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.

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