Seismic out-of-plane repair and strengthening of masonry infill walls using timber strong-backs

The study experimentally investigates a repair and strengthening solution that utilises vertical timber strong-backs, originally developed for strengthening masonry walls, to improve the out-of-plane performance of masonry infills in RC structures. The strong-backs are fixed to an RC frame and masonry infill surface using mechanical or adhesive point-to-point connections. The strengthening scheme is coupled with a ventilated cladding system having an insulated facade to combine a reduction of the seismic vulnerability of existing masonry infill walls, improve the energy performance of the building, and enhance the aesthetic appearance of the exterior. The proposed solution aims to provide an easily integrable and cost-effective seismic improvement for masonry infills, which can be seamlessly incorporated into energy efficiency upgrades. The out-of-plane behaviour of as-built and strengthened masonry infill walls was investigated by conducting full-scale static airbag tests. The infills were subjected to semi-cyclic out-of-plane loading via the application of a uniformly distributed force, using inflated airbags to simulate the inertia force induced by an earthquake. Ten different wall specimens were tested in the as-built and strengthened conditions, with the improvement in out-of-plane seismic capacity being assessed and the performance of the strengthening scheme for different types of infill walls being investigated. The retrofit solution proved to be highly effective in all analysed scenarios with improvements in lateral capacity exceeding 100 %. The seismic response of the non-structural layers was also analysed via specific testing, demonstrating that these layers can withstand the deformation observed for the retrofitted infills and hence proving the safety of the whole integrated retrofit system.