Seismic fragility assessment of ductile reinforced concrete building frames

What is it about?

Increasing awareness of the society and complying with design requirements of building codes for seismic safety of structures and inhabitants during severe earthquakes are the primary purpose of seismic analysis. This study is conducted to present the variability in seismic fragility functions for frames of different heights for the most vulnerable condition of structure using nonlinear time history analysis (NLTHA).Four, eight, and twenty story reinforced concrete (RC) moment-resisting 2D frames are considered for this study. Ground motions (GM) are selected as per conditional mean spectrum (CMS) and these are conditioned on a target spectral acceleration (Sa) at concern time period. RC frames are designed and detailed as per Indian standards. Concentrated plasticity approach is adopted for non-linear analytical modeling of the RC frames. Deterministic capacity limit states in terms of maximum inter-story drift ratio (MIDR) are considered as per ASCE guidelines for different damage states. Fragility functions have been derived following a lognormal distribution from incremental dynamic analysis (IDA) curves. Finally, maximum likelihood estimation of the response is obtained for fitting curves with observed fragility.The fragility functions of the three structures reflect that under critical or extreme conditions of GM the taller buildings have higher fragility than the shorter buildings for each level of limit states even though both are designed to meet their code-level design forces. The study is conducted on extreme scenario of GM conditioned on fundamental time period of each building whereas comparison can be developed selecting various methodologies of GM set. Probabilistic capacity model can be developed for future study to check the fragility variation with deterministic and probabilistic capacity. The investigation endeavours to present a comprehensive fragility assessment framework by analytical method. The outcome will be useful in the development of a disaster management strategy for new or old buildings and response of seismic force with variation of the building’s height. The findings will also be useful for updating the earthquake-resistant building codes for the new building construction in a similar context.

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