This work package is aimed to the development of design rules and to the specification of modelling parameters for steel moment resisting frames characterised by connections equipped with friction dampers. The following design issues will be investigated:
- Design criteria for gravity loads at ultimate limit states;
- Design criteria for serviceability limit state requirements under seismic actions;
- Design criteria for ultimate limit state requirements under seismic actions;
- Design criteria for structural robustness;
- Sustainability analysi
In particular, regarding gravity loading conditions, the attention will be focused on how the structural detail of the friction damper has to be calibrated in order to allow the exploitation of the bending resistance of the beam section.
Regarding serviceability requirements, attention will be paid on the need to reduce the deformability of the involved joint components aiming to reduce as less as possible the lateral stiffness of the structure, because of a semi-rigid behaviour of the connections.
Regarding ultimate limit state requirements under seismic actions, the stroke end limit state is mainly of concern. Therefore, particular attention will be devoted to the setting up of a design procedure to calibrate the stroke of the friction dampers as a function of the maximum design spectral acceleration expected with reference to the collapse prevention limit state.
Finally, with reference to structural robustness, it has to be underlined that, because of the specific behaviour of beam-to-column connections equipped with friction pads, significant benefits are expected in the catenary action resulting, as example, in case of a column loss due to blast loading or impact loading. In fact, the slippage of the friction dampers up to the stroke end, before the bolt engage in shear and the stem plate engage in bearing, allows to obtain an increased vertical component of the beam axial forces resulting from catenary behaviour after column loss. Therefore, it is expected a significant improvement of the structural behaviour under exceptional actions. To verify the expected connection behaviour, experimental impact tests will be carried out on joints. The test setup used in the experiments will consist of a very stiff structure anchored to the slab and connected to a rigid “flying column”, where the impact force is applied through a pneumatic driven cylinder (Figs. 4-5). The tested specimen is subjected to a dynamic bending moment thorough the arm of the “flying column”. The pneumatic cylinder was designed to work with a maximum operating pressure of 30 MPa in a period lower than 1 sec. Maximum strain rates of 500/sec are applied in the joint . During the impact tests, force, displacements, accelerations and strains are measured.
Equipment for impact tests.Example of impact test on a joint: a) initial; b) 1 ms after bolt fracture; c) 2.5 ms after fracture.
Furthermore, theoretical and/or numerical models to consider the behaviour of the proposed innovative connections under exceptional actions will be developed within this work package.
In addition, it is believed that the proposed structural typology provides a significant benefit not only in terms of initial cost and structural performance, but also in terms of sustainability due to the fact that all the structural parts do not undergo to any damage after an earthquake. Therefore, also the building sustainability issues will be examined demonstrating the increased sustainability with respect to traditional solutions.