Simulation of Cross Laminated Timber Boards under Fire Exposure

Abstract

The aim of this study [1] was to verify rules given in EN 1995-1-2 [2] for structural fire design for solid timber panels by applying the reduced cross section method (RCSM). The RCSM introduces a zero strength layer of 7 mm to compensate material reduction due to temperature load. Software written by Trätek based on fundamental mechanical relationships was upgraded and used to run studies with solid timber panels. Studies covered fire exposure to the tension as well as the compression side of samples in bending, different material characteristics and different cross sections. Furthermore, two different material reduction functions were compared. They were derived in previous studies of Trätek (Stockholm) and BOKU (University of Natural Resources and Applied Life Sciences, Vienna). For comparison purposes, simulations with solid cross sections without cross layers but with infinite dimensions in width (solid timber) were performed. The results of this study, which consider the standard fire load according to ISO 834 [3] show that the zero strength layer is first and foremost very sensitive to the location of fire exposure. Furthermore, dependence on the material reduction function as well as on the material characteristics can be observed. Fire exposure on the compression side leads to comparatively high values of the zero-strength layer (non-conservative results), while results of exposure on the tension side show a better concurrence with existing rules. The constant depth of a zero-strength zone of 7 mm given in EN 1995-1-2 [2] is exceeded in almost all cases depending on the time of fire exposure and tested build-up.