Successfully reported this slideshow.
We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. You can change your ad preferences anytime.
Upcoming SlideShare
×

# Residual capacity from aggregate interlock

2,652 views

Published on

Published in: Education, Business, Technology
• Full Name
Comment goes here.

Are you sure you want to Yes No
Your message goes here
• Be the first to comment

### Residual capacity from aggregate interlock

1. 1. 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
2. 2. 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
3. 3. 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
4. 4. 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
5. 5. 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
6. 6. 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
7. 7. 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
8. 8. 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
9. 9. 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
10. 10. Contact:Eva LantsoghtE.O.L.Lantsoght@tudelft.nl+31(0)152787449 Residual capacity from aggregate interlock of cracked concrete slab bridge 10