Seismic Strengthening of URM Buildings by Steel Bracing

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This project is supported under the Phase II (Second Year) program of the Seismic Repair and Rehabilitation Initiative (NSF 90- 23). There is a large inventory of older reinforced masonry (URM) buildings located in high seismic regions throughout the country which were not designed and detailed for adequate lateral strength and ductility as per current code standards. These buildings pose the greatest life hazard during moderate or severe earthquake, as attested to by damage suffered by many of such buildings during the 1987 Whittier earthquake and the 1989 Loma Prieta earthquake. A number of these buildings are being evaluated and strengthened using several different techniques, steel bracing and being one of the widely used schemes. However, there has been no experimental study on the seismic behavior of masonry wall-bracing systems under severe cyclic deformations and on rational procedures for their design which will ensure satisfactory performance during a severe earthquake. A joint cooperative research effort is conducted to study the in-plane seismic behavior of masonry (URM) walls strengthened with steel bracing. The objectives are to evaluate, through testing and analysis, currently used philosophy and design procedures, and to develop improved methods for strengthening existing buildings by using ductile steel bracing systems to enhance their safety during future earthquakes of severe "design level" intensities. The findings of the proposed study will be useful for formulation of code requirements for evaluation and strengthening of existing URM buildings.