Ductility Evaluation of inverted V-bracing and concentrically bracing systems

Abstract

The current design philosophy for buildings located in zones with high seismic risks is that the buildings must have sufficient strength and stiffness to remain elastic and serviceable under moderate but frequently occurring earthquakes and to have sufficient ductility to prevent collapse under extreme earthquakes. Conventional structural steel framing systems such as moment resisting frames (MRFs), concentrically braced frames (CBFs), and eccentrically braced frames (EBFs) I extensively used in seismically active areas. Each of the previously mentioned structural systems has different advantages and disadvantages.In this study, response modification factor of ordinary inverted V-braced frames and specially inverted V-braced frames are evaluated, result confirm that the proposed height for buildings with ordinary inverted braced frames in the ASCE7,can be increased up to 10.7 meter. also results indicate that by using ordinary inverted V-bracing systems in buildings .their height can be increased up to 6 story or 20 meter. Using special inverted V-braced systems can have saving about 0 to 30 percent on used materials for frames from 1 story to 16 stories. According to the results of this study, response modification factor proposed by Iranian seismic design code (2800 standard fourth edition),(R=5.5), is more logical than the one which is proposed by ASCE7, (R=6). Unfortunately, in special inverted V-braced frames, and when the story of the frames increases up to 12 stories, ductility demand can't be achieved .So as a result for frames which are more than 12 stories tall, lower response modification factor should be used. In addition, frames taller than 12 story height don’t experience specified target displacement and collapse before getting to preferred mechanism. This phenomenon shows the necessity of using different response modification factor for frames taller than 12 stories.

Keywords

• ductility
• ductility reduction factor
• concentrically v-braced frame
• pushover analysis
• target displacement