Exploratory investigation on timber beams under fire: FRP strengthening, fire-retardant coating, and sustained loading

This paper, for the first time, presents the fire performance of timber beams with considerations of fiber reinforced polymer (FRP) strengthening and application of intumescent fire-retardant coating. As a preliminary investigation, an experimental program involving twenty small-scale timber beams, under three-point bending, was conducted. The study reveals that while fire-retardant coatings can protect unloaded timber for over two hours, the fire resistance period significantly decreases to less than 30 min under sustained loading conditions for timber structural members tested in this study. In addition, the results indicate that FRP strengthening enhances the fire resistance of timber beams, particularly at higher load levels, due to its ability to distribute and bear the applied load before complete FRP–timber debonding prior to structural collapse. However, the fire-retardant coating’s effectiveness tested in this study diminishes as the load increases, showing a limited influence in fire resistance for timber beams under a 10 kN load (50 % of bending capacity) without FRP strengthening. Conversely, a combined approach of FRP strengthening and fire-retardant coating protection significantly improves fire performance under the same loading conditions. This exploratory investigation fills a critical gap in the literature by clarifying the importance of FRP strengthening, fire-retardant coating, and structural load in the fire resistance of timber structures and revealing the limitations of current fire-retardant considerations in protecting timber structures.