Shaking table tests on RC frame with dissipative bracings

The use of dissipative bracings in R.C. frames is of particular interest in seismic-prone European and Mediterranean countries for retrofit of existing buildings designed according to non-seismic specifications or old seismic codes, without a capacity design approach and therefore lacking ductility. The supplemental damping offered by the dissipative bracings allows the reduction of the ductility demands in R.C. structural members and thus can significantly reduce their damage. However, most of the experimental research carried out in recent years concerns the use of dissipative bracings in steel structures. This paper describes shaking table tests carried out on a one-bay, two-storey, full-scale spatial R.C. frame equipped with two different types of dissipative braces: fluid viscous dampers atop chevron braces, or buckling restrained braces along the diagonal. Tests were also conducted on the same frame without supplemental damping devices. Scope of these tests was the experimental verification of the effectiveness of dissipative braces in the retrofit of existing R.C.-framed buildings. Shaking table tests were conducted at increasing PGA levels. Various measurements were taken to monitor both overall as well as localized structure behaviour. Results demonstrate that the introduction of these devices could lead to the dissipation of up to 95% of input energy, thereby considerably reducing the ductility requirement of R.C. elements. A reduction of inter-storey drift of at least 50% was observed with all the dampers, in comparison with the bare frame. For example, in one case, the maximum interstorey drift in the test at PGA=0.23g was 0.29%, well below the limit of 0.5% usually given by the standards as the SLS limit to avoid damage to masonry infills.