Analysis and Quantification of the Target Safety Level Implied in Performance Verification Method for Fire Resistance against Localized Fires

Abstract

In the standard verification method for fire resistance of Building Standards Law of Japan, it is verified that the principal building construction elements shall not collapse by foreseeable fire effect. In case of localized fire scenarios, 20 minutes of fire is assumed close to the elements in question. Using the prescribed input parameters and calculation formulas, the conformance is evaluated. However the resultant safety level is not clear to practice engineers and building owners. To reveal the safety level attained by the verification method, the variability and uncertainties of input parameters were quantified by probability density functions. Then, the probability of failure is calculated by the method of reliability engineering. The analysis was carried over a group of column specifications that exactly satisfy the verification method for localized fire scenario. It was found that the safety index of the group was as large as around eight. The five governing parameters were specified as fire duration, basic temperature rise rate and correction temperatures for residual strength ratio of steel material, for ultimate temperatures for overall and local buckling. For generalization, sensitivity analysis was carried out for the practical range of column length, diameter and plate thickness. As a result, linear correlation between safety index and partial safety factors were proposed for rational design for target safety described by safety index.