Seismic Fragility Functions Grounded on State-Based Philosophy: Application to Low to Midrise Steel Frame Buildings

Abstract

In this study, a new formulation for structural fragility function based on the theory of state-based philosophy (SBP) is introduced. In this innovative approach, gradual changes in stiffness (or flexibility) of the structure is considered as a firm base for describing changes in the state of the structure due to damage from various sources. In this study, the source of damage data is considered ground motions. After formulating state changes by using SBP theory, a new fragility function is proposed. Therefore, this new function is based on observations of various failure stages of the structure and, besides, it is organized specifically for the structural damage data. In order to prove the accuracy of this method, some special moment frames (SMFs) are modeled, and incremental dynamic analysis (IDA) is performed on them. Thus damage data are provided as initial input to the fragility function. After that, the final results of the SBP fragility function are compared with the results of the conventional methods of plotting the fragility curve, and lastly, the fragility curve’s accuracy obtained by using this new function is verified. This new fragility function is called ‘SBP fragility function’ and has some advantages over the ordinary fragility functions, which are discussed in this article.