Assessment of UBC Seismic Design Provisions Using Recorded Building Motions From Loma Prieta and other Earthquakes

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This is a post-event investigation project to learn engineering lessons from the Loma Prieta earthquake (October 1989). Response data from this earthquake, together with recorded motions from other earthquakes, provides an excellent basis for evaluating seismic design procedures in the Uniform Building Code (UBC). With this objective in mind, this project considers several buildings (one in Watsonville and three in San Jose) where such strong motion records are available. A system identification method (named MODE-ID) will be applied to estimate normal modes of vibration. For each building, the optimal estimates of the model forces, overturning moments, interstory drifts, and lateral forces and torsional moments at each floor level throughout the building will be made. The variation of these quantities, together with the modal periods and damping ratios, over the range of excitation levels will be assessed. These results will be correlated with: (1) the building's type of lateral force resisting system; (2) the vertical irregularities in the building; and (3) the building's observed seismic performance during each earthquake. This information will be used to assess procedures and design parameters in the current (1988) UBC and the version of the UBC that was used in the building's original design. This effort will provide a critical assessment of the validity of the existing UBC seismic design provisions based on the real-world field performance data.