Vibration Analysis of the Structure Exposed to Multidimensional Base Excitation

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This study explores the directional property of dynamic characteristics of the base-excited structures. Structures often undergoes the base excitation in an arbitrary direction, i.e., earthquakes or ambient excitations. It is important to know how the response changes depending on the input direction and in which direction the response goes to maximum.Firstly this study investigates the directional properties of modal response of the structure. Modal Principal Axis (MPA) is introduced which gives the direction maximizing the modal response. The natural mode is regarded as the SDOF system having a certain direction called MPA.If the base is excited along with MPA, the response goes to maximum. And if the base is excited normal to MPA, the response goes to zero. It is proved that the Center of Gravity moves along with the MP axis at the natura1 mode.Secondly Response Principal Axis is introduced which gives the direction maximizing the total response of the structure for the given input. The response of the structure is generally given by superposition of several modal responses except the case when the input frequency coincides the resonant frequency of a natural mode. If the power spectrum of the input signal is given, the input direction maximizing the total response is detected by the response principal axis.Thirdly the directional properties of a beam structure is investigated. The MPAs corresponding to the fundamental natural modes are detected experimentally by using the three axial vibration table. The RPA is also determined assuming the input as an arbitrary sinusoidal wave. It is confirmed that the presented approaches are effective to design the structures exposed to the base excitation.