RISK EVALUATION OF EXISTING BUILDINGS USING RVS AS TOOL

Abstract

As per the studies conducted in past, it has been stipulated that it is not the earthquakes which kill humans, instead it is the poor and substandard practices involved in the construction of building which leads to its failure in the seismic event. Although, various IS codes for the design of building are available, but due to the rapid urbanization they have been overlooked. Being a seismic zone IV (as Per IS 1893:2016) and a rapidly urbanizing city without considering the standard construction practices, Delhi becomes a soft target for any severe seismic event. Hence, in order to safeguard deficit structures against seismic excitation; a rapid performance evaluation strategy is the need of hour. A lot of effort for the assessment of existing structures has been laid upon, but the basic idea could not be inherited. Eventually the strategy could not be implemented, owing to their technical complexities. Although, Various screening guidelines have been issued by different agencies, but FEMA P-154(2015) and FEMA P-155(2015) supplements the screening in the most comprehensive manner by scoring the screened building for its various attributes, like RVS score has been used to calculate risk of earthquake causing the collapse of building. Adopting the various fundamentals of practices in various guidelines such as FEMA, ATC etc., this dissertation aims to simplify the application of RVS in purview of various Indian Standard Codes, in order to achieve a better probabilistic approach in estimation of probable life building. In this dissertation, a detailed study has been carried out to calculate the probability of collapse of building using RVS score and subsequently that probability of collapse is compared with the probability of MCE shaking. Eventually, the result from comparison is used to decide, if the detailed vulnerability assessment of the building is required or not. Following the methodology prescribed by FEMA 154(2015), four Different types of existing structures have been taken as case study for the calculation of the collapse probability i.e., High-Rise RCC Building, Mid Rise RCC Building, RCC plus Masonry Combined Building and Load Bearing Masonry Building. In addition, RVS score has been used to calculate the Probability of the collapse mechanism to happen in a building under a significant earthquake within next 50 years. Following the calculation of Risk Score, its associated probability of at least one collapse causing earthquake within next 50 years has been calculated. Two different types of buildings i.e., RCC G+3 building and Load Bearing Masonry building, have been taken as a case study for the calculation of Risk Score using RVS score and its associated vulnerability using the technique as per FEMA for any seismic activity in the next 50 years.

Following the calculation of Probability of Collapse under the MCE shaking, RCC plus Masonry Combined Building is found to have the least likelihood of being collapsed under MCE ground shaking, i.e., 0.63%, whereas the Mid-Rise RCC Building shows the highest

likelihood of being collapsed under MCE ground shaking i.e., 100%. However, the High- Rise RCC Building has 50% likelihood of being collapsed under MCE ground shaking and

Load Bearing Masonry Building have been found to have fairly high likelihood of being collapsed under MCE ground shaking i.e., 63%. Following the calculation of at least one collapse causing earthquake within next 50 years, it has been found that the Load Bearing Masonry building has 3.11% chance of being confronted by an earthquake that can cause collapse. And, the probability of an earthquake causing the RCC G+3 building to collapse over the next 50 years has been calculated to be 1.57 %. The risk score is an indicator of the degree of fatality of the building and it has been calculated that Load Bearing masonry building is 100 times more fatal than the newly constructed Load Bearing masonry building. Therefore, detailed structural evaluation for retrofitting the Load Bearing masonry building to be safe under any seismic activity, is required. Hence, as per the study, the RVS guidelines of FEMA P-154(2015) can be used satisfactorily including permissible limits as per Indian standard for preliminary investigation. Based on which a fair decision regarding the necessity of detailed technical evaluation can be done and the methodology will help in prioritizing the building for detailed structural evaluation and retrofitting recommendations.