Increased load capacity of arch bridge using slab reinforced concrete

1. Increased load capacity of arch bridge using slab reinforced concrete T.G. Hughes & M. Miri Cardiff School of Engineering Arch 04, Barcelona, Nov. 17-19, 2004

2. Outline • Introduction • Strengthening Techniques • Model details and description • Soil / Masonry interaction • Service load results • Ultimate load results • Conclusions

3. Introduction • Considerable interest in the UK in repair techniques • Closure of the road during construction is an issue • Much debate about “Strengthening” v “Repair” • Objective of this study – to investigate a less intrusive form of reinforcement

4. Strengthening Techniques • Grouting • Saddling • Lining • Reinforced masonry

5. Grouting • Effectively stiffens soil and random rubble masonry • Can be achieved with minimum disruption from surface or soffit • Unquantifiable improvement • May create difficulties with future flexibility

6. Saddling • Forms new arch with existing barrel as shutter • Disruptive to traffic during construction • Composite action difficult to model • A “new” bridge • Some question marks on long term flexibility

7. Lining • Less disruption during construction • Normally “adds” to existing barrel • Loss of headroom • Loss of visual effect • Some concern about durability

8. Reinforced Masonry • Undertaken by drilling or slot cutting in intrados • Can be achieved with minimum disruption • Slot cutting can cause loss of visual effect • May create difficulties with future flexibility • May be issues about long term durability of bond between reinforcement and masonry

9. Surface Slab Reinforcement

10. Surface Slab Reinforcement • Can be achieved with minimum disruption • Maintains integrity of arch behaviour • Issues about utility service access • Relatively cheap solution

11. Surface Slab Reinforcement • Works by increasing load distribution without increasing load • Also provides additional support to soil in preventing sway movements • Increases resistance of soil

12. Effects 1

13. Effects 2

14. Effects 3

15. Centrifuge Models • Undertaken some 50+ scale models of arch bridges at 6, 12g, 20g and 55g • Stresses are as full scale, similar materials –therefore full scale strains • Full range of instrumentation pressure sensors, LVDTsm Load cells and moving loads

16. Model description • 1/12 scale, 6-m single span • Shallow & Deep geometry • Three ring arch • Bricks • Micro concrete • Reinforcement

17. Test Methodology • Build “New” Arch • Undertake service load – typically 14 passes • Load at 1/4 or 1/3 point to peak and unload • Remove and strengthen • Repeat service loading • Load at 1/4 or 1/3 point until collapse

18. Model Details

19. Model Package

20. Model under construction

21. Model under construction

22. Model under construction

23. Concrete slab being cast

24. Typical model under test

25. Service load • Steel roller (equal 12 tonnes) • Whole Width • Soil / Masonry interaction • Arch deflection • Load direction effect

26. Result Nomenclature • Actual benchmark (“new”) result • Average over a series of “new” arches • Strengthened result

27. Soil / Masonry interaction

28. Service load results Shallow arch at ¾ span

29. Service load resultsDeep arch at 3/4 Span

30. Service load resultsArch deflection (Load at 50% of Span)

31. Ultimate load results Load deflection curve for deep arch geometry

32. Ultimate load resultsLoad deflection curve for Sallow arch geometry

33. Conclusions • Better distribution of pressures within the soil at service loads • Decrease arch deflection after repair at service loads • Significant improvement in ultimate load capacity

34. Conclusions • Construction with limited disruption • Reinforced concrete equally as effective as when acting compositely with the barrel • Should maintain flexibility of exiting arch to respond to future movements