Effect of Spacing and Slenderness Ratio of Piles on the Seismic Behavior of Building Frames

The general assumption of a rigid base at the bottom of building structures during analysis and design underestimates the seismic response. Building structures resting on loose sand and soft clayey soil are vulnerable to earthquake forces. The amplification of ground motion occurs due to the presence of this loose and soft soil deposit. Moreover, the spacing and slenderness ratio of piles play a vital role in altering the behavior of the overall soil-foundation-superstructure system. This study aimed at investigating the effect of soil-pile-structure interaction using 1-g shake-table testing. Free and forced vibration tests were performed on scaled building frames with either a rigid base or a flexible base, supported on sandy soil with 50% relative density. A laminar shear box container is used for an experimental study of soil-pile-structure interaction. The design parameters, such as the spacing (S = 3D, 5D, 7D, and 9D) and slenderness ratio (L/D = 15, 30, 45, and 60) of the piles, where S, D and L are spacing, diameter and length of the piles respectively, are considered in the analysis. The results, in terms of natural frequency, damping, pile-bending moment, story lateral displacement, and inter-story drift are estimated. From the findings, it is clear that the effects due to pile spacing are more considerable than the effects due to the slenderness ratio of the piles. The bending moment in the piles spaced at 3D is increased by 102% compared to the large-spacing (S = 9D) piles. This subsequently amplifies the story lateral displacement by 180% and amplifies the inter-story drift by 167%.

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