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

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Presentation on theme: "1 ARCHING ACTION IN CONCRETE BRIDGE DECKS Research at Queens University of Belfast Dr. Su Taylor Dr. Barry Rankin Prof. David Cleland Prof. AE Long."— Presentation transcript:

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2 1 ARCHING ACTION IN CONCRETE BRIDGE DECKS Research at Queens University of Belfast Dr. Su Taylor Dr. Barry Rankin Prof. David Cleland Prof. AE Long

3 2 Introduction BackgroundBackground Previous researchPrevious research Changes to bridge designChanges to bridge design Recent laboratory and field testsRecent laboratory and field tests Comparison with existing standardsComparison with existing standards Future researchFuture research ConclusionsConclusions

4 3 Background to research Arching action or Compressive Membrane Action (CMA) applied load arching thrust K r = external lateral restraint stiffness

5 4 laterally restrained slabs have inherent strength due to in-plane forces set up as a result of external lateral restraintlaterally 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 conditionsexternal restraint occurs due to the slab boundary conditions e.g. beams diaphragms continuity of slab

6 5 Midspan deflection Applied load Arching capacity Bending strength first cracking Load vs. deflection for laterally restrained concrete slab

7 6 Previous research external lateral restraint, stiffness = K applied load arching thrust K, K, Le E, A Load, P Arching action and three-hinged arch analogy (Rankin, 1982)

8 7 Clinghans bridge test model Clinghans bridge test model (Kirkpatrick et al, 1984)

9 8 Model Clinghans bridge deck slab

10 9 Model Clinghans bridge deck slab failures loads (Kirkpatrick et al, 1984)

11 10 Clinghans bridge load test

12 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 AgencyUse of CMA in bridge decks is direct result of research at Queens University

13 12 Calgary bridge Canadian approach

14 13 Calgary bridge –reinforcement detail no internal reinforcement

15 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 (FRPs) Goal: maintenance free deck slabs

16 15 Beam and slab superstructures Total unit cost over service life standard deck (normal durability) CMA deck (normal durability ) CMA deck (enhanced durability) Unit cost Years in service

17 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

18 17 Slab strips test load arrangement Restraint, K 1425mm b=475mmh=150mm d=75 to 104mm KEY : Fixed End & Longitudinal Restraint = F/E+L/R Simple Support & Longitudinal Restraint = S/S+L/R Simple Support = S/S

19 18 Typical test set-up

20 19 K r =197kN/mm K r =410kN/mm BS5400 (F/E) BS5400 (S/S) F/E + L/R S/S S/S + L/R F/E + L/R Summary of test results Failure load (kN) Concrete compressive strength (N/mm 2 )

21 20 HSC - F/E + L/R model post-failure topside severe crushing in compression zone

22 21 Failure load (kN) Concrete compressive strength (N/mm 2 ) Comparison Phase 1 results with theory proposed method F/E + L/R (S1-S5) S/S + L/R (S8) BS5400 (F/E)

23 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)

24 23 Applied line load Applied load, PkN SECTION Support beam 50mm PLAN Typical one-third scale bridge deck model b b = 100, 150, 200mm

25 24 Typical reinforcement details

26 25 Typical test

27 26 Third scale bridge model test results - effect of reinforcement conventional bars T&B conventional bars C unbonded bars C fibres only (1%) Failure load (kN) % reinforcement Two wheel loads 45 units HB (ULS) trend line

28 27 Third scale bridge model test results – varied restraint to slab Failure load (kN) Edge beam width (mm) BS5400 shear capacity BS5400 flexural capacity conventional bars T&B in slab QUB capacity

29 28 Corick Bridge

30 29 Deck slab reinforcement

31 30 Test panel arrangement A1 B1 A2 C1 C2B2 D1 D2 F2 F1 E2 E1 Centre reinforce- ment T & B reinforce- ment 0.5%C 0.25%C 0.5%C reinforcement 0.6%T&B reinforcement = testing order

32 31 Typical test arrangement 2000mm 1500mm T1 T2 T3 T4 T5 hydraulic jack 300mm steel plate

33 32 Typical test set-up

34 33 Typical test set-up: deck underside centreline and span of test panel T1 T2 T4 T3 midspan of test panel

35 34 applied load (kN) midspan deflection (mm) max. wheel load (45units HB) =span/4250 2m test panels - comparison of midspan deflections

36 35 applied load (kN) crack width (mm) wheel load (45units HB) 2m test panels - comparison of crack widths

37 36 CMA in FRP Reinforced Bridges Series of tests on full-scale slab strips FRP and steel reinforcement compared variables: boundary conditions concrete strength

38 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

39 38 Test results for full scale laterally restrained slab strips predicted strength from arching theory Failure load (kN) Concrete compressive strength (N/mm 2 ) BS predictions

40 39Conclusions 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

41 40 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 Concluding remarks


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