Effectiveness of isolated vertical extension of masonry buildings as nonconventional TMD

In this paper, the strategy of Intermediate Isolation System (IIS) is proposed for the vertical extension of an aggregate of masonry buildings located in Pozzuoli, south Italy. The effectiveness of IIS working as a nonconventional Tuned Mass Damper (TMD) for the existing construction is assessed in terms of reduction of seismic demand and damage in the masonry structure undergoing inelastic deformation under seismic input. For this aim, a general step-by-step procedure is first defined and then applied to the case study building. In particular, the characterization of dynamic behaviour and seismic capacity of the building aggregate is first addressed through modal and push over analyses. Elastic parametric analyses are then carried out on lumped mass models to derive the so-called nonconventional TMD design spectrum and to define the design configurations of the isolated vertical addition that minimize the global seismic response of the overall structure. The effectiveness of the retrofit solutions is evaluated and compared to the AS-IS structure through nonlinear time history analyses; structural performance indexes accounting for both peak response and accumulated damage are defined and utilised for this purpose. The results of the time history analyses show that when the masonry structure rests in the elastic field, the displacements in the existing structure decrease, particularly for IIS solutions characterised by low-medium periods. When the masonry exhibits nonlinear behaviour, the effectiveness in terms of displacement reduction is not as significant as in the elastic range but the accumulated damage in the masonry structure is always mitigated.