Influence of Point-Supported Steel-to-Timber Interface Parameters on the Structural Fire-Resistance of Mass Timber Plates

Point-supported connections are an innovative modern connection design that can benefit from the 2-way structural action of cross-laminated timber (CLT) slabs, which is typically not considered in traditional timber design. It also allows for flatter ceiling surfaces where no beams are needed to support the mass timber floor slabs. In an attempt to better understand the structural behaviour of this type of connection in fire conditions, preliminary unloaded fire tests were conducted to evaluate their thermal performance. The test results indicated that, for these tested configurations, the presence of steel connection components does not inherently increase charring rates within adjacent mass timber elements. While the outcomes provided valuable insights on the thermal performance of such assemblies, their actual mechanical behaviour under structural loading in fire conditions remains unknown. This paper presents the results of two structural fire-resistance tests under load: Test 1 had the gap fully exposed to fire, and Test 2 had the gap protected by a firestop. Neither assembly reached failure during the 2 h of standard fire exposure, while the target load could not be fully maintained to the end of the tests. Test 1 experienced charring at the CLT-steel plate interface, while Test 2 did not. Their mechanical behaviours were also similar. Lastly, a preliminary design approach is being proposed, although it requires further validation.