Bridge Beam Design Manual =
3 4.1
a MP
1st Edition
y ikel re l a s ion Mpa ndit o c 29 . d 1 n bo = ood g e er h s w d m ran mm 0m (t) e st 5 r i 2 f d t w 7 n a η1 c 7 .7 th nd 935 = η p1 3 a greater : r y f bpt o b = f n ths re; 3. 2 give ϒc dep s whe i / r ) o h (t = 1f ngt η p1 .7 f ctm n le o 0 i s s = α ct smi η1 ran = t ) t e th f ctd( e of u w: l a / f bpt belo cv i e s 0 a h σ pm b of t 2ø The mm nds ble a 1α a r r α t u s = o 2 e 6 av l pt mm wir 48. unf e: 7 7 r e 2 e r d o 2.9 an wh = 1 he m 112 r3 t o = f s m a 1 a m α = .19 ed MP = 0 ulat 9 c 0 8 l . a .7 α2 c 95 15 h is 1, 2 ngt ø= e l = sion σ pm0 mis s n tra sign e d The 0.8l pt Precast concrete specialists = l pt1 . 2l pt 1 = l pt2
M. Slevin E. Stack
Acknowledgements Banagher Precast Concrete would like to thank the Concrete Bridge Development Group (CBDG) for asking us to present our Bridge Beam Manual at their annual conference in Oxford. We would also like to thank Abhishek Das in MIDAS for his help with the initial bridge model and his continued support throughout and a special thanks to our expert reviewers and researchers for their comments and help.
Irish Plant
UK Plant
Disclaimer This manual gives Banagher Precast Concretes view on prestressed bridge beam design and in particular our W-beam which we developed in 2005. Please note that the calculations presented in this design manual are for information only. Banagher Precast Concrete Ltd. do not accept any liability for the use of any presented material.
Precast concrete specialists
Contents 1. Introduction 2 2. Design standards required 2 3. Scheme design 3 4. Materials 4 4.1 Concrete 4 4.2 Prestressing Steel 4 4.3 Reinforcing Steel 4 4.4 Cement 4 4.5 Modular Ratio 4 5. Cover 5 6. Structural model and analysis 6 6.1 Modelling Assumptions 6 6.2 Loads 7 6.3 Boundary Conditions 7 6.4 Construction Stages 8 7. Section Properties 9 8. Calculation of Loads 10 9. Combinations of actions 13 10. Differential Shrinkage 14 11. Temperature Effects 15 11.1 Uniform Temperature Component 15 11.2 Temperature Difference Component 16 11.3 Non Linear Component 17 12. Prestress Design 18 13. Prestress Losses 20 13.1 Immediate Losses 20 13.1.1 Relaxation Loss 20 13.1.2 Elastic Shortening Loss 20 13.2 Time Dependent Losses 21 13.2.1 Relaxation Loss 21 13.2.2 Creep 21 13.2.3 Shrinkage 23 13.3 Summary of Long Term Prestressing Losses 24 13.4 Effective Prestressing Force 24 13.5 Transmission Length 24 14. Serviceability Limit State (SLS) 25 14.1 Decompression Check at Transfer of Prestress 25 14.2 Revised Stresses With Debonding 26 14.2.1 At End of Transmission Length 26 14.2.2 At End of Debonded Length 26 14.3 Stress Check at Construction Stage 26 14.4 Decompression and Stress Check at Service (midspan max) 27 14.5 Stress Check at Service (midspan min) 28 14.6 Decompression and Stress Check at Service (end of diaphragm) 29 14.7 Decompression and Stress Check at Service (end of transmission length) 30 14.8 Decompression and Stress Check at Service (end of different debonded lengths) 31 14.9 SLS Stress Summary 33 15. Ultimate Limit State (ULS) 35 15.1 Ultimate Limit State Flexure Check 35 15.2 Minimum Reinforcement Requirement Check 35 15.3 Global Vertical Shear Design (beam ends) 36 15.4 Shear at The Interface Between the Beam and The Slab 37 15.5 Shear Check Between The Web and The Flange of The Composite Section 39 16. Beam camber estimates 40 17 Creep Induced Sagging Moment at Supports 40 Appendix A 42 Appendix B 45 LIST OF SYMBOLS 46
Precast concrete specialists
1
1. Introduction Banagher Precast Concrete is pleased to introduce its bridge beam design manual. Prestressed concrete bridge beams are firm favourites in the short and medium span bridge market, of up to 50 metre spans and have been in successful use for the last 60 years. The Bridges for which the industry and of course Banagher Precast Concrete manufacture beams require considerable expertise in design. The design is usually carried out with a Contractor employed Engineer taking the project from planning to working drawings of the bridge for which the beams would be required. The design of the beams may be carried out by this engineer, by the engineer in cooperation with Banagher Precast Concrete the supplier or completely by Banagher Precast Concrete using the engineer’s analysis output as the starting point. In the last few years, the design regulations have been harmonised throughout Europe as part of the Common Market for Goods and Services with the introduction of a suite of Eurocodes and European Product Standards. Each Member State of the EU has the responsibility for Structural Safety and the Eurocodes therefore come with a National Annex in which National preferences with respect to safety factors etc are given. The designs in this manual have used the UK National Annexes which are very similar to the Irish National Annexes. Where the Irish regulation would be different, it is noted in the text. The coherence of the new regulations allow, with the use of Harmonised Product Standards, a common approach which is used as the basis of the CE Marking of Bridge Beams, in turn enabling them to be part of an open pan European Market.
This manual gives Banagher Precast Concretes view of the new design process for Prestressed Bridge Beams to the Eurocode and it is hoped will promote more use of Bridge Beams and a common and agreed understanding of the many new clauses in the codes. The manual considers the design of the innovative Banagher W beam in a typical two span road bridge. The internal beam is designed in detail and as the loading code is also new, the approach to the use of this code is also demonstrated. Other areas of the whole bridge design are commented upon, particularly where they can have an important influence on beam design. These are mentioned at appropriate places where they would naturally occur. Suggestions for further reading are also given. The format is for the manual to have the commentary and the design information followed by the example calculations. This design manual should be read in conjunction with our “Bridge Beam Manual” which includes our full range of precast prestressed beams and their associated span tables along with all other relevant information required by a bridge engineer in choosing a precast section.
2. Design standards required The following list contains the relevant standards that are required for the design of this bridge. 1. Eurocode - Basis of Structural Design - BS EN 1990 : 2002 2. Eurocode 1 Actions on structures - Part 1 and Part 2 - BS EN 1991-1 and BS EN 1991-2 3. Eurocode 2 Design of concrete structures - BS EN 1992-1-1 : 2004 4. Eurocode 2 Design of concrete structures. Concrete bridges. Design and detailing rules - BS EN 1992-2:2005 5. BS EN 206-1 : 2000 Concrete – Part 1: Specification, performance, production and conformity 6. BS 8500-1 : 2006 - Concrete – Complementary British Standard to BS EN 206-1 – Part 1: Method of specifying and guidance for the specifier 7. PD 6694-1 Recommendations for the design of structures subject to traffic loading to BS EN 1997-1 : 2004 8. BS EN 15050:2007+A1 : 2012 Precast concrete products - Bridge elements
2
Precast concrete specialists
9. BS EN 13369 : 2013 Common rules for precast concrete products 10. EN 10138 - Prestressing Steel Note: The standards referenced in this design example are those relevant at the time of print. Please make yourself aware of ammendments before proceeding with this design example.
3. Scheme design The foundations for the abutment are modelled as strip foundations 1m deep and 4m wide. The sizing of the foundations is taken from experience and for this example will suffice as the W11 beams are all that is being looked at in detail not the supporting structure. The precast columns are fixed into place with dowel bars projecting up from the foundation below. The columns will need to be propped and the sleeves filled with non shrink grout which will then need to be left to strengthen before placing of the precast crosshead.
The design is for a two-span integral bridge, with each span having a length of 30.75m from centre of abutment to centre of pier giving an actual beam length of 30.50m as per fig 3.2. The bridge carries a 6.0m wide carriageway with 1.5m wide footways on either side as per fig 3.1. The superstructure consists of six Banagher Precast Concrete prestressed W11-beams with a 230mm structural in-situ reinforced concrete deck slab 200mm over the top of the beam cast on ribbed fibre reinforced concrete (FRC) semi participating permanent shutter. There are in-situ diaphragms at the abutments and pier. A 500mm gap between the precast beams is used at the pier to allow projecting links from the crosshead. There is a 1500mm wide precast crosshead spanning between two precast columns which makes up the pier. The bridge beams span from abutment to crosshead with 500mm bearing/embedment and without the need for temporary support.
500
1500
10000 9000
1500
500
140
110
80
1500
1450
2000
7 1466.624
1700
200
600
230
350 350
600
250
15
1500
It is recommended that a number of transverse holes are located at various depths in the precast beam at the abutment and pier diaphragms. Whilst the number and position of these diaphragms will be at the discretion of the designer in conjunction with the precast manufacturer, a sufficient number of holes should be provided in order to ensure anchorage of the precast beams and that the pier and / or abutment diaphragms act as a torsional beam.
730
3000
2000
3 NO. W11 BEAMS AT 3000mm CENTRES = 6000
Figure 3.1 - Section through bridge deck showing W-11 beams at 3.0m centres
ABUTMENT
PIER
100
100
500
29500
400
30500 OVERALL BEAM LENGTH
400
100
500
500
1500 CROSSHEAD
100
29500
400
500
500
30500 OVERALL BEAM LENGTH
400
ABUTMENT
62500
1000
900 300 PIER COLUMN 300 500
500
29800 30750
450
450
29800
500
500
30750
Figure 3.2 - Elevation of bridge
Precast concrete specialists
3
Banagher Precast Concrete Ltd, Banagher, Co. Offaly, Ireland T(IRL) +353 (0)57 9151417 T(UK) +44 (0)161 300 0513 F +353 (0)57 9151558 E info@bancrete.com W www.bancrete.com
Bridge Beam Manual
please contact our technical department.
Precast concrete specialists
Produced by studio93.ie
For a copy of the