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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.. For
deriving the element mass matrix and stiffness matrix,the
bridge is considered to be an elastic body supported by many
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 momets induced by
the rolling motion and/or torsional vibration of the bridge are
also taken into account. To agree with the practical
situations, besides the general rigid-connected bridge (with
all joints rigid),a hinged-connected bridge (with part of the
joints to be hinged) is also studied. To tackle the problem
arising from the replacement of some of the rigid nodes by the
hinged ones,a method for deriving the property matrices and
external equivalent nodal force vector of the "rigid- hinged"
beam element is presented. The differences of free and forced
responses between the rigid-connected and hinged-connected
bridges are discussed.
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