Modified Critical Temperatures for Steel Design Based on Simple Calculation Models in Eurocode 3

Abstract

Critical temperature is defined as the temperature at which failure is expected to occur in a structural steel member given a uniform temperature distribution and load level. Determination of the critical temperature is a simple but efficient way for structural fire design. This paper proposed a new model which incorporated the buckling, load levels and non-dimensional slenderness to calculate the critical temperature of steel member under fire based on the simple calculation models in Eurocode 3. To advance the application of this new model, design charts for determining the critical temperatures were developed. The design charts showed that the critical temperature decreases with increasing load level, and increases as the buckling curve varies from “a₀” to “d”. It is also recommended to use higher grade steel in both normal and fire situations. The accuracy of this model was ascertained by comparing with the test results in available literature. The new model gave an average prediction-to-test ratio of 0.980 with a standard deviation of 0.077, indicating conservative and less scattered predictions. The percentage of over-prediction (i.e., prediction-to-test ratio >1.0) was less than 5.8% when the nominal yield strength of steel rather than its test strength was used for predictions. In general, reasonable agreements were obtained between the test results and the predictions.