Distribution of Shear Coefficient of Multi-story Buildings Subjected to Near-fault Ground Motions

In static seismic design, the strength demands of structural members are decided based on the expected shear force in a seismic event. A reasonable shear force distribution pattern leads to a reasonable configuration of structural parameters and thus makes the structure behave as expected in the design stage. In current seismic codes, the shear force distribution patterns are established based on the elastic response of structures subjected to ordinary far-fault ground motions. Because structural responses induced by pulse-like near-fault ground motions are substantially different from the responses induced by far-fault ground motions, shear force patterns specified in current codes are not suitable for the structural design against near-fault ground motions, and a shear force distribution pattern considering the near-fault effect should be established. This study aims to investigate the characteristics of shear coefficients resulting from near-fault ground motions and to provide a new shear force distribution pattern specifically for seismic design against near-fault ground motions. To achieve this goal, dynamic time history analyses are performed on elastic shear models based on 50 near-fault ground motions, and the shear force distributions are analyzed statistically. Findings from the study reveal that the higher modes contribute substantially to the shear coefficient, and the contribution is affected by the pulse period of the ground motion and the structural damping. The shear coefficients for floor levels 2/3 of the way up the height of the structure are significantly larger than code-specified values, if the structure has a limited damping ratio. Based on the numerical results, an empirical formula of the shear coefficient pattern is proposed. In this formula, the effects of damping ratio and period ratio are taken into account, and it can be used to derive shear coefficients more suitable for structures subjected to pulse-like near-fault ground motions.