We employed maturely developed methods and software, RIFLEX/SIMO/SIMA to look into the feasibilities of different floating tunnel/bridge design concepts. The global hydroelastic responses of two concepts, i.e. tether/pontoon supported hybrid tunnel concept and floating foundation supported girder concept and have been investigated. The distributions of maximum values of the deflection, bending moment and stress along the bridges under different sea conditions are presented.

Several bridge concepts for crossing deep and wide fjords along E39 at the west coast of Norway have been developed the last years. One of the most challenging fjord crossing is suspected to be the crossing of Sulafjord, 3 to 5 km wide, 400 m deep and with presence of relatively large swell waves. A suspended floating bridge concept is a marine slender flexible structure with large volume elements as floating support. The hydrodynamic actions on the floaters is an additional excitation compared to a traditional suspended bridge with fixed piles. In order to assess the effects of this excitation, it is important to consider the whole system and accurate hydrodynamic methods. While the superstructure type — a suspended bridge — is set, the type of floating foundation remains open. From the offshore experience, it is seen that different types of floaters are used for moored platforms, and these floaters have significantly different characteristics in particular with regards to wave response and stability. The design requirements for an offshore platform differ greatly from those of a suspended floating bridge crossing a fjord. For a floating bridge, the payload requirements are not the most challenging, while it is more difficult to limit the tilting and dynamic excitation of the tower (mounted on the floaters). The bridge beam is suspended at the top of the towers and will respond to any excitation due to motions of the tower tops. A global numerical model of the bridge to simulate nonlinear dynamic response due to regular and irregular waves is built. The numerical model of the bridge is simplified from a structural point of view. However, the dynamical properties and eigenmodes are verified against a more detailed structural model. Together with a 50-year long continuous time-series of wind, wind waves and swells a study of the bridge operability and extreme responses for different floater concepts is conducted. Normally the design phase should aim at avoiding any natural periods to fall within the wave frequency domain. This seems difficult for the proposed 3-span floating suspension bridge, instead solutions to minimize the excitation from waves for wave periods around the given bridge eigenperiods are sought.

Today's best engineering practice for the design of a stationary floating structure in ice infested water is articulated around physical testing in an ice basin and numerical modelling of the structure response to the relevant ice interactions.Ice basin testing is the best way to simulate the complex scenario of a moored floating structure interacting with drifting intact level ice and ridges. It is also per today the main source of experience for the design of such structures as full scale experience is sparse. However, ice basin testing suffers from deviations due to scaling effects or mismatch between one or several of the achieved and targeted properties (of the modelled ice and structure).As a consequence, the outcome of ice basin tests needs to be assessed and correction of measurements are required. An efficient way is to use an engineering numerical model to simulate the achieved ice-structure interaction in the ice basin, qualify the numerical model by comparing simulation results and measurements, and then simulate the targeted interactions with the numerical model. Such a numerical model may further be used to simulate the full range target design conditions for the ice structure interaction.The RITAS ice basin campaign tested a structure element designed to gain insight in the level ice bending and accumulation process around a traditional moored floating arctic structure design. These measurements are well suited to assess the validity of a numerical model designed to replicate this type of interaction. The SimShipIce numerical model is an engineering tool which focuses on replicating the steering processes during the interaction between a moored structure and drifting intact level ice and ridges. Such a model needs to be calibrated against ice basin test outcome.In order to gain confidence in the general applicability of the model for a traditional moored structure design for ice infested waters, the RITAS tests are simulated with the numerical model. It is shown that the simplified model of the interaction and subsurface transport implemented in SimShipIce captures: The variation in the ice load level with varying ice drift incidence,  The variation in the ice transport with varying ice drift incidence. In addition, some small local deviations are observed, indicating potential areas for improvement of the model. Background Design of moored structures for ice infested watersMoored floating structures are considered to be an attractive concept for the exploitation of offshore hydrocarbon fields in sea ice infested and deeper waters. There is little experience with previous design and operation of such moored structures. Per today, the screening, feasibility or detailed design phases of such concept rely greatly on ice basin tests. This is inline with ISO 19906 (2010).Ice basin testing provides the best way to physically model the complex interaction between a moored floating structure and drifting sea ice. However, ice basin tests have some limitations. Apart from the cost and time expenses, model...

Long floating bridges supported by pontoons with span-widths between 100m and 200m are discrete hydro-elastic structures with many critical eigenmodes. The response of the bridge girder is dominated by vertical eigenmodes and coupled horizontal modes (lateral) and rotational modes (about the longitudinal axis of the bridge girder). In this paper it is focused on design principles to reduce the response with regards to these eigenmodes. It is shown for a floating bridge with 200m span-width that by inserting a bottom flange the vertical eigenmodes can be lifted out of wind driven wave regime. It is also shown that selecting a pontoon length that give cancellation of excitation forces is beneficial, and that the geometrical shaping of the pontoon can be efficient to decrease the bridge response.

Long floating bridges supported by pontoons with span-widths between 100 m and 200 m are discrete hydro-elastic structures with many critical eigenmodes. The response of the bridge girder is dominated by vertical eigenmodes and coupled horizontal modes (lateral) and rotational modes (about the longitudinal axis of the bridge girder). This paper explores the design principles used to reduce the response with regards to these eigenmodes. It is shown for a floating bridge with 200 m span-width that by inserting a bottom flange the vertical eigenmodes can be lifted out of wind-driven wave regime. It is also shown that selecting a pontoon length that leads to cancelation of horizontal excitation forces is beneficial, and that the geometrical shaping of the pontoon can be efficient to decrease the bridge response.