Location: Norway
Phase: Conceptual design, research project
Year: 2011-ongoing
Design team: Multiconsult, DOF Engineers, NTNU University, WSP.



Crossing of wide fiords with floating bridges is a relevant topic in Norway. A standard long floating bridge will be greatly affected by lateral forces (such wind and waves); by designing the bridge as a floating chain, the side forces will be transformed in axial forces (easily supported by standard modular steel bridges). This new concept will allow a cost effective crossing of wide channels.



The idea of a chained floating bridge was introduced for the first time in 2011 by MSc. Jan Soldal from the company Akvator AS; since then Multiconsult is actively researching on developing this new bridge concept in order to implement it in crossing wide fjords.


Description of the concept


The chained floating bridge is composed by several floating bridge units (Catamaran elements) assembled together by simple bridge girders (Linker elements) to a continuous long floating bridge. The connection between catamarans and linker is made using swivel joints.



This means that no bending moments are transferred by the joints, and thus all the external horizontal loads (like wind, waves and currents) will be supported by the bridge through a longitudinal tension forces (similar to the behaviour of a horizontal catenary).



Bridge deck


The great vantage of this bridge typology is the possibility to use a standard steel deck structure (steel box girder or truss girder) pre-assembled and erected on site, with a unit costs independent by the length of the bridge. This can guarantee economic feasibility (and associated low investment cost) for long crossings with low traffic and/or relative low importance. The studies undertaken by Multiconsult shows that optimal element span varies from 120 m to 400 m. 



Pontoons


Each catamaran element is supported by two pontoons. The size of the pontoons will vary in function of the span widths and the bridge height (above sea level). The pontoons construction can be made by concrete or steel cellular box. An optimal solution is to have pontoons with the Eigen period higher than the wave period (generated by the wind). 



The moveable joints (swivel joints)


The joint between catamaran and linker elements is a key part of this new bridge concept. This joint has to be able to: allow rotations along the vertical axis and the transversal axis of the bridge transfer the tensile force along the deck, guarantee the support of the linker element over the catamaran and in addition allow the passing of vehicles on the deck. 



Construction and assembly of the bridge


All the components of the bridge can be constructed out-site, in special yards. The pontoons can be constructed in dry-dock and floated to the site.


The catamaran elements can be assembled on one or several barges and then mounted on the pontoon. When all catamaran elements are finished they will be anchored to the shore.


Then each catamaran element can be linked to another by a linker element. Following this procedure the entire bridge can be easily assembled from the two sides of the site. As final construction stage the bridge will be moved using several tugboats to the exact crossing position and hooked up to the anchors and to the abutments.


 Images © Multiconsult

© DOF engineers 2017 . All rights reserved. Disclaimer and legal notice