Static Behaviors of a Long-span Cable-Stayed Bridge with a Floating Tower under Dead Loads

Owing to the structural characteristics of floating-type structures, they can be effectively applied to overcome the limitation of conventional long-span bridges in deep water. Unlike cable-supported bridges with fixed towers, floating cable-supported bridges show relatively large displacements and rotations under the same load because of floating towers; moreover, the difference in the support stiffness causes differences in the behavior of the superstructures. In addition, the risk of overturning is greater than in conventional floating offshore structures because the center of gravity of the tower is located above the buoyancy center of the floater. A floating cable-supported bridge in which the tether supports the floating main tower is directly influenced by the tether arrangement, which is very important for the stability of the entire structure. In this study, according to the inclined tether arrangement, the outer diameter of the floater, and the buoyancy vertical load ratio (BVR), the static behavioral characteristics of the long-span cable-stayed bridges with floating tower are evaluated through nonlinear finite-element analysis. When the intersection of the tension line of the tether and a pivot point of the tower coincide, the tethers can no longer resist the tower's rotation. For this reason, a large displacement occurs to equilibrate the structure, and further increases as it approaches the specific slope, even if it is not exactly the specific tether slope. The analytical model of this study indicates that, in terms of increasing the rotational stiffness of the main tower, it is advantageous to increase the floater diameter until a BVR of 1.8 is reached and to increase the axial stiffness of the tether from a BVR of 2.0 or higher.