Summer Research Fellowship Programme of India's Science Academies

Seismic Fragility Assessment for Reinforced Concrete Buildings

Anirban Kundu

Indian Institute of Engineering Science and Technology, Howrah, West Bengal 711103

Dr. Jayadipta Ghosh and Dr. Meera Raghunandan.

Indian Institute of Technology, Bombay, Powai, Mumbai, Maharashtra 400076


In earthquake engineering, performance based design approaches enable more transparent assessment of life safety risk and damage analysis. ‚ÄčTo do so Ibarra, et al, 2005 developed a model on hysteretic strength and stiffness deterioration based on the lumped-plasticity element model. The model is calibrated from 255 RC column tests. For each test, the element model parameters like effective stiffness, chord rotation capacity etc. are calibrated such that the results of the analysis match with experimental results. Through his project, Ibarra developed a reliable and accurate model that has been used in OpenSees (Open System for Earthquake Engineering Simulation) to simulate a non-linear dynamic analysis on a multi-story building to predict its response. This model is composed of a tri-linear monotonic backbone. Ibarra, et al, 2005 produced a set of equations to find model parameters for the lumped plasticity element model with the help of regression analysis by relating the column design parameters with column element model parameters (Haselton, 2008). There are unknown parameters like load ratio, lateral confinement ratio, shear span ratio, concrete strength, rebar buckling strength etc. Given a column design, these parameters can be quickly determined and thus, element model parameters can be predicted accurately. Haselton et al. developed a calibrated element model that is capable of simulating the flexural response of RC beam-columns up to global structural collapse.

Haselton, et al, 2007 evaluated the risk of collapse of RC-SMF (special moment frame) buildings to evaluate the seismic-safety implied by building codes for simulating 30 archetypical buildings using OpenSees and subjected them to incremental dynamic analysis.

In this project I am going to use the building model developed by Haselton et al. and run the analysis. The target is to produce fragility curves quantifying the uncertainties in model parameters as well as in ground motion. The equations available lead us to the mean values of the parameters though they are stochastically distributed. So far I have run code for nonlinear dynamic analysis of 4 story RC frame building in OpenSees. The model type is Elastic beam column element with plastic hinges at the ends. On this model, static pushover and earthquake ground motion time history analysis are carried out for thirty earthquake ground motions. These ground motions are applied using the incremental dynamic analysis (IDA) method. A set of IDA curves is developed. From these curves, all the collapse Sa levels are noted and plotted in cumulative distribution function. The curve is called fragility curve, and it helps us to predict the probability of a collapse for a given intensity measure.

Keywords: earthquake engineering, hysteretic strength, stiffness, lateral confinement ratio, shear span ratio, incremental dynamic analysis, plastic hinges

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