The impact of the escalation of acceptable seismic risk on reinforced concrete frame structure

摘要

Eurocode 8 prescribes that structures are sufficiently designed if they are capable to withstand a design seismic action, which is defined for a given earthquake recurrence interval associated with ultimate and serviceability limit state. The first requirement is fulfilled if it is proven that the structure does not collapse for a seismic action associated with return period of 475 years. A shortcoming of such design procedure is that the decision is based on conditional probability of failure. In reality, “stronger” or even “weaker” earthquake can cause collapse of the building. This shortcoming of the existing standards for seismic resistant design of buildings can be overcome by introducing more scientifically-oriented design procedures, which is the main objective of the research thesis. The new design procedure used in this research is based on target reliability that is expressed by the acceptable annual probability of collapse of structure. As a case study, an eight-storey reinforced concrete frame building was designed taking into account different level of acceptable seismic risk in order to investigate the relationship between the escalation of target reliability and the global parameters of the structure. We found that the escalation of acceptable risk by a factor of 50 resulted in an increase of the total design seismic forces by about a factor of 10. This was reflected in the quantity of materials used. The amount of reinforcement was increased by about 4.6 times, while the volume of the concrete was greater by a factor of 1.9. It appeared that the structural system is not suitable if the criterion of acceptable risk is very strict. Based on the results of the study it can be concluded that the proposed force-based design procedure to target reliability is quite similar to that prescribed by Eurocode 8, as it essentially differs only in the definition of the seismic action, which, according to the new procedure, depends on the target reliability rather than earthquake recurrence interval.