A cement and concrete industry publication
Precast Concrete Arch Structures A state-of-the-art report
Technical Guide No. 12
Acknowledgements The Concrete Bridge Development Group is pleased to publish this report on behalf of the Highways Agency. The CBDG also wishes to acknowledge Ove Arup & Partners who were the consultants that produced this report on behalf of the Highways Agency. This report takes into account the particular instructions and requirements of the Highways Agency, and it is not intended for and should not be relied upon by any third party and no responsibility is undertaken to any third party. CBDG is pleased to acknowledge Techspan (ReCo), Matiere (AMB Group) and Bebo (Bebo) who provided comments on the draft and gave permission to use the illustrations and photographs used in this publication. CBDG acknowledges financial support fromThe Concrete Centre, part of the Mineral Products Association, in the production of this publication. www.concretecentre.com
Published for and on behalf of The Concrete Bridge Development Group by The Concrete Society Riverside House, 4 Meadows Business Park, Station Approach, Blackwater, Camberley, Surrey GU17 9AB Tel: +44 (0)1276 607140 Fax: +44 (0)1276 607141 www.concrete.org.uk CCIP-035 Published December 2009 ISBN 978-1-904482-58-1 © Concrete Bridge Development Group Order reference: CBDG/TG12 CCIP publications are produced by The Concrete Society on behalf of the Cement and Concrete Industry Publications Forum – an industry initiative to publish technical guidance in support of concrete design and construction. CCIP publications are available from the Concrete Bookshop at www.concretebookshop.com Tel: +44 (0)7004 607777 All rights reserved. Except as permitted under current legislation no part of this work may be photocopied, stored in a retrieval system, published, performed in public, adapted, broadcast, transmitted, recorded or reproduced in any form or by any means, without the prior permission of the copyright owner. Enquiries should be addressed to the Concrete Bridge Development Group. Although the Concrete Bridge Development Group (limited by guarantee) does its best to ensure that any advice, recommendations or information it may give either in this publication or elsewhere is accurate, no liability or responsibility of any kind (including liability for negligence) howsoever and from whatsoever cause arising, is accepted in this respect by the Group, its servants or agents. Printed by Information Press, Eynsham, UK
Precast Concrete Arch Structures Contents 1.
Introduction
3
2.
Summary of previous usage 2.1 Precast arch systems 2.2 Documents reviewed 2.3 Types of proposed structure 2.4 Key characteristics of the arch structure 2.5 Case histories 2.6 Structure geometry
4 4 5 6 6 11 11
3.
Current Practice 3.1 Design 3.2 Specification 3.3 Construction 3.4 Maintenance 3.5 Monitoring
17 17 21 26 28 28
4.
Recommendations 4.1 Design 4.2 Specification 4.3 Construction 4.4 Maintenance provisions 4.5 Monitoring
29 29 31 33 34 34
5.
Risk management 5.1 Interactions between parties 5.2 Sensitivity of design 5.3 Construction geometric control and tolerances 5.4 Verification of design during construction 5.5 Load–deflection serviceability criteria
36 36 36 37 37 37
6.
Checklist 6.1 Procurement stage 6.2 Design 6.3 Segment casting 6.4 Delivery 6.5 Site storage 6.6 Construction
Bibliography
2
38 38 38 38 39 39 39 40
Introduction 1
1. Introduction In 1999, the Transport Research Laboratory (TRL) undertook a comprehensive review of arch systems for buried structures on behalf of the Highways Agency (HA). The review covered masonry and modular arch structures. The work also identified potential benefits from the use of modular arch structures in infrastructure projects in the UK. This report provides guidance on the use of precast concrete arch structures. It is not intended to be a detailed design guide but to provide guidance for experienced structural engineers and advisers on the use of such structures. It provides guidance on good practice for the use of such structures utilising the experience of the industry suppliers. This document is also intended to enable the HA to continue benefiting from appropriate use of such structures, of which there are some 66 throughout the UK and Ireland. These structures have spans in the range 3–20 m and a length of 2.5–361 m. This demonstrates the adaptability of arch span structures and there are many more in the rest of Europe and elsewhere. There are two main types of precast concrete arch products currently used in the UK. Reinforced Earth Company (RECo) supplies TechSpan products while ABM markets Matiere structures. There is a third system currently marketed by Asset International called the BEBO system. This document has been largely compiled using technical details provided by the first two companies, namely RECo and ABM, and from experience gained by Arup in this type of structure. Information for the BEBO system provided by Asset International has been included in Sections 2 and 3. This report is only applicable for highway structures constructed using precast arch techniques that do not require mechanical ventilation provisions. This report note also refers to the following HA standard documents: Specification for Highway Works (SHW) Series 500 – Drainage and Service Ducts SHW Series 600 – Earthworks BD 74/00 – Foundations BD 31/01 – The Design of Buried Concrete Box and Portal Frame Structures BD 37/01 – Loads for Highway Bridges BD 2/05 – Technical Approval of Highway Structures
3
2 Summary of previous usage
2. Summary of previous usage There are several types of precast arch structures reported in the 1999 TRL report. However, at the time of writing (2008) the two most commonly used precast arch structures in the UK, namely TechSpan and Matiere, are supplied by Reinforced Earth Company (RECo) and ABM Group (ABM) respectively. A third system, BEBO, has recently been marketed by Asset International.
2.1 Precast arch systems 2.1.1 TechSpan system
The TechSpan system was developed in Spain by Groupe TAI (http://www.groupetai.com) in 1989 and it is currently used worldwide and supplied by the Reinforced Earth Company (RECo; http://www.recouk.com). RECo is a wholly owned subsidiary of Freyssinet Group and it supplies the TechSpan system in the UK. This TechSpan arch system was introduced into the UK, Australia, Canada and the USA in the early 1990s. In 2008 there were approximately 1000 custom-designed installations in the world utilising such structures.
2.1.2 Matiere system
The Matiere system originated in France in 1982. The system has been widely used in Ireland and there is growing interest in the UK. ABM Group is a Dublin-based construction company founded in 1991 and is distributor of the Matiere system in Ireland and the UK. ABM Group is made up of ABM Construction, ABM Design & Build and ABM Precon. ABM Precon was formed in 2005 and it specialises in the manufacture of precast reinforced and prestressed concrete for the UK market. The ABM Group official website cites more than 10 000 installations across 20 countries using buried precast concrete for arch and box structures. systems (http://www. abmeurope.com). It is not clear, however, how many are arch structures.
2.1.3 BEBO system
4
The third precast arch system reported in the 1999 TRL report is the BEBO system. Development of the BEBO arch system began in Switzerland in 1966. It has since been used in Switzerland, Germany, the USA, Canada, Malaysia and Australia. BEBO Arch International AG (see http://www.beboarch.com), a Swiss company, is (except for the USA, where the rights to the system belong to the BEBOTech Corporation) the worldwide owner of all rights to the BEBO system.
Summary of previous usage 2
Since the system’s inception, approximately 500 BEBO arch structures have been built in Europe. The system is marketed in the UK by Asset International, part of the Hill & Smith IPG Group (see http://www.assetint.co.uk).
2.2 Documents reviewed
2.2.1 Specifications
The following subsections list documents reviewed during the course of the production of this publication.
Technical Specifications for TechSpan Precast Arch System Standard specification for the manufacturing and installation of Matiere precast concrete
structures.
2.2.2 Other documents
Matiere Precast Concrete Arch Structure – Draft AIP Model Document Technical Approval of Highway Structures (RECo) Greater Bargoed Community Regeneration Scheme — Railway Bridge SWM2 (BEBO)
2.2.3 Design guidance
2.2.4 Construction guidance documents
2.2.5 Papers
ABM Design and Build Technical Note (Design Philosophy)
TechSpan Construction Manual and Quality Control Manual Matiere structures construction guide BEBO Arch System - Instructions
Application and Design of Segmental Precast Arches Non-linear Analysis of Buried Arch Structures Analysis of Buried Arch Structures, performance versus prediction Seismic Analysis of Buried Arch Structures
2.2.6 Miscellaneous articles/ documents
A new method for the construction of buried structures - the “Matiere Method” A review of arched systems for buried structures Matiere Patented Structures - foundation of structures Matiere Patented Structures - lateral backfills
5
2 Summary of previous usage
2.3 Types of proposed structure Table 2.1 Details of arch structures.
The arch structures currently supplied by the three companies are given in Table 2.1.
Type
Span (m) Description
Matiere system Matiere CM2
1.5 - 3.0
Single-segment system founded on a continuous concrete raft structure
Matiere CM3
3.0 - 8.0
Two-segment system founded on a continuous concrete raft structure forming a three-pinned arch
Matiere CM4
2.5 - 20.0
Three-segment system forming a two-pinned arch structure
Up to 20
Two-segment system forming a three-pinned arch structure
E-series
3.6 - 25.6
Single- and twin-leaf precast elliptical segments forming a twopinned arch. Twin-leaf system has a cast-in-place crown joint
C-series
9.1 - 12.8
Single- and twin-leaf precast circular segments forming a twopinned arch. Twin-leaf system has a cast-in-place crown joint
T-series
7 - 31
Single-leaf shallow arch forming a two-pinned arch
TechSpan system TechSpan BEBO system
6
2.4 Key characteristics of the arch structure
The following section outlines the main characteristics of each of the three arch systems discussed in this report.
2.4.1 Matiere structure
The most commonly used Matiere arch system is the CM4, the three-segment system. This structure is developed from its predecessors, the CM2 and CM3 (see Figure 2.1). The improvement made has led to a larger-span structure with added standard features to simplify casting of the precast segment and site installation. The CM4 system has two variations: the closed-cell system and the open-cell system (see Figures 2.2a) and 2.2b). Installation of this type of arch structure involves positioning the walls on pre-prepared foundations before lifting the roof onto the walls, see Figure 2.2c). The walls are designed to be stable without external support. In the majority of cases, the roof can be placed before casting of the in-situ floor slab or the external heel (Figure 2.2d). The joints (balland-socket type) are inclined at 45°, which is maintained for all standard units.
Summary of previous usage 2
Figure 2.1 The Matiere CM2 and CM3.
Figure 2.2 The Matiere precast arch system. Photos: ABM Roof Joint Wall In-situ reinforce concrete extern heel
In-situ floor slab
a) Closed cell system
c) Placement of roof structure on the walls (CM4)
b) Open cell system
d) Preparation of the in-situ heel (CM4)
7
2 Summary of previous usage
2.4.2 TechSpan structure
The TechSpan system is made up of three main components: the foundations, the arch segments (two halves) and the crown beam (see Figure 2.3(a)). The foundations are cast with a keyway to provide lateral restraint to the arch segment during installation, see Figure 2.3(b). Unlike the Matiere system, where the walls are self-supporting, the TechSpan segments are installed initially in pairs and staggered longitudinally to provide support for subsequent panels, as shown in Figures 2.3(c) and 2.3(d). Once four segments are in place, generally the structure will be stable under these temporary erection conditions. However, temporary support may be needed for special conditions where the geometry of the segment may dictate its temporary stability. The crown beam can be cast at any time up to placing the backfill to crown level. This crown beam provides the tie along the length of the structure at the crown and it does not form a moment connection at this point.
Figure 2.3 The TechSpan precast arch system Photo: RECo
CL Structure Crown beam Arch segment Shallow foundation Keyway cast as part of the foundation to provide lateral restraint to the segment
Foundation Deep pile foundation
8
a) Major components of a TechSpan arch
b) Foundation for the TechSpan system
c) Erection of the first two segments
d) Image showing erection process
Summary of previous usage 2
2.4.3 BEBO system
The BEBO system is a system of overfilled reinforced concrete arches that can be precast or cast in place. The precast system is similar to the TechSpan system and comprises three main components: the arch segments, the foundations and the crown joints. The arch is made up of either single- or two-leaf segments, as shown in Figure 2.4a & 2.4b. Similar to the TechSpan system, these segments are founded on shallow strip foundations or piled foundations. However, unlike the TechSpan system, the cast-in-place crown joint of the BEBO’s twoleaf system is designed to provide full structural continuity along the full length of the arch. During installation and prior to the casting of the crown joint, this two-leaf system behaves as a three-pinned arch. Figure 2.4a shows the crown joint with its reinforcement prior to casting.
Figure 2.4a The BEBO system crown joint prior to casting.
9
2 Summary of previous usage Figure 2.4b The BEBO system.
80 elliptical shapes -spans of 3.6 to 25.5 metres Single and twin leaf precast elements Standard overfill heights of 0.4 to 4.5 Designed for extreme traffic loads Type E24
E48 E84T
E36
E24
E16
E12 E20
Type E84T
E42 E30
E72T E60T
E54T E66T E78T
a) E-series (elliptical segments) b)
Type C30T
Type C42T
30 circular shapes - spans of 9.1 to 12.8 metres Single and twin leaf precast elements Standard overfill heights of 0.4 to 4.5 metres Dedicated design for up to 100 metres overfill Optimised high overfill elements and foundations
E20
E12
E16 E24
C30T C42T
C36T
b) c) C-series (circular segments)
Shallow arch shapes: span to rise ratios up to 10:1 Any span between 7 and 31 metres or more Precast or cast-in-place - no counterforms Bridges with up to 45o skew and more Ideal for low overfill applications
T102
T90 T80 T70 T50
c) T-series (shallow arch) d)
10
T60 T40 T30 T20
Type T30
Type T84T
Summary of previous usage 2
2.5 Case histories
During the course of this project, RECo provided a total of 38 case histories of the use of the TechSpan arch structures since 1992 in the UK and Ireland, with 31 of these in the UK. ABM provided 28 case histories of the use of their Matiere system since 2000, with three of these in the UK. From these records it can be seen that the precast arch structure was first used for the construction of modern underground structures in the UK in the early 1990s, with the TechSpan system used from 1992. The use of the Matiere system did not begin in the UK until 2003.
2.6 Structure geometry
Figure 2.5 shows the range of structural spans supplied by RECo and ABM for precast arch structures installed in the UK and Ireland. Based on the case history data provided, the maximum height of such structures is approximately 9 m. The thickness of such structures is between 200 and 350 mm, with exceptional cases of up to 400 and 520 mm. It is the physical size and the ability to lift and transport the precast segments that tends to govern the geometries of such structures. The distribution of the span of such structures together with the year of installation is shown in Figure 2.5. The maximum span for a TechSpan system is 20.25 m while the corresponding value for the Matiere system is 17.5 m.
11
2 Summary of previous usage
Figure 2.5 Precast arch structures in the UK and Ireland since 1992.
25
Span (m)
20
15
10
5
0 1992
1994
1996
1998
2000
2002
2004
2006
Year a) TechSpan system
20
Span (m)
16
12
8
4
0 1999
2000
2001
2002
2003 Year
b) Matiere system
12
2004
2005
2006
2007
Summary of previous usage 2
2.6.1 Span–height distribution
Figures 2.6a and 2.6b show the span–height distribution of the arch structures. From the information supplied by RECo on 38 arch structures, there are 14 with a span/ height ration greater than 2 but less than 3 (2>span/height3), and and 14 with a span/height ratio less than or equal to two (span/height 14.4
20
10
Element width: –5 mm to +5 mm Element thickness: –5 mm to +15 mm Surface finish: 5 mm over 1.2 m measured with a straight edge
These tolerance values are normally specified in the contract document and, in the UK, these will be based on the tolerances stipulated in the (SHW 1700 Series) for precast concrete. All supplied materials are manufactured in plants either operated or carefully selected by the local supplier of the TechSpan system.
21
3 Current practice
3.2.1.2 ABM
Table 3.2 ABM tolerances
Table 3.2 gives the ABM tolerances, which are in accordance with Section 6.2.8.3 of BS 8110 Part 1: 1997.
Tolerances Length* Up to 3 m
± 6 mm
3.5 - 4.5 m
± 9 mm
4.5 - 6.0 m
± 12 mm
Additional deviation every subsequent 6 m
± 6 mm
Cross-section* Up to 500 mm
± 6 mm
500 - 750 mm
± 9 mm
Additional deviation for every subsequent 250 mm
± 3 mm
Straightness or bow* Up to 3 m
± 6 mm
3-6m
± 9 mm
6 - 12 m
± 12 mm
Additional deviation for every subsequent 6 m
± 12 mm
Squareness (longer of the two adjacent sides should be taken as base line) Up to and including 1.2 m
6 mm
Over 1.2 m but less than 1.8 m
9 mm
1.8 m and over
12 mm
Twist
Note *The tolerances for length, cross-section and straightness or bow are those from the SHW document.
3.2.1.3 BEBO
3.2.2 Reinforcement tolerances
Up to 600 mm wide and up to 6 m in length
6 mm
Over 600 mm wide and for any length
12 mm
Flatness Maximum deviation from a 1.5 m straight edge placed in any position on a nominal plane surface should not exceed 6 mm
The BEBO system requires all dimensions to be accurate to ±6 mm.
The HA’s Interim Advice Note 95/07 Revised guidance regarding the use of BS8500 for the design and construction of structures using concrete (2006) suggests that reinforcement fixing tolerance should be 5 mm for precast concrete made in factory production conditions. The cover required for any concrete is a function of the exposure conditions. The HA document indicates that nominal cover should allow for the minimum cover plus the reinforcement fixing tolerance.
22
Current practice 3
3.2.3 Backfilling
Backfilling of the arch structure is one of the critical operations of the construction process. Backfilling of the TechSpan system is only allowed to commence once the grout at the bases/footings has been completed and cured. For the Matiere system this operation can only commence once the heel concrete is fully cured and the roof segment is in place. For the BEBO system, this operation is only allowed to commence once the grout of the keyway and, if a two-leaf system is used, the concrete for the crown joint have achieved the required strength.
3.2.3.1 Testing and placement requirements of fill material
Control of the backfill type, compaction efforts and equipment used are crucial elements in the successful construction of the arch structure. TechSpan system Granular backfills are generally specified as fill materials for such structures. Testing requirements are defined in the Techspan systems specifications. The moisture content during backfilling is recommended to be a minimum of 2% less than the optimum moisture content. The fill is recommended to be placed at 250 mm lifts and with a maximum difference in level between the opposite sides of less than 0.5 m to avoid eccentric loading of the structure panels. Three compaction zones are currently specified, as shown in Figure 3.2. Light compaction plant is allowed within the 1.0 m zone from the structure (Zone 1). Heavier non-vibratory compaction plant is allowed outside the above 1.0 m zone to 2.0 m measured from the footing/base of the structure (Zone 2). Outside the 2.0 m zone, vibratory compaction is allowed (Zone 3). The size of the plant is governed by the specifications.
Figure 3.2 Compaction zones for the TechSpan system.
CL Structure Zone1
Zone2
Zone3
1m 1m
23
3 Current practice
Matiere system Class 6 granular fill has been specified for the Matiere structure. Plate bearing tests have been specified to verify the stiffness value of the fill material on site. Compared to the TechSpan system, the Matiere system has a tighter tolerance of 0.25 m for the difference in backfill level between the opposite sides. Only hand-operated compaction plant is allowed within 2 m of the structure. Outside this zone normal compaction plant is allowed. The compaction zones are depicted in Figure 3.3. Figure 3.3 Compaction zones for the Matiere system.
Hand operated compaction plant only
2m
2m
BEBO system Backfill types and testing requirements are defined in the BEBO System Instructions document. These fills, divided into Zones A to C, as shown in Figure 3.4a, are predominantly granular soils. Zone A soil should be of similar quality and density to Zone B material and extends over a lateral extent of at least one arch span outside the footing of the structure. Placement of fill is restricted to 0.3 m layers with maximum difference in levels between opposite sides of 0.6 m. Compaction zones for the BEBO system are shown in Figure 3.4b and the following are applicable: Only hand-operated compaction plant allowed within 0.3 m of the structure. Heavy vibrating compaction equipment is only allowed outside the limits where
dumping is allowed, as shown in Figure 3.4b, and applies to vibration frequencies of more than 30 revolutions per second. There is no clear guidance on the compaction equipment between the above two regions.
24
Current practice 3
C
B A
¾H
H
A
B A o 45
Zone A: Existing soil, constructed embankment or overfill Zone B: Fill which is directly associated with bridge installation Zone C: Road structure
a) Zones of backfilling for the BEBO system
Dumping allowed
Dumping not allowed
Dumping allowed
b) Zones of compaction for the BEBO system
Figure 3.4 Fill and compaction zones for the BEBO system.
25
3 Current practice
3.2.4 Loading
3.2.5 Foundation soils
3.2.6 Waterproofing
All the three precast arch systems require that the structures be designed to live loads stipulated in BD 37/01.
Although the foundation system is an integral part of the structure, there is limited coverage of the foundation soils in the system documents provided by the suppliers.
Generally waterproofing has not been specified by the specialist suppliers. TechSpan system For the TechSpan system an impermeable geo-membrane, Bituthene 3000 membrane by W R Grace and Company, or equivalent to be approved by RECo, has been used. Where bitumen paint is used with filter cloth, it is only intended to prevent loss of fines. Matiere system When watertight conditions are needed, high-density polyethelene (HDPE) membrane is used. This type of waterproofing membrane is only recommended when the cover above the crown is more than 600 mm. Continuous weld joints at laps are also used. BEBO system BEBO recommends waterproofing the structures by means of caulking the joints (40 mm diameter preformed mastic), with subsequent covering of the joints with 300 mm wide membrane strips (e.g. Bituthene 3000 or equivalent). To ensure that the strips remain in place during backfilling, the strips must be bonded to the precast elements with an adhesive compound.
3.3 Construction
3.3.1 Transportation, handling and storage
26
During construction, the following requirements unique to each system need to be considered.
TechSpan system The segments are transported to site on flatbed trailers. Lifting points cast into the top edge of the segment allow easy handling on site. It is important to have well-prepared firm ground for storage of these units. The unit should be stored on its curved edge and not be left in the inverted position for longer than is necessary to lift it to the upright position. The units are checked for damage at each stage and care must be taken to protect the units during handling, especially while rotating the unit from its edge to the inverted position.
Current practice 3
Matiere system The segments are lifted by anchors cast into the units. They are transported in the position in which they are cast. BEBO system BEBO arch elements are designed to be stored in the casting yard and hauled in the position in which they are cast. It is not recommended to store the arch elements on site. The arch elements are lifted through the use of the anchors at specific designed positions. Generally, all BEBO system arch elements should be handled with a double-drum crane, i.e. a crane having two independent drums with equal capacity. Where no such equipment is available, BEBO engineers will be able to develop appropriate installation procedures.
3.3.2 Construction geometry control and tolerances
TechSpan system For installation geometry control, RECo specifies the following: Offset between the centreline of the structure to the inside edge of the keyway:
+0 to –5 mm. Centreline offset of the inside edge of the keyway along a 2.5 m length in the longitudinal direction: < 3 mm. Vertical tolerances (including sloping footing) at the base of the keyway: ±5 mm. Tolerance values for installation are specified as: Maximum allowable horizontal offset between any adjacent segments: < 25 mm. Maximum allowable vertical offset between opposite segments at crown: < 20 mm.
Matiere system ABM has the following requirements for construction geometry control: Flatness of the screed ±3 mm over 6 m (survey at 2.5 m grids).
3.3.3 Site presence
In the UK, RECo usually provides on-site assistance for the first day of erection. Alternatively the company will recommend the use of an erection subcontractor who has had previous experience of installing these types of structure. When using the Matiere system, ABM will provide its own crew to install the structure. For the BEBO system, an experienced representative will attend a preconstruction meeting to provide installation instructions to the installation contractor. BEBO will also provide a representative for the first day of installation.
27
3 Current practice
3.4 Maintenance
There is no clear guidance from the suppliers with regard to the maintenance requirements of the arch structure. However, the following are indications that such structures require a low level of maintenance provision: Such structures are buried and therefore remote from the carriageway; consequently,
problems associated with ingress of chlorides is greatly reduced or eliminated. The structure is precast offsite under a strict quality controlled environment and
therefore contact surfaces and concrete covers will meet the design tolerances. The waterproofing layer will act as an effective barrier preventing water ingress from
the concrete surface.
3.5 Monitoring
28
At the time of writing there are no special requirements to monitor the structures to confirm their behaviour with regard to the design predictions.
Recommendations 4
4. Recommendations The following best-practice recommendations have been based on experience of reviewing and designing a number of these precast concrete arch structures and on discussions with and contributions from the specialist suppliers.
4.1 Design
Due to the complex soil–structure interaction, it is essential that this type of structure is designed using appropriate numerical modelling techniques. Different numerical modelling methods are adopted by the three respective suppliers and there are no fundamental objections to the use of these methods. Since the most fundamental design assumption for this type of structure is the maintenance of uniformity of load, it is essential that the design assessment (a) covers the loading sequence that produces non-symmetrical loading during erection and (b) continues through to long-term conditions.
4.1.1 Temporary conditions
Temporary loadings due to casting, handling and transporting shall be considered in the design of the precast segment. This is in line with the requirement of BS 5400 which states that: The configuration of the structure and the interaction between the structural members should be such as to ensure a robust and stable design. The structure should be designed to support loads caused by normal function, but there should be a reasonable probability that it will not collapse or suffer disproportionate damage under the effects of misuse or accident.
4.1.2 Erection and working conditions
In this section of the guidance note, it is assumed that the designer has sufficient experience and knowledge of the derivation of input parameters for the soil model to be used for the design analysis. The modelling of soil–structure interaction behaviour of buried arch structures using any numerical modelling tool shall incorporate the following considerations: Proposed construction sequence. Proposed lateral extent and geometry of the filling operation. When the horizontal extent of the backfilling cannot be maintained symmetrically, the
numerical model should allow for a temporary backfill profile of the earthworks such that the boundary conditions do not affect the behaviour of the soil–structure system. The use of a symmetric model representing horizontal layers of fill is not always valid.
29
4 Recommendations
Any potential source of eccentric loading conditions due to difference in ground level
of filling operation must be identified and addressed in the design model. Provision of compaction effort during filling operation. Short- and long-term behaviour of the foundation soils, where appropriate. If fine-grained soil is present, effects of consolidation on the foundations of the
structure. All future dead and live loads on the structure and the combination to generate the
highest possible eccentric loading. Appropriate interface/fixity provisions for soil–structure and structure–structure
connections at the foundations and the crown. Appropriate boundary conditions of the finite-element or the beam-spring model. Sufficient sensitivity analyses to address the issues relating to site variations such as
compaction effort, soil input parameters and interface/fixity types.
4.1.3 Eurocodes
In the UK it has been decided that EC7 Design Approach 1 (DA1) will be used for geotechnical design. This requires the consideration of DA1 taking the worst case of Combinations 1 and 2 (DA1/1 and DA1/2). Consequently, in order to comply with the requirements of EC7, the arch structure shall be designed to DA1 taking the worst case for Combinations 1 and 2. Sensitivity analyses on critical parameters shall be undertaken to derive the range of forces to allow for determination of design values. The selection of design situations shall be ‘sufficiently severe and varied so as to encompass all conditions that can reasonably be foreseen to occur during the execution and use of the structure’ (Clause (3)P BS EN 1990).
4.1.4 Tolerance for joint and joint design
It is common that the installation of the precast segments is unlikely to produce a continuous contact due to casting and construction tolerances. The supplier shall provide details of acceptable joint tolerance values for its system and the joint design shall allow for stress concentrations resulting from these casting and construction tolerance values.
30
Recommendations 4
4.1.5 Design check
The appropriate design checking category needs to be selected based on scheme-specific requirements. There are no specific needs to undertake Category 3 checks (BD 2/05) because of the structural form of the precast arch.
4.1.6 Verification criteria
The designer shall consider if it is appropriate to carry out site verification to confirm the structural design intent. This depends on the nature of the structure and its intended use. Where appropriate, the design shall also include assessments to derive clearly defined verification criteria in order to confirm the performance of the structure during construction and future working conditions of the structure. These shall be in the form of measurable parameters, e.g. crown and base settlements and spread of bases.
4.2 Specification 4.2.1 Casting
Casting tolerances proposed by the three suppliers are similar across the three respective systems (see Section 3.2.1). Segment suppliers shall provide adequate evidence from previous projects of the track record of their casting facilities in the production of the required segments to the quality and standards specified.
4.2.1.1 Geometry control during casting
All arch segments shall be measured for compliance to the casting and design specification prior to delivery to site. They shall be inspected for any damage before and after being loaded onto the transporter for delivery to site.
4.2.2 Backfilling
Backfill material shall be Class 6N/6P or similar, or other materials to be agreed with the client. It is recommended that backfilling operations should involve the minimum number of compaction zones in order to prevent confusion in site control during construction. However, if there are specific needs to adopt a more complicated compaction procedure, the site operatives shall be thoroughly briefed in order to avoid any misunderstanding during construction. Testing of the selected fill material shall be specified in accordance with SHW Series 600 and additional tests to verify any design parameters; for example, stiffness for the Matiere system shall be undertaken in accordance with the testing procedure agreed with the client. The sequence of filling shall be specified with a minimum difference in fill level to maintain uniform loading on the structure.
31
4 Recommendations
4.2.3 Minimum cover above crown
4.2.4 Loading
A minimum cover of 0.5 m above the crown is acceptable, with an accompanying design assessment of the effects of surface loading on the structure. Such design assessment shall incorporate a combination of loading which would produce the worst eccentric loading on the structure.
Live loads shall be applied in accordance with BD 31/01. The nominal carriageway loading shall be HA or HB loading as described in BD 37, whichever is the more onerous. Dispersion of a wheel load through the fill may be assumed to occur both longitudinally and transversely from the contact area at ground level to the level of the top of the structure at a slope of 2 vertically to 1 horizontally. Details of the treatment of overlapped dispersion zones of the wheel load can be found in BD 31/01. The combination resulting in the worst eccentric load shall be used for the design.
4.2.5 Foundation soils
The foundation shall be designed in accordance with BS EN 1997-1. The specialist designer shall state the performance requirements of the foundation soils. The contractor shall confirm such requirements can be met on site.
4.2.6 Waterproofing and drainage measures
Waterproofing of the concrete decks of HA structures usually involves the use of an approved bridge deck waterproofing system which may be either a spray-applied system or a sheet system. This is a specific requirement of HA irrespective of the type of structure. However, for these precast arch structures, other systems may be considered appropriate if manufacturers’ information and independent test data are available to confirm their resilience, watertightness and long-term durability. Details of waterproofing to be provided for the precast arch structure shall be agreed with the client to suit the specific operational requirements and the constraints of the site. Where appropriate, methods of waterproofing proposed by ABM, RECo and BEBO are acceptable with the following considerations: Special measures for fittings and fixings, e.g. overhead lighting, which penetrate the
structure. An understanding of the structural behaviour under operational loading to identify vulnerable locations. If a waterproofing system is included then consideration should be given to an appropriate interface friction between structure and soil in the design.
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Recommendations 4
Drainage requirements for the arch structure are entirely dependent on the location, its use and the design groundwater assumption in a project. Therefore drainage shall be provided in accordance with SHW Series 500 to suit the site requirements.
4.3 Construction
4.3.1 Transportation and storage
The supplier shall outline clearly the expected potential handling-induced damages of the precast segments. All handling damages during transportation and storage shall be recorded in detail. The supplier shall visit the site to inspect the storage area and agree with the contractor the necessary preparation and confirm by subsequent visit(s) that such measures have been implemented before the segments are delivered on site. Both casting plant and site storage areas shall be carefully prepared to provide sufficient storage space and adequate support to prevent damage to the segments prior to delivery and installation. If a well-prepared concrete surface is not available, engineered and wellcompacted surfaces may be used for storage purposes.
4.3.2 Damage inspection
4.3.3 Construction inspection and control
All segments shall be inspected prior to installation. Any unexpected damage observed on the segment prior to installation shall be checked for structural integrity before it is allowed to be installed.
Construction inspection and control is essential to ensure future performance of this type of structure. For the following reasons it is recommended that the structure be monitored during erection as part of the construction tolerance control: It is a flexible structure vulnerable to unsymmetrical/non-uniform loading. Non-uniform loading tends to occur or be more critical during the construction stage. There is limited experience in the use and performance of such structures in the UK. Under Eurocode 7’s Design Requirements, this type of structure may be classified as a
Geotechnical Category 31 structure due to its unusual form.
1. Definition in accordance with Eurocode 7 Geotechnical Design – Part I: General rules. This should also be linked with its scheme-specific requirements – see also Section 4.1.5 on Design check
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4 Recommendations
In accordance with EC7, for unusual structures, records shall be maintained of the following: significant ground and groundwater features sequence of works quality of materials deviations from design as-built drawings results of measurements and of their interpretation observations of the environmental conditions unforeseen events.
The tolerance values specified shall be linked and checked with the permissible deformation limits and trigger criteria derived from the design. If the structure is installed out of tolerance, design checks shall be undertaken to confirm that the out-of-tolerance structure does not pose future performance problems. Revisiting the design shall be undertaken under the Technical Approval procedures BD/02. At the end of construction, the designer should review the construction monitoring data to confirm that the precast arch structure has performed in accordance with the design intent. Where appropriate, further monitoring may be required to confirm the performance of the structure during operation.
4.4 Maintenance provisions
The following areas shall be covered during routine maintenance of the structure: Visual inspection for watertightness of the structure based on design and operation
requirements. Where monitoring during operation is required, measurement of crown and base movements to ascertain overall performance of the structure compared with design prediction. When there is any concern about the performance of the structure, detailed surveys of the internal profile of the structure shall be undertaken. Inspection of any fixings or fittings within the structure.
4.5 Monitoring
Following construction, the designer shall decide if longer-term monitoring of the arch structure is necessary (see Section 4.3.3). If this is needed, adequate provision shall be incorporated in the long-term monitoring scheme to confirm the design behaviour of the arch structure. This includes the following important stages during construction: Initial installation stage under structural dead weight. Intermediate construction stages during backfilling operation. Final installation stage when the structure is fully backfilled.
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Recommendations 4
For structures installed in fine-grained soils, progress of settlement until long-term
conditions under working conditions. Monitoring shall cover the vertical movement of the crown and the horizontal and vertical movements of the two bases. Detailed surveys of the internal profile of the structure at selected cross-sections along the structure are also recommended. The monitoring shall be referenced to a fixed datum to allow possible long-term monitoring and for comparison between different stages of the work. Monitoring during operation is not generally required unless the designer recommends such work to be undertaken due to unexpected measurements during installation or unexplained structural behaviour being observed that warrants further investigation.
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5 Risk management
5. Risk management This section of the report covers risks specific to the use of precast arch structures. It is not intended to cover all aspects of risks on a construction site, which will be covered by any competent contractor.
5.1 Interactions between parties
Interaction between the specialist contractor supplying the arch structure, the contractor on site and the client’s representative is essential to ensure successful installation of the arch structure. The following matters will need to be addressed for a successful installation to be achieved: Derivation of the design parameters, especially the foundation soils. This needs clearer
guidance from the designer on the assumptions made and any site verification requirements. Storage facility on site. To minimise any handling damage a clear division of responsibility between the specialist contractor and the main contractor is needed with respect to the handling of segments delivered to site. Construction geometry and tolerance control. This can only be properly controlled with the specialist contractor maintaining full-time site presence. Control of backfill and verification of material placed. This needs careful management, with the contractor providing plant and labour to assist the specialist contractor in its installation work. Management of the interaction between parties early in the project clarifies the responsibilities of all parties and should reduce potential future misunderstanding and conflicts.
5.2 Sensitivity of design
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Sensitivity of the structure to the design parameters shall be clearly quantified by the designer prior to the construction phase of the work. This allows proper management of the installation process so that critical parameters or operations can be closely monitored on site.
Risk management 5
5.3 Construction geometric control and tolerances
This is a vital part of the construction process. Controlling the geometry and construction tolerances within the preset limits ensures validity of the original design dimensions. Such control allows the effect of any out-of-tolerance dimensions to be investigated in order to ascertain how it affects the structure, if at all. It is important to be able to call on the input of the designer during the construction phase to provide any necessary further design analysis when the structure is out of tolerance.
5.4 Verification of design during construction
Adequate monitoring provision is needed in order to confirm the behaviour and performance of the structure under temporary construction loads. Measurements made during installation allow site verification and, if needed, back-analysis can be undertaken to reassess the performance of the structure to confirm any unforeseen behaviour/ measurement is within the intended design limits. Again, it is important to be able to call on the input of the designer during the construction phase to provide any necessary further design analysis when the structure performs differently to the design prediction. Monitoring can also form part of the longer-term maintenance strategy for the structure.
5.5 Load–deflection serviceability criteria
Precast arch structures are inherently very flexible. An understanding of their load– deflection characteristics is therefore important in order to determine whether the structure lies within its design serviceability criteria. This affects operation headroom, water¬tightness and aesthetics of the structure. Light fittings or fixings in the structure are also likely to be affected. Recording of handling damages provides useful data to assess performance of the structure for serviceability criteria. This allows identification of critical damage and, where appropriate, corrective measures implemented to prevent future durability problems.
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6 Checklist
6. Checklist It is assumed that Technical Approval procedures are required for any construction site. The following is a list of checks recommended for the precast arch structure at different stages of the construction process.
6.1 Procurement stage
Evidence of past experience of the construction of such structures. Evidence of past experience of the casting facility/plant supplying the segments. Ensure supplier allows the cost of providing adequate site support for the whole
duration of the project. Ensure supplier allows for adequate support of the designer during and post
construction to evaluate adequacy of the as-built structure. Identify design responsibility of the structure. Identify design coordinator to lead the design process. Identify responsibilities of all parties for construction stage.
6.2 Design
Detailed design methodology. Source of input parameters and design assumptions made. Outline all temporary design cases. Design has covered installation and working conditions. Design has allowed for stress concentration from construction tolerance provision,
especially at the joint. Provision of detailed construction sequence. Identify potential non-symmetrical geometry and load conditions. Adequate sensitivity analyses, especially on backfill and stiffness parameters. Adequate considerations on the approach of site verification for design assumptions
used. Detailed trigger criteria derived for the purpose of monitoring and verification during construction. Any specific requirements relating to the use of the structure.
6.3 Segment casting
All relevant certificates and evidence to support the quality of materials used to cast
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the segment. Dimension checks of the moulds. Provisions for lifting points. Sufficient storage area in the plant is available. Type of marking used to identify individual segments and orientation of storage and transportation. List of potential handling damages. Any damage repair methodology.
checklist 6
6.4 Delivery
List of potential handling damages. Any damage repair methodology. Geometry checks prior to delivery. Damage inspection before and after delivery. Sufficient and adequate storage area on site.
6.5 Site storage
Agreement between supplier and contractor on storage facilities. Adequate storage facilities. Damage inspection upon delivery to site.
6.6 Construction
6.6.1 Section 1: prior to construction
The checklist can be divided into two sections: the first section deals with checks prior to the construction activities and the second section involves checks during installation/ construction of the arch.
Preconstruction workshop to give the designer/supplier the opportunity to explain to
6.6.2 Section 2: during construction
responsible individuals from all parties the critical aspects of the construction and performance of such structures. Agreement of construction sequence to be adopted between the designer and the contractor. Identify individuals from all parties responsible for construction stage. Outline monitoring strategy. Confirmation of adequacy of foundation formation prior to installation of the foundation system. Complete all geometry checks of prepared foundation system. Concise installation procedure. Identify the specialist advisor on site during installation.
Recording of as-built details, e.g. using pro forma, for all stages of the construction phase. Review handling damages prior to backfilling. Review as-built details of the contact at the joint. If installation is out of tolerance, the designer to confirm with supporting design
documents that the effect on the structure is not problematic. Undertake monitoring during construction. If monitored performance does not follow the design prediction, the designer to make
further design assessments to explain the difference and to quantify the effects on the structure. Adequate provision for the designer to evaluate any out-of-tolerance construction. If monitoring is necessary, adequate provision of designer input to such works. Technical Approval procedure shall be revisited if the installation is out of tolerance.
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Bibliography
Bibliography HUTCHINSON, D. Application and design of segmental precast arches. Geotechnical
Engineering for Transportation Projects, Proceedings of Geo-Trans 2004, ASCE Special Publication, 2004. JENKINS, D. A. Analysis of buried arch structures, performance versus prediction. Conference Proceedings of Concrete Institute of Australia Biannual Conference, Adelaide, 1997, pp. 243–252. JENKINS, D. A. Non-linear analysis of buried arch structures. Proceedings of Australasian Structural Engineering Conference (ASEC), Auckland, 1998. TRANSPORT RESEARCH LABORATORY. A review of arched systems for buried structures. TRL, 1999, Project Report PR/CE/111/99. WOOD J. H. and JENKINS D. A. Seismic analysis of buried arch structures. Proceedings
of the 12th World Conference on Earthquake Engineering, Auckland, New Zealand, 2000. Internal documents provided by RECo REINFORCED EARTH COMPANY. Technical approval of highway and associated structures by Reinforced Earth Company. RECo, 2002. TECHSPAN. Techspan construction manual and quality control manual. TechSpan, 2002. TECHSPAN. Technical specifications for TechSpanTM precast arch system. TechSpan, 2005.
Internal documents provided by ABM ABM. ABM design and build technical note (design philosophy). ABM. Matiere precast concrete arch structure – AIP model document. Matiere structures construction guide. 1990. A new method for the construction of buried structures – the “Matiere method”. Matiere patented structures – foundation of structures. 1988. Matiere patented structures – lateral backfills. 1988. Specification for the manufacturing and installation of Matiere Precast concrete structures. 2002
Internal documents provided by BEBO BEBO System – Instructions. 2006. Greater Bargoed Community Regeneration Scheme – Railway Bridge SWM2 AIP. 2006. BRITISH STANDARD INSTITUTION. BS5400, Steel, composite and concrete bridges. BSI, London. HMSO. Manual of Contract Documents for Highway Works. Vol 1, Specification for
Highway Works. HMSO, London (Also available from the Highways Agency website www.highways.co.uk BRITISH STANDARD INSTITUTION. BS EN 1997-1 Eurocode 7. Geotechnical design. BSI,
London, 2004. HIGHWAYS AUTHORITY. Interim Advice Note No. 74/6. Guidance regarding the use
of BS8500 for the Design and Construction of Structures using Concrete.
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CONCRETE BRIDGE DEVELOPMENT GROUP
A cement and concrete industry publication
The Concrete Bridge Development Group aims to promote excellence in the design, construction and management of concrete bridges. With a membership that includes all sectors involved in the concrete bridge industry –bridge owners and managers, contractors, designers and suppliers– the Group acts as a forum for debate and the exchange of new ideas. A major programme of bridge assessment, strengthening and widening is already underway to accommodate European standards and the increasing pressures on the UK road network. The Group provides an excellent vehicle for the industry to co-ordinate an effective approach and to enhance the use of concrete. Through an active programme of events and seminars, task groups, newsletters, study visits and publications, the Concrete Bridge Development Group aims to:
Address the challenge of the national bridge programme Provide a focus for all those involved in concrete bridge design, construction and management Promote an integrated approach and encourage development of innovative ideas and concepts Promote best practice in design and construction through education, training and information dissemination Make representations on national and international codes and standards Identify future research and development needs Maximise opportunities to develop the wider and better use of concrete. Membership of the Concrete Bridge Development Group is open to those who have an interest in promoting and enhancing the concrete bridge industry. Five main types of membership are available:
Group membership for industry organisations and associations Corporate membership for contractors, consultants, suppliers and specialist service companies Associate membership for academic organisations Bridge owners for all organisations that commission, own, maintain and manage concrete bridges Individual consultants
By being representative of the whole industry, the Concrete Bridge Development Group acts as a catalyst for the best in concrete bridge design, construction, maintenance and management. PUBLICATIONS FROM THE CONCRETE BRIDGE DEVELOPMENT GROUP An Introduction to Concrete Bridges A publication dedicated to undergraduates and young engineers (2006) Integral bridges Technical Guide 1 A report of a study visit in August 1997 by a CBDG delegation to North America, sponsored by DTI (1997) Guide to testing and monitoring of durability of concrete structures Technical Guide 2 A practical guide for bridge owners and designers (2002) The use of fibre composites in concrete bridges Technical Guide 3 A state-of-the-art review of the use of fibre composites (2000) The aesthetics of concrete bridges Technical Guide 4 A technical guide dealing with the appearance and aesthetics of concrete bridges (2001) Fast construction of concrete bridges Technical Guide 5 The report of a Concrete Bridge Development Group Working Party (2005) High strength concrete in bridge construction Technical Guide 6 A state-of-the-art report (2005) CCIP-002 Self-compacting concrete in bridge construction Technical Guide 7 Written by Peter JM Bartos (2005) CCIP-003 Guide to the Use of Lightweight Aggregate Concrete in bridges Technical Guide 8 A state-of-the-art report, written by Philip Bamforth (2006) CCIP-015 Guidance on the Assessment of Concrete Bridges Technical Guide 9 A Task Group report (2007) CCIP-024 Enhancing the Capacity of Concrete Bridges Technical Guide 10 A Task Group report (2008) CCIP-036 Modular Precast Concrete Bridges Technical Guide 11 A state-of-the-art report (2008) CCIP-028 Precast Concrete Arch Structures Technical Guide 12 A state-of-the-art report (2009) CCIP-035 You can buy the above publications from the Concrete Bookshop at www.concrete.org.uk and please visit www.cbdg.org.uk for further publications, including free download.
For further details please contact: The Concrete Bridge Development Group Riverside House 4 Meadows Business Park Station Approach Blackwater Camberley Surrey GU17 9AB UK Tel: +44 (0)1276 33777, Fax: +44 (0)1276 38899 e-mail:
[email protected] website www.cbdg.org.uk.
Precast Concrete Arch Structures: A state-of-the-art report
This report on the use of precast concrete arch structures provides guidance on good practice based on the experience of the industry suppliers. It is not intended to be a detailed design guide but to provide guidance for experienced structural engineers and advisers on the use of such structures. The document is also intended to enable the Highways Agency to continue benefiting from appropriate use of such structures, of which there are some 66 throughout the UK and Ireland. These structures have spans in the range 3-20m and a length of 2.5-361m. This versatility demonstrates the adaptability of arch span structures, a structural form used effectively in many locations around the world.
CCIP-035 Published December 2009 ISBN 978-1-904482-58-1 © Concrete Bridge Development Group Riverside House, 4 Meadows Business Park, Station Approach, Blackwater, Camberley, Surrey, GU17 9AB Tel: +44 (0)1276 33777 Fax: +44 (0)1276 38899 www.cbdg.org.uk
