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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 main objective of this research is to investigate nonlinearly the flexural behavior of Polypropylene Fiber (PF) Lightweight RC beams. The finite element (FE) method utilizing ANSYS program was used to build the models and study the effects of some parameters on the response of PF lightweight RC beams in flexure. The considered parameters include the effect of main steel and its yield strength, beam width, beam depth and shear span. The obtained results were compared with those calculated based on the ACI 318-19 and the AS 3600-2018 design building codes and the comparison showed a great match between results, especially the ACI 318-19 code.