Experimental Assessment of the Fire Resistance Mechanisms of Timber–Steel Composites

Hybrid structures known as timber–steel composites (TSCs) have been extensively studied due to their potential use as alternative construction materials that can satisfy demands related to sustainability. In addition to load capacity, fire resistance is a major consideration regarding the extensive use of TSCs. In this study, 12 specimens were tested using a glulam timber material covering cold-formed steel at the center. Specifically, the TSCs were fabricated from two timber blocks and an I-shaped steel core assembled using dowels or glue as a major structure. In order to use additional timber as a fire protection layer to protect a major structure by its charcoal produced after being burned, an additional timber with 5 cm in thickness was used to cover the major structure. The 1-h fire testing of TSC following the ISO 834-1 standard was applied, in order to achieve the potential application for a 4-story timber building. The results showed that temperatures at the steel flange increased by more than 300 °C for the final 5 min in 10 out of the 12 TSC specimens, indicating that the fire protection provided by the timber structure was not sufficient. The charcoal layer surpassing the extra timber was originally set and entered the steel structure of the TSC, which was expected to retain its physical qualities after a fire. Methods for evaluating the charring properties, based on the conventional method for wood and the standard specification set by Eurocode 5, were used to assess the structural degradation of TSCs. The conventional assessments showed a divergence from the actual performance of TSCs. Such variations demonstrated the limitations of models for conventional wood in assessing the structure of a TSC. A realistic assessment was conducted to expand knowledge related to this composite under destructive processes and provide fire reference values for the practical implementation of TSCs.