Cyclic response of low yielding connections using different friction materials

The experimental activity presented in this work intends to study in detail the cyclic behaviour of a set of three different friction shims preliminary selected in a previous experimental work regarding the behaviour of friction dampers of Sliding Hinge Joints (SHJs). These connections are able to dissipate seismic energy by means of friction through a proper application of capacity design principles. Their bending resistance is proportional to the slip resistance of a friction device which is usually installed at the bottom beam flange and can be governed controlling only two parameters: the friction coefficient and the clamping force of the high strength bolts. The main goal of the experimental campaign presented is to investigate the dependence of the friction coefficient on some of possible significant parameters. In particular, the 51 tests presented are devoted to evaluate the response of the interfaces taking into account the effect of the bolts preloading, the effect of the type of washers and the influence of the random material variability. In detail, the tests have been carried out with four different configurations of washers (with flat washers and disk springs), considering a possible range of values of the clamping forces (between 40% and 100% of the standard proof preload). The results of the experimental activity are reported in the paper proposing a possible definition of the values of the friction coefficients to be used in design and regression analyses of the experimental data of the slip tests to be used in simplified rigid-plastic modelling for seismic analyses.