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Reliability Based Comparison of Ductility and Energy Based Design

Abstract

In this paper, a reliability based study has been incorporated to compare the categories of Performance Based Seismic Design (PBSD) of a reinforced concrete frame which are the ductility based design and the energy based design respectively. For this purpose, a two dimensional reinforced concrete frame consisting of one bay and one storey is modelled in Opensees 2.4.0 in order to evaluate the capacity of the structure. Based on the analysis results, an equivalent bi-linear model is developed and the two different limit states are defined based on the ductility demand and overall damage index(ODI) of the structure whereby material property of concrete, steel and loads are considered as the random variables. A dynamic analysis has been carried out in Opensees 2.4.0 on the bilinear model by varying the peak ground acceleration (PGA) from 0.05g to 0.4g of the simulated results of the El-Centro earthquake to quantify its nonlinearity in damage index scale and ductility factor scale. The Damage Index (DI) has been computed from the modified Park and Ang Damage Index while the Ductility factor (DF) has been obtained from the top node displacement of the structure. It has been observed that at low PGAs, DF has higher values, as the structure does not yield . With increment in the PGAs, it is seen that, DI values are greater than DF after a certain PGA level. Also fragility curves has been developed where probability of failure has been plotted against PGA, for both ductility and energy based design for the respective durations of 20-25 and 40-50 seconds and it has been observed that at higher values of PGA, pF values for DI will be greater than that of ductility which establishes the fact that a Damage index or energy based design is better than ductility based design for higher PGA levels.

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