This study focuses on an approach to improve the behavior of low-rise shear walls with a rectangular cross-section and a height-to-length ratio of unity. The significance of this study lies within the need for a better understanding of the complex shear mechanism, not to mention the shear-flexure interaction in low-rise shear walls which results in different failure patterns under seismic loading. Shear forces may cause diagonal tensile or compressive failures. Moreover, cracks at the foot of the wall during elastic deformation could cause the shear slip failure which could limit the ductility of the wall. To this end, validation studies were conducted on a shear wall specimen chosen from the literature (i.e., the specimen tested by the nuclear power engineering corporation of Japan (NUPEC) (1996).
2.1. Finite element modeling
Numerical analyses were initially carried out in a nonlinear finite element software specifically developed for concrete structures, namely ATENA. “3D nonlinear cementitious 2” material, a fracture-plastic model that combines models for fracture and plastic behavior was used. The classic orthotropic smeared crack formulation and crack band model are used in this model. In this model, the tensile softening branch is defined by two parameters, fracture energy, and the maximum crack width. Moreover, the post-peak branch of the compressive behavior is characterized by the ultimate strain. Bi-linear strain hardening stress-strain curve was used for reinforcements. Eight-node isoparametric brick elements and 2-node truss elements were used to define concrete and reinforcements, respectively. The “Newton-Raphson” solution method with an updated stiffness matrix in each iteration was used to solve the nonlinear system of equations. In order to investigate the behavior of low-rise concrete shear walls, a short shear wall with dimensions of 0.2 m (thickness), 3.5 m (height), and 3.5 m (length) with a rectangular cross-section resting on a 9-m length strip foundation proposed by the International Institute of Earthquake Engineering and Seismology was used. To investigate the influential parameters governing the behavior of the wall, the so-called wall was numerically modeled and was subjected to lateral increasing loads; details of the wall were according to ref Iiees (2011).
3.1. Validation studies
Comparison of experimental and numerical results in terms of shear strength and displacement values showed that the values are in very good agreement with one another and therefore the methodology was verified
3.2. Effect of slots Results obtained from the analysis for the specimen (as shown in Fig. 2) shows that the failure pattern of the wall is mainly shear-dominant with a sudden decrease in shear strength value after the peak load. As for the effect of openings, it can be observed in Fig. 3, when compared to the wall without slots, the post-peak ductility of the wall increases noticeably which could act as a warning prior to its failure. Moreover, according to Fig. 4, it can be seen that the tensile cracks have propagated throughout the height of the wall which helps to avoid stress concentration and make efficient use of the tensile capacity of the concrete.
Results showed that walls with slots have an overall improved ductility in comparison to models without slot. Additionally, creating slot in the wall helps in the redistribution of internal forces, prevents stress concentration. Furthermore, the presence of slots changes the failure pattern of the wall from shear-dominant to shear-flexure dominant. Finally, for a wall with a slot ratio of 0.15, displacement corresponding to the peak load increases by 138% compared to its counterpart with no slots.