An innovative timber system for the seismic retrofit of unreinforced brick masonry buildings

A new timber-based seismic retrofit technique was investigated at the EUCENTRE laboratories (Pavia, Italy) within an extensive experimental campaign on the vulnerability of existing Dutch unreinforced masonry (URM) cavity-wall terraced houses. These structures typically consist of a single-wythe, calcium-silicate-brick inner leaf with load-bearing function, and an external clay-brick veneer with no structural purposes, connected to each other by steel ties. The first floor is usually built with precast reinforced concrete slabs, while the second floor and roof often consist of timber joists and planks. The main objective of the retrofit was to improve the seismic capacity of Dutch URM terraced houses with a light, cost-effective and low-invasive intervention. The proposed retrofit system included timber frames fastened to the internal surface of masonry piers and to the building floors, on which oriented-strands boards (OSB) are nailed. The retrofit was designed to increase both in-plane and out-of-plane capacities of masonry piers as well as to improve the overall connections between masonry elements and floor diaphragms. After performing quasi-static in-plane cyclic tests on two calcium-silicate URM piers, two identical full-scale two-storey buildings were tested dynamically on the shake-table, one in bare and the other one in retrofitted configuration. This paper focuses on the experimental performance of these buildings, with emphasis on the improved seismic response of the specimens, and proposes simple design equations.