Nonlinear Seismic Assessment of Irregular Coupled Wall Systems Using High Performance Fiber-Reinforced Cement Composites

Abstract

Reinforced concrete (RC) coupled wall systems that consist of multiple shear walls linked by coupling beams are known to be very effective for resisting lateral loads in high-rise buildings. The response of irregular tall coupled wall systems is sophisticated to understand when subjected to seismic ground motions. Thus, nonlinear history analysis is necessary for accurate seismic performance assessment. With regard to improving the capacity of coupled wall systems, high-performance fiber reinforced cement composites (HPFRCCs) are recently being considered. These materials are characterized by a strain-hardening behavior in tension that can improve ductility and toughness of structures subjected to reversed cyclic loading. In this study, nonlinear finite element (FE) analyses for coupled wall specimens and irregular tall buildings with such systems are conducted using PERFORM-3D software in order to predict the nonlinear behavior of this system including HPFRCCs more accurately. In the FE models, the coupling beams are modeled using Moment Hinge Elements and the structural walls are modeled using Fiber Elements. In case of the HPFRCCs beam, Moment Hinge Elements have the increased strength of 20% and 2 times of ductility compared with the normal concrete beams. The strain-hardening behavior of HPFRCCs material model for Fiber Elements is represented such as a confined concrete material model. From the comparisons between modeling and test results, the proposed modeling methods well represent the overall behavior of the reviewed coupled wall specimens such as the strength, stiffness, and energy dissipation. Also, the nonlinear FE models well demonstrate potential improvements in the seismic performance of the considered specimens resulted from the use of HPFRCCs. Subsequently, the nonlinear analysis was performed to observe the behavior of a 56-story tall building with coupled wall systems depending on the used materials. The system responses are discussed through the comparisons of the results including interstory drift, base shear, overturning moment, and failure process. In spite of the use of HPFRCCs in all coupling beams and structural walls in 1/4 height from the base, an unacceptable system performance such as the shifted plastic hinges is simulated in the tall building model, and the reason can be assumed due to a large differences of wall capacities resulted from the use of HPFRCCs. Therefore, when designing a coupled wall system using HPFRCCs, it is recommended that a proper ultimate shear stress at any horizontal section shall be considered to prevent these results.