Viscous dampers placed between different portions of the same structure: a case study

Dissipative systems have widely proven their effectiveness in mitigating seismic effects in sheartype structures. This paper presents the results of a case study carried out to verify the effectiveness, for the mitigation of the seismic effects, of placing viscous dampers so that they connect different portions of the same structure (i.e. frame structure and lateral-resisting elements). The case study here developed regards an 18-storey building structure which represents the enlargement of the existing city Hospital “C.A. Pizzardi” in Bologna, Italy. The structure is composed of a central non moment-resisting steel frame characterized by a small horizontal stiffness, which supports essentially the vertical actions, and two external lateral-resisting concrete cores which mainly support the horizontal loads. Two structural solutions have been compared as subjected to 7 groups of artificial accelerograms: the reference model of the structure, in which steel frames and concrete cores are linked through adequate rigid connections; and the model of the structure equipped with viscous dampers which connect the steel frames and the concrete cores at several levels. The comparison of the results obtained for the two models indicate that positioning viscous dampers at the connection between the concrete cores and the steel frames allows to obtain substantial improvement in the seismic performances (roughly 50% reduction in the values of peak top-storey displacements, peak base shears and peak base bending moments). Finally, an economic analysis shows how the savings in the structural members compensate the additional costs of the dampers.