Implications of Measured Near-Field Ground Motion for Structural Response

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9416174 Iwan The objective of this project is to determine the nature and importance of potentially serious structural response problems associated with near-field earthquake ground motions such as those observed during the Northridge earthquake. Measured near- field ground motions from the Northridge earthquake indicate very high velocities and pulse-like ground displacements. These motions are capable of causing high levels of demand for a wide range of different types of structures including base-isolated buildings and multi-story buildings. The high velocity pulses observed in the near-field of the Northridge earthquake are of great concern for the performance of taller multi-story buildings. The stress waves in the structure that are caused by these high velocities can result in very high story drift that may, in turn, cause failure of structural elements. Preliminary indications are that story drifts induced by near-field velocity pulses during the Northridge earthquake may have significantly exceeded the code allowable values. In light of the poor performance of a number of steel moment resisting frame buildings in the earthquake, this is an issue that demands urgent resolution. In this project, simple linear shear-beam model is employed to determine the magnitude of the problem and to identify the factors that are most important in developing solutions to the problem. The results of this investigation will provide insights in to whether changes are needed in the seismic design of multi-story structures to account for the near-field effects. If changes are needed, they need to be identified as quickly as possible before more serious consequences occur. ***