This paper describes numerical modelling to predict the fire resistance of engineered timber-concrete composite floor systems. The paper describes 3D numerical modelling of the floor systems using finite element software, carried out as a sequential thermo-mechanical analysis. Experimental testing of these floor assemblies has also been undertaken to validate the models, with multiple full scale tests conducted to determine the failure mechanisms and assess fire damage to the system components. The final outcome of this research is the development of simplified design methods for calculating the fire resistance of a wide range of engineered timber floor systems, as part of a larger research project on multi-storey timber buildings.
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.
This article summarizes the design procedures for ensuring fire safety in cross laminated timber (CLT) buildings in Australia and New Zealand, with reference to the Building Codes in both countries. New Zealand and Australia are located close together geographically and have similarities in some areas of building control, but prescriptive code requirements are often very different. There is a small but growing local CLT industry, but CLT materials for large projects are imported from Europe.
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