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Presentation held at my PhD defense

Presentation held at my PhD defense

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  • 1. Challenge the future Delft University of Technology Shear in Reinforced Concrete Slabs under Concentrated Loads close to Supports Eva Lantsoght
  • 2. 2 Overview • Background • Slabs under concentrated loads • Overview of experiments • Beams vs. slabs • Modified Bond Model • Application to practice • Conclusions
  • 3. 3 Background (1) Bridges from 60s and 70s The Hague in 1959 Increased live loads common heavy and long truck (600 kN) End of service life + larger loads
  • 4. 4 Background (2)
  • 5. 5 Background (3) • First checks since mid-2000s • 3715 structures to be studied • 600 slab bridges • But: checks according to design rules • => Residual capacity??? • Hidden reserves of the bearing capacity Highways in the Netherlands
  • 6. 6 Slabs under concentrated loads (1) • Transverse load redistribution • Additional dimension in slabs • Expected higher capacity than beams • First experiments: Regan (1982)
  • 7. 7 Slabs under concentrated loads (2) • Shear stress over effective width • Fixed width, eg. 1 m • Load spreading method
  • 8. 8 Goals • Assess shear capacity of slabs under concentrated loads • Determine effective width in shear
  • 9. 9 Experiments (1) Size: 5m x 2.5m (variable) x 0.3m = scale 1:2 Continuous support, Line supports Concentrated load: vary a/d and position along width
  • 10. 10 Experiments (2) • 2nd series experimental work: • Slabs under combined loading • Line load • Preloading • 50% of strength from slab strips • Concentrated load • loading until failure • Conclusions from 1st series valid when combining loads? • Total: 26 experiments, 8 slabs
  • 11. 11 Experiments (3)
  • 12. 12 Slabs vs. beams (1) • Transverse load redistribution • Geometry governing in slabs • Location of load • result of different load-carrying paths • Mid support vs end support • influence of transverse moment • Wheel size • more 3D action
  • 13. 13 Slabs vs. beams (2) 5000 1000 1500 2000 2500 b (mm)
  • 14. 14 Modified Bond Model (1) • Based on Bond Model (Alexander and Simmonds, 1990) • For slabs with concentrated load in middle
  • 15. 15 Modified Bond Model (2)
  • 16. 16 Modified Bond Model (3) • Adapted for slabs with concentrated load close to support • Geometry is governing as in experiments • Determine factor that reduces capacity of “radial” strip • Maximum load: based on sum capacity of 4 strips
  • 17. 17 Modified Bond Model (4)
  • 18. 18 Modified Bond Model (5)
  • 19. 19 Modified Bond Model (6)
  • 20. 20 Modified Bond Model (7)
  • 21. 21 Modified Bond Model (8)
  • 22. 22 Modified Bond Model (9) Experiments vs Eurocode shear Experiments vs Modified Bond Model
  • 23. 23 Application to practice (1) • Evaluating existing solid slab bridges: • EN 1992-1-1:2005 • 25% reduction of contribution concentrated load close to support • β =av/2d • Combined: βnew =av/2,5d • Effective width: French method and minimum 4d
  • 24. 24 Application to practice (2) Detail of load spreading
  • 25. 25 Application to practice (3) • Checks at indicated sections • 9 existing Dutch solid slab bridges + MBE example
  • 26. 26 Application to practice (4) • Shear stresses: influence of recommendations • QS-EC2: wheel loads at av = 2,5dl • QS-VBC: wheel loads at av = dl • QS-EC2 18% reduction in loads • Shear capacity: • QS-EC2: vRd,c ~ ρ, d • low reinforcement + deep section = small shear capacity • QS-VBC: τ1 ~ fck only • QS-EC2 improved selection ability
  • 27. 27 Economics • Repair cost • Demolition cost • Recycling cost • New construction Environment • Impact of repair • Impact of replacement • CO2 emissions • Materials • Transport Social • Visual impact • Traffic delays • Employment Sustainability
  • 28. 28 Summary & Conclusions • Slabs under concentrated loads behave differently in shear than beams • Beneficial effect of transverse load redistribution • Modified Bond Model improvement as compared to Eurocode • Application to practice: reduction in loads
  • 29. 29 Contact: Eva Lantsoght E.O.L.Lantsoght@tudelft.nl +31(0)152787449