Equivalence between Top and Base Excitations of Pillar-type Structures.

Abstract

Generally, it is difficult to carry out seismic tests of tall pillar-type structures using a vibration testing table, because the table must resist a huge rotating moment, on the structures are too big to mount on the table. In this paper, we discuss an equivalent test using a top excitation method. At resonant or nearly resonant conditions, it is easy to realize equivalent conditions between top and base excitations. At off-resonant conditions, only one among displacement, moment, or shear force can be equivalent, but other components cannot. From the analysis of transient response using seismic wave, impulse wave and sinusoidal wave of three periods at resonant frequency, it is found that nearly equivalent conditions can be realized, because normal modes are excited and are dominant in the response. The amplitude magnification factor at the top of pillar-type structures is usually expressed as m/2ζ, where m≥1. For a uniform beam, m is 1.56. The value of m changes according to the profiles of the structures, such as diameter or cross-sectional width and length at the top and bottom of the structure.