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Recommendations for the Shear Assessment of Reinforced Concrete Solid Slab Br...

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For an initial design or assessment of a reinforced concrete solid slab bridge, spreadsheet-based or hand calculations are typically used. The shear stress is compared to the shear capacity as prescribed by the code. The distributed loads result in a uniform shear stress at the support. Concentrated loads are less straightforward to take into account. It is known that transverse load redistribution occurs in slabs. To explore the topic of transverse load redistribution, experiments on elements subjected to a concentrated load close to the support were carried out. These elements had an increasing width, starting at 0.5 m and increasing with steps of 0.5 m up to 2.5 m, so that the effect of transverse load redistribution could be studied. The threshold effective width resulting from the experiments was then compared to load spreading methods, in order to give recommendations for the practical use with concentrated loads. It was found that the load spreading method as used in French practice is to be preferred. As compared to load spreading methods that were used previously, the French load spreading method results in smaller shear stresses at the support. This result allows for more economic designs and provides a better assessment tool.

Assistant Professor at Universidad San Francisco de Quito

- 1. 18-07-2014 Challenge the future Delft University of Technology Practical application of transverse load redistribution in reinforced concrete solid slab bridges Eva Lantsoght, Ane de Boer, Cor van der Veen
- 2. 2Practical application of transverse load redistribution in reinforced concrete solid slab bridges Overview • Introduction • Principle of Levels of Approximation • Experiments • Load spreading method • Consequences • Summary
- 3. 3Practical application of transverse load redistribution in reinforced concrete solid slab bridges Introduction Problem Statement Bridges from 60s and 70s The Hague in 1959 Increased live loads heavy and long truck (600 kN > perm. max = 50ton) End of service life + larger loads
- 4. 4Practical application of transverse load redistribution in reinforced concrete solid slab bridges Introduction Highway network in the Netherlands • NL: 60% of bridges built before 1976 • Assessment: shear critical in 600 slab bridges • LoA I method: Quick Scan Highways in the Netherlands
- 5. 5Practical application of transverse load redistribution in reinforced concrete solid slab bridges Principle of Levels of Approximation Model Code 2010 • Approach from fib Model Code 2010 • Solution strategy = different levels of approximation • Eg: Shear capacity in Model Code 2010
- 6. 6Practical application of transverse load redistribution in reinforced concrete solid slab bridges Experiments 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
- 7. 7Practical application of transverse load redistribution in reinforced concrete solid slab bridges Load spreading Effective width in shear 45° load spreading - Dutch practice 45° load spreading – French practice Or: fixed value (eg. 1m = 3.3ft)
- 8. 8Practical application of transverse load redistribution in reinforced concrete solid slab bridges Load spreading Results of experiments BS = 0.5m = 1.6 ft wide BX = 2.0m = 6.6ft wide
- 9. 9Practical application of transverse load redistribution in reinforced concrete solid slab bridges Load spreading Results of experiments 5000 1000 1500 2000 2500 b (mm)
- 10. 10Practical application of transverse load redistribution in reinforced concrete solid slab bridges Load spreading Statistical analysis • Calculated from series vs. 45° load spreading • Comparison between database (literature) + experiments and methods • French load spreading method underestimates less • Lower COV for French load spreading method • Database: 63% vs 42% • Delft experiments: 26% vs 22%
- 11. 11Practical application of transverse load redistribution in reinforced concrete solid slab bridges Load spreading Finite element results (1) Models of 1.5m = 4.9ft wide a = center-to-center distance between load and support Effective width from shear stress distribution over support
- 12. 12Practical application of transverse load redistribution in reinforced concrete solid slab bridges Load spreading Finite element results (2) Models of 2.5m = 8.2ft wide a = center-to-center distance between load and support Effective width from shear stress distribution over support
- 13. 13Practical application of transverse load redistribution in reinforced concrete solid slab bridges Load spreading Finite element results (3) Models of 3.5m = 11.5ft wide a = center-to-center distance between load and support Effective width from shear stress distribution over support
- 14. 14Practical application of transverse load redistribution in reinforced concrete solid slab bridges Load spreading Finite element results (4) • French load spreading method gives safe estimate of beff • NLFEA: beff depends slightly on slab width • NLFEA: influence of a/d less than in French method • French method sufficient for LoA 1
- 15. 15Practical application of transverse load redistribution in reinforced concrete solid slab bridges Load spreading Application to slab bridges (1) • Loading at edge • Asymmetric effective width
- 16. 16Practical application of transverse load redistribution in reinforced concrete solid slab bridges Load spreading Application to slab bridges (2) Effective width per axle instead of per wheel print
- 17. 17Practical application of transverse load redistribution in reinforced concrete solid slab bridges Load spreading Consequences • Larger effective width • Smaller shear stress • More economic design • Sharper assessment
- 18. 18Practical application of transverse load redistribution in reinforced concrete solid slab bridges Summary & Conclusions 1. Level I of Assessment: Quick Scan method 2. French load spreading method 1. Experimental results 2. Statistical analysis 3. Finite element results
- 19. 19Practical application of transverse load redistribution in reinforced concrete solid slab bridges Contact: Eva Lantsoght E.O.L.Lantsoght@tudelft.nl elantsoght@usfq.edu.ec

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