Description and Analysis of Floating Bridges
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- Institutt for marin teknikk 
During the project Ferry-free coastal route E39, directed by National Public RoadAdministration, NPRA, seven ferry-crossings are intended to be replaced by straightcrossing. One of these is Bjrnafjorden, where a proposed crossing is a multi-spansuspension bridge, supported by two tension leg platforms, TLPs. A simpliedmodel of this proposed crossing was created in Abaqus/CAE. Further, three additionalmodels were created to study how the number of supports and alterationof cross-section aect the responses.The rst two horizontal eigenfrequencies were compared to available eigenfrequenciesfrom NPRA. All models had higher eigenfrequencies, which indicates that themodels are stier, or that the mass and added mass are smaller, or a combination.For the static analysis, three loads were applied. These were current at the oaterand trac and wind along the bridge. The environmental loads were determinedfor 1-year, 50-year and 100-year return periods. The longitudinal and vertical displacementalong the bridge, in addition to bending moment, were determined forevery model. When the number of supports were increased, the vertical displacementwas signicantly reduced, while the largest vertical displacement occurredfor the model with reduced thickness of the horizontal beams in the cross-section.This was also true for the longitudinal displacement when only the environmentalloads were applied.For the dynamic analysis, an incoming harmonic wave was applied in horizontaland vertical direction at the oater. Two wave periods were utilized; the rst is afeasible period and the second is the rst obtained eigenperiod. Resonance causedsignicantly larger motions for the oaters. Generally, a reduction of the crosssection'sthickness on horizontal beams resulted in an increased sway response,while the largest response in heave occurred for a reduced cross-section height.