TOWARDS AN APPROPRIATE SEISMIC VULNERABILITY ASSESSMENT MODEL IN INDIA
Earthquakes have across history, led to heavy death tolls and monetary losses, forcing nations to deal with catastrophic repercussions. While the reasons behind these deaths and monetary losses can be attributed to a number of factors, a statistical analysis of the major cause of these fatalities worldwide, clearly points towards the collapse of buildings and other structures. The fact that the seismic hazard and exposure in a region cannot be controlled, suggests that any attempt to mitigate seismic risk should focus on minimizing the vulnerability of the building inventory. The Indian subcontinent, geographically spread over 3.287 million km of landmass, is highly non homogenous with respect to its seismogenic features. The seismic design code IS 1893 Part 1: 2002, that lays down the standards for seismic design of structures in India, recognizes four such seismic zones Zone II, Zone III, Zone IV and Zone V, indicating regions with low, moderate, high and very high levels of seismic activity respectively. Indian buildings exhibit significant heterogeneity with respect to their architectural and structural features. The performance of many building typologies in India during past earthquakes have not been satisfactory. From ill conceived design and detailing to poor quality control and construction practices, a wide spectrum of factors hinder the desirable seismic behavior of buildings. Various classes of methods exist in literature for quantifying the vulnerability of structures. Although there have been many studies in the past to assess the seismic vulnerability of individual buildings in the country, it was not until 2013 that a technical document was released by the National Disaster Management Authority (NDMA) for the territorial scale assessment of Indian building stock. Out of the fifty four typologies that have been proposed for Indian buildings, many are combined together and represented using single vulnerability function. This paper briefly describes the seismological setting of India, and the performance of various building typologies in past earthquakes, with the view of emphasizing on the need for seismic vulnerability assessment. It further focuses on the state of the art methodologies for assessment and the development of appropriate vulnerability models in the Indian context. Important issues that need to be addressed by these models form the central theme of discussion in this paper.