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ARCHING ACTION IN CONCRETE BRIDGE DECKS

ARCHING ACTION IN CONCRETE BRIDGE DECKS. Research at Queen’s University of Belfast Dr. Su Taylor Dr. Barry Rankin Prof. David Cleland Prof. AE Long. Introduction. Background Previous research Changes to bridge design Recent laboratory and field tests Comparison with existing standards

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ARCHING ACTION IN CONCRETE BRIDGE DECKS

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  1. ARCHING ACTION IN CONCRETE BRIDGE DECKS Research at Queen’s University of Belfast Dr. Su Taylor Dr. Barry Rankin Prof. David Cleland Prof. AE Long

  2. Introduction • Background • Previous research • Changes to bridge design • Recent laboratory and field tests • Comparison with existing standards • Future research • Conclusions

  3. applied load arching thrust Background to research Kr = external lateral restraint stiffness Arching action or Compressive Membrane Action (CMA)

  4. laterally restrained slabs have inherent strength due to in-plane forces set up as a result of external lateral restraint • external restraint occurs due to the slab boundary conditions e.g. beams diaphragms continuity of slab

  5. Arching capacity Applied load Bending strength first cracking Midspan deflection Load vs. deflection for laterally restrained concrete slab

  6. applied load external lateral restraint, stiffness = K arching thrust Load, P E, A K, K, Le Previous research Arching action and three-hinged arch analogy (Rankin, 1982)

  7. Clinghan’s bridge test model(Kirkpatrick et al, 1984)

  8. Model Clinghan’s bridge deck slab

  9. Model Clinghan’s bridge deck slab failures loads (Kirkpatrick et al, 1984)

  10. Clinghan’s bridge load test

  11. Advantages from CMA in bridge design • NI bridge code amendment in 1986- reinforcement reduced from 1.7% to 0.6%T&B • Improved durability and cost benefits • BD81/02 – Highways Agency ‘Use of CMA in bridge decks’ is direct result of research at Queens University

  12. Canadian approach Calgary bridge

  13. Calgary bridge –reinforcement detailno internal reinforcement

  14. Developments in UK Majority of bridges RC Advance knowledge of CMA: • High strength concrete and fibres • Reinforcement • Single layer at mid-depth • Fibre Reinforced Polymer (FRP’s) • Goal: maintenance free deck slabs

  15. standard deck (normal durability) CMA deck (enhanced durability) Unit cost CMA deck (normal durability ) Years in service Beam and slab superstructures Total unit cost over service life

  16. Recent Laboratory tests • Series of tests on full-scale slab strips typical of a bridge deck slab • Variables were: Concrete compressive strength Reinforcement type and position Boundary conditions

  17. Restraint, K b=475mm h=150mm d=75 to 104mm 1425mm KEY : Fixed End & Longitudinal Restraint = F/E+L/R Simple Support & Longitudinal Restraint = S/S+L/R Simple Support = S/S Slab strips test load arrangement

  18. Typical test set-up

  19. F/E + L/R S/S S/S + L/R F/E + L/R Kr=410kN/mm Kr=197kN/mm Failure load (kN) BS5400 (F/E) BS5400 (S/S) Concrete compressive strength (N/mm2) Summary of test results

  20. severe crushing in compression zone topside HSC - F/E + L/R model post-failure

  21. BS5400 (F/E) F/E + L/R (S1-S5) S/S + L/R (S8) proposed method Failure load (kN) Concrete compressive strength (N/mm2) Comparison Phase 1 results with theory

  22. Bridge model tests • Final series of tests on one-third scale bridge deck models • HSC with variables of: lateral restraint stiffness reinforcement (type & amount)

  23. Applied line load PLAN Applied load, PkN 50mm b = 100, 150, 200mm b Support beam SECTION Typical one-third scale bridge deck model

  24. Typical reinforcement details

  25. Typical test

  26. conventional bars T&B conventional bars C unbonded bars C fibres only (1%) trend line Failure load (kN) Two wheel loads 45 units HB (ULS) % reinforcement Third scale bridge model test results - effect of reinforcement

  27. conventional bars T&B in slab QUB capacity Failure load (kN) BS5400 shear capacity BS5400 flexural capacity Edge beam width (mm) Third scale bridge model test results – varied restraint to slab

  28. Corick Bridge

  29. Deck slab reinforcement

  30. Test panel arrangement 0.5%C 0.25%C 0.5%C reinforcement Centre reinforce-ment A1 C1 D1 B1 A2 B2 C2 D2 = testing order F2 E2 T & B reinforce- ment F1 E1 0.6%T&B reinforcement

  31. hydraulic jack 300mm  steel plate T1 T2 T3 T4 T5 1500mm 2000mm Typical test arrangement

  32. Typical test set-up

  33. midspan of test panel centreline and span of test panel T1 T2 T3 T4 Typical test set-up: deck underside

  34. applied load (kN) max. wheel load (45units HB) =span/4250 midspan deflection (mm) 2m test panels - comparison of midspan deflections

  35. applied load (kN) wheel load (45units HB) crack width (mm) 2m test panels - comparison of crack widths

  36. CMA in FRP Reinforced Bridges • Series of tests on full-scale slab strips • FRP and steel reinforcement compared • variables: boundary conditions concrete strength

  37. Preliminary results on GFRP slabs In simply supported slabs • service behaviour of GFRP poor • ultimate strengths similar In laterally restrained slabs • GFRP & steel slab behaved similarly in service • GFRP slabs higher ultimate capacities

  38. Test results for full scale laterally restrained slab strips predicted strength from arching theory Failure load (kN) BS predictions Concrete compressive strength (N/mm2)

  39. Conclusions • Degree of external restraint and concrete strength influence capacity • deflections up to 45 units HB wheel load were independent of %As • crack widths up to 45 units HB wheel load were substantially narrower than BS limits • strength of panels with centre reinforcement in excess of ultimate wheel load

  40. Concluding remarks • Structural benefits of CMA well understood • CMA incorporated in Ontario & UK codes • Improved strength/serviceability  less problems for assessment • Arching phenomenon has potential for substantial economies

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