| dc.description.abstract | Floating bridges, also known as pontoon bridges, are structures intended to connect two sides of land separated by a body of water and differentiated from standard bridges by the use of floating elements (generally pontoons) which give the structure enough buoyancy to support its own weight and that of the traffic, as well as the different environmental loads which marine structures are generally subjected to (like waves, currents and wind loads).
These types of structures use water as a mean of buoyancy, instead of as an obstacle when gravity can’t be overcome by traditional means like suspension cables or piers. Most of the cases in which the latter can’t be used are related either with the distance to cross, the depth of the water beneath it, or the characteristics of the seafloor in which the foundations are to be laid, among others. Locations with abrupt and dramatic coastlines, like Norway, have to make use of these novel and complex structures, as the technical limitations of conventional bridges leave no other option. It is of special interest the case of the E39 highway in the aforementioned country, a coastal road covering a distance of 1100 km from Kristiansand, to Trondheim, characterized by its numerous ferry crossings (up to nine), which lead to an inefficient and long trip (up to 21 hours to cover the whole distance).
To design and build these structures, extensive knowledge regarding, not only civil engineering, but also marine engineering and ocean structures is needed. When it comes to the superstructure, notions regarding civil structures are needed to design a safe and efficient solution which compiles with the standard regulations and codes; on the other hand, the foundations of the structure (which includes mainly the floater elements) require a deep understanding of marine structures, marine dynamics and marine loads, so a proper assessment of the design can be made. These two approaches must be taken not only individually, but combined, as there are important interactions between the two main parts of the systems components.
Phenomena like dynamics coupling between the superstructure and the floaters is remarkably important, hence an hydro-elastic approach must be used when analyzing these designs (also known as coupled analysis).
This thesis analyzes the global dynamics of two existing floating bridges, the Bergsøysund bridge, in Norway, and the Yumemai Bridge, in Japan. Starting from the modeling of the bridges from available blueprints, through the creation of hydrodynamic models of the pontoons and a finite element model of the superstructure, ending in a coupled dynamic analysis of the system; important response parameters are obtained and further discussed.
Due to the complexity of these structures, the focus is set in the marine loading of the floating bodies and the global response of the bridges, hence no special attention is put in the structural details of the superstructure, and no further analysis of the local deformations and stresses of the structural members of the bridges is made.
The global dynamic response of these type of structures is critical throughout the design of this type of structure as it affects the system in different ways. Firstly, the bridge stability is highly dependent on the loads which are applied to its different members; maximum values of displacements can’t exceed certain thresholds imposed by the static and dynamic stability of the bridge (both at intact and damaged conditions). Secondly, the dynamics of a floating bridge are closely linked to its structural integrity; the natural modes of vibration of the structure may be excited by the its loading conditions, amplifying the motions and internal stresses on the structural members. Fatigue plays an important role in marine structures, given the cyclic character of this environment.
The structure must be design based on different limit states. Thirdly, understanding the dynamics of a certain design helps engineers and technicians setting operational limits, ensuring a safe operation at every moment. Lastly, but not less important, the environmental impact these structure can have on the surrounding environment must be reduced. The dynamics of floating bridges can affect, among others, water currents, sedimentation patterns, and marine life. Environmental studies must be carried out to minimize the impact of the final design on the nature. In summary, considering the dynamics of floating bridges is crucial for ensuring their stability, structural integrity, safety, functionality, and environmental compatibility. By understanding and accounting for these factors, engineers can design and operate floating bridges that effectively serve their purpose while minimizing risks and maximizing efficiency. | |