Moving-load-induced vibrations of a moored floating bridge
The natural frequencies and mode shapes, and the coupled rigid-body (rolling) motion and elastic (flexural and torsional) vibration of a partial-catenary-moored floating bridge (in still water) subjected to a moving load are investigated. The mathematical model is obtained by simplifying one of the floating bridges in Lake Washington at Seattle, U.S.A. To derive the element mass matrix and stiffness matrix, the bridge is considered to be an elastic body supported by a number of uniformly distributed springs (to simulate the water buoyancy) and concentrated springs (to simulate the partial-catenary mooring cables). In addition to the vertical restoring forces, the axial preforces induced by the horizontal cables located at the two ends of the bridge, and the righting moments induced by the rolling motion and/or torsional vibration of the bridge are also taken into account. To agree with the practical situations, both the rigidly connected (or r-c) bridge (with all joints rigid) and the hinge-connected (or h-c) bridge (with part of the joints to be hinged) are all studied. To tackle the problem arising from the replacement of some of the rigid nodes of a rigidly connected bridge by the hinged ones, a method for deriving the property matrices and external equivalent nodal force vector of the rigidhinged (or r-h) beam element is presented. The differences between free and forced dynamic behaviors for the hinge-connected (h-c) bridge and rigidly connected (r-c) bridge are discussed.
floating bridge partial-catenary mooring rigid-body motion elastic vibration rigidhinged (r-h) beam element finite element method (fem)