Predicting the effective char depth in timber elements exposed to natural fires, including the cooling phaseLucherini, Andrea (Avtor) Šejnová Pitelková, Daniela (Avtor) Mózer, Vladimír (Avtor) timber structuresfire safetyheat transfercharringzero-strength layercoolingThis paper presents a numerical study on the effect of the heating and cooling phases on the reduction of the effective cross-section of timber elements, in particular on the evolution of the char depth (300°C isotherm) and zero- strength layer. An advanced calculation method based a finite-difference heat transfer model is compared to the simplified approach suggested by Eurocode 5. For the heating phase, defined as the standard fire curve (ISO 834), the simplified Eurocode 5 method generally provides more conservative char depths, while the zero-strength layer is under-predicted. Nevertheless, the values of effective char depth are comparable. Including the cooling phase evidences that, during this phase, the heat wave penetration leads to a significant increase in the char depth and zero-strength layer. Particularly, this increase directly depends on the fire cooling rate: a slower cooling phase further reduces the effective cross-section of timber members. As a result, this research highlights how the heat wave penetration during the fire cooling phase can significantly reduce the load-bearing capacity of timber elements.World Conference on Timber Engineering20232025-01-14 11:46:20Neznano21196UDK: 624DOI: 10.52202/069179-0226COBISS_ID: 158332931OceCobissID: 156463107sl© (2023) WORLD CONFERENCE ON TIMBER ENGINEERING 2023 (WCTE 2023) All rights reserved.