i f o s l e t n i l h t i w s l e d o m A S G e l p m i s f o s e i r e s a m o r f d e t a r e n e g , h p a r g g n i y n a p m o c c a e h t n i n w o h s s i s i h T ff fi l a . l e t n i l e t a i d e m r e t n i n a t a r u c c o r a e h s d n a t n e m o m m u m i x a m e h t , s l e t n i l s s e n i t s - e t i n e r h t i W ) 2
l e t n i l p o t – 2 e s a C l e t n i l m o t t o b – 1 e s a C : C n o i t p O n o i t s e u q n i a M
. t n e m o m e h t s w o l l o f r a e h s e h T ) 1 s n o i t s e u q l a n o i t i d d A
n o i t s e u q s ’ r e b o t c O o t s r e w s n A
… Y L L A N I F D N A
41 thestructuralengineer.org thestructuralengineer .org | October 2019
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Diary dates
Unless otherwise stated, evening technical meetings start at 18:00 (with refreshments from 17:30) and are free of charge to attend. History Study Group meetings start at 18:00 (with refreshments from 17:30) and are free of charge to attend. Registration is not required except for the Annual Business Meeting held in January. Industry workshops and CPD courses are held at HQ unless otherwise stated.
MEETINGS AT HQ
Dia iarr y dates
Note that more current information may be available from the Institution website: www.istructe.org/events
Wednesday 16 October Engineering challenges challenges in a warming world Tim Hetherington 18:00–19:30 Tickets: www.istructe.org/events
CPD COURSES
Abigail Matthews Matthews Members £261 + VAT; standard £333 + VAT 10:00–17:30 Booking: www.istructe.org/events
Tuesday 1–Wednesday 2 October Design of steel bridges (2-day course) Ben Lau Members £427 + VAT; standard £553 + VAT
Friday 11 October Foundation design to Eurocode 7 for small practitioners Bob Benton
Thursday 17 October Pai Lin Li Lecture: Moving towards a sustainable future 1) Shell structures from Catalan to Mapungubwe Kavinda Isuru Nanayakkara 2) The next generation of buildings: wired for health and wellbeing Amy Brander Brander 18:00–19:30 Tickets: www.istructe.org/events
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Members £261 + VAT; standard £333 + VAT 10:00–17:30 Booking: www.istructe.org/events
47–58 Bastwick Street, London EC1V 3PS, UK
HISTORY STUDY GROUP Tuesday 15 October The conservation of The Providence Chapel, Charlwood, Surrey Robert Bowles Tuesday 10 December Rochester’s Roman bridge and its
INDUSTRY WORKSHOP Thursday 24 October SCIA Industry workshop (Manchester) Pendulum Hotel and Manchester Conference Centre, Weston Building, Sackville Street, Manchester M1 3BB Speakers: Marwan Al-Taie, Al-Taie, Iveta Georgieva, Vladimir Vladim ir Pribramsky Pribramsky,, Theodore Theodore Tsirozi sirozidis, dis, Herman Oogink 08:30–16:15 Sessions: 09:00–09:30 Introduction 09:30–10:30 Concrete design with focus on flat slabs 11:00–12:00 Steel design with focus on composite floors
management Sue Threader
Thursday 10 October Design of retaining walls to Eurocode 7 for small practitioners David Beadman Members £261 + VAT; standard £333 + VAT 10:00–17:30 Booking: www.istructe.org/events
Monday 14 October October The Party Wall Act Simon Pole Members £50 + VAT; standard £63 + VAT 18:00–20:00 Booking: www.istructe.org/events
Thursday 10 October Vibration serviceability: Applications Aleksandarr Pavic Aleksanda Members £261 + VAT; standard £333 + VAT 10:00–17:30 Booking: www.istructe.org/events
Wednesday 16 October Blast Bob Sheldon and Piroozan Aminossehe Members £261 + VAT; standard £333 + VAT 10:00–17:30 Booking: www.istructe.org/events
Friday 11 October Temporary demountable structures: Guidance on procurement, design and use
Thursday 17 October Structural robustness and disproportionate collapse Ruth Haynes Members £261 + VAT; standard £333 + VAT 10:00–17:30 Booking: www.istructe.org/events
12:00–12:30 Flexibility in modelling 13:30–14:00 The benefit of using engineering reports (calculation reports) + practical user story 14:00–14:30 Advanced design of steel connections with IDEA StatiCa (CBFEM) and SCIA Engineer 14:30–15:30 openBIM and BIM solutions with SCIA Engineer, Revit and Tekla + practical user story 15:45–16:15 Current trends in parametric engineering + practical user story, AECOM 16:15 Networking
REGIONAL GROUPS Chester and North Wales Thursday 10 October Consultancy contracts Patrick Waterhouse Holiday Inn Chester – South, Wrexham Rd, Chester CH4 9DL 18:00 for 18:30
Registration: www.scia.net/en/company/
Secretary: James Drew
events/industry-workshop-scia-engineermanchester
(
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42 October 2019 | thestructuralengineer.org
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East Anglia Monday 7 October Norwich ground level downward (joint meeting with ICE) Matthew Williams Park Farm Hotel, Hethersett, Norwich NR9 3DL 18:30 for 19:00
University Belfast, 185 Stranmillis Road, Belfast BT9 5EE Tickets: £75 Associate Members, Members, Fellows and guests; £35 Retired, Graduate or Student members Dress: Formal Prosecco reception 19:00, dinner at 20:00
De Vere Horsley Estate, Ockham Road South, East Horsley KT24 6DT Tickets: £60; £30 Technician, Graduate or Student Dress: Lounge suits 19:00 for 20:00 Contact: Brendan Brophy (
[email protected])
Secretary: Andrea Johnson Johnson Secretary: Paul Wilson
(
[email protected])
(
[email protected])
Secretary: Ruslan Koutlukaev
(
[email protected])
Scottish East Midlands Tuesday 8 October BIM The Yew Lodge Hotel, 27 Packington Hill, Kegworth, Derby DE74 2DF 18:00 for 18:30 Contact: Azhar Raoof (
[email protected]) Tuesday 15 October 33rd EMESP Annual Prestige Lecture – 2019: Engineering theme park rides Dr John Roberts The Albert Hall Conference Centre, North Circus
Street, Nottingham NG1 5AA Registration: 19:30; Lecture: 19:50 Contact: Azhar Raoof (
[email protected]) Secretary: Rozina Aslam
Thames Valley Thursday 3 October Substance with style – The importance of engineering design (joint meeting with IESIS) Naeem Hussian Room K325, John Anderson Building, 107 Rottenrow East, Glasgow G4 0NG 18:00 for 18:30 Contact: Laura Clow (
[email protected]) Friday 25 October Annual Social Event Event – Awards, dinner dinner,, networking & ceilidh
The Grand Ballroom, The Grand Central Hotel, Glasgow G1 3SF Tickets: £25–£40 19:00 for 19:30 Contact: Laura Clow (
[email protected])
(
[email protected]) Secretary:
[email protected]
Midland Counties Singapore Tuesday 22 October Statutory planning consent process Matthew Fox University of Birmingham, Room G34, Building Y3, Mechanical Mechanical and Civil Engineering Engineering Building, University of Birmingham B15 2TP 18:00 for 18:30 Secretary: Mitchell Gray
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North Thames
Non-IStructE/IES members; S$288 Full-time students/retired 09:00–17:00 Contact: Shelly Ng (
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Surrey
Northern Ireland
Monday 14 October Young members’ technical meeting John Galsworthy Building, Kingston University, 7 Fassett Rd, Kingston upon Thames KT1 2TD 18:00 for 18:30 Contact: Natalja Petkune (
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Friday 11 October Annual Dinner Dinner The Isdell Courtyard, Riddel Hall, Queen’s
Friday 18 October Annual Awards Awards Dinner Dinner Gordon Harris
Secretary: Simon Leung (
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Secretary: Parmindar Mann
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Wales Tuesday 8 October Design of Central Square Development, Cardi ff Matthew Hartley, Tom Tom Firth and Rob Powell Trevithick Trev ithick Lecture Theatre Th eatre T2.09, Cardi ff University, The Parade, Cardi ff CF24 3AA 17:30 Secretary: James Parsons
Friday 18 October 10th Asia-Pacific Forum on Structural Engineering: Amazing Structures Pan Pacific Hotel, Singapore, 7 Raffl es Boulevard, Marina Square, Singapore 039595 Tickets: S$388 IStructE/IES members; S$488
Secretary: Reve Chin
Thursday 3 October AGM and One Blackfriars Aret Garip Garip and George George Parker International HQ, 47–58 Bastwick Street, London EC1V 3PS 18:00–19:30
Thursday 17 October Engineering inside a main contractor – examples of temporary works and constructability for projects Craig Dolby Brunel University, Kingston Lane, Uxbridge UB8 3PH 18:00 for 18:30 Contact: Daljit Matharu (
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(
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Yorks Y orkshire hire Friday 11 October Annual Dinner Dinner Richard Gibson The Metro Hotel, King Street, Leeds LS1 2HQ Tickets: £40; £25 Student and Graduate member; Table of 10 £350 Limited number of free graduate and student tickets available on a first-come basis Dress: Black-tie/Lounge suits 19:00 drinks reception followed by a three-course dinner Contact: Richard Gibson (
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Regional Group Committee members should submit details of forthcoming events to:
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43 thestructuralengineer.org | October 2019
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Spotlight on Structures
Access to Structures is free to paying-grade Institution members as one of their membership benefits, via the ‘My account’ section of the Institution website. The journal is available online at: www. structuresjournal.org
Spotlight on Structures
Editor’s Featured Articles
Have you read the Editor’ Editor’s s Featured Articles in Structures? From each issue of the journal, the Editor-in-Chief (or Guest Editor) selects an outstanding paper which is made available free of charge for six months to promote the high-quality research published in Structures. Here, we highlight the three latest Featured Articles.
Volume Volum e 20 (August (August 2019) Optimum use of composite structures for demountable construction Ana M. Girão, Mark Lawson Lawson and Eleftherios S. Aggelopoulos This paper explores the concept of the optimum span to depth ratio of reusable composite beams with demountable bolted shear connectors so that the beams may be designed most effi ciently in terms of their weight and the shear connector distribution along the span. Three patterns of shear connectors were evaluated by a simple pseudo-plastic model and calibrated by finite element modules in terms of their eff ect ect on the overall composite beam stiff ness ness in the range of 9 to 15m span. The optimum span to depth ratio of symmetrical and asymmetrical beams was determined and compared to equivalent beams with welded shear connectors. It was found that the optimum span to depth ratio of uniformly loaded unpropped composite beams with demountable bolted shear connectors may be taken as 22 which allows for a utilisation factor of 0.7 at the ultimate limit state to ensure that plasticity does not occur in the first use cycle. It was found that the eff ect ect of asymmetry on the optimum span to depth ratio is small. For propped beams with demountable shear connectors, the optimum span to depth ratio may be increased to 24. |
Read the full paper at https://doi. org/10.1016/j.istruc.2019.03.005 .
Volume Volu me 19 (June (June 2019) Least Cost Design of Curved Cable-Stayed Footbridges with Control Devices Fernando Ferreira and Luís Simões Cable stayed footbridges have appealing aesthetics but they are flexible and slender and these properties result in vibrational prone structures. Its design is governed by dynamic comfort requirements in particular the horizontal and vertical accelerations and the synchronous lateral instability (also known as ‘lock-in’). This paper concerns the optimum design of curved cable stayed footbridges with control devices using a three dimensional model. The structure is designed to guarantee the standard static (live loads, wind, temperature and self-weight) and dynamic (pedestrian induced vibration) requirements. An optimization algorithm is
employed to find the least cost design for varying bridge lengths. The goals include finding the bridge geometry (tower shape, number of cables and their location), cross section sizes, control devices properties and cable prestressing. Diff erent erent bridge lengths lead to di ff erent erent minimum costs, design variables, stress distribution and dynamic response and these solutions are compared. The influence of the tower shape and control device properties on the optimum design is included. |
Read the full paper at https://doi. org/10.1016/j.istruc.2018.12.004.
Volume Volu me 18 (April 2019) 2019) Rwanda Cricket Stadium: Seismically stabilised tile vaults Michael Ramage, Timothy J. Hall, Ana Gatóo and M. Wesam Al Asali The Rwanda Cricket Stadium, Stadium, completed in 2017, uses compressed soil-cement tiles, thin-tile vaulting, vaulting, and geogrid reinforcement for seismic stabilisation in Kigali’s moderate risk earthquake zone. The vaults follow the natural resolution of forces toward the ground, closely mimicking the parabolic geometry of a bouncing ball and evoking the cherished hilly topography of Rwanda. The masonry vaults in compression allow the use of geogrid embedded within the mortar layers, adding global ductile behaviour to the thin shell composite of low strength tiles. Structural analysis is based on thrust lines, with additional envelope for the thrust lines to leave the pro file of the masonry computed from the tensile capacity added by the geogrid. Construction follows traditional thin-tile techniques adapted for new environments and uses compressed earth tiles as pioneered at the Mapungubwe Interpretive Centre in South Africa. Here, the two approaches are combined in a permanent structure, with the largest vault spanning 16m with a rise of 8m. The Rwanda Cricket Stadium is a fusion of advanced structural analysis and architectural design with labour intensive, locally-sourced material production o ff ering ering a much-needed solution to building sustainably in the developing world. Employing air-dried, hand-pressed soil tiles, produced using local labour,, this method of construction has proved to be innovative, cost eff ective labour ective and beautiful. |
Read the full paper at https://doi.org/10.1016/j.istruc.2019.02.004.
44 October 2019 | thestructuralengineer.org
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Future Designs installs longest Vane V ane luminaire lu minaire in i n Europe Europ e in Amsterdam redevelo redevelopment pment Future Designs, the international manufacturer of luminaires and bespoke lighting solutions, has completed the lighting for the new WPP Amsterdam campus. The campus, which was designed by BDG architecture and design and consulting engineers Hoare Lea, features the longest lineage of Vane luminaire in Europe. The Amsteldok building is part of WPP’s global co-location strategy which is to provide world-class spaces that bring together its people and agencies into one location, encouraging greater collaboration and giving clients easier access to all of WPP’s talent and expertise. When it was originally completed in 1973 the Rivierstaete building (as it was formerly known), located on the river Amstel 3.2km south of Amsterdam city centre, was the largest office building in Europe. The 60m of Vane creates a striking visual link in the expansive and spacious (8m-high) ground floor reception and café area reception and lobby area, creating an impressive arrival experience. Other products used throughout the project include 1672 units of the BEEM downlight and SEEL the IP 65 rated fitting which was utilised in the kitchen’s food preparation and clean room areas. In total Future Designs provided 6500m of aluminium profile weighing 23 636kg, 3279 LED drivers feeding 29 511 LED boards, 70 500m of cable and 183 760 fixing screws for the project. The Amsteldok building brings together 15 WPP agencies, from 11 locations into a single location. The redevelopment has transformed the building into a 19 000m², innovative and creative workplace to support the 1500 people that work from it. Redeveloping existing structures instead of constructing new buildings avoids the emission of thousands of tonnes of embodied carbon – equivalent to over 30% of the building’s lifetime carbon emissions. The new WPP campuses have been developed with sustainability at their heart and are aiming for a BREEAM rating of Very Good or higher. Vane is designed Vane designed to be sustainable sustainable by optimising optimising exception exception lumen lumen output output whilst utilisi utilising ng minimum minimum wattage. wattage. The energy energy saving lightin lighting g has low and easy easy maintenance maintenance and links with lighting control systems and power over the ethernet. Further information: Future Designs (web: www.futuredesigns.co.uk)
Encon Group expands into construction products market The Encon Group has expanded its portfolio with a new division, Encon Construction Products, which the company has established to service the growing g rowing UK infrastructure sector. In launching Encon Construction Products, the company is aiming to become the UK’s ‘distributor of choice’ for masonry components, concrete and reinforcement, waterproofing, construction chemicals, geotechnical, and groundworking products. The division will offer tailored solutions to new and existing customers from market-leading suppliers such as Adomast, Ancon, Expamet, GCP, Maccaferri, Sika, Visqueen, and Weber. Vaughan Taylor will head Vaughan head up up the new division division as national national sales direc director tor,, while while Ed Matthews Matthews takes on the role of business business develo development pment direct director or.. Supported Supported by a team team of specialists from across the Group, the Construction Products Division will be offering its services through Encon’s Dundee, Glasgow, Leeds, North West, Cardiff, East London, West London, Bristol, and Plymouth branches. Further information: Encon Construction Products (tel: +44 (0)1937 524 200; email:
[email protected]; web: www.encon-cp.co.uk)
ESAB launches new HS steel cored welding wire ESAB is launching Coreweld 69 LT H4, a metal-cored welding wire for high-strength steels. It is suitable for manual, mechanised or robotic welding and achieves a yield strength of 690MPa or more with excellent sub-zero toughness down to —60°C. The very low diffusible hydrogen feature is vital for avoiding hydrogen induced cold cracking. Coreweld 69 LT H4 is suitable for spray arc transfer welding in downhand PA and PB positions using an argon/CO 2 gas mixture with 5-15% CO 2. It is available in diameters of 1.2, 1.4 and 1.6mm as either 16kg wire baskets or Marathon Pac™ bulk packs. The new CE marked consumable meets the requirements of AWS H4 and EN ISO H5. Further information: ESAB (web: www.esab.com)
Helifix restores Welsh period cottage A Welsh Welsh Grade Grade IIII listed listed cottage cottage had had a number number of of defects, defects, inclu including ding outward outward moveme movement nt of the gable gable end end wall, wall, internal internal cracking along the ceiling lines and cracking over the front front door entrance. By bonding pairs of stainless steel HeliBars intogable slots cut andstainless below the firstanchors and second deep masonry beams were created the full width the wall.above SockFix steel werefloor thenjoists inserted into clearance holes drilled withinacross the Helibeam zone,of through the rubble-filled wall and the first two parallel floor joists. This provided lateral restraint and restored structural integrity to the damaged masonry without compromising its aesthetics. Further information: Helifix (tel: +44 (0)20 8735 5200; email: kirsty.carr@helifix.co. kirsty.carr@helifix.co.uk) uk)
46 October 2019 | thestructuralengineer.org
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with logo Featured in top section of search results Included on two job newsletters
£1,575
¼ page in The Structural Engineer
RAPID RESPONSE
Job board ad live for 1 month, with logo Featured in top section of search results Included on two job newsletters ¼ page in The Structural Engineer Targeted email sent to matching candidates
“
Call Beth Fifield o on n 020 7880 6235 to book your advertising today
The Structural Engineer magazine and website have consistently provided Walker Dendle Technical with placeable candidates and high-profile branding since we started utilising both in 2004. Martin Dendle, Walker Dendle
48 October 2019 | thestructuralengineer.org
Telephone: T elephone: +44 (0)20 7880 6235 Email:
[email protected]
Recruitment
SEVENOAKS OPEN Engineering is seeking a dynamic, extremely motivated and condent senior structural engineer to join this expa expandin nding, g, exciti exciting ng Seveno Sevenoaks aks-bas -based ed consu consultan ltancy cy.. The successful candidate will need to demonstrate exceptional organisational skills, prove themselves to be a self-starter and have a desire to grow with and take on responsibilities early for this in-demand practice. They will need to be technically-strong and highly creative, able to work alone, but also keen to learn and develop, with a minimum of 4-5 years’ experience in the industry. Good communication skills are a must in order to represent us adeptly at meetings with our clients and architects across Central London and the South-East. For more information on the projects we are currently involved in, visit our website www.openeng.co.uk website www.openeng.co.uk Apply by emailing your CV and a covering letter to
[email protected]
Project Engineer States of Guernsey Unrivalled work-life balance, spectacular scenery and a vibrant economy – when are you moving to Guernsey? Wee are looking W looking to appoin appointt a Project Project Engineer Engineer to to provide provide engineering advice and design, contract administration and project management project management as as required required on a mixed portfo portfolio lio of civil civil and construction projects entered into by the States of Guernsey. Shortlisted applicants will be invited to Guernsey for interview and the successful candidate will be eligible to receive relocation assistance, details of which will be provided. An attractive attractive remuner remuneration ation package package will be given given in addition addition to a Long Term Employment Permit required which will provide you, and and your family family,, with the the opportunity opportunity to become become permanent permanent residents residen ts in Guernsey Guernsey.. Contact: Sean Harvey, Project Services Manager. Tel: 01481 747316. Email:
[email protected] Find out more at www.gov.gg/careers
States of Guernsey
Director of Engineering, BCSA Excellent package depending on experience An exciting position has become available available at the British British Constructional Constructional Steelwork Association. Association. Are you passionate passionate about the design and fabrication of constructional steelwork? steelwork? If so then apply to BCSA for the position of Director of Engineering. The British Constructional Steelwork Association is the national national organisation organisation for the steel construction construction industry whose member companies undertake the design, fabrication and erection of steelwork for all forms of buildings and civil engineering. The Director of Engineering is a senior position within the BCSA, reporting to the Chief Executive Officer. As Director of Engineering you will be responsible for setting the technical direction of the association, participate in the development of the steel design and fabrication standards, managing a number of BCSA’s committees, developing practical design and fabrication guides and advising BCSA’s member companies on the design and fabrication of steel structures. The successful candidate should be educated to degree level or equivalent and be a chartered structural engineer. You should have at least 10 years’ experience in the design and execution of steel structures structure s and be familiar with national and international standards development. You should be self-motivated and have good communication communicatio n and written skills. You will predominately work from BCSA’s London office and will be required to travel throughout the UK, and Europe with some nights away. Benefits include a car allowance and employer pension contributions. A position description is available available from
[email protected]
Interested candidates candidates should send their CV to: Dr David Moore, Director of Engineering, BCSA, 4, Whitehall Court, Westminster, London SW1A 2ES or email:
[email protected] Closing date for application is 18 October 2019. 2019. www.steelconstruction.org
49 thestructuralengineer.org | October 2019
At the back And finally...
Test your understanding of structural behaviour and problemsolving ability. If you would like to submit a problem, contact
[email protected]
And An d finally... This month’s from Clayton was inspired by the design of the question core lintels forBen a project in Bristol. The answer can be found on page 41. 41. Top
Question Assuming linear elastic elastic behaviour behaviour,, which lintel lintel has the maximum maximum moment under lateral loading for the following cases? | Case 1: All lintels are perfectly rigid. | Case 2: All lintels are perfectly flexible (i.e. have infinitesimally small flexural stiffness). Option A:
Option C:
Case 1 – top lintel Case 2 – top lintel
Case 1 – bottom lintel Case 2 – top lintel
Option B:
Option D:
Case 1 – top lintel Case 2 – bottom lintel
Case 1 – bottom lintel Case 2 – bottom lintel
Lintel
wind loading
Additional Additio nal questions questions
1) Where does the maximum shear occur? 2) Where do the maximum moment and maximum shear occur for real finite-sti ffness lintels? Bottom Correction
A production production error meant meant that the solutions given to September’ September’ss question were incorrect. See page 41 for corrected solutions.
Core: elevation
Submit your problem for consideration to
[email protected] to
[email protected].. The author of each published question will receive a single e-book of their choice from the Institution’s current catalogue.
Enter a sketch in the next competition – deadline 31 January 2020 The Drawing Board is The Structural Engineer’s quarterly quarterly sketching competition,
Sketches must be: • hand drawn (no CAD, except for ‘guided freehand’) • from a real project or assignment • at a suitable scale for publication (i.e. not too
judged by Ron Slade FIStructE of WSP.
intricate/detailed). Please also submit a short description (150 words) to put the sketch into context.
To take part, submit your entries to:
[email protected] Each published entry will receive a free single e-book from the Institution’s current list of titles. Background sketch by Kevin Lyons (Lyons O’Neill)
50 October 2019 | thestructuralengineer.org
www.steel-sci.com
UK Steel Construction Day 2019 Innovative Steel Solutions Thursday 7th November 2019, 1 Birdcage Walk, London.
This year our main theme is ‘ Innovative steel solutions’. We will look at a range of different solutions that address the multiple needs to build with improved speed, quality, safety , predictability, and using less materials. Some of these solutions are already being applied, others are for the future. Speakers from both SCI and industry will present how innovative designs and
Speakers include; Kevin Masters, Bryden Wood Pete Winslow, Expedition Matthew Gilbert, Matthieu Mallié,
product manufacturers can provide the industry with economical and energy savings solutions .
Theodore Tsiroz Tsirozidis, idis,
constructed and used.
Nigel Banks,
This event will provide a platform to hear latest developments in the steel industry and to meet industry peers.
Sponsors of this event include;
SCI has been the trusted source of information and engineering expertise globally for over 30 years.
Visit the SCI Portal to book you place https://portal.steel-sci.com/trainingcalendar.html
@SCIsteel
steel-construction-institute
E:
[email protected] | T: +44 (0) 1344 636500
