The current floating bridge concepts of Norwegian Public Roads Administration (Statens vegvesen, NPRA) use a flange shape part at the bottom part of the pontoons. The flange is in principle similar to the damping plates used in the offshore industry for SPAR type of structures. The project group initiated the flange part based on the requirement of extra added mass for tuning the bridge system Eigen-modes. Thus, the important modes can be shifted out of the main wave energy zone. The current study will focus on the damping effects of such structure. The damping effects on weak axis bending moment prediction is studied. The modelling of such damping is first proposed according to relevant literature based on both numerical and experimental studies. Since the reference studies were mainly focused on cylindrical structures, it is difficult to obtain an accurate estimation of the damping coefficient for the current bridge pontoon design, which contains a rectangular part between two half-cylindrical parts. In addition, the estimation of pontoon motions needs the input of damping coefficient, which means that the evaluation of damping coefficient is an iteration process. In order to include the uncertainties, a conservative value was adopted to represent the damping effect. The comparison of accounting for the damping effects or not has been given for all the bridge pontoons. The results show that the damping effects are important at the peaks of the responses; in addition, the reduction of the predicted maximum bending moments can be expected around 10–15 percent along different positions of the bridge. However, a further investigation also shows that viscous excitation would increase the bending moments slightly. The comparison also indicates the value of further investigating the effects by CFD or model test methods.

This paper describe the development of floating bridge projects along the coast of Norway. Over the decades, the need to replace existing ferry connections with fixed linkes has beed rapidly increasing. However, the Norwegian nature with its deep and wide fjords, together with low traffic numbers have given the engineers big challenges in designing cost effective bridges for many of the crossings. One solution that was developed in the late 80s and early 90s by a combination of offshore technology and bridge technology was the end-anchored floating bridge concept. So far, two bridges of this design have been completed, the Bergsøysund Bridge and the Nordhordland Bridge. Prof. Moan was a key contributer in the developing work, enabling a safe design of the bridges. As the remaining ferry crossings are even deeper and wider, there is a need to further develop this concept, as well as developing new concepts, so that we are able to replace even further ferries with fixed links. The paper will look back at the two already buildt floating bridges, as well as the floating bridge concepts that might be used to cross the Bjørnafjord, on the west coast of Norway.

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The paper will look into the hydrodynamic loads and responses on the proposed Submerged Floating Tube Bridge (SFTB) through the Digernessund by the Norwegian Public Roads Administration (Statens vegvesen, NPRA). The aim is to show how different hydrodynamics aspects during the prelimiary design can be simply addressed under the given environmental conditions. Different SFTB systems are introduced as the first step. A simplified method based on modal analysis is introduced and implemented for evaluation of the motions and stress, bending moments along the bridge. Firstly, a 2D Boundary Element Method (BEM) solver is developed and verified, which is further used for solving the hydrodynamics coefficients of different bridge cross sections. The 3D hydrodynamic coefficients of pontoons are solved by the commercial software AQWA. The analysis procedure of the simplified method for the global SFTB responses is presented. The Eigen periods of the Bjørnefjord SFTB is re-calculated by the present model as a first validation of the implementation. The loads and responses of the bridge under given wave conditions are then estimated. The evaluation of the possibility of vortex induced vibrations of the current SFTB design is given.