Investigation on friction features of dissipative lap shear connections by means of experimental and numerical tests

Background: Beam-to-column joints equipped with friction dampers are a viable solution to improve the dissipative capacity of moment Resisting Frames without any damage after severe seismic events. Recently, novel systems have been developed within the RFCS FREEDAM research project. Objective: The objective of the work is to provide a rational selection based on engineering judgment, of possible materials to be used in friction dampers. Methods: Both experimental analysis and Finite Element (FE) simulations have been carried out to assess the friction coefficients of several interfaces evaluating also their ability to withstand cyclic loading histories. Results: The experimental campaign showed that both hard and soft metals can be used in combination with stainless steel obtaining satisfactory performance under cyclic loads. In addition, at high slip velocities, large temperatures are developed within the specimen. Modelling this effect is crucial as it causes a reduction in the slip force capacity. This is due to the transverse dilatation that initially increases the pressure, while bolt tightening reduces due to elongation of the shank. Conclusion: The experimental results, together with other similar data selected from technical literature, have been employed to validate FE models able to simulate the behaviour of lap shear friction connections, showing the influence of different modelling approaches over the simulated data. Subsequently, the validated model has been used to perform a set of simulations devoted to highlight the key parameters affecting the response of the lap shears and the possible strategies to improve the performance of the friction dampers.