Experimental and numerical investigation of the behavior of RC shear walls with smooth bars

Experimental and numerical investigation is conducted to determine the behavior of RC shear walls found in old and existing buildings that do not comply with the design rules in modern earthquake standards (nonconforming shear walls, NCSW). Seven (7) scaled reinforced concrete shear wall specimens are built with smooth bars and low concrete quality to consider the properties of buildings in Turkey built before 1997. The dimensions of the shear wall specimens were selected by taking into account the laboratory capacity and the pre-study results with an aspect ratio bigger than two. Six (6) specimens are representative of nonconforming shear walls (NCSW), and one wall used as a reference specimen which was designed in accordance with recent building codes using deformed bars. The behavior of the shear walls is determined experimentally by displacement-lateral load relationship under quasi-static lateral cyclic loading. This study investigated the behavior of the test specimens in terms of lateral force capacity, rigidity, ductility, dissipated energy, and displacement components contribution to the total lateral response of the walls. The results showed a substantial loss of stiffness, ductility and energy dissipation capabilities for the tested nonconforming shear walls. Moreover, it was proven that these specimens are governed by the bar slip phenomena which demonstrated more than 80% contribution to the total lateral displacement capacity. In contrast, the reference shear wall exhibited a notable flexural behavior and plastic hinge formation. Additionally, the shear walls built with smooth reinforcement bars lost about 48% of their theoretical potential flexural capacity due to the observed bar slip failure. In the second part of this study, numerical models were developed for all the tested RC shear walls, and validated against the experimental results using the widely accepted and used finite element program, OpenSees. Using an empirical approach, a new quadrilinear analytical bar slip model is developed to predicate the response of nonconforming shear walls. And by introducing the slip effect into the numerical model, a realistic simulation of NCSWs (GDYGS) was obtained. According to the comparison study on the experimental and numerical results, it was determined that the newly developed slip model for NCSWs is successful in reproducing the test results and effectively reduced the differences between the numerical models and the experimental outcomes.