Estimation of system-level seismic responses and seismic damage analysis of steel structures

Abstract

Consideration of structural system behavior in aseismic design is largely still implicit and semi-empirical. Important parameters of inelastic behaviors, such as the maximum and permanent displacements, the ductility factor, the seismic damage etc., are indirectly considered in aseismic design by reducing the magnitude of the required strength estimated from the elastic response level using the response modification factor. In other words, the system-level seismic response parameters are essential factor for the earthquake resistant design of structures. Particularly, the system-level ductility factor is related to the response modification factor (or force reduction factor), commonly used in the aseismic design procedures. To improve the seismic design code, the system-level response parameters of inelastic behaviors and cyclic behaviors shall be studied. The ductility demands for single-degree of freedom structures or individual structural members can be determined easily. However, there is no established method of determining the ductility demands for structural systems. The object of this study is to develop a method for the estimation of the seismic responses at the structural system level. Verification of the proposed method is carried out by comparing the representative responses obtained by the proposed and the equivalent single-degree of freedom (ESDOF) system methods with the responses of the multi-degree of freedom (MDOF) system. The seismic energy components obtained by the proposed and ESDOF system methods are also compared with those related to the MDOF responses. Numerical example studies are carried out on four multistory steel frames with 8 and 20 stories designed by two different concepts: i.e., the strong-column weak-beam (SCWB) and weak-column strong-beam (WCSB) concepts. The system-level ductility demands are estimated by the proposed and the ESDOF system methods. The trends of the system and element-levels ductility demands are compared. ...