Seismic Demands of Tall Moment Frame Skeletons Exposed toNear-Fault Motions Including Rotational Excitation

The consequences of near-fault earthquakes including translational and rotational accelerograms are investigated in this study. In some cases, relatively significant rotational excitations are induced to the structure during the ground intensive shaking. A three-dimensional 40-story steel moment frame structure is utilized in this paper in order to evaluate the effects of near-fault ground motions including rotational components. A number of scaled earthquake records which contain forward, backward and neutral directivity effects are enforced to the mentioned structural model. Presence of energized coherent velocity pulses as well as high amplitude acceleration spikes in the time history of earthquake records were the major criterion for selecting the ensemble of ground motions. The results obtained by numerical nonlinear time history analyses subjected to six components of each earthquake record are compared to those captured by analyses including only three transitive components.The seismic response parameters of the studied model are intensively influenced by those strong earthquake records which contain powerful forward directivity effects. The computational results indicate that tall buildings with the moment resisting frame system possesses substantial reserve strength exposed to the most of the selected records while it would not be able to satisfy the seismic design requirements under rotational components of the Bam record.

Keywords:

seismic design , near-fault record , rotational components , steel rigid frame structure