Shear strength of RC slabs under concentrated loads near clamped linear supports

Abstract

Reinforced concrete slabs without shear reinforcement subjected to concentrated loads near linear supports are usually designed or assessed in shear using design provisions that have been calibrated on the basis of tests on one-way slabs or beams with rectangular cross-section (slabs loaded over their full width). This approach may however be inconsistent, as the actual behavior of slabs under concentrated loads reflects a two-way slab response, with the shear forces not developing in a parallel manner in the failure region and with potential redistribution of the internal forces for increasing levels of load.In this research, a series of 12 tests on 6 full scale slabs (3.00m×3.00m×0.18m) is presented. The slabs were centrally supported on an aluminum profile and were subjected to two concentrated symmetrical loads. The support profile was equipped with vertical strain gauges, allowing to trace the distribution of reactions at the supported line and its redistributions as the value of the concentrated loads increased. Significant redistributions of the reactions were actually measured prior to failure, which are presented and discussed within the paper. The aim of these measurements was to improve the understanding of the mechanical behavior of such members and the role of shear cracking on the distribution of internal forces. A number of parameters was investigated, such as the location of the concentrated loads and the presence of ducts in the slab. This latter case (typical of prestressed concrete balanced cantilever bridges and residential buildings) has not been investigated in the past, despite its potential influence on the shear strength.The performance of these specimens is finally investigated and compared to the prediction of the fib-Model Code 2010 and the Critical Shear Crack Theory. This analysis shows that accurate predictions of the strength can be obtained if the influence of direct load strutting (for loads acting near supports) and redistribution of internal forces is accounted.