Shake‐table testing of two full-scale URM cavity‐wall buildings: effect of an innovative timber retrofit (EUC-BUILD-6 & -7)

Two full-scale building specimens were subjected to a series of shake-table motions to assess the effectiveness of an innovative timber-based retrofit solution for URM structures. The buildings were identical: they represented the end unit of a two-storey terraced house typical of the Groningen region in the Netherlands. The structural system consisted of cavity walls: the interior load-bearing leaf was made of calcium-silicate bricks, while the exterior leaf was a clay-brick veneer. The first floor was realized with a reinforced concrete slab, while the second floor was made of timber beams and floorboards. A timber roof structure was supported by masonry gables prone to out-of-plane overturning mechanisms. This building typology is particularly vulnerable to earthquake actions due to large openings in longitudinal load-bearing walls and the lack of seismic-proof construction details.

An innovative timber-based retrofit system was designed and implemented in the second building specimen. The intervention aims to increase the in-plane and out-of-plane strength and displacement capacity of masonry piers, thus reducing the seismic vulnerability of this typology of URM construction with a light, cost-effective, sustainable, and reversible approach. The retrofit technique consists of a timber frame mechanically connected through steel fasteners to the masonry piers and building floors. Oriented strand timber boards are then nailed to the frame. Steel ties were added between the cavity-wall leaves. The application of the retrofit system significantly enhanced the overall global response of the building.

The shake-table tests were conducted in 2018 and 2019 at the SHAKELAB testing facilities of the EUCENTRE in Pavia, Italy. They were part of the EUCENTRE Foundation project 'Study of the vulnerability of masonry buildings in Groningen', within the research framework programme on hazard and risk of induced seismicity in the Groningen province, sponsored by the Nederlandse Aardolie Maatschappij BV (NAM). The project was carried out in collaboration with the research group of Masonry Structures from the University of Pavia in Italy.