Numerical and Design Analysis of Protected Steel Columns in Standard Fire

Abstract The high thermal conductivity of steel, combined with its rapid degradation in mechanical properties with increasing temperature, makes it vulnerable to fire. Fire protection materials are effectively designed to control the temperature rise within steel members. This paper is a companion to a previous numerical analysis study on protected square hollow section (SHS) steel columns using thermally enhanced gypsum-based mortars. It offers a more detailed numerical investigation into the thermal performance of different gypsum-based mortar compositions used as a passive fire protection material for different types of steel columns. Firstly, finite element models for SHS steel columns were developed and verified against data from previous fire resistance tests. Then, a parametric study was conducted to explore how factors like fire protection thickness and composition, cross-section (square, rectangular, and H-shaped sections), steel tube thickness, column slenderness, and applied load level (serviceability load states) affect their fire performance under the ISO-834 standard fire curve. Comparisons were made between numerical results and current design methods from Eurocodes. It was observed that existing design methods excessively underestimate the actual fire resistance of protected columns, particularly for class-4 cross-sections especially when mortars with highest thermal insulation capacity are used. Moreover, the thermal properties of fire protection mortars should be considered in the structural steel temperature prediction as a function of temperature during fire conditions. Based on the study’s findings, modifications to current design methods for predicting the temperature evolution of columns as a function of the cross-sections and fire protection compositions, were presented with enhanced accuracy. These proposed modifications can potentially contribute to future development in Eurocode and improved fire resistance predictions.