Qualitative Methodology for Earthquake Disaster Risk Assessment of the Existing Buildings

Abstract

ndia has experienced some of the world's most devastating earthquakes. In the past thirty years, earthquake losses in the country have been substantial, and the collapse of buildings is the principal cause of life loss. The experience of past earthquake events indicates that even moderate earthquakes caused significant property damage and fatalities. Most existing buildings in India are of the vernacular housing type and were constructed with limited or no engineering input. The remaining structures are considered engineered buildings of Reinforced Concrete type, but many of them were built without the assistance of professionals or trained assistance from the builders, placing them outside the scope of formal building codes. Rapid urbanization places pressure on the housing industry to expedite building structures. The expansion of urban areas because of population growth and migration results in unplanned and uncontrolled urban infrastructure, jeopardizing the built environment's safety. About 57% of the land area in India lies within the moderate-to-severe seismic zone, where approximately 80% of the population resides. Consequently, a substantial proportion of India's buildings are at risk due to seismic hazard and building stock in seismically active regions. Thus, pre-earthquake safety assessment of the built environment significantly reduces damage and losses by identifying buildings prone to earthquakes and implementing appropriate mitigation measures. Given the large number of existing buildings in cities and towns, conducting a detailed assessment of each structure is challenging. Therefore, two qualitative methods for assessing earthquake disaster risk, with a focus on building level and projection onto a city scale, provides a thorough understanding of risk and the ability to prioritize mitigation measures. The Earthquake Disaster Risk Index (EDRI) is a first-cut method for estimating the earthquake risk of a city’s-built environment. It is a nonlinear combination of the existing earthquake hazard representing the spatial aspects , vulnerability of the building’s thematic characteristics and the exposure representing temporal characteristics. The method is based on a detailed visual survey of the building stock of specific typologies and reflects hazard, exposure, and vulnerability factors contributing to earthquake risk . The risk of individual buildings evaluated is used to calculate the average risk of each building type in the city. The Earthquake Disaster Risk Index of the surveyed buildings is computed. The overall EDRI of the city/town is estimated using the housing census data. risk of an individual building is estimated in terms of Demand Factor and Capacity Factor of the building. The seismic design coefficient from 1893 (Part 1):2016, is the Demand Factor. The Capacity Factor is from the Level 2 Detailed Qualitative Assessment of buildings built in the Town or City. A final qualitative earthquake rating is assigned to the building by calculating the Capacity Factor/Demand Factor. The method helps in understanding, managing, and reducing seismic risk overtime. In this study, the data collected from fifty cities by National Disaster Management Authority (NDMA) and the International Institute of Information Technology Hyderabad (IIIT H) is used for analysis. Two types of data were gathered: building information and city information, where the former is collected by Rapid Visual Screening (RVS) and photographs of the building and the latter by collected by visiting the municipal office. Risks associated with cities in Seismic Zones III, IV and V are compared. This aids in the identification of techniques for retrofitting buildings in such regions; improving local construction techniques and adhering to the Indian Standard Code of Practice, as well as regularizing construction on hilly regions, will reduce the seismic risk of these cities.