The Italian building heritage is aged and inadequate to the high-performance levels required nowadays in terms of energy efficiency and seismic response. Innovative techniques are generating a strong interest, especially in terms of multi-level approaches and solution optimizations. Among these, Nested Buildings, an integrated intervention approach which preserves the external existing structure and provides a new structural system inside, aim at improving both energy and structural performances. The research presented hereinafter focuses on the strengthening of unreinforced masonry (URM) buildings with cross-laminated timber (CLT) panels, thanks to their lightweight, high stiffness, and good hygrothermal characteristics. The improvement of the hygrothermal performance was investigated through a 2D-model analyzed in the dynamic regime, which showed a general decreasing in the overall thermal transmittance for the retrofitted configurations. Then, to evaluate the seismic behavior of the coupled system, a parametric linear static analysis was implemented for both in-plane and out-of-plane directions, considering various masonry types and connector spacings. Results showed the efficiency of the intervention to improve the in-plane response of walls, thus validating possible applications to existing URM buildings, where local overturning mechanisms are prevented by either sufficient construction details or specific solutions.

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Some strengthening techniques, aimed to increase the infill Out-Of-Plane (OOP) resistance and its safety against OOP collapse, have been recently tested at the University of Padova. Based on this experimental work, a new infill macro-model consisting of two nonlinear fibre struts for each diagonal direction, able to predict the combined In-Plane/Out-Of-Plane (IP-OOP) seismic response of the panels, is proposed in this paper and calibrated on the abovementioned experimental results for thin clay masonry panels strengthened by two external plaster layers, directly applied on the masonry surface, containing a biaxial basalt fibre grid. These macro-models were then used to carry-out parametric nonlinear static analyses on typical reinforced concrete infilled frames, designed both traditionally and seismically, with the aim of evaluating their lateral response both in the case of IP forces only (by assuming two force distributions applied to the frame) and in the case of IP-OOP combined forces (by applying OOP equivalent static forces to the panels). The main effects of the OOP forces are presented through pushover curves and drift profiles associated to the achievement of the various infill and frame limit states. Numerical results show the effectiveness of the infill strengthening in terms of improvement of the infills OOP performance and thus of the overall structural response.

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