Influence of Intumescent Coating Thickness on the Thermal Response of HEA-Profile Steel Columns Under Standard Fire Exposure

Fire protection of structural steel is essential for limiting heating and preserving load-bearing capacity under fire exposure. This study investigates how intumescent coating thickness affects the thermal response of six HEA 300 specimens made of S235 steel. Measured mean dry film thickness (DFT) ranged from 1.01 to 1.88 mm. Specimens were exposed on four sides to the nominal ISO 834 standard fire curve, without applied mechanical loading and their time to reach selected steel-temperature thresholds was compared. At an adopted reference temperature of 550 °C (assumed utilization factor μ0 = 0.6160), the times reported in the experimental dataset ranged from 32 to 36 min. Specimens S4, S2, and S3 (DFT of 1.34, 1.60, and 1.88 mm) each reached 550 °C after 36 min, whereas specimen S6 (1.78 mm) reached it after 34 min. These results indicate a non-monotonic relationship between mean coating thickness and thermal response under the investigated conditions. Post-exposure observations showed local detachment of the coating, although its occurrence during the test was not determined. The reported times provide comparative thermal-performance indicators, not a standalone standardized load-bearing fire-resistance classification.