A DISSIPATIVE FRICTION DEVICE FOR HYBRID STEEL-TRUSSED-CONCRETE BEAM TO COLUMN CONNECTION

The most recent design strategies of multi-storey framed structures are increasingly welcoming the adoption of innovative techniques for the seismic energy mitigation, in order to guarantee a highly dissipative global behaviour able to prevent the structure from collapse with consequent loss of human lives. In particular, there is a large interest in the study of those devices able to absorb the whole seismic energy avoiding the damage of the primary load-bearing structural elements connected to the device, which could irreversibly damage after a violent seismic event, resulting in extremely high economic costs for their structural repair. In this context, steel frames are often equipped with dissipative beam to column connection, able to avoid any plasticization on the structure. In order to avoid interruption of use, the device include re-centering system, that avoid appreciable residual displacement at the end of the seismic event. In reinforced concrete structure, only few dissipative beam to column connections have been developed for precast element, while the use of such devices for steel concrete hybrid frames have not been extensively investigated. In the last thirty years, Hybrid Steel-Trussed-Concrete Beams (HSTCBs) have been widely used in civil and industrial building. HSTCBs are often designed to exploit the steel reinforcement made up of an encased steel truss in order to cover large spans with reduced depth. In such cases, a large amount of steel reinforcement is required within the panel zone which is often made using large diameter rebar. These features make both the end of the beam and the joint potentially vulnerable to the effects of cyclic actions induced by the earthquake and dramatically reduce the dissipation capacity of the entire structure. For this purpose, the present work investigates the introduction of friction dampers in the HSTCB-to-column joints of framed structures in seismic areas, adequately designed for their application on R.C. frames. The use of friction devices prevents the main structural elements from damage and limits the cracking of the panel zone thanks to the increase of the bending moment lever arm transmitted by the beams, which reduces the shear forces in the joint. The feasibility study is firstly conducted through the development of design criteria for the pre-dimensioning of the device and, successively, the proposed solution is validated through the generation of finite element models.