Mechanical Properties of S235 Steel Protected with Intumescent Coatings Under High Temperatures: An Experimental Study

This study investigates the impact of high temperatures on the mechanical properties of fire-protected versus unprotected S235 cold-formed steel (CFS) specimens with variable thicknesses. Through axial tensile tests, we assessed how intumescent coatings influence the behavior of steel under fire-like conditions. The results reveal that as temperatures increase, the mechanical strength of unprotected steel diminishes significantly, especially at temperatures beyond 400 °C. However, at temperatures between 500 and 900 °C, coated specimens demonstrate considerably enhanced strength compared to their uncoated counterparts. The coating effectively reduces the steel’s temperature exposure by approximately 200 °C, crucially preserving its integrity at critical temperatures. The thickness of the steel also plays a role, with thicker specimens maintaining higher ultimate strength up to a threshold temperature. The study culminates in a predictive analytical model that estimates the ultimate strength of coated and uncoated steel based on temperature and specimen thickness. These insights contribute substantially to the design of safer, more fire-resistant steel structures.