Simulation of the Fire Resistance of Cross-laminated Timber (CLT)

Abstract

Cross-laminated timber, typical abbreviations CLT or XLAM, is currently one of the most innovative product in building with wood. This solid engineered timber product provides advantages compared to other solid timber slabs as the dimension stability, i.e. swelling and shrinkage, is controlled by the crosswise laminations. As for other components, the fire resistance has to be verified for this type of product. While fire testing is time consuming and costly, simulations provide flexibility to optimize the product or to develop simplified design models for structural engineers. In this paper, a simulation technique is presented which can be used to determine the fire resistance of CLT. The technique was then used to develop simplified design equations to be used by engineers to predict the behavior of CLT in fire resistance tests and verify its fire resistance. Following existing models, the simplified design model aims for a two-step process whereby in a (i) first step the residual cross section and in (ii) a second step the load bearing capacity of the partly heated residual cross section is determined. The presented simulations consider the effective thermal-mechanical characteristics of wood exposed to standard fire and perform an advanced section analysis using a temperature profile corresponding to the actual protection and the location of the centroid together with the possibility of plasticity on the side of compression. It was shown that simulation results agree well with test results and that they can be used to determine layup specific modification factors used by the reduced properties method or zero-strength layers used by the effective cross section method. It was shown that the use of the zero-strength layers is favorable compared to the modification factors to calculate the resistance of the residual cross section. This is due to the large range of modification factors answering the typical layup of CLT comprising layers with their fiber direction cross the span direction. Subsequently, the methodology was used to determine design equations for initially unprotected and protected three-, five-and seven-layer CLT in bending and buckling. While the zero-strength layer for glulam beams in bending is assumed to be 7 mm (0.3 in), for CLT the corresponding value is in most of the cases between 5 mm and 12 mm but is different for other loading modes such as buckling (wall elements) and depending on the applied protection.

Simulating real compartment fire conditions in a furnace

“…[14][15][16] However, it is known that the char rate is significantly affected by the severity of the fire exposure, and data on charring rates for nonstandard fire exposures have been limited to more recent studies related to the recent increase in interest in mass-timber buildings. [17][18][19][20] The lack of information on char rates under these conditions makes it difficult to perform fire resistance calculations under nonstandard fires. Recently, several full-scale fire tests on mass timber compartments have been conducted.…”

“…Others have found that the charring rate is proportional to the ratio of external heat flux divided by density . However, it is known that the char rate is significantly affected by the severity of the fire exposure, and data on charring rates for nonstandard fire exposures have been limited to more recent studies related to the recent increase in interest in mass‐timber buildings . The lack of information on char rates under these conditions makes it difficult to perform fire resistance calculations under nonstandard fires.…”

Experimental and numerical analysis on fire behaviour of loaded cross-laminated timber panels

“…Fire safety is always an important issue in the development of these new generation massive timber materials. Current research believe that the fire behaviour of wood is predictable (Bisby and Frangi, 2015;Klippel and Frangi, 2017;Ostman et al, 2017;Schmid et al, 2018). International design codes, such as EN 1995EN -1-2:2004EN (2004 and CLT Handbook (FPInnovations, 2013), have provided design strategies to determine the fire resistance-engineered timber structures based on a simplified reduced cross section calculation methodology.…”

Simplified approach for analyse of shear walls for multistorey timber buildings

“…Development of new timber based structural materials which provide producing of mass structural members enables to delete the limitation on the timber use for the multi-storey buildings. The mass timber structural members are characterized by the increased fire resistance in comparison with the light timber members with the small cross-sections (Green & Karsh, 2012;Green & Taggart, 2017;Nedryshkin, Gravit, & Grabovyy, 2018;Buka-Vaivade, Serdjuks, Goremikins, Pakrastins, & Vatin, 2018;Saknite, Serdjuks, Goremikins, Pakrastins, & Vatin, 2016;Schmid, Klippel, Just, Frangi, & Tiso, 2018). Construction of multi-storey timber buildings represent the most practical, effective and environmentally responsible solution to the global housing shortage which is caused by the increased urbanization and the densification of cities.…”