Vulnerability of cyclone shelters in Bangladesh due to Tsunami

Abstract

Bangladesh is struck by cyclone and cyclonic surge almost every year. However, after the devastation caused by tsunami due to the great Sumatra Earthquake in 2004, tsunami is also considered as a probable hazard in the Asia Pacific region. Though tsunami did not cause any disaster in this country in the past but it can cause in future. So studies related to tsunami are now necessary mainly for the coastal region of Bangladesh. The study is conducted considering tsunami loading only. Very few studies have been performed on tsunami in Bangladesh. The present study does not investigate whether tsunami may hit Bangladesh or not rather the effect of tsunami on structures is examined here. If tsunami strikes Bangladesh then people can survive only by taking shelter on places which is moderately higher than sea level. For this purpose, cyclone shelters in the coastal areas of Bangladesh may be suitable. The cyclone shelters, however, were not constructed considering tsunami load. So their vulnerability should be checked before using them as a safe shelter for tsunami. Considering this fact, the study assessed the vulnerability of the existing cyclone shelters for tsunami. A number of three dimensional finite element models of the cyclone shelters were created for this study. Different heights of tsunami were assumed to identify the effect on different condition. Structure type, loading pattern for tsunami, loading combinations and the result of the analysis are provided in this project report. The analysis was performed on the information available. Concrete strength of the existing structures was assumed 3000 psi as actual concrete strength was not available. Strength of reinforcing steel was assumed 40 ksi as design strength and actual strength data of steel was not available. Structural details of these structures were not available so checking the adequacy of the members of the structures was difficult. To solve this problem it was assumed that 3% longitudinal reinforcement was provided in the columns of the structures. When the required steel reinforcement exceeded 3% the members were assumed vulnerable. A time history analysis was performed also but the time history data used was taken from a laboratory test result. It was performed as an experimental dynamic analysis. Foundations of the structures were not checked as these structures might have different types of foundations and foundation design related data were not available. Moreover different structures will need different types of foundation design depending on the soil condition of different sites. From the study it is found that most of the structures are vulnerable in the analysis for tsunami, but this vulnerability is found depending on some assumptions due lacking of actual data. For tsunami, load was applied considering 1m, 2m and 3m tsunami height. Different types of cyclone shelters were found vulnerable for different heights. Only JICA type cyclone shelter survived up to 3m tsunami loading. For some structures column can survive 3m loading but beams are vulnerable due to torsion. Recommendations of further study are also discussed in this report.