Fire safety of greener, hybrid buildings explored in new study

Photo caption: UC Associate Professor Anthony Abu is leading hands-on research into the fire safety of hybrid timber-steel buildings.

Led by University of Canterbury (UC) | Te Whare Wānanga o Waitaha Structural Fire Engineer Associate Professor Anthony Abu, the research team hopes to resolve fire safety concerns that have so far restricted the wider adoption of hybrid timber buildings. 

“We believe our research programme can remove the fire safety barrier preventing hybrid timber-steel construction from becoming mainstream, and as a result improve housing affordability and supply and reduce carbon emissions by over 1 million tonnes annually as mass timber replaces high-emission materials,” Associate Professor Abu says.

His team plans to carry out world-first experiments in a controlled fire laboratory at UC to develop new engineering design methods and guidelines that improve fire resistance and allow timber walls and floors to be safely combined with steel-frame construction.

Associate Professor Abu says, if successful, the project could lead to a $1.2 billion boost to the domestic timber processing industry rather than the current $199 million gained from raw log exports, driving job opportunities in the regions and boosting economic growth. It would also make the construction industry more sustainable by driving demand for renewable plantation forests. 

“The outcome we want for New Zealand is a thriving, high-value domestic timber processing industry supporting safer and more sustainable hybrid timber buildings,” Associate Professor Abu says.

“One of the most pragmatic uses for mass timber products is in hybrid timber-steel buildings which combine economical design and construction practices with sustainability benefits,” he says.

Currently, a combination of steel and concrete is commonly used in construction because of uncertainties about the structural safety of hybrid timber and steel-framed buildings in intense fires. This has restricted their popularity despite the lower costs of using timber and the fact that it’s more sustainable than concrete.

Associate Professor Abu’s team, which includes UC Civil and Natural Resources Engineering Lecturer Dr Paul Horne and UC School of Forestry Senior Lecturer Dr Hyungsuk Thomas Lim, is currently working on a study funded by the Building Research Association of New Zealand (BRANZ), investigating the performance of cross laminated timber (CLT) floors in combination with steel beams as a safer and more sustainable building option. 

Associate Professor Abu hopes this project, which is in partnership with Christchurch engineering firm PTL Structural and Fire, will be expanded with additional funding from the Government. He says this would allow the team to explore in more detail how timber products, which are more sustainable than concrete, can be used more widely in construction.

“What makes financial sense, and to some extent engineering sense, is to progressively increase the amount of timber used in the building industry. However, we need to get fire safety and structural performance right before that can happen.”

While the fire resistance of steel and timber has been established individually, there are unknowns in how heated steel beams and columns will interact with timber elements when they are loaded and exposed to a fire and uncertainties around the whole-structure performance. “The two materials will expand differently when we heat them up so that can be an issue at those interface points where they connect. The compatibility of the two materials is a key issue that we want to investigate further,” he says.

The research team will build a series of structures in the Fire Engineering Lab at the University of Canterbury to test and monitor their performance in a fire. These will include small-scale studies using segments of different types of timber; medium-scale studies that will involve bedroom-sized compartments; and finally, a full-scale building to test fire dynamics and structural integrity.

Associate Professor Abu says the team will use comprehensive experimental testing, advanced modelling and industry collaboration to provide the evidence, design tools and guidelines needed to help hybrid timber-steel construction become standard practice.