Fire Resistance of Connections Using Steel Plates and Mechanical Fasteners in Timber Structures

This paper describes a series of experiments to obtain the embedment strength of wood at elevated temperatures. The results will be used in Johansen's yield equations to predict the fire resistance of nailed, screwed, and bolted timber connections. To date, Johansen's yield equations have only been used at ambient temperatures. Embedment strength varies with temperature. Recent studies have proposed a tri-linear relationship for bolted connections in LVL and this research extends the investigation to determine if the model is accurate for other types of connections. Bolts, nails and screws were tested by loading in shear through exposed steel side plates. Two different heating regimes were used. The results from short-term heating tests (Part 1) and longer-term heating tests (Part 2) show very different answers. The two hour heating tests (Part 1) showed a tri-linear decline of the embedment strength, as found by earlier experiments, while the longer-term oven tests (Part 2) shows a more linear decline. The difference is attributed to different moisture profiles in the wood. Afire test (Part 3) was carried out on a screwed connection and the results compared with predictions using the experimentally determined embedment strengths in Johansen's equations. The paper shows how this information can be used in design of timber fasteners for fire resistance. A proposal for the degradation of the embedment strength of bolted, screwed and nailed connections is made based on the results of the longer-term oven tests. Such proposal could be included in current codes of practice such as the Eurocode 5 Part 1-2 which do not explicitly provide any relationship for the embedment strength under fire conditions.