The seismic response of three reinforced masonry buildings with flexible diaphragms is investigated, two buildings with instrumentation, and one without. An instrumented three-story building is investigated for its response during the Whittier Narrows (1989), Landers (1992), and Northridge (1994), California, ear thquakes, and the response of an instrumented two-story building during the Loma Prieta (1989) earthquake is presented. Flexibility of the diaphragms of the two instrumented buildings was also stud ied by using the 1997 UBC criteria. Static and dynamic analyses were used to evaluate the code criteria for determining the flexibility of the diaphragms. It was found that for the two inst rumented buildings, the classification of the diaphragm depended largely on the type of loading used in the analyses. A third building studied in this report is a one-story building lacking instrumentation and modeled using ETABS (version 7). Dynamic time history analyses were conducted on this model using a total of 6 sets of ground motions representative of strong ground motions, including motions containing multi- sided displacement pulses. Base shear and displacement time histories suggest that this building would not suffer significant structural damage in an earthquake having similar ground motion characteristics. However, damage to nonstructural components and equipment may occur due to high accelerations.
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