PSI - Issue 78

Francesca Mattei et al. / Procedia Structural Integrity 78 (2026) 2169–2175

2170

constructed buildings and infrastructure, addressing them in existing structures presents additional complexities, most notably, the high cost typically associated with simultaneously meeting both structural and energy performance requirements. To address this challenge, several systems and materials have been explored over the last decade with the aim of achieving combined structural and energy retrofitting through a single intervention. For instance, Bournas et al. (2018) proposed inorganic textile-based composites coupled with thermal insulation systems for reinforced concrete and masonry envelopes, while Yang et al (2025) developed a lightweight square steel tube frame combined with a hybrid grid shear wall composed of various material strip members. The present research contributes to this research trend by investigating the development, experimental testing, and numerical simulation of an innovative system for the combined seismic and energy retrofit of existing buildings Caprili et al. (2024). Initially conceived for unreinforced masonry structures, the proposed system involves lightly reinforced concrete (RC) walls cast within expanded-clay formwork blocks. The geometry of the blocks is specifically designed to accommodate not only the concrete casting but also the insertion of a Neopor® insulation layer, thus enabling a single intervention to provide both seismic strengthening (through the RC wall) and thermal improvement (through the insulated layer). The research is frame within the collaboration between the University of Pisa and PAVER Costruzioni S.p.A. The current paper presents the experimental results of the first horizontal monotonic loading test conducted on a composite sample comprising the retrofit panel and a masonry wall. This work is part of a broader experimental campaign aimed at validating the proposed system and providing practical guidance to designers for the application of this integrated retrofit solution. The retrofit solution was an update of what already presented in 2011 by Eucentre (2011). 2. System design and preliminary tests The proposed system consists of a lightly RC wall constructed using expanded-clay formwork blocks. The blocks have a thickness of 235 mm allowing for the placement of an internal concrete core, reinforced both vertically and horizontally, and the insertion of an insulation layer ( Fig. 1 ). The retrofit panel is connected to the existing masonry walls only at the levels of the horizontal floors and is supported by its own independent foundation system In this configuration, the RC wall functions as a shear wall, providing lateral bracing against seismic actions, while the existing structure continues to carry the vertical loads.

Fig. 1. Scheme of the proposed block.

The preliminary design of the retrofit panel, detailed in Caprili et al. (2024), considered its application to typical unreinforced masonry walls of two-storey residential buildings from the Italian twentieth-century heritage. The system was dimensioned to include a 100 mm nominal concrete core cast within 235 mm-thick expanded-clay formwork blocks, reinforced with B450C rebars in both directions and incorporating a Neopor® insulation layer. An equivalent continuous RC wall thickness was estimated to accoun t for the discontinuous concrete casting, and the panel’s reinforcement layout, 2 ϕ 6/20 horizontal (two layers) and ϕ 10/25 vertical (single layer), was defined from linear dynamic analyses comparing the pre- and post-retrofit conditions for different wall slenderness ratios. The results confirmed a substantial stiffness increase, a marked reduction in the vibration period, and a redistribution of seismic