11-07-2012 Challenge the future Delft University of Technology Residual capacity from aggregate interlock Case: cracked concrete slab bridge Eva Lantsoght, Cor van der Veen, Joost Walraven
Jul 07, 2015
11-07-2012
Challenge the future
DelftUniversity ofTechnology
Residual capacity from aggregate interlockCase: cracked concrete slab bridge
Eva Lantsoght, Cor van der Veen, Joost Walraven
2Residual capacity from aggregate interlock of cracked concrete slab bridge
Introduction (1)
• 50-year-old concrete slab bridge withtraffic restrictions
• Extensive cracking in southernconcrete approach bridge
• Result of settlement• Flexural reinforcement yielded at
crack
• Cores: C33/45• Reinforcement QR 240: fyd =209 MPa; εsu = 19% – 38%
3Residual capacity from aggregate interlock of cracked concrete slab bridge
Introduction (2)
d = 413mm (side) to 493mm (mid)φbottom 14mm – 200mmφtop 25mm – 100mm
flexural through crack
4Residual capacity from aggregate interlock of cracked concrete slab bridge
Aggregate 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
through crack
5Residual capacity from aggregate interlock of cracked concrete slab bridge
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
, ,clamp s bottom s top y ctk iF A A f f d b
6Residual capacity from aggregate interlock of cracked concrete slab bridge
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
7Residual capacity from aggregate interlock of cracked concrete slab bridge
Calculations (3)Maximum crack width (2)
• Find: crack width Vu_unr < VVBC or Fax < Fclamp
wmax ≈ 1 mm
8Residual capacity from aggregate interlock of cracked concrete slab bridge
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
9Residual capacity from aggregate interlock of cracked concrete slab bridge
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
10Residual capacity from aggregate interlock of cracked concrete slab bridge
Contact:
Eva Lantsoght
+31(0)152787449