Rapid Visual Screening for Seismic Evaluation of Existing Buildings in Himachal Pradesh

Abstract

India faces serious earthquake problems by a rapid growth of urban population. Nearly 60% of landmass in India is under moderate to severe earthquake prone area. During 2001 Bhuj earthquake, massive damage was happened to moderate buildings. Reconnaissance survey reports suggested that the need for seismic evaluation of existing buildings. Different methods for seismic evaluation of existing buildings have developed in various countries. Most of the methods follow three level assessment procedures (or something quite similar to it) namely, (a) rapid visual screening, (b) preliminary assessment, and (c) detailed evaluation. Rapid Visual Screening (RVS) was conducted on 9099 buildings in Himachal Pradesh state. In this study, five different typologies like Reinforced Concrete, Brick Masonry, Stone Masonry, Hybrid and Rammed Earth buildings were selected. The RVS methodology is referred to as a “sidewalk survey” in which an experienced screener visually examines a building to identify features that affect the seismic performance of the building, such as the building type, seismic zone, soil conditions, horizontal and vertical irregularities, apparent quality in masonry and RC structures and short column etc. This walk survey is carried out based on the checklists provided in a proforma for all five typology of buildings. Other important data regarding the building is also gathered during the screening, including the occupancy of the building and the presence of nonstructural falling hazards. A performance score is calculated for the building based on numerical values on the RVS form corresponding to these features. The performance score is compared to a “cut-off” score to determine whether a building has potential vulnerabilities that should be evaluated further by an experienced engineer. Gaussian distribution is applied for cut off score in this study. An attempt has been made to do rapid visual screening of five varieties of buildings in Himachal Pradesh state. RVS score has calculated for 9099 buildings and plotted normal distribution curves for each typology of building to understand the distribution of buildings in HP state. From the study, it is clearly shown that Kangra district have more buildings in all five different typologies. As per statistics of surveyed buildings by TARU consultants in Himachal Pradesh, around 17% (1541 out of 9099) of buildings are reinforced concrete, 48% (4363 out of 9099) of buildings are brick masonry, 15% (1341 out of 9099) of buildings are stone masonry, 5% (518 out of 9099) of buildings are rammed earth and 15% (1318 out of 9099) of buildings are hybrid. However, there are some low RVS score buildings which are potentially vulnerable to future earthquakes. Also it is suggested that preliminary analysis needs to be performed on 47 buildings and detailed analysis for 15 buildings for calibrating RVS scores.