Seismic testing of unreinforced masonry building with flexible diaphragm.

摘要

Appendix 1 of the Uniform Code for Building Conservation (UCBC) presents a systematic procedure for the evaluation and seismic strengthening of unreinforced masonry (URM) bearing wall buildings having flexible diaphragms. However, even though this procedure is founded on extensive component testing, full scale testing of an entire 3-D building having wood diaphragms has not been conducted. Such a test would complement the computer simulations and small-scale shake table tests done by other researchers. For those reasons, a full-scale one-story unreinforced brick masonry specimen having a wood diaphragm was subjected to earthquake excitations using pseudo-dynamic testing. The specimen was designed to better understand the flexible-floor/rigid-wall interaction, the impact of wall continuity at the building corners and the effect of a relatively weak diaphragm on the expected seismic behavior. The unreinforced masonry walls of this building were also repaired with fiberglass materials and re-tested. The dynamic response of the shear walls with piers having a rocking and/or a sliding behavior is analyzed, as well as the response of the wood diaphragm and its interaction with the shear wails. These results are compared with predictions from existing seismic evaluation methodologies and demonstrate how fiberglass strips can be used to improve the rocking behavior.; Furthermore, for masonry walls subjected to out-of-plane seismic forces, while it is required to anchor the wall at every floor as a minimum, questions arise as to whether it is also necessary to retrofit the walls between floors. Notably for the facade of many older (circa 1900) residential buildings in North America 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 partly answer these questions, three specimens were extracted from an existing building, and were tested using a shake table, submitting them to multiple ground motions of progressively larger intensity until structural failure. Different retrofit methods to increase out-of-plane stiffness and strength were investigated, and various analytical procedures to explain the observed behavior are discussed.