Mitigation of Wind-Induced Vibration of Stay Cables: Numerical Simulations and Evaluations

CHAPTER 9: RECOMMENDATIONS FOR FUTURE RESEARCH

Future research in the following areas addressing some of the remaining issues would positively supplement the current project:

• Research on the combined use of external dampers and cable crossties: In particular, viscous dampers attached to the crosstie anchorages have been identified as a potentially efficient mitigation strategy. This strategy needs to be further investigated before the concept can be transformed into a mitigation measure that can be implemented. For example, determination of optimal damper coefficients and spring constants (for retraction springs) is one of the issues that needs to be resolved.
  
  
• Research on other potentially viable types of external dampers: Viscous or hydraulic dampers have been most commonly specified as external dampers for controlling stay cable vibrations. Despite their widespread use, viscous dampers have been reported to have weaknesses in terms of long-term durability and maintenance requirements. Other types of dampers, such as viscoelastic dampers and friction dampers, have certain strengths over viscous dampers and have been successfully used in other areas of application including wind mitigation of high-rise buildings and seismic mitigation of highway bridges. For example, viscoelastic solid dampers are known to offer optimal damping for a broad range of frequencies (or vibration modes), and friction dampers offer threshold vibration amplitudes below which dampers remain unengaged, resulting in elongated longevity of the dampers. Viscoelastic solid dampers and friction dampers are generally viewed as less demanding in terms of maintenance requirement than viscous dampers.
  
  
• Development of a set of additional input wind profiles and testing the effectiveness of the mitigation strategies under these profiles: The effectiveness of various vibration mitigation strategies have been tested using a limited number of input wind profiles. Expanding the scope of wind profiles would allow more reliable conclusions to be drawn regarding the effectiveness of such mitigation strategies.
  
  
• Research on the parametric vibration of a cable/deck/tower system: Current research is based on the simplifying assumption that the deck and tower are fixed or immovable with respect to stay cables. Recent studies by others suggest that the vibration of the bridge deck or tower could significantly affect the vibration of stay cables subjected to wind flow. Finite element analysis of an extended domain including the deck, tower, and stay cables may be carried out by expanding the existing analysis model. Clarification of this issue would add a substantial value to the current research study.