STUDY ON GOVERNING PARAMETERS FOR AMPLIFICATION OF EFFECTIVE INPUT MOTION OF SINGLE PILE

Abstract

 It is generally known that with regard to the structures supported by pile foundation or caisson foundation, input loss effect is expected due to the soil-pile interaction. However, effective input motion at low frequency may amplify as compared to free field when the flexural rigidity of the foundations is large, as in the case of caisson foundations. In this study, in order to evaluate the effect of the flexural rigidity and the horizontal and rotational resistance of the foundations on amplification of the effective input motion, effective input coefficients targeting a single pile in a single layer ground at the primary vibration mode of the free field are evaluated by solving the differential equation of a beam on elastic foundation. From the evaluation, it is confirmed that the effective input coefficients asymptotically approach 1.0 when 𝛽𝑙 of a single pile is 2.0 or more regardless of the boundary conditions at the tip of the pile, while the effective input coefficients range from 0 to 1.2 depending on the magnitude of the rotational resistance at the tip of the pile when 𝛽𝑙 is less than 2.0. It is also confirmed that the amplification of the effective input motion is suppressed by restraining rotation of the pile head.