Model building codes in the United States limit timber construction to six stories, due to concerns over fire safety and structural performance. With new timber technologies, tall timber buildings are now being planned for construction. The process for building approval for a building constructed above the code height limits with a timber load-bearing structure, is by an alternative engineering means. Engineering solutions are required to be developed to document and prove equivalent performance to a code compliant structure, where approval is based on substantive consultation and documentation. Architects in the US are also pushing the boundaries and requesting load-bearing timber be exposed and not fully encapsulated in fire rated gypsum drywall. This provides an opportunity for the application of recent fire research on exposed timber to be applied, and existing methods of analyzing the impact of fire on engineered timber structures to be developed further. This paper provides an overview of the performance based fire safety engineering required for building approval and also describes the engineering methodologies that can be utilized to address specific exposed load-bearing timber issues; concealed connections for glulam beams; and the methodology to address areas of exposed timber.
This paper documents the findings of a series of full-scale room fire tests, which includes tests on fully protected, partially protected CLT rooms as well as light-frame timber/steel rooms under real natural fires, aiming to investigate the fire behaviour and performance of CLT panels as an increasingly popular engineered wood product and to compare it to the performance of more traditional construction methods. Results show that the CLT panels when left unprotected get involved in the room fire as part of the combustible contents, responsible for over 60% of total heat release in the fully unprotected CLT room and double the heat release rate of a fully protected room fire where the CLT does not contribute. Partially-protected CLT rooms also demonstrates various levels of fire contribution. The amount of CLT exposure is also related to the occurrence of re-ignition and a second flashover after all the movable fuels are consumed. The behaviour of CLT delamination and charring as well as the performance of gypsum boards in fire are also discussed.
With new engineered timber products such as cross-laminated timber becoming more prevalent, this study evaluated the current knowledge of tall timber construction to identify gaps in knowledge, and where if fulfilled, will provide a better understanding of the potential fire safety performance of tall timber buildings.
The study identified a number of knowledge gaps, of which most were related directly to the new technology of engineered timber products that have resulted from the use of CLT. These included system-level fire testing, use of composite assemblies, CLT char fall-off and construction fire safety. The study concluded that the priority for future research should target three areas of research, being the contribution of exposed timber to room fires; connections between timber components and timber composite assemblies; and penetrations for building services.
As timber buildings are constructed taller, architects and building owners are asking for more timber to be exposed. Addressing how exposed timber and in particular cross laminated timber, influences a fully developed fire through to self-extinguishment is a current and complex fire safety issue. There is limited research available on how exposed timber alters heat release rate, temperatures and fire duration. This paper provides a summary of the relevant research to understand similarities in findings and how the results of fire tests can be applied. Research shows that large areas of exposed timber has a significant impact on heat release rate, but limited areas of exposed timber can be accommodated within a fire safe design. The location of exposed timber and avoiding two or more adjacent exposed surfaces, is an important finding. It is evident from the limited testing that a single exposed timber wall of approximately 20% of the total wall area has little impact on a compartment fire. The development of a calculation methodology to account for the change in compartment fire dynamics when two or more surfaces are exposed is the next step in the advancement of exposed timber fire safety engineering.
