CKI-14: PASSIVE CONTROL OF HIGHWAY STRUCTURES
The objective of this project is to introduce recent development, in seismic-counter measure techniques to assess analytical and experimental effectiveness, feasibility and limitations of damping augmentation devices, such as lead rubber bearings, elastometric bearings and damped resonant appendages, with respect to the seismic performance of cable-stayed bridges. To achieve this objective, emphasis was placed on: (1) the results of the USC two shake tables (4 ft x4 ft with separating distance 12 ft center-to-center) tests of a 1:100 reduced scale model of an existing Japanese cable-stayed bridge; (the Yobuko Bridge) tests were carried out without the energy absorption device and with the hysteric energy dissipation device, (2) the results of damped resonant (tuned) appendages with relatively small mass and high damping ratio using a pair of small shaking tables (at UCI) to longitudinally shake the 12-ft long bridge model of the same cable stayed in Part 1, and (3) the results of computational analysis of the prototype by the Kajima research team to improve the earthquake resistance of floating type prestressed concrete cable-stayed bridges by introducing passive vibration systems such hysteretic type devices and tuned mass damper devices.
This report includes the following:
Improvement of Earthquake Resistance of PC Cable-Stayed Bridges by Hysteresis Type Damper and Tuned Mass Damper
Tetsuo Takeda, Seiji Tokuyama, Masaomi lizuka, and Toshimichi Ichinomiya
Kajima Technical Research Institute
Tomohiko Arita, Katsuhisa Kanda, and Kazuhiko Yamada
Kobori Research Complex
Hachiro Ukon and Yoshihide Okimi
Information Processing Center
Civil Engineering Design Division
A three-span PC cable-stayed bridge of floating type is widely adopted for a long-span bridge to improve earthquake resistance. 'In a floating type PC cable-stayed bridge, the girder is supported by stay cables only without using bearing supports, so that long natural periods reduce seismic forces. That is, the girder of a bridge of this structure is designed to behave like a swinging log, thereby reducing seismic forces. However, since horizontal displacement at the girder ends is large and since the inertia forces of the girder are subjected to the tower through stay cables, the section forces of the tower in a floating type bridge may become greater than those in a fix type bridge, in which the inertia forces of the girder are subjected to the main piers through bearing supports. Thus, a floating type bridge is not necessarily superior to a fix type bridge in earthquake resistance.
Chapter 2 looks at reduction in the sectional forces of the towers and the main piers and in the displacement of the main girder due to the hysteresis type damper and tuned mass damper introduced into the floating type, three-span PC cable-stayed bridge through parameter analysis.
Hysteresis type dampers were applied to the PC cable-stayed bridge, at the main girder-main pier connections and at the main girder-end pier connections, and reducing effects were analyzed parametrizing the stiffness and yield strength of the dampers. It was confirmed that there are certain stiffnesses of the hysteretic dampers at which responses of the sectional forces of the towers and the main piers, and displacement of the main girder can be reduced effectively. It was also confirmed that the hysteresis type dampers dramatically reduce the displacement of the main girder and the sectional forces of the towers without affecting the sectional forces of the main piers.
The mass and damping of the TMD were parametrized. In the analysis the TMD-structure mass ratio was set at 0.01, 0.1 and 0.5 (damping factor remaining 10%), and the damping factor of TMD was set at 0, 5, 10, and 20% (mass ratio remaining 0.1). As a result, it was confirmed that the combination of a mass ratio of about 10% and a damping of about 5% reduces the longitudinal displacement of the main girder by about 25%.
Chapter 3 focuses attention on three methods for analyzing the earthquake resistance of long-span PC cable-stayed bridges: (a) large deformation analysis, (b) multiple-input analysis for long spans, and (c) modeling of passive devices for seismic isolation. This chapter reports on a newly developed the static and dynamic analysis program that combines all of the above.
2 PARAMETER ANALYSIS
- Structure with Hysteresis Type Dampers
- Structure with Tuned Mass Damper
3 PROGRESS OF NONLINEAR ANALYSIS PROGRAM
- Numerical Techniques
- Numerical Examples
- Concluding Remarks
4 CONCLUSIONS AND FUTURE PROBLEMS
- Prototype Bridge and Simplification of Bridge Model
- Effects of Dry Shrinkage, Creep and Temperature variation
- Contributed Papers and Papers to be Contributed
Also listed as Report No.: 1992.8