Study on the vibration characteristics of the pre-twisted pillar and beam

Abstract

For the past several years, large scale earthquakes happened. A lot of industrial facilities were damaged. For example, a lot of power plants were stopped in The 2011 off the Pacific coast of Tohoku Earthquake or The Southern Hyogo prefecture earthquake in 1995. These earthquakes have larger acceleration level than the seismic design level. Therefore, the earthquake proof measures are required. In this study, earthquake proof effect of the beam and the long column having initial twist is focused. The design guidelines for application to the pre-twisted beam structure and the long column structure is proposed. The pre-twisted beam and long column are modelled by FEM and calculated. The natural frequency of the pre-twisted beam and long column are related to the Young's modulus, density, length and cross-sectional area. The tendency of the natural frequency respected to the total twisted angle and the aspect ratio of the cross-section is obtained considering the vibration mode and the natural frequency. Furthermore, when attention is focused on the vibration mode, the influence of the total twisted angle is different for the modal shapes, and the case where the modal shapes are interchanged is shown. The acceleration response to the vibration input is determined by the natural frequency of the primary cross-section, the aspect ratio and boundary conditions. In order to evaluate the response reduction effect, the acceleration amplification respected to the total twisted angle and the 1st natural frequency of the system is analyzed. And the response reduction map is proposed. Using this map, it is possible to estimate the advantage of the pre-twisted effect for the vibration characteristics in a simple manner.