Vulnerability Assessment of Typical Residential Buildings of Chattogram City Corporation with Post Seismic Hazard Consideration

Abstract

The seismic hazard map of Bangladesh shows that the northern and eastern regions of Bangladesh are particularly susceptible to seismic hazards. There is a high risk that a moderate to strong earthquake may result in widespread damage especially in the densely populated urban set up of Bangladesh. Being the second largest metropolis in Bangladesh, Chattogram has been built up to accommodate fast-growing population of Bangladesh. In this project, building data is collected by conducting Rapid Visual Screening (RVS) survey in a typical residential area of the city. Commonly used methods of RVS is used to collect general information of typical reinforced concrete buildings of the study area and an assessment of seismic vulnerability of the buildings is done with emphasis given post seismic hazard consideration as well. A comparative analysis of the results using FEMA 154, FEMA 310 and ASCE 41-13 RVS methods show that there exist significant problems of seismic vulnerability of buildings in the study area in relation to building parameters such as load path discontinuity, soft stories, weak brick joints, horizontal and vertical plan irregularities, strong beams/weak columns, diaphragm discontinuity etc. The results of FEMA 154 RVS method indicates that 35% of the buildings of the area fall below a cut-off vulnerability score of 2. With an average 49% percent of non-compliance of building vulnerability parameters of FEMA 310, an average or relative score of vulnerability score of 2.1 is calculated. The results of these two RVS methods seem to be an underestimate of the conditions of seismic vulnerability considering the poor conditions of buildings observed during the field study. When compared to the results of average 60% non-compliance of building vulnerability parameters of the ASCE 41-13 checklist, the relative score of seismic vulnerability of 1.9 better represents the observed poor conditions of buildings‟ physical conditions. According to FEMA 154, the percentage of buildings with cut-off score less than 2 is high in areas with insufficient width of roads which is indicative of the fact of narrow exit pathways or insufficient evacuation facilities during emergency situations. A few guidelines of BNBC regulations may be considered important considerations for mitigation of risks of post seismic hazards. Therefore, RVS checklists of parameters may need inclusive considerations of some additional parameters in the checklist of building vulnerability parameters such as front road width, electric and gas lines distance, built purpose and rescue facility etc. which are required to ensure earthquake resilient residential infrastructures and urban seismic resilience.