Design of Timber-Concrete Composite Floors for Fire Resistance

This research investigated the fire performance and failure behaviour of timber-concrete composite floor systems currently under development in New Zealand, resulting in a design method for evaluating the fire resistance of these floors with different types of connections. Furnace tests were performed on two full-size floor specimens at the Building Research Association of New Zealand (BRANZ). Both floor specimens were 4 m long and 3 m wide, consisting of 65 mm concrete topping on plywood formwork, connected to double LVL (laminated veneer lumber) floor joists. They were tested over a 4 m span, subjected to a nominal design live load of 2.5 kPa. Both floors were subjected to the ISO 834 test fire for over 60 minutes. Two separate connection types were tested; concrete notches cut into the timber beams with an incorporated shear key, and metal toothed plates pressed between the double beams. It was found that the reduction in section of the timber beams due to the fire governed the failure mode of the floors. The test data and visual observations aided in the development of an analytical model for evaluating the fire resistance of timber-concrete composite floors. This was implemented into a spreadsheet that is able to predict the expected fire resistance of these floors, taking into account some major time dependent variable properties that can have an effect on the overall performance. Load-span tables have been produced to give the estimated fire resistance of floors with differing dimensions, span lengths and applied loads.