Evaluation of Seismic Performance Factors for Concrete Filled Steel Tube Diagrid Structural System

Abstract

Seismic performance factors are used in current building codes and standards to estimate strength and deformation demands on seismic force resisting systems that are designed using linear methods of analysis, but are responding in the nonlinear range. Many recently evolved seismic force resisting systems have never been subjected to any signi?cant level of earthquake ground shaking. As a result, the seismic response characteristics of many systems, and their ability to meet seismic design performance objectives, are both untested and unknown. Therefore, it is necessary to determine the seismic performance factors of new seismic force resisting systems proposed for inclusion in building codes that will result in equivalent safety against collapse during an earthquake when properly implemented in the seismic design process. In this study, the response modification factor, overstrength factor and period based ductility for concrete filled steel tube (CFST) diagrid structural system are evaluated. To quantify these factors, the rational procedure introduced in Federal Emergency Management Agency (FEMA) P695, which is based on low probability of structural collapse and encompasses nonlinear static and dynamic analyses, is used. To this end, performance group consisting of 4, 8, 16 and 24 storey diagrid structures with 50° angle of external braces is considered. Nonlinear static analyses are performed to obtain overstrength factor and period?based ductility. Incremental dynamic analyses are then performed to assess collapse margin ratio of the archetypes. For modelling and numerical analysis, Open System for Earthquake Engineering Simulation (OpenSees), an open source software is used.