Response of structures to near-fault ground motion

The special characteristics of near-fault ground motion have been recognized for sometime. However, their importance in earthquake design of civil structures was not fully realized until several failures occurred during the 1994 Northridge and 1995 Kobe earthquake events. In the near field in the forward directivity zone, the records are characterized by pulse type motion of long duration. The effect of this pulse type motion on the response of structures is important in the design of structures for near-field events. The objective of this study was to evaluate the response of various structures to available near-fault ground motion records.A set of 8 near fault records from major earthquake events were selected. Four reinforced concrete moment resisting frame buildings of three, six, twelve and twenty storeys were designed according to current codes.The nonlinear response of the structures when subjected to the near-fault ground motion was analyzed.Results were obtained in the form of maximum inter-storey drift and storey shear demand.It was found that the response of structures to near-fault ground motion is substantially different from the response to far-field earthquake records. It is concluded that codes should address the near-fault motion explicitly in time history form and not by the implicit form of increasing the coordinates of the design response spectra.