Out-of-Plane Seismic Evaluation and Retrofit of Turn-of-the-Century North American Masonry Walls

Three masonry walls with their wood backing were extracted from an old three-story residential building. These specimens are representative of a type of construction widely used in North America circa 1900, in which a single wythe exterior masonry wall was tied only with nails to the timber structure, leaving an irregular gap between the masonry and timber walls. To seismically retrofit such buildings, special seismic-resistant anchorage of the walls would be required at every floor at a minimum. Questions remained, however, as to the out-of-plane resistance of the remaining walls spanning between floors. To partly answer these questions, the three specimens extracted from the existing building were tested using a shake table, submitting them to multiple ground motions of progressively larger intensity until structural failure. These tests have demonstrated that such walls could resist significant out-of-plane inertial accelerations without failure. Performance can be increased by different retrofit methods such as providing anchors at midheight to force the wood and masonry wall to move as a unit, and adding fiberglass strips epoxied to the masonry wall to increase its out-of-plane stiffness and strength.