Dynamic Shake-Table Tests on Two Full-Scale, Unreinforced Masonry Buildings Subjected to Induced Seismicity

This paper presents the results of an experimental campaign which is part of a wider research project, aimed at assessing the seismic vulnerability of buildings in the Groningen region of the Netherlands. The area, historically not prone to tectonic ground motions, has been subjected to seismic events induced by gas extraction during the last two decades. As part of this campaign, unidirectional dynamic shake-table tests were performed at the EUCENTRE laboratory on two full-scale, unreinforced masonry buildings, designed without specific seismic considerations or detailing. The first specimen simulated the end-unit of a two-story terraced house, built with unreinforced masonry cavity walls. These walls were composed of an inner load-bearing leaf, made of calcium silicate bricks supporting the floors, and an outer veneer, made of clay bricks with aesthetic and weather-protection function. The floors consisted of reinforced concrete slabs, providing rigid diaphragms; the pitched roof was made of longitudinal timber beams, supported by end gables perpendicular to the shaking direction, and wood boards. The second specimen represented a one-story detached pre-1940's house, built with double-wythe unreinforced clay masonry walls. The structure included large openings and a re-entrant corner, causing significant horizontal irregularities; the two facades perpendicular to the shaking direction simulated two common gable geometries. The first floor was made of timber beams and planks, resulting in flexible diaphragm; the steep-pitch roof consisted of timber trusses connected by wood purlins and boards. Two similar incremental dynamic tests were performed up to the near-collapse conditions of the two buildings; the selected input ground motions represented realistic scenarios of seismic events for the examined region. This paper summarizes the main characteristics of the two specimens and the shake-table experimental results, illustrating the evolution of the damage mechanisms and the hysteretic response of the structures.