FRICTION JOINTS EQUIPPED WITH SPRAYED ALUMINIUM DAMPERS (original) (raw)

The design of modern seismic resistant structures is based on the selection of the so-called dissipative zones which have to provide, through their plastic engagement, the dissipation of the earthquake input energy. Dealing with Moment Resisting steel Frames (MRFs) it is well known that, according to Eurocode 3 [2,4], they can be designed either following the full-strength criterion or the partial-strength criterion. The first approach is based on the possibility of dissipating the seismic input energy at the beam ends, the second one concentrates damage in connecting elements and/or panel zones. The application of partial strength joints to MRFs has been supported in last decades by a high number of research programs both theoretical and experimental devoted to characterize the behaviour of connections under monotonic and cyclic loading conditions . Nevertheless, even though the effort provided by the scientific community has already been significant there are still some issues which deserve further investigation, such as the development of design criteria for dissipative joints or the development of new types of dissipative connections. Within this framework, in this paper, a new strategy to provide partial strength joints with high dissipative capacities is proposed. In particular, it is suggested to modify the classical detail of Double Split Tee Joints (DST) by introducing a friction damper at the level of the lower beam flange. With the proposed layout, under bending actions, the joint is forced to rotate around the upper T-stub and the energy dissipation supply is provided by the slippage of the lower beam flange on the layers of friction materials. In this way, provided that the steel components of the connection are properly overstrength, the joint resistance and rotational capacity can be easily governed by calibrating the preload applied to the frictional interfaces and realizing slotted holes with an adequate length on the beam flange. In order to validate the proposed approach, within this paper, the results of an experimental programme are presented. In particular, the results of the preliminary tests aimed to characterize the properties of the employed frictional materials are described and, afterwards, the results of two tests on real-scale external beam to column joints are presented. Furthermore, a procedure based on the component method adopted to design the specimens is described, evidencing the possibility to easily control the design of the proposed connection in order to concentrate the energy dissipation in the friction damper and to prevent from plasticization all the other joint components. Within the experimental activity described in this paper two different joints characterized by the application of the friction damper previously tested under uni-axial loading conditions have been tested. In particular, the two joints fastening an HEB 200 column to an IPE 270 beam are both made of steel S275. In the paper they are identified in the following way: