Structural properties of cross laminated timber under elevated temperature due to fire

Abstract

At the time of this thesis work, one of the fastest growing materials in timber construction is Cross Laminated Timber (CLT). This building material has many appeals, from sustainability of production to visual aesthetics, and offers a multitude of benefits in design and construction. However, there are still areas of the design that need more research in order to better understand CLT as an engineered wood structural material in order to design safer as well as boost public trust of the material. In particular, the material behavior at elevated temperatures due to fire has a limited amount of research. This study aims to fill in the gaps in terms of material behavior of CLT as a one-way slab is heated uniformly along the bottom of its span. Through the use of computer aided finite element modeling, the stresses and deformation of CLT can be better understood and the overall impact of high temperature to beam strength, stiffness, and over-all deflection can be studied in a quantitative fashion. The simulation study for a total of 12 different wood and glue combinations in order to determine the behavior of CLT with different manufacturing material options. The small-scale experimental data from an earlier FPL study is used to obtain the material properties of wood and glue as a function of temperature. The temperature distribution along the thickness of CLT was modeled based on experimental testing data from CLT panel burning tests. The overall findings of this study suggest that the material properties behave in a linear fashion as the temperature increases. The reduction of panel stiffness and strength is very limited before charring of the wood (under 10% for most of the cases simulated). The wood materials are most likely to reach its strength limit before the glue, due to the protection of the wood and the buried glue lines. However, this study does not consider the fire condition where wood is charred and loses all its strength. The results of this study still need to be validated using full-scale panel heating tests.