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The effects of imperfection on the dynamic characteristics of a tall TV-tower | |
Author | Sia, Pie King |
Call Number | AIT Thesis no.ST-94-24 |
Subject(s) | Structural dynamics |
Note | A Thesis submitted in partial fulfilment of the requirements for the degree of Master of Engineering, School of Civil Engineering |
Publisher | Asian Institute of Technology |
Abstract | Ideally, TV-tower with perfect axisymmetry cross-section will exhibit planar motion when subjected to planar excitation. In reality, large displacement and some degrees of imperfection may induce nonplanar motion on the structural systems. Based on continuum mechanic and the concept of generalized coordinates, finite deformation and imperfection effects are incorporated into the governing equations of motion by using the principle of virtual work. Modal analyses are employed to obtain the decoupled equations of motion. From these uncoupled equations, we found that the imperfection effects will be significant when two orthogonal modes have closely spaced natural frequencies. In addition, after conducting order analysis, nonlinear coupling terms due to the finite deformation are neglected. Therefore, in the present dissertation we focus on the imperfection effect of the TV-tower. Since it is difficult to predict the vibration characteristics of the imperfect structural systems, thus the experimental studies were necessary to carry out for further investigation. A scaled TV-tower was constructed for the shaking table test. Both preliminary and comprehensive harmonic tests were conducted. Of particular interest, steady state response of in-plane and out-of-plane motions was measured to identify the imperfection coefficients and damping ratios. Consequently, the obtained experimental results were compared qualitatively with the theoretical results, and very good agreements were found between both. Furthermore, earthquake excitation tests were carried out to verify the calibrated analytical model. The time histories of the earthquake response were measured and compared with those predicted from the calibrated analytical model. From time histories of the in-plane motion, fairly good agreements were found between the theoretical predictions and the experimental results especially for the earthquake contain low frequency components; but some discrepancies were found in the out-of-plane motion. Both in-plane and out-of-plane motions from earthquake contain high frequency components were found to have significant discrepancies between theoretical predictions and experimental results. Finally, we can conclude that the higher modes must be considered in analytical model in order to predict more accurate earthquake responses. The present study is believed to provide essential background for further research of the imperfection effects on structural systems. Moreover, the experimental studies on scaled TV-tower also give more physical insight various response characteristics of imperfect structures. |
Year | 1994 |
Type | Thesis |
School | School of Civil Engineering |
Department | Other Field of Studies (No Department) |
Academic Program/FoS | Structural Engineering (STE) /Former Name = Structural Engineering and Construction (ST) |
Chairperson(s) | Pennung Warnitchai |
Examination Committee(s) | Worsak Kanok-Nukulchai ;Karasudhi, Pisidhi ;Jiaru, Qian |
Scholarship Donor(s) | Japanese Government |
Degree | Thesis (M.Eng.) - Asian Institute of Technology, 1994 |