RISK EVALUATION OF EXISTING BUILDINGS BY USING RAPID VISUAL SCREENING

Abstract

Poor and substandard construction practices results in the failure of a structure during a seismic event. Delhi is a rapidly urbanising city and lies in Seismic zone IV as per IS 1893:2016, without considering the standard construction practices a major earthquake will lead to huge damages to the structures or structure may fail. In order to protect deficient structures from seismic occurrences, a quick performance review technique is required. There are many guidelines for screening of buildings but FEMA P-154, 2015 and FEMA P-155, 2015 provides the screening in the most comprehensive manner by scoring the screened building for its various attributes. Using this score, risk of an earthquake causing the building to collapse cam be calculated. In this dissertation, a thorough investigation on 100 buildings was conducted and Level 1 RVS score has been calculated. On the basis of RVS Level 1 score two buildings from each typology has been selected and probability of collapse was then compared to the probability of MCE shaking, to determine the chance of building collapse. Considering the technique provided in FEMA P-154, 2015, four distinct typologies of existing structures were chosen as case studies for the computation of collapse probability i.e., Concrete Moment-Resisting Frame Buildings (C1), Concrete Shear Wall Buildings (C2), Concrete Frame Buildings with Unreinforced Masonry Infill Walls (C3), and Unreinforced Masonry Bearing Wall (URM). Along with that, RVS score has been used to calculate the 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., Concrete Frame Buildings with iv Unreinforced Masonry Infill Walls (C3), and Unreinforced Masonry Bearing Wall (URM) 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. Implementing the calculation of Probability of Collapse under the MCE shaking, Concrete Moment-Resisting Frame Buildings (C1) is found to have 0.02% and 0.63%. While the Concrete Shear Wall Buildings (C2) has the likelihood of failure with MCE tremor, 0.004% and 4%. The Concrete Frame Buildings with Unreinforced Masonry Infill Walls (C3) have the probability of collapsing with MCE ground shaking, 3.16% and 100%. The Unreinforced Masonry Bearing Wall (URM) has the possibility of collapsing with MCE tremor, 5% and 63%. Implementing the calculation of at least one collapse causing earthquake within next 50 years, it has been found that the Concrete Frame Buildings with Unreinforced Masonry Infill Walls (C3), its probability of encountering an earthquake that might lead to collapse is 6.11%. Whereas for, Unreinforced Masonry Bearing Wall (URM), its probability of encountering an earthquake that might lead to collapse is 3.11%. As a result, both buildings must undergo a thorough structural study for retrofitting in order to function safely during seismic activity. As a result, according to the study, the RVS criteria of FEMA P-154(2015) may be applied adequately for preliminary inquiry, including acceptable limitations as per Indian standards. Based on this, a reasonable judgement about the need for thorough technical evaluation may be made, and the technique will assist in prioritising the building for full structural examination and retrofitting suggestions.