A study of system damping in cable-stayed bridges | |
| Author | Yee Yee Nwe |
| Call Number | AIT Thesis no.ST-94-35 |
| Subject(s) | Damping (Mechanics) Bridges, Cable-stayed |
| Note | A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering, School of Civil Engineering |
| Publisher | Asian Institute of Technology |
| Abstract | Cable-stayed bridge is a type of structural system which has complex dynamic behaviors. This is mainly due to the effect of vibration in stayed cables. Despite of their relatively light masses, the local vibration of cables can modify the overall (global) vibration of the whole structure. Since it appears that the vibration of cables tends to reduce the global vibration, in similar manner as the effect of adding damping, the effect of cables' vibration is named " system damping ". However, as no systematic investigation of system damping is available to date, there are still controversial discussions among practical engineers on the existence and significant of system damping in cable-stayed bridges. In this study, basic mechanism of system damping is investigated in detail by using a single cable-stayed beam structure as an example. Governing equations of structural motion are formulated in terms oflocal and global generalized coordinates by using Lagrange's equation. The local and global coordinates represent the local vibrations of cable and the global vibrations of whole structural assembly, respectively. The dynamics properties of global vibrations ,i.e., mode shape, modal frequency, are obtained from finite element analysis while those of local vibrations are derived from analytical study of taut strings. The structural damping matrix is determined such that damping ratio in every modes of interest is approximately identical. By this way, the effects of local vibrations on global vibration can be clearly observed. Then, the analysis of cable-stayed beam subjected to harmonic load is carried out for several cases by varying frequency tuning ratio of local to global natural frequency which can be adjusted by initial tension in cable. Modal analysis is applied for response analysis. From the parametric studies, significant reduction of beam displacement (global) due to cable vibration (local) is observed when the natural frequencies of these two vibrations are tuned together. The observation confirms that there is system damping in cable-stayed structures. Since there is high possibility to achieve this effect in multi-cable systems due to closely distribution of natural frequency around global natural frequency, the study is then extended to the case of multi cable-stayed beams. The higher reduction in displacement is obtained in wider range of frequency ratio. This indicates that system damping effect is more pronounced for the case of multi cable-system. |
| 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) | Karasudhi, Pisidhi ;Aoyagi, Yukio |
| Scholarship Donor(s) | Government of Switzerland |
| Degree | Thesis (M.Eng.) - Asian Institute of Technology, 1994 |