Fire Behaviour of Timber-Encased Steel Composite Structures: A Meta-Analytic Review of Experimental Findings and Design Implications

Timber-encased steel composite (TESC) systems have emerged as a promising structural solution combining strength, sustainability, and enhanced fire performance. This meta analytic review synthesises experimental and numerical findings reported between 2020 and 2025 to assess the influence of timber encasement on the fire resistance of steel members. Data from full-scale and small-scale fire tests were statistically aggregated using random-effects models to determine pooled fire resistance and to quantify the effects of parameters such as timber thickness and moisture content. Results show that complete timber encasement markedly delays steel heating and improves fire endurance. On average, each additional millimetre of timber cover contributes approximately 1.9 minutes of fire resistance (p < 0.01), with 50 mm of encasement providing roughly 1 hour of protection under ISO 834 conditions. Moisture within the timber further reduces the rate of temperature rise by absorbing latent heat during evaporation. The study confirms that the insulating and charring behaviour of timber functions as an effective passive fire-protection layer, offering an alternative to conventional coatings or boards. The design implications are significant: empirical correlations between cover thickness and fire resistance can inform future fire design models and code calibrations. Remaining research needs include long-term performance of composite joints and validation under realistic fire scenarios. Overall, the review provides quantitative evidence supporting timber encasement as a viable, sustainable, and code integrable approach for improving the fire safety of composite steel structures.