This study investigates numerically utilizing nonlinear finite element (ANSYS software) and analytically the shear response of the Reinforced Concrete (RC) beams. Different beams are considered in the current study, such as RC, steel fibre reinforced concrete (SFRC) without web reinforcement, and RC externally reinforced in the shear zone with carbon fibre reinforced polymer (CFRP) sheets. Nonlinear finite element model (FEM) is designed to simulate the performance of the designed beams. The results of FEM are compared to experimental measurements and standard design codes (ACI 440.2R-17, FIB 14, CNR-DT200, and ACI 318-19). According to the experimental approach and nonlinear finite element, the enhancement in the load carrying capacity of SFRC beam due to CFRP strengthening decreases with a volume fraction of steel fibres of 2%. However, the effect of CFRP strengthening on the shear behaviour of RC beams was observed in increased load carrying and ultimate deflection capacities as a result of the CFRP strengthening. The results show that CFRP has a significant contribution to shear strength. At each load increment, the created model accurately reproduced the initial and progressive crack patterns. A comparison of nonlinear finite element and analytical models was conducted using the codes ACI 440.2R-17, FIB 14, CNR-DT200, and ACI 318-19. Numerically, the FEM results showed a high agreement with ACI 440.2R-17 standard code, with correlation approach to 99%. The comparison experimental load capacity of beams to FEM and ACI 440.2R-17 shows that the FEM can be significantly used to estimate the shear strength of beams in the X-Y directions with simulating different scenarios of CFRP and SFRC characteristics. The discrepancy between the nonlinear FEA and the theoretical predictions from the ACI 440.2R-17 code is less than 1%, from the FIB14 code is less than 2%, from the CNR-DT200 code is less than 15%, and from the ACI 318-19 code is less than 30%. The ultimate load capacity evaluated based on ACI 440.2R-17 code provision shows a good agreement with the experimental data as compared to the others’ code provision. The results of the finite element analysis and analytical models were in good agreement with the experimental results. The most significant advantage of finite element analysis over experimental approaches was that it can aid in the investigation of different output results that cannot be measured experimentally, such as shear stress in the XY direction throughout the beam strengthened in shear with different CFRP properties and steel fibre reinforced concrete (SFRC).

The strut-and-tie model (STM) has been widely applied for the design of reinforced concrete (RC), members particularly discontinuity regions. In this paper, on the basis of available experimental results of crack patterns, failure modes, and trajectories of internal stresses from elastic finite element analysis (FEA), STMs have been suggested for many shallow and deep beams with openings, which had been tested experimentally. In addition, for comparison purposes, 3-D nonlinear FEA using ANSYS-12 package has been performed for selected beams. Some of the important factors affecting the behavior of RC beams, namely concrete compressive and tensile strength, span-to-depth ratio, shear span-to-depth ratio, physical and mechanical properties of horizontal, vertical web reinforcement and main steel, loading position, opening dimensions, and location, are investigated via a parametric study with the aid of 3-D nonlinear FEA. With such analysis, results of crack pattern, deflection, failure mode, and strain and stress distributions, which cannot be determined using the STM, are obtained. A comparison of the FEA with test results and proposed STMs has been carried out. The present study reveals the reliability of the STM method in obtaining a reasonable lower bound estimate of the load carrying capacity of RC ordinary/deep beams with openings. In addition, the 3-D nonlinear FEA of simple and continuous NSC and HSC ordinary/deep beams with/without openings yields accurate predictions of both the ultimate load and the complete response.

The ductility and capacity of reinforced concrete beam-column connections depend mainly on the concrete’s strength and the provided reinforcements. This study investigates numerically the role of low-strength concrete in beam-column joints utilizing ABAQUS software. In this simulation, a newly developed stress-inelastic strain relationship for both confined and unconfined low-strength concrete is used. This study recommended a specific value of the concrete dilation angle for both substandard and standard joints. Also, stirrups’ yield strength value was found to play an insignificant role in improving the shear resistance of such joints with low-strength. In addition, the joint shear strength prediction using empirical models that implicitly consider the stirrups contribution in improving joint resistance was found to be better than the prediction of other models that explicitly consider the stirrups’ presence. The numerical results also showed that the use of a diagonal steel haunch as a joint retrofitting technique significantly increases the joint shear capacity and changes its brittle shear failure into a ductile beam flexural failure.

A robust structure will survive and remain serviceable during its design life where unforeseeable events or attacks are likely to occur. Examples of such unforeseeable events are: change of use; sudden and large settlements of supports; extreme impact; war; fire; extreme wind; catastrophic events, etc. Two case studies are presented in this paper, a multi-story flat plate building subjected to column loss and a cable-stayed bridge subjected to cable(s) loss, in order demonstrate such a role of robustness. The finite element method considering both material and geometric nonlinearity, with the aid of the software ABAQUS, is employed in this study to perform both static and dynamic analysis of the relevant structures. The two examples reveal how robustness can prevent progressive collapse of structures due to unforeseeable events. The flat plate building with continuous bottom reinforcement could survive column loss. The system robustness enabled the cable-stayed bridge to survive cable(s) loss.

Column loss in a flat plate building, due to punching shear, explosion, impact load or any acci-dental event, can lead to what is termed progressive collapse. Progressive collapse is inherently a dynamic process, which makes it difficult to experimentally explore structures with real scale. Therefore, this paper aims to numerically investigate the behavior of flat plate systems due to column loss utilizing nonlinear finite element analysis with the aid of the computer software (ABAQUS). In this investigation, the nonlinear dynamic re-sponse of both an old flat plate building, designed according to the ACI 318-71, and a similar modern building, designed according the ACI 318-14, subjected to an instant removal of a column is examined. The obtained results clearly reveal that the old flat plate building without continuous slab bottom reinforcement at columns is highly vulnerable to progressive collapse and the efficiency of the continuous bottom reinforcement within the column strip, as recommended by the ACI 318-14, in preventing the disproportion or progressive collapse of a reinforced concrete flat plate building. Such reinforcement is able to produce alternate load path through the tensile membrane action, thus providing ductility and robustness in the system.