Flutter Stability of Very Long Suspension Bridges

Abstract

As longer suspension bridges are being built and planned around the world, many feasibility problems arise. Experiences related with preliminary studies on the Gibraltar Bridge are presented. Flutter is considered to be the main feasibility problem for a very-long-span bridge, and it is analyzed in this paper for span lengths ranging from 1,600 to 6,000 m. As conventional deck designs present unacceptably low critical velocities, several alternative suspension schemes are analyzed to determine their qualities to prevent flutter instability. These systems use a variable number of main cables (from one to four) and hangers arranged in such a way as to produce the highest stiffening effects on the statical system. Flutter is analyzed by means of a multimodal finite-element-based method, and critical conditions are defined by observation of the U-f diagrams. The crossed-hangers system is chosen as the simplest way to improve flutter stability, although the results of this study indicate that it is useful only for very long spans.