Investigating the thermal penetration in structural timber elements exposed to natural firesLucherini, Andrea (Avtor) Mózer, Vladimír (Avtor) timber structuresfire safetycharringzero-strength layercoolingThis study investigates fire-induced charring and thermal penetration in structural timber elements exposed to natural fire conditions, with a focus on the critical role of the cooling phase. A simplified 1D heat transfer model, based on Eurocode 5 temperature-dependent material properties, is implemented to simulate the thermal response of timber members subjected to Eurocode parametric fire curves. The analysis quantifies the char depth (300 °C isotherm) and the zero-strength layer, using both temperature-based (80-300 °C and 120-300 °C) and reduced mechanical properties approaches (tension and compression). Results show that, while the char depth predominantly develops during the heating phase, the zero-strength layer continues to grow during cooling, often reaching a thickness comparable to the char layer. The effective char depth (char depth + zero-strength layer) typically reaches its maximum towards the end of the cooling phase, representing the most critical condition for load-bearing capacity. The most severe conditions arise in low ventilation and high fuel load scenarios, characterised by long-duration fires rather than the highest temperatures. The findings highlight the need to explicitly consider the cooling phase in performance-based fire design for timber structures.World Conference on Timber Engineering20252025-07-16 08:13:59Neznano23009UDK: 624DOI: 10.52202/080513-0450COBISS_ID: 241463811OceCobissID: 239752963sl© WORLD CONFERENCE ON TIMBER ENGINEERING 2025 (WCTE 2025)