Constructing a prototype cardboard building: Westborough School
Buro Happold
Job No: 4928
Literature Review
July 2001
Buro Happold
This report has been prepared for the sole benefit, use and information of the DETR and the liability of Buro Happold Limited, its Partners and Employees in respect of the information contained in the report will not extend to any third party.
Author Andrew Cripps
Approved
Signed
Signed
Date
September 2001
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Date
Helen Gribbon
September 2001
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Constructing a prototype cardboard building : Literature Review By Buro Happold and Cottrell & Vermeulen Authors: Richard Cottrell Martin Waters Helen Gribbon Andrew Cripps 1
Executive summary
Cardboard is a material that is almost entirely made from recycled material. At present it is mostly used for packaging and storage, but this need not be the case. It is possible to make cardboard products that have sufficient compressive strength to carry structural loads, thereby offering an alternative to the use of other more material and energy intensive products such as concrete or steel. Further there are also opportunities to use cardboard in other building components, particular in combination with coatings to make it water and / or fire resistant. Obvious examples of possible components include large panels for walls and ceilings. This research project proposes to explore the possibilities, and to assess the benefits, of innovative uses of cardboard within buildings. This can then bring benefits to the country through reduced energy and material usage. This applies particularly to buildings intended for short lifetimes, where the waste of high quality and price material is particularly inappropriate. This document is a review of the existing literature and built examples that feature the use of cardboard. This formed the starting point of our project work in developing realistic and useful products to use in the planned school building at Westborough School, Westcliff-on-Sea, near Southend, Essex. It has been updated at the end of the project to include the school project, and other developments that have taken place over the life of our project. The material is divided into two parts: •
Case studies
•
Existing products, materials and other data sources
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2
Case Studies
2.1
Shigeru Ban
Shigeru Ban is perhaps the only architect to have used cardboard on any regular basis, certainly the most published. He first experimented with paper tubes in 1986 for a show of Alvar Aalto's work in Tokyo, where the tubes replaced more expensive wooden columns intended to represent the trees of Finland. At Expo'89 he began to use cardboard tubes structurally after tests at the Gengo Matsui Laboratory at Waseda University. He claims to have used paper tubes - at least initially - not as part of an environmental argument, but for aesthetic and material reasons. The tubes are roughly half as strong (in compression) as a wooden column of the same diameter, but are lighter and cheaper, and can be positioned with varying spacings and curves to be equally wall, screen or portal frame. Nine projects by Ban work towards paper tubes as permanent structural elements. The Paper Tube Structures are numbered here as they are numbered in the 'Japanese Architect' retrospective of his work, and not necessarily the chronological order. All of the 9 projects are reported in the same book [Ban 97]. 2.1.1
PTS1 Paper Arbor
A small circular shelter; the first in the series. Forty-eight tubes (33cm diameter, 15mm thickness and 4m height), originally intended as formwork for concrete, were fitted onto a precast concrete floor. The tubes were dropped onto precast bases and joined at the top by a timber compression ring. A tent membrane with a central strut covered the arbor. All tubes were first treated with paraffin waterproofing.
The Paper Arbor 2.1.2
PTS2 Odawara Main Hall
This temporary multi-purpose hall was commissioned at short notice for the Odawara festival. A square space-frame roof sits over a paper tube wall, which roughly follows the perimeter, but is also curved and, in places, broken. The tubes were suggested as a response to the time limit and budget. As it was, there was no time to get the permit needed if paper tubes were to be used for the main structure and so the card elements effectively act as screens inside and out, taking the wind loads only. A second, steel, structure supports the roof. There are 330 self-supporting paper tubes (53cm, 15mm, 8m) which form a wall around the 1300 sq.m. interior. Where the line of the wall moves outside the plane of the roof the wall is topped with a timber restraint. Clear vinyl tubes sandwiched between the paper tubes let in natural light.
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Odawara Main Hall 2.1.3
PTS3 Odawara East Gate
With the East Gate at Odawara, no permit was needed and a pure paper tube structure was possible. Ban's solution was a post-and-beam Vierendeel gate structure, a four-legged table supporting a corrugated steel roof. Tubes of 15mm and 12.5mm thicknesses were used with steel angle joints and steel reinforcement (post-tensioning) joining the angles within the tubes. 2.1.4
PTS4 Library for a Poet
An annex to an existing house, this was the first permanent building to use card as primary structure. Paper tubes trusses support curtain glass walling and a curved steel roof. This is a development of the paper-tube truss used in Odawara's East Gate. Again, paper takes compression only with steel wires within the tubes to handle tensile forces. Post-tensioned wires are used for the spanning section. The tubes have a diameter of 10cm and thickness of 12.5mm. Cubed timber pieces (10cm cube) are used for joints instead of the gate's steel angles. Four full height bookcases are cantilevered off the floor to take horizontal loads. These bookshelves are insulated and finished to form much of the exterior wall: they rise between the trusses to brace all six legs of the cardboard structure.
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2.1.5
PTS5 Paper House
Ban's own house has 110 paper tubes within a 10m x 10m square floor area. (All tubes 28cm, 15mm, 2.8m) The tubes, all standing vertically, are arranged in an 'S', part inside and part out, similar to the festival hall. Ban favours curved tube walls as revealing the nature of the tube construction and the beauty of the material. Ten tubes take the vertical load of the flat roof while all 80 interior tubes transfer lateral forces through cruciform wooden joints anchored to the foundation. The tubes are fixed by lug screws to act as vertical cantilevers from the floor. A large circle of tubes defines the interior living area with a gallery around it. One free-standing column, 123cm in diameter, holds the toilet. A smaller circle marks the bathroom and a small courtyard, the exterior tubes standing apart from the structural tubes as a screen. 2.1.6
PTS6 Miyake Design Studio Gallery
This small gallery has one cardboard tube wall inside, providing vertical support. The wall is curved inside a glazed rectangular box; sited in a fire zone in the city, a fire-resistant external wall is necessary if recycled paper tubes are to be part of the primary structure. While the curved paper wall takes vertical loads, the firewalls take all horizontal forces so the junction between tubes and floor can be simple, for slippage only. The plan is a 16.5m x 5.3m rectangle defined by the columns and with shadows cast through the slit gap between tubes onto the back wall. 2.1.7
PTS7 Paper Loghouse
This simple hut type has been developed as short-term, emergency housing. Each hut is a square in plan with one window on each of three sides and a door. The walls are of vertical tubes, with a simple pitched tent roof over a tube frame. Initially designed for Japan's earthquake victims, the prototype has since been adopted by the High Commission for Refugees (HCR) in Rwanda. Ban had previously been to Tanzania, Uganda and Rwanda where the HCR was issuing tarpaulins for roofs, to be held up by branches. This led to the immediate problem of deforestation but when the HCR started providing aluminium the refugees sold it. Bamboo was considered, but as a naturally occurring material a large order would have driven up prices. Cardboard was chosen as a cheap, light material, easy to handle and with no scrap value. The brief for the shelters was that they should be cheap, easily constructed by anyone and insulated for both summer and winter. Ban's shelters, which cost less than $2000 for a 16sq.m. unit, could house four people and take only 6 hours to build. Another advantage is that the paper tube machine can be brought into the disaster area rather than transporting bulk materials, which is difficult in a crisis. Afterwards the huts are easily dismantled and the materials cheap to recycle. Beer crates, on loan from the maker, provide a thick peripheral base, which raises the hut above ground water. The crates are filled with sandbags and tied to the structure, weighing it to the ground. Walls are made from 2m long tubes (10cm diameter, 4mm thickness), joined laterally by bolted metal rods. These tubes are sealed and made waterproof by hand, a process repeated every year. Sandwiched between the paper tubes is waterproof sponge tape backed with an adhesive strip. The same tubes, laid between sheet plywood, are used for the floor. Plywood is also used for frames, flaps and connecting elements. The roof structure of tube and plywood is covered with teflon tarpaulin with a second teflon sheet suspended from the ridge node as the ceiling. There is a ventilation flap at one gable end. These prototypes led to 200 shelters for the Sudanese in Nairobi: the poorest refugees in the camps were making mud houses, i.e. mud drying on wood frames rather than as fired bricks. Ban worked with the architecture school at the University of Nairobi on the development of semi-permanent housing for refugees, paper tubes combined with traditional mud walls. 2.1.8
PTS8 Paper Church
Over 160 volunteers - architecture students - completed construction of this church in five weeks to replace that destroyed in the 1995 Kobe earthquake. Materials were donated by a number of companies. A 10m x 15m rectangle of corrugated polycarbonate sheeting on a light steel frame contains an ellipse of 58 industrial grade paper tubes (33cm, 15mm, 5m) sitting on a concrete foundation. The Constructing a prototype cardboard building Literature review Admin:4928/reports/ lit review update
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tubes are made from laminated layers of recycled paper with wooden stoppers at each end; their structural role is not clear. The separation of the ellipse and rectangle creates a corridor. The spacing of the tubes changes around the ellipse to define the entrance side - with increased spacing of tubes and fully openable facade - and the altar side opposite. Teflon-coated fabric is used for a stressed membrane roof. Light enters through the walls and roof passing between the columns. 2.1.9
PTS9 Paper Dome
A contractor of wooden buildings commissioned this shelter for working outside, to be assembled by his own crew. The structure is basically an single arched roof - like a hangar - with a 27.2m span covering a space 22.8m wide and 8m high at the centre. The paper tube frame is covered with a layer of plywood and one of polycarbonate sheeting. As the paper tubes cannot be curved the arch is split into 18 straight 1.8m lengths connected with laminated wood joints. With the arches at 0.9m centres only two tubes are used throughout: 1.8m, 29cm, 20mm and 0.9m, 14cm, 10mm. Horizontal rigidity is through structural plywood laid over the tubes rather than cross-bracing. Each plywood panel has a round hole as large as possible to allow light through an outer layer of corrugated polycarbonate panels. The cardboard tubes are waterproofed by immersions into liquid clear urethane to prevent expansion or contraction through changes in humidity. Tube ends are in full contact at the joints to transmit loads directly and reduce bending moments. As a precaution against sudden changes in loads - e.g. snow falling from roof - there are reinforcing steel tension members and braces in the plane of the arch.
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2.1.10 The Shared Ground Zone (also known as Local Zone) This building was one of the exhibition buildings in the Millennium Dome. The architects Spence Associates Limited with Philip Gumuchdjian and Shigeru Ban as consultants developed the concept for the project. In addressing issues of sustainability and environmental concerns the building along with the exhibition are intended to highlight how the individual can make a difference to the world around them. Children nation-wide sent cardboard to be recycled and form part of the structure. The zone was a two-storey elliptical spiral of 100 vertical cardboard tubes (10.5m to 24m high) with smaller tubes for mullions and louvers. At roof level a deep steel truss provided a diaphragm, transferring lateral loads to the braced columns. The “splayed wing” at the entrance to the building was tied back to the lift towers via the roof truss and ties. As with earlier projects, the tubes were joined through cruciform wooden fillets inserted into the tubes at all joints. The tubes were braced vertically at the line of the wall using steel rods. In the opposite direction out of plane bending was achieved by the introduction of a timber fin. This project has received much press coverage already [local]. Local zone materials In the Local Zone the following cardboard elements were used: • • •
500mm diameter, 15mm thick cardboard tubes as columns in a braced frame, 200mm diameter cardboard tubes at mid-height form part of the frame. Infill panels between the 500mm diameter tubes are formed using a cardboard honeycomb sandwiched between two flat boards. 100mm diameter cardboard tubes positioned horizontally clad the building.
All of the members are coated with an intumescent varnish providing a class 0 equivalent surface spread of flame. The 500mm diameter cardboard tubes have an internal and external membrane to prevent moisture ingress and protecting the inner structural core. The membrane was an aluminium foil which is sandwiched between layers of paper and when wound around the tubes with lap joints to further minimise moisture ingress.
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The Local Zone 2.1.11 Hannover Expo: Japanese Pavilion The building provided temporary accommodation for the Japanese exhibitors at the exhibition Hanover 2000. The building was there for one year including the construction period. The primary structure of the building utilises cardboard tubes to form a corridor and a grid shell over the exhibition space. A raised floor to the corridor was constructed from scaffolding. Corridor Structure The roof was formed from cardboard tube purlins at approximately 1m centres. The purlins spanned onto cardboard tube beams below. The roof beams were 600mm diameter cardboard tubes spanning between columns. They have internal timber stiffeners to prevent crushing at connection points.
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The columns were 600mm diameter cardboard tubes. They cantilevered in both directions from the stage structure thus providing lateral stability to the corridor. The cantilever moment from the columns was resisted by horizontal reactions at stage and ground level. At their base the columns was supported on a timber stub, fixed via a steel plate to supporting steel beams. The beams span between steel piles. Exhibition Hall The exhibition hall was a single space enclosed by a grid shell. The grid shell was close to funicular in shape under uniform loading and consisted of a lattice of cardboard tubes 120mm in diameter in two layers with 6mm cables in pairs to every second joint. The cables were used to triangulate the lattice and so produce a shear stiff surface that was capable of resisting in plane forces generated from the applied loads. Before the cables were fixed the structure was jacked from a flat grid at ground level. The saddle shape of the shell surface enhanced its stiffness. At cable node locations the tubes were connected together with a steel fabrication. These joints prevented the tubes sliding past each other, allowing the tubes to rotate about their own axis and relative to each other. This set of restraints and freedoms was required during the erection of the grid shell. Relative rotation on plan was prevented in the permanent condition by using this fitting to clamp the cables. The arrangement shown on the drawings used the minimum number of mechanical fixings to ensure that each tube is adequately held in position. At intermediate nodes, where no cables were connected, polyester tapes join the tubes. At the ends of the shell, the cables were terminated in a timber arch which transmits the axial tension back in to the tube lattice. This arch and the tube ends were sandwiched between sheets of plywood. At the base of the shell the tubes and cable terminations were fixed to a plywood board which follows the surface of the shell. A further plywood sheet was fixed via shear blocks on top of the tube lattice to form a plywood box beam. This plywood box beam was attached to prefabricated steel frames that also follow the profile of the shell. These frames were used to transmit uplift and horizontal reactions to the foundations.
2.1.12 Museum of Modern Art: New York Constructing a prototype cardboard building Literature review Admin:4928/reports/ lit review update
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This structure was built in the garden of the Museum of Modern Art in New York as a temporary exhibit in 2000. It is similar in design and concept to the Hanover pavilion, and designed by the same team of Shigeru Ban and Buro Happold. Unlike the pavilion it had no covering, so is essentially a sculpture rather than a building.
2.2 2.2.1
Other built examples Durakit Shelters
This Canadian company have very recently developed a new product line of very low cost, nearly instant houses / shelters. These are starting to be used for emergency shelters and 'outback' accommodation. The following pictures show the kit, and the process of construction leading to a 4m by 4m house. The images are taken from the website: www.durakit.com
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They are starting to market this product worldwide, and welcome approaches from possible dealers. 2.2.2
Akemo Ino
Master of Science Degree, 1984: Study of durability of corrugated paperboard painted with varnishes, oils, asphalts etc., as a temporary solution to minimum housing in undeveloped countries. A single room house was built and studied over two and a half years. 2.2.3
Temporary Theatre in Apeldoorn
The HET KARTEN THEATRE 1994 – Architect Hans Ruyssenaars, Engineers ABT Consulting The town of Apeldoorn in Holland, famous for paper making, celebrated 1200 years by constructing a. cardboard theatre [Koetsier 94]. They used cardboard in a lattice grid structure with a 12m span. The members were made of a laminate if 7 layers of cardboard with hardwood connector fins (again, paper). The nodes were made of timber. Many tests were undertaken and a Youngs Modulus of 500N/mm2 was found. The structure was designed to last for six weeks in the summer of 1993. The structure is particularly interesting as it uses flat laminates of cardboard, rather than the tubes preferred by Shigeru Ban, and also contained innovative and simple connection details. The theatre is a cylindrical shell with a radius of 6m and a length of 20.5m. It is built up from the following elements An end wall Bars of cardboard Plates of cardboard Fabric Foundations The theatre was successfully achieved in a short space of time and showed how card could be used as a structural material as long as it is protected from the weather.
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2.2.4
Atsuko Cotani. 1998
Graduate student at the Architectural Association last year, wrote on, 'The Paper Shelter' The dissertation explores the history of paper in architecture and products, explaining the how paper is made and utilised, From screens in traditional architecture to modern IKEA type cardboard storage systems. There is also an exploration of folded plate structures using origami as a starting point. A folded paper shelter is made.
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3
Existing Products, Materials and other data sources
From our search of the printed and electronic sources of information, we have found a limited amount of information on the direct applications of cardboard in buildings, but a wider range of general information on the material. This shows that there have been few building applications to date, but a number of important related developments, particularly in components of furniture. 3.1 3.1.1
Existing Products Honeycomb panels
Kraft- or aramid-paper honeycomb, used in composite boards, is a well established cardboard building technology. The idea of honeycomb spacing two veneers is familiar from door construction: the same principle is used to build panels for boats, aeroplanes and military vehicles where weight is an important consideration, e.g. the Rutan Voyager [Rutan]. This plane, the first to circumnavigate the globe in a single flight, was made almost exclusively from a 6.35mm sandwich of paper honeycomb and graphite fibre. Paper has had limited applications in construction since Monsanto's 'House of the Future' of 1957 [House of the Future], where phenolic-paper honeycomb panels, reinforced by a polyester coating, were used for the floor. The house was intended to promote not paper, but plastic technology: though potentially a paper building system, the honeycomb technique currently depends on a second material to face the panel - usually wood, aluminium or fibreglass - and the application of phenolic resin or similar to the honeycomb for strength. Also, honeycomb seems most effective in monocoque construction, which is very different to the truss and node constructions of Ban. Bellcomb, an American company, has tried to market a honeycomb panel system. Though they claim their structures to be stronger than traditional buildings, the company no longer sells the system as it could not be made profitable - the system could not offer a significant advantage in cost. Also, lumber companies would not store the panels and freight imposed a limit on the distribution area (transport of bulk rather than weight) and the time taken to educate builders, architects and clients for each sale. Bellcomb caution against, 'great claims regarding honeycomb housing,' and suggest the Structural Insulated Panel Association, 1511 K Street NW, Washington DC 20005 for enquiries. (email
[email protected]). During the 50’s the US government carried out testing of honeycomb panels of timber and card. However, the advent of polystyrene and related products were quickly adopted, so that further development of cardboard honeycomb products halted. Car panels Honeycomb panels with glass fibre impregnated top skins to improve the impact resistance and susceptibility to failure due to water have been used in self made cars [DCAb 98]. 3.1.2
Gridcore
'Gridcore' is perhaps more appropriate than paper honeycomb. Honeycomb panels are made from recycled fibre sources, e.g. cardboard, or agricultural fibres, e.g. kenaf, rice/wheat straw and oil palm fronds. The fibres are pulped and moulded as slurry, without resin or binders, into three-dimensional structures under extreme heat and pressure which removes the water from the slurry and compacts the particles. The resulting panels have one smooth face with integrated honeycomb ribs. Two panels are then glued rib-to-rib. The manufacturer claims no off-gassing and little pollution during the process. The final product could well be recycled. An American company called Gridcore developed a number of cardboard products for the construction sector, which are discussed on various web sites [Gridcore]. However they were not successful commercially and were bankrupt before being taken over by the Tiago Kogyo Corporation of Japan. It is not yet clear if the building product lines will be continued.
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However the Gridcore systems are an interesting development, using a cardboard honeycomb to give greater strength to a panel. The panels can be supplied up to 75mm thick, cut, painted, edge banded, veneered, and curved to custom radii. The panels can be potentially used for wall, roof and floor elements [Good wood] and have been used in stage sets and furniture. The air trapped in the structure also gives it good thermal insulation properties.
Gridcore table 3.1.3
Doors
Cheap domestic doors are commonly made of veneers of plywood with a honeycomb cardboard construction in the middle and there is certainly opportunity to develop this method as a panel system. 3.1.4
Related panel products
There are a number of panel products that are related to cardboard, in that they use fibres in different ways. These are discussed briefly here. Homasote www.homasote.com is a wood / paper based board product, with many similarities to cardboard, but bound together in a different way to give a higher performance product that has been in use for nearly 100 years. Sundeala make a pinboard product also using recycled newsprint, see: www.sundeala.co.uk. Tectan is made from recycled drinks cartons, cut up and pressed to form a panel product. See www.tectan.de for details. Ceramiboard is a brand new product, launched in 2001 by a firm based in Sydney Australia. They have developed and patented a new coating product, a form of ceramic, that enhances the properties of cardboard in terms of fire, acoustics and stiffness. There is more information on their website: www.ceramiboard.com. They are keen to develop contacts and new ideas for applications.
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3.1.5
Pile sleeves, column and void formers
Essex Tube Windings Limited have a number of building related products [Essex] and produce tubes up to 700mm diameter and 15mm thick. The most widely used of these are pile sleeves (called Heavesleeve) and temporary formwork for concrete, but their tubes are also used as void formers within concrete, and in a range of temporary structures, e.g. for cinema work, including featuring in the 1999 released Star Wars prequel. Although not relevant to this building, the pile sleeves are an interesting example, and have had further research undertaken into them. In a study by BRE into the movement of foundation piles in clay, the piles poured into cardboard were found to move the least, presumably as the soil is more easily able to slip on the card surface [BRE 91]. Similarly we do not plan to form concrete columns for our single storey building, but this application is also effective, particularly in cost and time savings. Cardboard tubes are used as form work for concrete, and because of their low price the contractor can afford to pour the columns for a whole floor at once, and then move on more quickly to the next levels. There is also no need to wait to remove the formwork from the lower levels until the concrete is fully hardened. A concern might be that the cardboard formwork is only used once as it is cut away from the column after use. Water pressure tests have been undertaken on tubes used as column formers and 3 tubes were tested proving their suitability [Cambridge 96] 3.1.6
Insulation
Warmcell produce a insulation made of recycled newsprint [Excel]. The product is installed replacing conventional insulation by being blown or sprayed. It achieves U-values of 0.31Wm2K-1 with 90mm thick insulation. It meets British fire regulations and does not prejudice the fire resistive properties of the wall or roof. It is an established product and has been used in domestic and commercial applications.
Warmcell being installed (from their brochure) 3.1.7
Papercrete
There have been a number of buildings in the USA that incorporate papercrete. This is a form of concrete that uses paper instead of stone as the aggregate. It results in a much lighter and better insulating form of concrete, but needs to be protected from excess moisture. We considered trying to use it at Westborough school but felt it was not right for us. For more information refer to http://www.zianet.com/papercrete/.
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3.1.8
Pallets
Smurfit have developed a pallet [Stonestreet 98] which is capable of carrying loads of up to 1000kg, it is interesting that beams within the pallet have been made by folding and gluing corrugated cardboard. In conjunction with the pallet, a no strap pallet pack has been developed which clip to the pallet. The pallet has found particularly useful application as a substitute for alternative pallets used for airfreight, offering substantial cost advantages over its heavier rivals.
Smurfit cardboard pallets 3.1.9
Boats
Many Universities in Australia and America annually hold cardboard boat regattas, constructed entirely of cardboard, they have been built to carry up to 16 people and are raced [boats].
Cardboard boat race
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3.1.10 Furniture applications In recent years cardboard has increasingly been used in furniture and storage design. Card board has been used as a packaging material, and recently companies such as IKEA and MUJI have marketed mass produced card board storage systems made entirely from paper and cardboard. Cardboard in these systems form an important part of the aesthetic. This use has most probably come from the more abstract use of cardboard by architects such as Frank Gehry who designed a range of corrugated cardboard chairs [Gehry 1972].
Cardboard chair 1
Cardboard chair 2 Another source of information in this area (especially for storage systems) is the current IKEA catalogue!
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3.2 3.2.1
Material properties General
General paper is made of highly compresses cellulose fibres, the manufacturing process leads to approximately 70% of the fibres falling in the direction of the machine which makes the paper, 20% in the other direction, and 10% in the thickness direction [Buro Happold 99]. Moisture affects the strength of paper, with a peak moisture content of 5%. A change in moisture content leads to a change in strength of approximately 10%. The fibres in paper are bonded by hydrogen bonds that can be destroyed with uncontrolled moisture content. Under indoor conditions this does not normally happen, because of the relatively constant humidity. 3.2.2
Strength, stiffness and creep considerations
Recently Buro Happold has undertaken work on the Hanover Expo 2000 project and on the Local Zone. This was with Shigeru Ban and architects Spence Associates Limited. This involvement has given a more detailed understanding of the importance of creep, or visco-elastic behaviour, as a design consideration. Preliminary conclusions and recommendations of load tests [DCAb 99] carried out on tubes, indicate a 2 Youngs modulus of 1000N/mm2 and a failure stress of 8.0-8.8 N/mm . Other conclusions were that the material is sensitive to small changes in moisture content and suggests that a vapour barrier is one method of reducing the possibility of moisture ingress. It was noted that the tubes creep under small loads, as low as 10% of the failure load. University of Bath undertook tests [Bath 98], subjecting tubes to bending, compression, tension, and creep tests. The bending tests indicated that the tubes deflected elastically, but with small increments of 2 permanent deformation. The compression tests indicated a compressive stress at failure of 8.75N/mm . The mode of failure is as indicated below. Creep test indicated that even below 20% of failure load, the material continued to creep after days of application of the load. Tension tests indicated that failure stresses similar to the compressive failure stress was found, however, the method of connection at the end of the tube was important. Dowelled, nailed and glued connectors were used, the glued being the weakest as the paper failed within the paper lamination. 2
In the Hanover report [Buro Happold 98] compression failure loads of 9.23N/mm were found with a 2 2 standard deviation of 0.5N/mm . A Youngs Modulus (E) of 1800N/mm was found. To limit the effects of creep, a high creep factor of 5 was used and a long-term permissible compression stress of 1.6N/mm2 used in the design. With testing being carried out at Imperial College, London, where much larger diameter tubes are being assessed, an additional factor has come into play, the winding angle of the tube. Cardboard tubes are manufactured using a winding process and whatever the diameter of the tube the same width of paper is used to make the tube. Therefore the larger the diameter the shallower the winding angle and, as we have found at Imperial, the lower the failure stress. For bending, values of 8.2N/mm2 and for compression 7.8N/mm2. Creep tests, which are still ongoing, are recording movement in tubes loaded with 10% of the failure load 3.2.3
Water resistance
It is a significant weakness of cardboard that in its natural state it degrades significantly in the presence of water. However there are clearly options to give it resistance to the uptake of water or moisture, through a range of surface treatments, or the inclusion of one or more layers of a different type of material in its manufacture. Possible examples are polyethylene or aluminium “sandwiches”. Extensive work has been undertaken on the effects of water content on the compression strength of paper tubes for the paper dome project [Koumouten 97]. In summary, the strength of the tubes was found to remain constant up to about 7% water content and the strength then reduces at about 10% for every 1% increase in water content. The equilibrium water content is approximately 7-10% at a relative humidity of 30-70% that is a typical range of relative humidities expected in an internal environment in Britain. A waterproof coating applied to the tubes was found to reduce frequency and range of the variations in external humidity, and was found to improve the bearing performance of the tubes. Constructing a prototype cardboard building Literature review Admin:4928/reports/ lit review update
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Three of Shigeru Ban’s Paper refugee tents have been erected at the Vitra factory to assess resistance to environmental conditions. These results were unavailable at the time of writing. One interesting example of the effectiveness of varnish and glue treatments is highlighted in a web site about a cardboard boat race [boats]. This clearly shows that it can be made water-resistant for the length of a race. This is an area that we will be researching at much greater length as we propose product ideas. One of the issues in water resistance is that many of the potential treatments are not choices we would like to make from an environmental point of view. For example we could add a layer of PVC to card to give it good resistance, but this would probably not be considered acceptable. One traditional system is to use egg white as a coating material, although the durability of this will need more consideration. 3.2.4
Fire resistance
Given that paper burns easily, it is natural to be concerned about the effect of fire in a cardboard building, or the effectiveness of a cardboard component. Recent tests (not published) have indicated that cardboard has similar properties to wood in fire, and the more dense the cardboard, the less easy it is to light. In ensuring the integrity of cardboard in a fire, a series of tests were carried out as part of the research and development for the Local Zone in the Millennium Dome. By applying in intumescent varnish to cardboard tubes a Class 0 equivalent surface spread of flame can be achieved. Warrington Fire Laboratories carried out this test and have provided certification of such. This was sufficient for the requirements of this building. As part of this series of tests, ad-hoc tests were carried out on cardboard tubes to establish whether a o fire classification could be achieved for the raw and treated material. A 1000 C flame was held at the end of the tubes tested and in the same way that the surface of timber chars and protects the underlying material, cardboard behaves similarly. After 60 minutes 150mm of a tube had been affected. The application of the intumescent varnish to the external face did not provide different results. These tests did not result in obtaining some form of classification as it was not a requirement of the project. In addition, tests were carried out on honeycomb panels made-up of cardboard sheets sandwiching a honeycomb core, the surface of which was coated with intumescent varnish. The purpose of this test was to demonstrate that the air pockets inside the honeycomb did not promote the spread of fire through the panel as the varnish foamed up and protected the panel. A fire rating could have been achieved on the panels by providing a 1mm thick steel plate to the rear face. Gridcore have undertaken fire tests. This information was not available at the time of writing. The panels have been detailed around the edges to prevent direct access of moisture 3.2.5
Adhesives and glues
Because of the way in which cardboard is made, a series of layers of paper joined with a glue, there is considerable importance to the type of glue used in the process and the ways that this glue may affect the behaviour of the material. Typically poly-vinyl acetate, pva or dextrine glues are used. Pva is a thermo plastic glue usually used with timber. As a thermo plastic glue it is affect by moisture and temperature and its low creep resistance may not assist the long term properties of the cardboard. Dextrine glue behaves well when kept dry and is not as susceptible to creep behaviour, but when wetted turns to “mush”. An alternative option would be a thermosetting glue. These glues set permanently when heated and can therefore improve the long-term performance. However, they usually have formaldehyde as a consistent part and are therefore environmentally unfriendly. They also make the cardboard material difficult to recycle. Recent interesting developments in glues include a soya based, water resistant glue which is stronger than timber [New Scientist 99]. Constructing a prototype cardboard building Literature review Admin:4928/reports/ lit review update
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There are many books on glue including 'Adhesives in construction', an ICE book, and these are areas we will consider in more detail as the project develops.
4
Conclusions
This review shows that there has been more work carried out using cardboard than might have been anticipated. However much of the work has related to temporary exhibition or emergency building, so that there is considerable scope for further work to develop practical and useful products for the construction industry. In particular we need to address the following issues in the context of the school, or any other planned medium lifetime building: • • • • • •
Durability Impact strength Security Fire Moisture ingress Internal moisture
If we are able to find satisfactory solutions to these issues then we will be able to produce a prototype building. Further work will be needed to demonstrate whether there are widespread applications. 5
Acknowledgements
The support of the DETR (now in the DTI) through its Partners in Innovation scheme, Westborough School, Paper Marc Ltd, Essex Tube Windings, Quinton and Kaines Ltd, C G Franklin Ltd and the Cory Environmental Trust in Southend on Sea, is gratefully acknowledged.
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References
[Akemo Ino]
http://loislane.sel.eesc.sc.usp.br/set/lamem/htm-mest/iakemim.html
[Ban 97]
ed. Galfetti, G G, Shigeru Ban (CG portfolio), 1997.
[Bath 98]
University of Bath, Durolene Tube Tests, Private communication, July 1998.
[Bellcomb]
http://www.bellcomb.com/panelbp.htm
[boats]
http://gcbr.com/index.html.
[BRE 1991] BRE, Seasonal Foundation movements in London Clay, from Ground movements and th Structures, published in the proceedings of the 4 International conference, the University of Wales, 8-11 July 1991 [Buro Happold 98] Buro Happold, Japanese Pavilion Expo 2000, Scheme Design Report, Revision 2, Private Communication, November 1998. [Buro Happold 99] Buro Happold, Japanese Pavilion Hanover Expo 2000, Summary of Knowledge About Paper, internal communication February 1999. University of Cambridge, Tests on cardboard column forms, January 1996,
[Cambridge 96] [DCAB 98] July 1998.
DCAb, Card and Paper product notes, private communication from DCAb for NMEC,
[DCAb 99] DCAb, Millennium Dome, Local Zone, Preliminary Conclusions and Recommendations of Load Tests, Private communication 8 Feb 1999. [Essex]
Essex Tube windings Ltd, various manufacturers information, available from
[Excel]
Warmcell product information, published by Excel Industries Ltd, Ebbw Vale, Wales.
[FEDRA 98] Buro Happold FEDRA, Results of tests on cardboard, private communication from Andrew Nicholson, November 1998. [Gehry 72]
The architecture of Frank Gehry, chapter on Easy Edges (1972)
[Good wood]
http://forests.org/ric/good_wood/cardbrd.htm.
[Gridcore] http://www.usda.gov/aarc/srbk/0100.html, http://www.gridcore.com, also http://oikos.com/esb/50/gridcore.html, email
[email protected]. [House of the Future]
http://builder.hw.net/monthly/1997/jun/hotf/hof6.htx
[Koetsier 94] Koetsier, R H, A theatre with finite cardboard elements, from Finite Element News, Issue no2 (April) 1994. [Koumuten 97] Koumuten, I, Wooden Structure Assessment Committee BCJ-W489, Experimental Structure “Paper Dome”, July 25, 1997. [Local]
Local zone in Architects Journal 18/3/1999, Building Design magazine 5/3/1999
[New scientist 99]
Short item from 1998 edition, date unknown.
[Rutan Voyager]
http://www.nasm.edu/NASMDICS/AERO/AIRCRAFT/rutanvoy.htm
[Stonestreet 98] Stonestreet, B, Pallet solution for the future, from International Paper Board Industry, December 1998.
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