Multi-storey Building Retrofit by ADAS- Equipped Braces

Incorporation of dissipative bracing systems is an emerging seismic retrofit strategy for frame structures. Among the several types of devices currently adopted as passive protection elements, Added Damping and Stiffness (ADAS) steel dissipaters have a well-established tradition. This is a consequence of their plain working principle, based on the elastic-plastic behaviour of the constituting plates, as well as of their relatively easy installation. In spite of this, the design of ADAS dampers is not simple, because it requires a proper balance between the addition of energy dissipation and horizontal translational stiffness. An energy-based design criterion is formulated to this aim in this study, which directly relates the total number of plates of the dissipaters to the supplemental damping energy needed to jointly reduce stress states and storey drifts, expressly taking into account the reduction of the fundamental vibration period due to the stiffening effect of the bracing system. A seismic retrofit intervention is demonstratively designed by applying this criterion for a 6-storey building with reinforced concrete structure, an assessment analysis of which shows poor seismic performance capacities. A comparative analysis among three different installation hypotheses of the ADAS devices allows to select the distribution capable of attaining the best performance of the retrofit measure.