Ultimate and residual strength assessments of intact and collision damaged columns of the Bjørnafjorden floating bridge

Abstract

The Norwegian Public Road Administration (NPRA) has initiated an ambitious project to replace the current ferry crossing solutions with floating bridges over the wide and deep Norwegian fjords. This will substantially reduce the travelling time among major cities in Norway. It is found that ship collisions represent major critical loads to the safety and integrity of floating bridges that governs the structural design. This paper investigates the ultimate and residual strength of columns in an initial design of the Bjørnafjorden floating bridge before and after ship collisions with an initial kinetic energy of 125 MJ and 150 MJ respectively corresponding to a 10,000-year event as estimated from risk assessment. The ultimate bending and torsional capacities are assessed. Three different approaches are adopted, (1) the nonlinear finite element method using LS-DYNA; (2) A semi-analytical code PULS based on energy methods; (3) DNV rules-based formulations. The results are compared and discussed.