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Type of publication:Peer reviewed journal article a b s t r a c tReinforced concrete (RC) two-way slabs without shear reinforcement are commonly used in many structural systems. This paper investigated the structural behaviour of RC slabs subjected to concentrated loads leading to punching shear failure using shell and continuum nonlinear finite element analysis (NLFEA). Shear force distributions are studied for four types of slabs with different geometry of support, geometry of slab and layout of reinforcement. All factors investigated have been proven to influence the shear force distributions along the control perimeter around the support. Significant shear force redistributions due to cracking and reinforcement yielding have been observed using NLFEA. Reduced control perimeters to be used for simplified approaches accounting for calculated shear force distributions are calculated using both NLFE approaches.

The fib Model Code for Concrete Structures 2010 introduced the concept of levels of approximation (LoA) as a strategy for simplifying the procedures involved in preliminary design stages or the design of non-critical structural elements while still providing the tools for engineers to use state-of-the-art techniques in the assessment of existing structures or in the advanced stages of design for critical structural elements. In this paper, this concept is applied to the determination of the punching shear resistance of reinforced concrete slabs. A procedure is validated for the highest LoA involving non-linear finite element analysis (NLFEA) with multi-layered shell elements and the critical shear crack theory (CSCT). The safety format proposed for use in the safety verification assisted by NLFEA is based on the definition of a global resistance safety factor. A semi-probabilistic approach is followed, based on the assumption of a lognormal distribution for the resistance and on an estimate of its coefficient of variation. This approach is validated by means of a comparison with the results from a probabilistic analysis. The LoA approach is initially applied to the study of statically determinate slabs supported on one column to verify the effectiveness of the procedure presented here compared with other validated methods available in the literature. The paper concludes with a case study illustrating the application of the proposed procedure to a bridge deck slab and highlighting the benefits of using a higher LoA.

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Type of publication:Peer reviewed conference paper AbstractThe shear resistance of RC slabs without shear reinforcement subjected to concentrated loads near linear support is usually calibrated on the base of tests on one -way slabs with rectangular cross section. However, the actual behavior of slabs subjected to concentrated loads is described properly by a two-way slab response. The aim of this paper consists in the evaluation of the shear resistance of bridge deck slabs using analytical formulations and Nonlinear Finite Element Analyses (NLFEA). The obtained numerical results are consequently compared with experimental observations from two test campaigns. The case studies were analysed by NLFE analyses carried out using the constitutive Crack Model PARC_CL (Physical Approach for Reinforced Concrete under Cycling Loading) implemented in the user subroutine UMAT.for in Abaqus Code. In order to predict properly global and local failure modes through a NLFE model, a multi -layered shell modelling has been used. As shell element modelling is not able to detect out -of -plane shear failures, the ultimate shear resistance of these slabs is evaluated by means of a post -processing method according to the Critical Shear Crack Theory (CSCT).