Mounir Khalil El Debs

In precast concrete structures, optimizing the design of corbels by considering the contributions of secondary reinforcement elements can significantly improve construction economy, especially when corbels are repeated multiple times. This paper proposes a strut‐and‐tie model for reinforced concrete corbels subjected to vertical and/or horizontal loads, focusing on the effective utilization of secondary reinforcement, which is often neglected in conventional load capacity calculations. The proposed model was validated using experimental data from 397 corbels reported in the technical literature. Additionally, a comparative analysis was performed with three reference models to evaluate its performance. Key parameters, such as the horizontal‐to‐vertical load ratio and corbel aspect ratio, were analyzed for their influence on corbel strength. The results demonstrated that the proposed model provides a broader and safer application range compared to the reference models, with approximately 99% of the tested corbels aligning with its predictions. Furthermore, incorporating secondary reinforcement in the proposed model enhanced structural efficiency, yielding a mean strength improvement of approximately 22% based on the tie‐yielding failure criterion. These results highlight the model's potential to achieve both safety and economic viability in the design of precast concrete corbels.

Linear elastic finite element analyses (LEFEAs) have become more frequent in the design and assessment of reinforced concrete slabs under concentrated loads, as they enable low‐cost evaluation of the distribution of shear forces over critical sections. However, few publications have addressed the benefits of combining LEFEA with mechanical‐based models to predict the most critical shear failure mechanism and the corresponding shear and punching capacities. Notably, most previous studies employed a similar approach for a specific boundary condition or evaluated only the one‐way shear capacity of slabs under concentrated loads near line supports. This study investigates the accuracy of the expressions based on the critical shear crack theory (CSCT) combined with LEFEA to assess the shear and punching capacity of one‐way slabs under concentrated loads. Since such slabs may develop different failure mechanisms, this study also evaluates the level of accuracy to predict the governing shear failure mechanism identified in the tests, a topic rarely discussed until now. For this purpose, a dataset of 112 experiments was selected, covering different boundary conditions and loading arrangements. LEFEA was used to evaluate the uneven distribution of shear forces and bending moments on the critical shear regions. Some outputs from LEFEA were used in the analytical calculations with the CSCT‐based expressions to predict the shear and punching capacity of such tests. The use of LEFEA also aided in understanding the change of shear failure mechanisms according to parameters such as the member width to load size ratio b _slab / l _load and the shear slenderness a _v / d _l . The combination of the CSCT expressions with the LEFEA allows for predicting the governing shear failure mechanism and the shear capacity of the slabs for most tests accurately at a low computation cost. When the governing failure mechanism was not correctly identified, a conservative estimate of the shear capacity was provided, which is desirable in such cases.

Non-linear finite element analysis (NLFEA) has been frequently used to assess the ultimate capacity of reinforced concrete (RC) structures under the most complex conditions. Nevertheless, the guidelines using such methods to evaluate RC corbels are limited. In addition, the influence of material modeling options regarding the behavior of such members was not investigated until now. This paper proposes to present a framework for the NLFEAs of RC corbels using the Concrete Damaged Plasticity (CDP) model. the influence of several modeling choices related to this constitutive model also is discussed in detail, including the assumed stress–strain behavior in compression and tension and the parameters related to the yield criterion and flow rule. For this, a first set of test results was used to validate the proposed approach to the NLFEA. Afterwards, the sensibility of the numerical results for several modeling choices was investigated. In the end, the proposed framework for the NLFEA was checked against a database of 36 test results from the literature. The mean ratio between the predicted and experimental test results was 1.015 with a coefficient of variation of only 8.57%. The governing failure mechanism of the tests was predicted correctly in approximately 88% of the simulations. In summary, the proposed approach allows for predicting the ultimate capacity and failure mechanism of RC corbels accurately.

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.

Reinforced concrete pipes are usually designed to attend a three-edged-bearing test (TEBT) using the partial safety factors from building structures. This study presents an alternative approach to designing RC pipes based on simplified reliability analyses. The procedure consists of providing curves of failure probability according to the reinforcement areas used in the pipes. The results indicate that RC pipes with simple reinforcement show a failure probability of around 1% with the most traditional design method, even using the partial safety factors from buildings, due to the higher dispersion of the concrete cover and the use of a single reinforcement layer to satisfy different control sections. Meanwhile, RC pipes with double reinforcement show a significantly lower failure probability as each reinforcement layer is designed to satisfy the bending moments from different control sections and due to the larger pipe thickness. In summary, the large randomness of the reinforcement position increases the failure probability of these members compared to traditional building structures.

This study describes a set of recommendations to improve the precision of shear and punching shear capacity predictions for one-way slabs under concentrated loads, regardless of the governing failure mechanism, using the ABNT NBR 6118:2014 code provisions. For this purpose, a database of 143 test results was developed, including one-way slabs with different support conditions and loading layouts and that failed by different shear failure mechanisms: one-way shear, punching shear or a mixed mode. The key parameters influencing the load capacity and failure mechanism of these slabs were considered for the proposed recommendations: load position and slab width. Adjustments to the effective shear width definition and shear resisting control perimeter were described. Arching action for loads close to the support was also considered in both one-way shear and punching shear predictions. Considering the whole database and without separation by the failure mechanism, the ratio between tested and predicted resistances with the one-way shear expressions shows an average value of 1.22 and a coefficient of variation of 18.3%. The respective ratio between tested and predicted resistances with the punching shear expressions reached an average ratio of 1.23 with a coefficient of variation of 21.3%. Therefore, the proposed recommendations allow for reaching enhanced levels of precision in assessing the shear and punching shear capacity of one-way slabs under concentrated loads, regardless of the governing failure mechanism of the slabs.