SEISMIC VULNERABILITY AND RISK ASSESSMENT OF INDIAN URBAN HOUSING

Abstract

A seismic risk assessment methodology, based on socio-economic clustering of urban housing stock, is presented in this Thesis. The methodology is particularly useful for Indian cities, where comprehensive building stock databases are not available, and a natural division of the city, in a number of clusters with different socio-economic levels, exists. The seismic risk parameters are assumed to be uniform within a socio economic cluster. The methodology is based on an optimum utilization of high resolution satellite data and a Stratified Random Sample Survey. Ten different classes of socio-economic clusters found in Indian cities are defined and 34 Model Building Types (MBTs) prevalent on the Indian subcontinent have been identified. Seismic vulnerability of the proposed MBTs has been assessed by comparing with the classifications of MSK64, EMS98, PSI and HAZUS. Lower and upperboundDamage Probability Matrices (DPMs) are proposed based on the MSK and EMS scales and experiences of past earthquakes in India. The DPMs based on PSI have also been evaluated. Two analytical models, based on equivalent frame approach, are presented, which automatically simulate the effect ofvariation ofaxial forces in piers. The models have been validated for results of two walls, studied in the 'Catania Project'. An exercise has also been carried outto select representative building plans based onthe statistical analysis of plans of 32 buildings selected randomly from field survey. The seismic behaviour of the representative buildings has been simulated using one of the proposed models and Capacity Spectra have been developed for URM buildings, in mud, lime and cement mortars, representing typical north Indian construction. Fragility Curves have been developed using the variabilities defined in HAZUS. in Intensity based DPMs have been obtained from the developed Fragility Curves and compared with the other DPMs, and damage data of Bhuj earthquake. It has been observed that Bhuj earthquake damage data is much more scattered than that predicted by MSK, EMS, PSI scales, and the analytical simulation. The damage predicted by the analytical simulation is higher than that predicted by PSI scale, but lower than that observed during Bhuj earthquake. The developed methodology is demonstrated through a case study of a typical north Indian city of Dehradun, located in the foothills of Himalayas. DPMs based onMSK and EMS-98 scales, and PSI scale, have been used to assign the vulnerability of the building stock. The risk scenario of the city has been generated for the seismic intensity (MSK VIII) assigned by Indian seismic macrozonation map. The risk estimates using the two sets of DPMs, have been compared. At moderate intensities, the two estimates are in fair agreement, but, at lowand high intensities, the estimates based on PSI scale are more reasonable as the descriptive scales saturate at these intensities. The distribution of seismic risk across different socio-economic clusters has been studied and it has been observed that poorer people are subjected to higher seismic risk, both, in terms of casualties, and in terms of economic losses. Limitations and assumptions in the case study have been discussed elaborately and different sources of uncertainty have been identified. In the absence of adequate information on each of the components of risk, it is concluded that the risk estimates obtained in the case study are to be considered only as a coarse indicator of the perceived seismic risk.