Type: Academic PhD
Period: 2011-2014
Student(s): Joan Hee Roldsgaard
Supervisor: Christos Georgakis
Background
Bridges often form indispensable components of transportation links. The preservation of the robustness and residual lifetime of these structures is thus of great interest for bridge operators and society as a whole.
The number of long span cable-supported bridges has increased significantly since the 1970’s and is still increasing. With this, the number of reports of unanticipated bridge cable vibrations has also increased, despite the fact that in many cases cable vibration countermeasures have been installed [1].
Very limited research has focused on the probabilistic assessment of fatigue damage of bridge cables due to wind-induced vibrations. The mechanisms, including those linked to rain, ice or sleet, often cause large amplitude vibrations under varying combinations of meteorological conditions. The often unanticipated cable vibrations in combination with the effects of traffic loading cause concern, as regards the lifetime and risk of failure due to fatigue damage of the cables.
The damage assessment of the cables is not straightforward though, as the mechanisms causing the large amplitude vibrations and fatigue failures are not yet fully understood. It can be understood that the wind-induced vibration mechanisms mainly cause bending stresses around the anchorages of the cables and that the traffic loading mainly causes axial stresses in the cables. Depending on the characteristics of the loading and the material, the stresses may lead to fatigue failure of the cables.
Project
The objective of the research is to establish a probabilistic risk assessment model that is able to include both axial and bending fatigue of stayed bridge cables.
The research will include a classification of the different vibration mechanisms, which are inducing fatigue failure of the cables. The risk assessment model will be based on the Probabilistic Model Code (PMC) of the Joint Committee on Structural Safety (JCSS). Finally a verification of the probabilistic risk assessment model of stayed cable fatigue will be performed on a real-life structure.
Perspective
The project will lead to enhance of the engineering best practices concerning the assessment of fatigue performance of cable supported structure by a probabilistic model. The enhance will be obtained by a deeper understanding of the governing vibration mechanisms, which induces fatigue failure, probabilistic representation of the both axial and bending fatigue spectra and relevant probabilistic techniques suitable for this type of risk assessment.
References:
[1] Sun, L. & Dong, X. 2011. Researches and applications on vibration control of long stay cables in China. Key-note lecture at the 9th International Symposium of Cable Dynamics, 18-20th Oct. Shanghai, China.