Structural performance of RC frames retrofitted with CLT panels: experimental evidence from the e-CLT system

Abstract

The rehabilitation of Europe’s existing building stock requires integrated solutions that simultaneously address seismic safety, energy efficiency, and architectural renewal. This paper introduces and validates an innovative retrofit system (e-CLT) developed within the EU Horizon 2020 e-SAFE project. The system combines prefabricated Cross-Laminated Timber (CLT) panels with friction dampers, designed to enhance the lateral resistance and energy dissipation capacity of Reinforced Concrete (RC) buildings constructed prior to seismic code enforcement. An extensive experimental program was conducted on full-scale RC frame specimens, including bare, masonry-infilled, and retrofitted configurations, tested under cyclic quasi-static loading. Results demonstrate that the e-CLT retrofit substantially increases initial stiffness and peak strength of the RC frame while providing stable and repeatable hysteretic behaviour. Once activated, the friction dampers dissipate significant amounts of seismic energy, reducing damage to RC elements and preventing brittle failure of infill walls. At drift levels close to collapse prevention limits, the retrofitted system dissipated up to three times more energy than the unstrengthened counterpart. The findings confirm the structural reliability of the e-CLT system, highlighting its potential as a multifunctional retrofit solution for the large-scale renovation of vulnerable RC buildings across seismic prone aeras.