Finite element study on the behaviour of free from damage connections under fire

The free from damage connection, developed during the recent RFCS FREEDAM has shown to be a promising solution to dissipate high amounts of energy due to its sliding system given by the friction damper with slotted holes, located at the lower beam flange. Additionally, this sliding mechanism proved to be also efficient in the event of exceptional loading scenarios such as impact loads or even in column loss scenarios, because it allows the dissipation of part of the action through slipping and, on the other hand, gives an extra “elastic” ductility to the connection since, up to the end of the slip, the components of the connection are designed to remain in the elastic range.

In this paper, this specific behaviour is exploited in the case of fire scenario. During fire events, axial forces can develop in the beams (initially in bending, only) due to the expansion of the steel elements and the restraint provided by the boundary conditions. For the cases where the high axial forces develop, the moment‐rotation behaviour of the connections will change due to the interaction between the axial forces (N) and bending moment (M) as well as the effects due to the increase in temperature. The the use of connections such as the free from damage connection is interesting also from this point of view since it delays the development of great axial forces due to its slipping mechanism. This analysis is carried out through FEM analysis using ABAQUS software.