Effect of pulse-like near-fault ground motions on inelastic response of structures including foundation flexibility

• Main Author: Ramin, Latifi
• Language: English
• Published: University of British Columbia 2013
• Online Access: http://hdl.handle.net/2429/45534

For the sites in close proximity to a causative fault where formation of near fault long period velocity pulses is conceivable, consideration of flexibility of the foundation system is very important. This is due to the fact that when the flexibility of the base is taken into account the period of the system is longer than the period of the same system assuming a fixed base. Depending on the depth and the stiffness of the underlying soil the period of the system approaches the period of the near fault long period pulses, hence the response of the structure could be much larger. The purpose of this research is to study the nonlinear response of structures to pulse-like near fault ground motions with and without allowing for the foundation system flexibility. To highlight the impact of the near fault ground motions the nonlinear responses of single degree of freedom systems (resembling fixed base structures) to the near fault ground motions are compared to the responses of the same systems to the equivalent far field ground motions. The effects of (translational and rocking) flexibility of the foundation system is also considered using equivalent linear springs and lumped masses added to the base of the single degree of freedom systems. A major parametric study is performed to determine which parameter has the most significant impact on the response of the structure for near fault ground motions when effect of flexibility of the foundation system is explicitly accounted for. An efficient procedure has been developed for predicting the response of a structure with a flexible base to near fault ground motions deduced from the response of an equivalent single degree of freedom system to the equivalent far field ground motions. Validity of the proposed procedure for assessing the effects of near fault ground motions, and the influence of flexibility of the foundation system on the structures’ responses is verified using different analytical models, including a full 3D analysis of a bridge structure; the results proved to be quite satisfactory.