Shake Table Testing of a Half-Scaled RC-URM Wall Structure

Abstract

With the introduction of higher seismic design forces in the Swiss loading standard of 2003 most unreinforced masonry (URM) buildings fail to satisfy the seismic design check. For this reason, in new construction projects, a number of URM walls are nowadays replaced by reinforced concrete (RC) walls. The lateral bracing system of the resulting structure consists therefore of URM walls and some RC walls which are coupled by RC slabs and masonry spandrels. The same situation characterises a number of seismically retrofitted URM building across Europe in which RC walls are added to the original structure to improve its seismic behaviour. Within the framework of the FP7-SERIES project, a four-storey RC-URM wall structure was tested on the shake table at the EUCENTRE TREES Laboratory (Laboratory for Training and Research in Earthquake Engineering and Engineering Seismology) in Pavia (Italy). The test was conducted at half-scale and is part of a larger research initiative on mixed RC-URM wall systems initiated at EPFL (École Polytechnique Fédérale de Lausanne, Switzerland). The key objective of the testing campaign was to gain insight into the dynamic behaviour of mixed RC-URM wall structures and to provide input for the definition of a performance-based design approach of such mixed structural system. Multiple shaking at increasing intensity was used to test the dynamic behaviour of the examined building. During the final shaking several of the URM walls lost their axial load bearing capacity, however, the structure did not collapse as it was subjected to uni-directional loading only and the axial load was transferred to the RC walls and the URM walls that were loaded out-of-plane. Random noise vibration tests were performed to monitor the elongation of the natural periods induced by the damage progression. The paper presents details on the structural system and the selected ground motion, the test set-up and the instrumentation. Additionally, initial results of the shake table test are presented with a first interpretation of the observed structural behaviour.