Load Bearing Capacity of Light Timber Frame Walls Under Fire

Abstract

Light Timer Frame Walls are made of solid timber elements and are usually fire protected by other materials. This investigation determines the residual load bearing capacity of Light Timber Frame Walls for fire rating periods of 30, 60, 90 and 120 min. The timber frame is made with 3 studs and 2 tracks, using two different fire protection levels (one and two gypsum layers). The computational model includes the thermal analysis under standard fire, including all types of materials and a sequential mechanical analysis with incremental load applied for each fire rating periods, applied just for the load bearing material. Nonlinear solution methods are used with small tolerance values for solution convergence, to determine the correct temperature and displacement fields. The thermal and the mechanical properties are considered temperature dependent. The mechanical analysis considers large displacement behaviour, and the charring effect of wood is included by the reduction of the stiffness and strength of the timber. The results show that the load bearing capacity decreases with the fire exposure time. A new proposal is presented between the load bearing capacity and the fire rating and finally the char layer is compared with the current and future version of Eurocode 5, part 1.2.