Insertion of additional viscous dampers for the seismic design of a pre-cast reinforced structure

Precast concrete structures characterised by non moment-resisting frames present a relatively large flexibility (w.r.t. lateral loads) which may lead to a difficult satisfaction of the performance requirements imposed by the regulations, both in terms of resistance and deformability. In this paper, the advantages offered by the insertion of added viscous dampers in such structures with respect to the use of traditional lateral-resisting bracing systems are shown through the illustrative applicative example of the executive design of a shopping mall built in Italy. Firstly, a traditional structural solution is considered which sees the insertion of stiff diagonal steel braces in some specifically selected bays (traditional bracing systems). Secondly, other structural solutions are envisaged which sees dampers inserted into the structure according to different schemes. The results of the numerical time-history simulations show that the solution with viscous dampers makes it possible at the same time to limit the drifts of the structure and to keep the actions in the diagonals and consequently the vertical traction/compression actions on the foundations within acceptable values. This paper also proposes and illustrates two original procedures to be used in the design process using viscous dampers: (i) the first one providing for an effective dimensioning of the damping coefficients of the added viscous dampers, and (ii) the second one providing for the passage from a linear modelling to a non linear modelling for the constitutive law of the viscous dampers which leads to similar performances under same inputs.