Development of fragility curves for RCC frame structures : Bangladesh context

Abstract

[n recent past, severe earthquakes have caused substantial physical losses and casualties in this sub-continent. Parts of Bangladesh are in high risk of facing devastating earthquakes. Since a majority of the population is living in earthquakeprone areas, it is probable that such terrible events may take place again in the near future. Moreover, it is not easy to cope with the substantial direct and indirect economical losses after each devastating earthquake for a developing country like Bangladesh. Because in this country many reinforced concrete buildings are not designed according to the current building code, seismic behavior is not taken into consideration during selection of the structural system and in most cases supervision in the construction phase is not adequate which in turn induces deficiencies like poor concrete quality, inadequate detailing of reinforcement etc. It is, therefore, vital to quantifY the earthquake risk and to develop strategies for disaster mitigation. In order to achieve this goal, an extensive and inter-disciplinary study is required. This study describes the methods by which it is possible to determine the vulnerability of existing engineering structures and building stock. The tool thai is employed to assess the seismic performance of reinforced concrete frame structures is the fragility curve. By definition, fragility curves provide estimates for the probabilities of reaching or exceeding various limit states at given levels of ground shaking intensity for an individual structure or population of structures. A limit state, which is in the same terms as the response, usually represents a damage condition or a limitation of usage. The primary focus of this research is to present a proper methodology that can be followed to construct fragility curves for RCC frame structures in Bangladesh and to generate fragility curves for common type of RCC frame structures using this methodology. The findings of the study i.e. the suggested guideline can be used to develop fragility curves for any structures in Bangladesh analytically. Following these guidelines fragility curves are constructed for three story and six story frame structures of Dhaka city which can be used to assess the seismic vulnerability of these types of RCC structures in Dhaka. From the fragility curves of 3-story RCC structures it is found that if an earthquake of DAD g occurs then 90% of this type of structures V[ would suffer light damages. In case of 6-story RCC building the probability of exceedance of severe damage is 100% for the same magnitude of earthquake. Similarly the seismic vulnerability of these structures for different earthquake can be interpreted from the developed fragility curves. A rough estimation of damages in terms of cost is also calculated from the fragility curves for these structures for different earthquakes. Utilizing the suggested guidelines fragility curves for any RCC frame structures in any region of Bangladesh can be constructed and corresponding regional loss estimation studies in different earthquake prone zones of Bangladesh can be conducted.