A Study on Seismic Response Analysis of Long Spanned Systems Subjected to Multiple Excitations Having Large Displacement

本文研究了大型三维结构如厂房管道系统和框架结构的试验响应分析，重点研究了这些结构在多个方向同时作用下的动力特性。以长约18.0m的带法兰三维管道模型为典型结构，利用大型振动台和可向管道提供轴向位移荷载的作动器进行了振动试验。通过试验研究，分析了弯管的位移响应特性和法兰部分的弯矩响应特性，主要结果如下：1.当在工作台激振过程中向轴向施加大振幅载荷时，地震应力和固定部分（如约束）上的响应力明显增加。与无轴向载荷的情况相比，第一阶和第二阶模态频率以及相应的阻尼系数都有所增大.轴向载荷作用后，直管段的位移响应明显增大。该值远大于振动台共振激励下的响应.轴向位移载荷作用下，法兰部分出现较大的弯矩。该弯矩值在轴向振动共振时保持相当稳定，然而，在垂直方向的共振激励下，观察到该值的主导波动。

Tuis study deals with the experimental response analysis of large scaled three dimensional structures such as plant piping systems and frame type structures.In this basic work, particular intension is focused on the dynamic behavior of these systems due to multiple seismic excitations simultaneously given load from different directions. A mock-up three dimensional piping model having about 18.0m length with flanges was taken as a typical structure and vibration test was performed by using large scaled shaking table and also actuator which can provide axial displacement loading to the piping. From this testing, characteristics related to displacement response of the piping elbow and bending moment of the flange part were evaluated.Followings are main results obtained from this experimemtal investigation.1. When large amplitude loading was additionally given to the axialdirection during table excitation, seismic stress and response force on the fixed portions such as restraints clearly increased. Also, 1st and 2nd model frequencies and corresponding dainpings became larger compared with the case having no axial loading.2. Displacement response of the straight portion of the piping remarkably increased after the axial loading. This value was much larger than the response at the resonant excitation by the shaking table.3. Large bending moment appeared at the flange portion when axial displacement loading was provided. This bending moment value kept quite stable at the axial shaking resonance, however, dominant fluctuation of the value was observed at the resonance excitation from the perpendicular direction.