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This paper describes a numerical study of the punching shear resistance of unbonded post-tensioned slabs without shear reinforcement. This research aimed to develop a methodology for modeling unbonded tendons and numerically evaluate the prestressing effects on the punching shear capacity. To validate the modeling approach, a series of well documented experimental tests were simulated using the finite element software DIANA. The nonlinear analyses were performed using three-dimensional solid elements, incorporating the cracking behavior of concrete by the smeared crack approach. In addition, interface elements were included, providing bond-slip properties to simulate the friction between tendons and concrete. A good agreement was found between the numerical results and experimental data. Load capacity, cracks patterns, and the prestressing effects were accurately simulated. After the validation, a parametric study was conducted to analyze the influence of distribution, force and profile of prestressing tendons. Finally, the numerical results were compared with current design code provisions and the approach provided by the Critical Shear Crack Theory.

Numerous studies have shown that incorporating fibers in concrete can improve its mechanical properties, including tensile strength and toughness. Due to these outstanding properties, the use of fiber‐reinforced concrete (FRC) composites has been investigated for applications in structural members subjected to shear, in which brittle failure mode may occur. An example of this type of application is the use of high/ultrahigh‐performance fiber‐reinforced concrete (HPFRC/UHPFRC) in flat slab‐column connections as an alternative to shear reinforcement. The experimental results revealed that the use of advanced concrete materials led to an increase in the punching shear and deformation capacities. Despite these advantages, the use of HPFRC/UHPFRC in practical design is somehow limited by the lack of guidelines in codes for this type of new material. Furthermore, the study of constitutive models for nonlinear finite element analysis is also necessary. In this regard, this article addresses the simulation of two‐way slabs with HPFRC, subjected to concentrated monotonic vertical loading, tested in a previous experimental study, where the HPFRC was used only in a limited slab region around the column, and the rest of the slab was cast with normal strength concrete. The numerical models were developed in the commercial finite element software DIANA. The concrete nonlinear behavior was modeled by a total strain‐based constitutive model, in which the HPFRC softening is represented by a tensile stress‐crack width (σ − w) relationship. The validity of the numerical model is checked by the comparison with the experimental results and a punching shear mechanical model, leading to the formulation of a closed‐form equation. Finally, a parametric study was conducted to extrapolate the results obtained in the experimental campaign and to optimize the use of HPFRC to obtain a more economical and sustainable solution.

The present work simulates and analyzes numerically two one-way walls (OW) with a central unforeseen cut-out-opening, which were previously tested experimentally. The models are based in the Finite Element Method and consider nonlinear behavior of the concrete material, such as hardening/softening and fracture. The first wall model was analyzed without any type of strengthening whereas the second one was strengthened using externally bonded CFRP along the opening edges. The strengthening modeling process was discussed through three different approaches suitable for unidirectional CFRP wrap. Load results were presented with load-displacement and load-strain curves that evidenced the flexural behavior of these structures. The crack pattern and failure mode observed showed good agreement with reported literature. The CFRP strengthening presented a small influence in the load capacity for big opening size.

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<p>The Response Surface Method (RSM) has become an essential tool to solve structural reliability problems due to its accuracy, efficacy, and facility for coupling with Nonlinear Finite Element Analysis (NLFEA). In this paper, some strategies to improve the RSM efficacy without compromising its accuracy are tested. Initially, each strategy is implemented to assess the safety level of a highly nonlinear explicit limit state function. The strategy with the best results is then identified and used to carry out a reliability analysis of a prestressed concrete bridge, considering the nonlinear material behavior through NLFEA simulation. The calculated value of &#120573; is compared with the target value established in Eurocode for ULS. The results showed how RSM can be a practical methodology and how the improvements presented can reduce the computational cost of a traditional RSM giving a good alternative to simulation methods such as Monte Carlo.</p>

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