Deformation and strength-based assessment of damped cable system for seismic retrofit of R/C structures

The damped cable system (DCS) represents an innovative seismic protection strategy, especially attractive for retrofitting existing reinforced concrete structures. This technology is based on inseries coupling of fluid viscous re-centring dampers and pre-stressed steel cables. The cables go through the building stories and exert reaction forces on the floor-slabs, which are in opposite direction to the earthquake loads. Since each cable makes sliding contact with the slabs, its reaction includes the damping force component supplied by the fluid viscous device connected to it. The combination of cable elasticity and device energy dissipation gives rise to a highly performing protection system, characterised by lower architectural intrusion and installation work as compared to traditional rehabilitation techniques. The DCS is currently the subject of a Research and Technological Development Project funded by the European Community. The previous stages of the planned research programme resulted in the assessment of system feasibility, as well as of its preferable fields of application. Afterwards, attention has been devoted to the structural design aspects. Relevant developments, presented in this paper, concern: (a) a mixed deformation/strengthbased evaluation of system performance, with careful control of local stress states, besides member and story drifts; (b) the assumption of an enhanced design objective, according to advanced guidelines for the seismic rehabilitation of buildings; and (c) direct comparisons between the response of frame structures retrofitted by DCS and different protection strategies. These three points are herein discussed with special reference to a four-story frame, selected as one of the basic case study structures in this section of the research programme.