Masonry-infilled RC frames strengthened with cross-laminated timber panels

Abstract

Southern regions of Europe are characterized by presenting a large number of existing buildings with reinforced concrete (RC) structures with masonry infills. From a structural point of view, they are characterized by one-way RC frames, with poor structural details and masonry infills, contributing to the high seismic vulnerability of these constructions. Current retrofitting technologies, such as reinforced concrete jacketing of columns, concrete shear walls or FRP wrapping, could be effective but require the occupants' relocation, available perimetral space and legislative constraints. The use of CLT panels, as an innovative retrofitting technique, seems to be a reasonable alternative for existing buildings given their easy and fast assembly, high performance and reversibility. This paper presents a numerical analysis to evaluate the seismic behavior of masonry-infilled RC portal frames strengthened by an external CLT panel. The 20 cm thick masonry wall was represented by two nonlinear diagonal elements with a multi-linear plastic constitutive law, including a Pivot hysteresis type in the axial direction. On the other hand, the 100 mm thick CLT panel was modeled through an orthotropic elastic shell-element. The study comprises four different connections between the RC frame and CLT panels. These connections are modeled through nonlinear Pivot links in both uplift and lateral directions. Their cyclic response, including degradation parameters, effective stiffness and force-deformation envelope curve, was calibrated based on previous experimental results. Numerical results confirm that CLT panels can be an efficient strengthening solution to increase the initial stiffness, as well as energy dissipation, while decreasing the impact of strength degradation on the response of masonry-infilled RC frames against in-plane quasi-static cyclic loading.