Acceptable values of collapse margin ratio with different confidence levels

摘要

Determining a reasonable seismic safety margin target (acceptable value) for a structure is an important first step in preventing structural collapse and ensuring life safety. Based on the confidence interval method, expressions for collapse fragility-based and risk-based acceptable collapse margin ratios (CMRs) with different confidence levels are proposed; additionally, the abovementioned expressions are derived by the mean estimates approach. Subsequently, acceptable CMRs applicable to Chinese specifications are provided. Compared with the mean estimates approach, the confidence interval method can be used to provide acceptable CMRs with different confidence levels to satisfy specific seismic targets. When the structural parameters are set to median values, the acceptable values calculated by the mean estimates approach exhibit only a 50% confidence level. However, these values are higher than the acceptable CMRs calculated using the confidence interval method at 50% confidence. As the confidence level increases, the acceptable CMRs calculated using the confidence interval method become much higher than those calculated using the mean estimates approach. Under the same conditions (same uncertainties and confidence levels), the collapse fragility-based acceptable CMRs are lower than the risk-based acceptable CMRs.