Post-Fire Performance of Bolted Steel T-Joints with Varying Coating Thicknesses: Experimental and Finite Element Analysis

This study investigates the structural performance of bolted T-joints in steel elements exposed to elevated temperatures, with a focus on the influence of fire-resistant coatings. A total of 36 T-joint specimens were tested under four different temperature levels (300 °C, 450 °C, 600 °C, and 900 °C), incorporating three IPE section sizes and three fire-resistant paint thicknesses (200 µm, 400 µm, and 600 µm). The experimental program aimed to evaluate the combined effects of temperature, cross-sectional geometry, and coating thickness on the axial load-bearing capacity and deformation characteristics of T-joints. To examine the influence of web geometry, T-sections were designed in accordance with Eurocode 3, and the flange-to-web thickness ratios (tf/tw) were varied between 1.52 and 1.58. Results showed that applying 200 µm and 400 µm coatings at 300 °C and 450 °C improved the axial load capacity by approximately 10% and 20%, respectively, compared to uncoated specimens. However, effective fire protection at higher temperatures (600 °C and 900 °C) required a minimum coating thickness exceeding 400 µm. Finite Element Models developed using ABAQUS (2017) were designed to predict post-fire load–displacement behavior, stiffness degradation, and failure modes. Predictions were validated against experimental results, with deviations ranging from 0.97% to 9.73% for maximum load and 1.18% to 42.13% for energy dissipation, confirming the model’s reliability in simulating the thermo-mechanical response of steel joints under fire exposure.