In Situ Out-of-Plane Testing of As-Built and Retrofitted Unreinforced Masonry Walls

Abstract

The out-of-plane behavior of as-built and retrofitted unreinforced masonry (URM) walls was investigated by conducting in situ static airbag tests in four buildings. The age of the buildings varied from 80 to 130 years, and all but one were constructed using clay brick masonry with timber floor and roof diaphragms. The fourth building was a reinforced concrete frame structure with precracked clay block partition walls in addition to partition walls that appeared undamaged. The test program was composed of testing five one-way vertically spanning solid URM walls from the group of three URM buildings and testing four two-way spanning URM partition walls from the reinforced concrete frame building. All walls were tested with their original support conditions, but three one-way spanning walls were additionally retested with modified support conditions. These additional tests allowed the effects of wall support type to be investigated, including the influence of a concrete ring beam used at the floor levels and the influence of wall-to-timber diaphragm anchorage by means of grouted steel rods. Several walls were next retrofitted by adding either near-surface mounted (NSM) carbon fiber–reinforced polymer (CFRP) strips or NSM twisted steel bars (TSBs) and were then retested. A comparison between the results of the tests on as-built walls and the tests conducted on retrofitted walls suggests that the simple retrofit techniques that were used are suitable for URM wall strengthening to ultimate limit state (ULS) design. The test results in two buildings highlighted significant inherent variability in masonry material properties and construction quality, and recommendations were made for the seismic assessment and retrofit of URM walls. An analytical trilinear elastic model especially useful when assessing the dynamic stability of cracked one-way spanning walls proved to satisfactorily predict the maximum wall strength, excluding those walls that developed arching action.