Article No.7
Cable Vibration Research and the Femern Crossing
DTU Byg has assembled a world-class team of researchers to undertake a research project, which aims to provide design guidelines for the mitigation of wind-induced vibrations of cables on long-span cable-supported bridges.
The newly proposed crossing between Denmark and Germany will push the limits in engineering design. The selection of a cable-supported bridge will lead to one of the longest bridges of its type in the world. The challenges in designing a bridge are immense and the prospects of cable-vibrations will undoubtedly preoccupy both the bridge owners and designers. In this connection, Femern Bælt A/S is funding an €1.8 million collaborative research project to examine ways of reducing the probability of cable-vibrations on a bridge solution.
Main cable of Storebælt bridge. The vertical hanger cable are under
certain climatic conditions subjected to large amplitude vibrations.
Danish Cable Vibration Group
In the fall of 2004, a group of engineers gathered at DTU to discuss the lingering problem of cable vibrations on structures. Cable vibrations have long affected many structures and the recent willingness of bridge owners and designers to openly discuss the vibrations afflicting their bridges made the meeting even more relevant. The group agreed on a path: collaboration with the goal of better understanding and controlling wind-induced vibrations of cables. The members - Sund & Bælt A/S, COWI A/S , Force Technology and the Department of Civil Engineering of the Technical University of Denmark, DTU Byg, - would later form the core of the Danish Cable Vibration Group.
Research activity within the group has since been rife. In response to ongoing hanger vibrations on the Great East Belt Bridge - connecting Jutland and Sealand, a COWI sponsored industrial PhD was initiated in 2005 with the title “Understanding and simulating wind-induced vibrations of iced vertical cables.” The research work, currently being undertaken by PhD student Henrik Gjelstrup, has led to the development of a new theoretical model for the prediction of aerodynamic instabilities of cables – one that COWI has indicated they shall adopt for the future prediction of cable vibrations early in the design process of a bridge.
Simulation of ice accretion to study brdige cable shape alteration
influencing the cable aerodynamic (DTU PhD-project).
Fehmern Crossing
With the prospect of a choice of a cable-supported bridge for the Fehmern crossing, a larger collaborative research proposal on cable-vibrations was approved by Femern Bælt A/S in early 2008. To support the research project, a new state-of-the-art climatic wind tunnel (CWT) was also approved. With the research contract signed in August 2008, DTU Byg, Femern Bælt, Sund & Bælt and Force Technology entered a collaborative research agreement for 5 years.
Wind-induced cable vibrations are predominately due to buffeting, vortex shedding, galloping or wake buffeting. DTU Byg will be coordinating an international team of researchers from the Universities of Bristol, Stavanger and Reggio Calabria to examine these vibration mechanisms and find ways of mitigating them. Furthermore, the dedicated climatic wind tunnel, capable of producing sub-zero temperatures and precipitation, will give the research team a quantum leap in capabilities for researching the excitation mechanisms and the means of vibration control.
Large cumbersome external dampers and partially effective aerodynamic countermeasures are the only known means for mitigating cable vibrations. Nevertheless, investments in innovation for an engineering project of this size are generally limited due to the inherent risk associated with them. One of the main motivations for the research team will be its ability to suggest improvements and innovation in cable design early in the Fehmern Bridge design process. The current research could lead directly to design guidelines that the bridge’s final design would have to adhere to.