Messina Straits and Beyond – Active or Passive Flutter Stabilisation?

It is well known that a major factor that limits the span that can be achieved with a cable-suspended bridge deck is ‘flutter’ instability at high wind speed. This tendency can be alleviated but not necessarily eliminated by increasing the torsional stiffness of the deck. As the span increases, the stage is eventually reached where the required torsional stiffness is no longer realistically achievable, due to the disproportional impact on the mass of the deck and its supporting structure. What is then needed is some form of aerodynamic stabilisation.

One possibility is ‘passive’ aerodynamic stabilisation, with dual or triple laterally-disposed deck sections allowing air flow between them. The Xihoumen Bridge for example has two parallel deck sections while the proposed Messina Straits Bridge has three. In fact it is this ‘third generation’ design concept, with its two roadway decks and one railway deck, which is also being suggested for the Sunda Strait, the Strait of Gibraltar and the Yemen-Djibouti crossings. The alternative is to adopt ‘active’ aerodynamic stabilisation of a conventional single deck by means of aerofoils. This technique has been commonplace in aircraft for over half a century.

In this paper, an attempt is made to compare and contrast some of the issues relating to these two alternative aerodynamic stabilisation approaches. It must be emphasised that the treatment is essentially qualitative and purely intended to form the basis of discussion. However it is hoped that in the future it will lead to quantitative analyses for specific applications.