With the aim of contributing for the development of design guidelines capable of predicting with high accuracy the punching resistance of steel fibre reinforced concrete (SFRC) flat slabs, a proposal is presented in the present paper and its predictive performance is assessed by using a database that collects the experimental results from 154 punching tests. The theoretical fundaments of this proposal are based on the critical shear crack theory proposed by Muttoni and his co-authors. The proposal is capable of predicting the load versus rotation of the slab, and attends to the punching failure criterion of the slab. The proposal takes into account the recommendations of the most recent CEB-FIP Model Code for modelling the post-cracking behaviour of SFRC. By simulating the tests composing the collected database, the good predictive performance of the developed proposal is demonstrated.

a b s t r a c tThe present paper deals with the experimental assessment of the effectiveness of steel fibre reinforcement in terms of punching resistance of centrically loaded flat slabs, and to the development of an analytical model capable of predicting the punching behaviour of this type of structures. For this purpose, eight slabs of 2550 Â 2550 Â 150 mm 3 dimensions were tested up to failure, by investigating the influence of the content of steel fibres (0, 60, 75 and 90 kg/m 3 ) and concrete strength class (50 and 70 MPa). Two reference slabs without fibre reinforcement, one for each concrete strength class, and one slab for each fibre content and each strength class compose the experimental program. All slabs were flexurally reinforced with a grid of ribbed steel bars in a percentage to assure punching failure mode for the reference slabs. Hooked ends steel fibres provided the unique shear reinforcement. The results have revealed that steel fibres are very effective in converting brittle punching failure into ductile flexural failure, by increasing both the ultimate load and deflection, as long as adequate fibre reinforcement is assured. An analytical model was developed based on the most recent concepts proposed by the fib Mode Code 2010 for predicting the punching resistance of flat slabs and for the characterization of the behaviour of fibre reinforced concrete. The most refined version of this model was capable of predicting the punching resistance of the tested slabs with excellent accuracy and coefficient of variation of about 5%.

In this paper analytical formulations are developed for the prediction of the punching resistance of flat slabs of steel fibre reinforced concrete (SFRC) flexurally reinforced with steel bars. By performing statistical analysis with a database that collects experimental results on the characterization of the post-cracking behaviour of SFRC, equations are determined for the evaluation of the residual flexural tensile strength parameters (fRi) from fundamental data that characterize steel fibres. The fRi strength parameters proposed by CEB-FIP 2010 were used for the definition of the stress-crack width law (σ-w) that simulates the fibre reinforcement mechanisms in cement based materials. In the second part of the paper is described an 2 analytical formulation based on the concepts proposed by Muttoni and Ruiz, where the σ-w law is conveniently integrated for the simulation of the contribution of steel fibres for the punching resistance of SFRC slabs. By using a database composed of 154 punching tests with SFRC slabs, the good predictive performance of the developed proposal is demonstrated. The good performance of this model is also evidenced by comparing its predictions to those from other models.