Several studies investigated the precision of non-linear finite element analyses (NLFEA) to predict the shear capacity of beams or the punching capacity of slab-column connections. However, in the literature, there is little discussion regarding the results of NLFEA to predict the ultimate capacity and failure mechanism of slabs susceptible to different failure mechanisms. In this study, a set of tests from literature that developed different shear failure mechanisms was evaluated by NLFEA. A total of thirteen slabs were modeled, where slab's width and shear span varied. A coupled damaged-plasticity model was employed to simulate the concrete behavior. The proposed model was calibrated to simulate specimens that failed as wide beams in one-way shear and specimens that failed by punching shear. Besides, the effect of different modeling choices was investigated: (i) the assumed stress–strain behavior in compression; (ii) tensile stress–strain behavior; (iii) the inclusion or not of damage parameters and (iv) the viscosity parameter. The results indicated that, on average, the proposed modeling strategy represented the failure mechanism and ultimate loads well. Also, the same calibrated model was found capable of representing one-way shear failure and punching shear failure or mixed modes. The sensitivity study demonstrated that the tensile stress–strain behavior and viscosity parameter influences the results of the numerical models more significantly than the assumed stress–strain behavior in compression or including/not including the damage parameters. This paper concludes that modeling strategies during the calibration process shall be checked carefully before performing any parametric analyses to identify the accuracy of the numerical models to represent the different failure mechanisms. Moreover, the validation step of the modeling strategy shall identify possible limits of the numerical model to be considered in the parametric analyses.

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One-way slabs under concentrated loads may fail by one-way shear, two-way shear, flexure, or a combination of these modes. This paper reviews shear and punching shear-failure mechanisms of one-way slabs under concentrated loads tested from the literature and investigates the accuracy of different approaches to predict the ultimate capacity for such slabs using the ACI code expressions. A database with 160 test results was evaluated. Shear and concentrated loads measured at failure were reviewed according to parameters such as the load position, slab width, and reinforcement ratios. The load position and slab width play a marked influence on the failure mechanism and tested loads. The analyses improved the understanding of the main parameters influencing the behavior of one-way slabs under concentrated loads. Finally, the proposed effective shear width expression enables accurate shear capacity predictions using the ACI code expressions.

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One-way slabs under concentrated loads may fail by one-way shear such as wide beams, punching shear, flexure, or by combining two or more of these mechanisms. Nevertheless, most publications have only addressed shear and punching failures without flexural reinforcement yielding. This study investigates the ultimate shear capacity of one-way slabs under concentrated loads with local reinforcement yielding. In total, 12 tests were conducted on six reinforced concrete slabs. Simply supported slabs of 1.60 m × 3.40 m × 0.15 m were tested. Three parameters were varied: the load position, the span length and the reinforcement ratio. All slabs failed initially by punching with limited or extensive reinforcement yielding. Due to the relatively large amount of transverse reinforcement (0.44 %), most slabs underwent a large shear redistribution around the load, resulting in a wide beam shear failure after the local punching failure. The test results were compared to the theoretical predictions of shear, punching and flexure capacity using code expressions and the Extended Strip Model (ESM). The ESM resulted in the closest predictions of the experiments. These experiments confirm that a brittle shear and punching failure mechanism can occur even after extensive reinforcement yielding. Moreover, the results indicate that the ESM can be used to assess one-way slabs under concentrated loads with local reinforcement yielding.

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Reinforced concrete one-way slabs under concentrated loads can develop different shear failure mechanisms: as wide beams in one-way shear, punching shear around the load or a mixed mode between them. Until now, most publications presented recommendations to assess the shear capacity considering only the one-way shear failure mechanism. This study proposed developing recommendations to assess both the one-way shear and punching shear capacity of such slabs. Different codes of practice were addressed, including the current Eurocode and fib Model Code 2010 expressions. The recommendations were validated against 143 test results from the literature. Following these recommendations, one-way shear and punching capacities predictions achieved enhanced and almost the same level of accuracy.@en

One-way slabs under concentrated loads may fail by one-way shear, punching, flexure or a mixed-mode between them. This study examines the benefits of using Linear Elastic Finite Element Analyses (LEFEA) combined with analytical expressions to predict the shear and punching capacities of such slabs. Besides, the determination of the most critical shear failure mechanism is also addressed. A simplified approach is proposed to predict the shear and punching capacity without numerical models. Forty-eight tests of simply supported slabs under concentrated loads were evaluated. The LEFEA was conducted with ABAQUS. The analytical expressions are based on the Critical Shear Crack Theory (CSCT). The coupling of the CSCT-expressions with the LEFEA accurately predicts the governing shear failure mechanism and the shear capacity of most test results. In this study, it was also found that the punching capacity predictions may be improved by considering the influence of the slab width and load size on the governing failure mechanism. A similar level of precision was achieved using only analytical expressions when properly calibrated. Therefore, the CSCT expressions can be used at different stages of design and assessment of existing structures according to the Level of Approximation required.

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The outstanding mechanical properties of ultra-high-performance fiber-reinforced concrete (UHPFRC) can be used to improve the punching behavior of new slab-column connections. This study investigates the punching capacity of flat slab-column connections built with a rational combination of normal strength concrete (NSC) and UHPFRC in critical shear regions through non-linear finite element analyses (NLFEA) and by a punching shear model based on the critical shear crack theory (CSCT). Ten control tests from the literature were used to validate the Finite Element Models (FEM) developed to capture the behavior of slab-column connections made entirely with NSC, UHPFRC, and a combination of both materials. Parametric analyses were performed to investigate the behavior of connections with the rational use of UHPFRC, varying the reinforcement ratio, area, and thickness of the UHPFRC layer. The results indicated that placing a UHPFRC layer near the column in the slab compression zone significantly increases the punching capacity and deformation capacity compared to placing UHPFRC on the tensile side. The punching capacity enhancements varied between 26% and 156%, according to the reinforcement ratios and configurations of the UHPFRC layer investigated. The mean ratio between predicted punching capacities by advanced NLFEA and the analytical method proposed was 1.09, with a coefficient of variation of 10.3%. Therefore, the results indicated that the design of flat slabs with UHPFRC at the critical shear regions is a viable solution. Finally, the CSCT model can be used in design to predict the punching capacity of these connections.@en

The shear strength evaluation of reinforced concrete bridge deck slabs by accurate models can indicate strength reserves and avoid costly operations necessary for the extension of their lifetime. This article introduces an approach that extends the Critical Shear Displacement Theory model (CSDT) for reaching higher levels of approximation of the shear strength for slabs subjected to concentrated loads close to the support. A database with 141 tests of wide reinforced concrete members under concentrated loads close to the support failing in one-way shear was built. The tests represented typical loads in bridge slabs and were assessed through a combination of CSDT with different models of effective shear width. In other analyses, the entire database with 214 test results of slabs failing by different mechanisms was evaluated and a general effective shear width model was proposed (GESW). The best results, which are a function of the effective shear width model used, reached a mean ratio between experimental and predicted shear capacities of 1.06 with a coefficient of variation of 14%, which is similar to that reported by some studies including linear and non-linear finite element analyses. Furthermore, this level of accuracy was insensitive to the shear slenderness and support conditions of the tests. The extended CSDT predicted the shear capacity of bridge deck slabs in preliminary analyses more precise than semi-empirical models provided in the current design codes, and the level of accuracy is comparable to methods using Linear Elastic Finite Element Analyses (LEFEA). Moreover, our proposed combination of the CSDT with a general effective shear width model (GESW) provides reasonable levels of accuracy for slabs under concentrated loads regardless of the failure mode of the tests. Therefore, the proposed approaches can be applied to bridge deck slabs, which are subjected to a variety of loading and support conditions.

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