Transcript of "Residual capacity from aggregate interlock"
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Residual capacity from aggregate interlock Case: cracked concrete slab bridge 11-07-2012Eva Lantsoght, Cor van der Veen, Joost Walraven Delft University of Technology Challenge the future
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Introduction (1)• 50-year-old concrete slab bridge with traffic restrictions• Extensive cracking in southern concrete approach bridge• Result of settlement• Flexural reinforcement yielded at crack• Cores: C33/45• Reinforcement QR 240:fyd =209 MPa; εsu = 19% – 38% Residual capacity from aggregate interlock of cracked concrete slab bridge 2
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flexural through crackIntroduction (2) d = 413mm (side) to 493mm (mid) φbottom 14mm – 200mm φtop 25mm – 100mm Residual capacity from aggregate interlock of cracked concrete slab bridge 3
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through crackAggregate interlock• Aggregates stronger than cement paste• Particles interlock with opposite face + resist shear displacement• Contribution to shear capacity: 33% - 90%• Slab bridge, 1% rebar: aggregate interlock is main shear carrying mechanism• Fundamental model by Walraven• Shear + axial stress: σ & τ, ∆ & w• Unreinforced sections: crack-opening• Reinforced sections: capacity Residual capacity from aggregate interlock of cracked concrete slab bridge 4
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Calculations (1)Shear & Aggregate interlock• Shear capacity (inclined cracking load)• VVBC = 273 kN/m (side) and 325 kN/m (mid)• Aggregate interlock – no tension on cross-section• Based on shear stress capacity τ of reinforced crack• Plain reinforcement => 0.5ρl• Vagg = 1575 kN/m (side) and 1679 kN/m (mid)• Large resistance provided by aggregate interlock action• Rusted bearings => deformation due to ∆T is restrained• Conservative assumption: full concrete cross-section in tension Fclamp As ,bottom As ,top f y f ctk d i b Residual capacity from aggregate interlock of cracked concrete slab bridge 5
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Calculations (2)Maximum crack width (1)• Relation between w and aggregate interlock capacity• Expressions for unreinforced section• Based on graph (Walraven, 1981): Δ = 1.25w Residual capacity from aggregate interlock of cracked concrete slab bridge 6
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Calculations (3)Maximum crack width (2)• Find: crack width Vu_unr < VVBC or Fax < Fclamp wmax ≈ 1 mm Residual capacity from aggregate interlock of cracked concrete slab bridge 7
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Calculations (4)Axial force equilibrium• wmax ~ rebar, tension in concrete cross-section (vary % Ftc)• Requirement: Vagg ≥ 2VVBC• Find associated ∆• Find Nagg(wmax,∆) (clamping effect)• Remaining capacity of top reinforcement to resist tension: Ntension = As,topfy – Nagg• Compare to Ftc => Equilibrium?• Result: maximum 71% of restraint Residual capacity from aggregate interlock of cracked concrete slab bridge 8
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Proposed actions + Conclusions• Replace rusted steel bearings by elastomeric bearings• Open bridge for all traffic• Quantify amount of restraint through measurements at support• Measurement points for cracks every 3m (lane width)• Special cases: use aggregate interlock to check cracked cross- sections in shear• Quantifies residual bearing capacity• Shear and axial compression Residual capacity from aggregate interlock of cracked concrete slab bridge 9
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Contact:Eva LantsoghtE.O.L.Lantsoght@tudelft.nl+31(0)152787449 Residual capacity from aggregate interlock of cracked concrete slab bridge 10
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