Mechanical Characterization of Energy Dissipation Devices in Retrofit Solution of Reinforced Concrete Frames Coupled with Solid Wood Panels

Abstract

Deep renovation interventions on existing buildings remain currently unattractive due to technical, financial and cultural/social barriers. Now that the European Union 2018Energy Performance Directive aims to "reach the long-term greenhouse gas emission goal and decarbonize the building stock", Member States may use their long-term renovation strategies to address risks also related to fire hazards and seismic loads in addition to energy renovation. This opens a wider market for innovative approaches in retrofit of existing buildings.The current paper illustrates the primary outcomes of an ongoing multidisciplinary Horizon 2020 research project (called e-SAFE), tackling the integration of energy, seismic and architectural renovation interventions through an innovative and combinable technological solution, applicable to non-historic RC framed buildings (i.e. built after 1950) and easily adaptable to specific climatic conditions, seismicity levels and other boundary conditions. Hence, the proposed solution will contribute to the de-carbonization of the EU building stock, reducing the occurrence of natural hazards related to climate changes, and, at the same time, to the improvement of the social resilience against earthquakes and to the enhancement of buildings architectural image.The seismic retrofit technology consists in the external application of modular prefabricated Cross Laminated Timber (CLT) panels on the existing perimetral walls. These panels are connected to the beams of two consecutive floors by means of friction dampers and provide additional lateral stiffness and strength to the existing structure, thus reducing the storey drift demand in case of earthquake. The friction dampers cut the force transmitted by the CLT panel to the structure and dissipate energy, which further reduce the drift demand. Strength, stiffness and dissipation capacity provided by the system are controlled by modulating the thickness and the number of CLT panels, as well as the friction dampers size.

Experimental Cyclic Response of a Novel Friction Connection for Seismic Retrofitting of RC Buildings with CLT Panels

“…13(i). Both twisting and bending deformations were almost absent during this test, meaning that the reduced eccentricity and the single bend played a vital role in obtaining stable loops, confirming the initial FEM results of Tardo et al (2020). The loop shape presents a corner chipping when the load is changing direction: this is common in asymmetrical friction connections (Loo et al 2014a;Fitzgerald et al 2021) and depends on dragging phenomena of the cap plate.…”

“…This design originated from the simpler production process, faster mounting phase, and a more uniform force distribution between the two aligned bolts. The FEM investigations presented in Tardo et al (2020) evidenced significant deformability of all the previous prototypes with STD shape due to (1) the eccentricity between the points of application of the slip force and the reaction force transmitted by the CLT panel, and (2) the multiple bends that characterize their geometry. Hence, in order to improve the expected performance, the authors developed the ALT prototype.…”

“…Other three different designs were obtained by modifying the STD in order to improve the mechanical behavior and the possible weaknesses evidenced in finite-element modeling (FEM) (Tardo et al 2020). The FEM analysis carried out in Ansys by Tardo et al (2020) on the STD design highlighted significant stress concentrations and deformations around the bend of the bottom profile [Fig. 3(a)], which is the profile that is free to slide.…”

“…The loading condition is not symmetric and the specimen presents a complex shape. Therefore, the authors expect the occurrence of a certain deformation level; see Tardo et al (2020) and Hatletveit (2020) for FEM analyses of the specimen. The testing procedure was the following: the bottom profile was mounted on the right column and the top profile was mounted on the T-element.…”

“…The system proposed by the authors is called e-CLT (Fig. 1) and consists of installing a CLT panel from the outside of the building while leaving the masonry infills unchanged, without discomfort for the people living inside the building (Tardo et al 2020). CLT panels have light weight (around 470 kg=m 3 ), thus not increasing too much the mass of existing buildings.…”