Comparison of Single-Brace and Knee-Brace Configurations in Regular and Plan-Irregular Reinforced Concrete Buildings Using Nonlinear Static (Pushover) Analysis

Abstract

Iran is located in one of the seismically active regions of the world. Experience from recent earthquakes has demonstrated that the importance of designing structures resistant to earthquake loads is no less than that of designing structures to withstand gravity loads. Therefore, in recent years, increasing attention has been paid to providing appropriate measures for constructing earthquake-resistant buildings. In the design of earthquake-resistant structures, two different parameters should be considered separately. First, under weak or moderate earthquakes, the structure should possess sufficient stiffness to minimize lateral displacement and prevent damage to nonstructural members. Eccentrically Braced Frames (EBFs) are one of the lateral load-resisting systems used for the seismic retrofitting of reinforced concrete buildings. These systems provide high stiffness in the elastic range, together with good ductility and energy dissipation capacity in the plastic range. Depending on the number and configuration of vertical link elements, two types of eccentrically braced systems are considered in this study: EBFs with a single vertical link and Knee-Braced Frames (KBFs). The present study investigates the effect of the configuration of EBFs with a single vertical link and knee-braced systems on the seismic behavior of plan-irregular reinforced concrete buildings. To obtain the required results, three plan-irregular reinforced concrete building frames with 4, 8, and 12 stories were considered. The buildings were first designed using a single-link eccentric bracing system and subsequently using a knee-bracing system with four different configurations. The buildings were designed in accordance with the fourth edition of Iranian Standard No. 2800. In addition, the designed building frames equipped with the two aforementioned systems were evaluated using nonlinear static (pushover) analysis. Finally, based on the comparison and evaluation of the results, it was observed that the buildings retrofitted with the KBF system exhibited greater energy dissipation and a greater reduction in the stress ratio of columns. However, from a constructional perspective, the connection of the KBF system to the beams and columns of the frame at five points may increase the possibility of cracking and weakening of the primary structural members. Furthermore, among the four bracing configurations investigated, the second configuration exhibited better overall performance.