Push-and-release tests of a steel building with hybrid base isolation

Experimental testing of a two-storey 5875 square meters steel braced-frame structure resting on a reinforced concrete slab isolated from the foundations through a hybrid system (28 high-damping rubber bearings and 36 low-friction sliding bearings) is presented. The building incorporates a push-and-release device to evaluate its actual global dynamic response up to displacement amplitudes induced by extreme seismic events, allowing test repetitions during its service life. The testing set up and the experimental campaign, consisting of quasi-static push tests (slow loading and unloading) and push-and-release dynamic tests (slow loading and subsequent sudden release), are described. The experimental results have peculiarities related to the building (structural typology and size, foundation geometry on a steep slope, presence of the push-and-release device for future additional tests), the magnitude of the maximum horizontal displacement never achieved before (285 mm and 227 mm in the quasi-static and dynamic tests, respectively), the global and local monitored parameters (horizontal and vertical displacements, strains, accelerations, in addition to environmental conditions) providing a comprehensive insight into the behaviour of the hybrid isolation system and superstructure.