Seismic Fragility Analysis of Plane Frame Structures

Keywords: Structural Response Analysis, Fragility Analysis, Reinforced Concrete Structures, Dynamic Structural Analysis, and Plane Frame Structures.

Abstract: This report presents a practical and simplified fragility analysis method for plane reinforced concrete frame structures subject to in-plane earthquake ground accelerations. The frame modeling is based on the approach used in the computer program TABS77. A condensation technique is used in TABS77 to transform the frame structure into a stick model with lumped mass at each floor level. Dynamic characteristics of the structure such as natural frequencies and mode shapes are also obtained using TABS77. The earthquake ground acceleration is represented by a segment of stationary Gaussian random process with mean zero and a Kanai-Tajimi power spectrum. The power spectrum together with the dynamic characteristics of the structure are utilized in the random vibration analysis to derive the covariance matrices of the structural response. A simplified limit analysis procedure is utilized to determine the failure mechanism and the corresponding story shear capacity of the frame structure. Thus, the limit state used in this study is the failure mechanism established by the simplified limit analysis. For this failure mechanism, the limit state probability of each story, i.e., the story limit state probability, can be evaluated. Then, the limit state probability of the structure is measured in terms of the largest story limit state probability. The fragility curve for the frame structure is generated by evaluating the limit state probability at different levels of peak ground acceleration. A four-story test structure is used for numerical illustration. A five-story building assumed to be located in New York City is also evaluated.