Development of Peak Ground Acceleration (PGA) based pre-code reinforced concrete frame building fragilities for Istanbul

Abstract

An important portion of pre-code building stock in Istanbul runs significant earthquake risk. Given a building class, the uncontrolled construction of pre-code buildings in the past leads to a considerable model variability and complicates the prediction of losses for future earthquakes in Istanbul. However, the social and economic loss estimations are necessary for Istanbul to have planned actions to improve the earthquake resilience in the city. At this point, fragility curves; which represent the exceedance probability of a particular damage state are one of the most important components of resilience-based building inventory studies for large building stocks at large metropolitan areas. This study aims to provide fragility curves for pre-code reinforced concrete frame residential buildings in Istanbul. For this purpose, 800 mid-rise frame buildings located in the Zeytinburnu district in Istanbul are compiled and 16 representative building models are developed to account for the model variability of the same building class. The examined buildings do not comply with the code requirements of any period after 1975 and they can be considered as low code. The fragilities are based on Peak Ground Acceleration because such practical ground-motion intensity measures are being popularly used in the loss assessment of large building stocks. Nonlinear building responses are derived from three-dimensional nonlinear response history analysis that are carried out by using OpenSees Software (Open System for Earthquake Simulation). Incremental Dynamic Analysis is performed to determine the statistical distribution of the response parameters. A set of real ground motions, which are consistent with the disaggregation results of a probabilistic seismic hazard assessment for Istanbul are considered in the development of fragilities for each building model. Therefore, the variability in building models of the same building class as well as the record-to-record variabilities are considered in the developed fragilities. The fragility model is a backbone cure with upper and lower bounds covering the model and ground-motion variabilities for mid-rise low-code reinforced concrete frame buildings in the investigated building stock.