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Transverse load redistribution and effective shear width in reinforced concrete slabs

E.O.L. Lantsoght1,2, C. van der Veen1, A. de Boer3, J.C. Walraven1

1 Delft University of Technology, the Netherlands
2 Universidad San Francisco de Quito, Ecuador
3 Ministry of Infrastructure and the Environment, the Netherlands

In slabs subjected to concentrated loads close to the support, shear is verified for two limit states: beam shear over an effective width, and punching shear on a perimeter around the concentrated load. In current practice, the beam shear strength of slabs is calculated as for beams, and thus the beneficial effects of transverse load redistribution in slabs are not considered. An experimental program was conducted at Delft University of Technology to determine the shear capacity of slabs under concentrated loads close to the support. This paper presents the results of the tests conducted on continuous slabs and slab strips. The influence of the loading sequence, size of the loaded area, moment distribution at the support and distance between the load and the support is studied and discussed with regard to the behaviour in slabs and slab strips. It is recommended to use the effective width based on a load spreading method as used in French practice. This recommendation is based on the experimental results, a statistical analysis and non-linear finite element models. The parameter analyses show an increased capacity in slabs as compared to beams as the result of transverse load distribution. The shear capacity of slabs under concentrated loads close to supports can be calculated based on the Eurocode provisions for shear over the recommended effective width.

Key words: Effective width, load redistribution, punching, reinforced concrete, slabs, shear