Experiments on fire-protected and hot-dip galvanised steel bolted connections

Connections are of high significance in the stability and integrity of steel structures. Connections play a key role in structures exposed to fire because they are supposed to support the entire elements against a variety of loads. In steel beams, a connection is generally implemented to join (at least) two perpendicular members. A thorough understanding of the heat transfer in structural members is a prerequisite to a reliable design. In the case of R30 requirements, a large number of members can be left unprotected if they are hot-dip galvanised. If hot-dip galvanising of a structure is not sufficient to provide required fire resistance, one part of the structure could be hot-dip galvanised while another part to be protected with a reactive fire protection system. When connecting a protected beam to an unprotected hot-dip galvanised beam, information regarding the heat transfer between these beams is required. Additional heating in a connection due to hot dip galvanisation needs to be taken into account when verifying the load-bearing capacity of the component protected by reactive fire protection according to EN 1993-1-2. This study investigates the effect of heat development and transfer in full-scale steel I-beams from a hot-dip galvanised secondary beam to an intumescent-coated main beam through various bolted connections such as fin plates, double angles, and stiffeners with lugs. Fire protection was applied to the main beams, while the secondary beams were hot-dip galvanised. A thorough experimental, numerical and theoretical study was implemented as presented in this paper, the results of which are deemed to provide significant input into improving safety, hence mitigating the risk of steel beams.