Structural safety analysis of bow doors

Artikel i vetenskaplig tidskrift, 2006

Bow doors are one of the most vulnerable parts on a RoRo vessel. At the same time, they are necessary for the profitability of today's RoRo vessels. The minimum design rules for bow-door systems, stated in the International Association of Classification Societies (IACS) UR S8, constitute the basis for the class rules. In this work, the Rules of IACS UR S8 have been assessed regarding the structural integrity for bow doors of the 'clam door' type. The work is based on previous damage, compared to the design rules, so as to find weaknesses in the rules. Damage was mapped and weak points in the rules as well as in the design and construction stages were identified. For the problem areas found, part analyses were performed. Fractures and cracks dominate as being the cause of damage to bow-door systems. In most of these cases, cracks in welds are involved. Fatigue appears to be a major cause for the development of fractures and cracks. Assuming the bow door as being a rigid body and distributing the forces equally on each support, as prescribed by IACS UR S8, appears to be an approach that leads to inadequate results. The deformation of the door causes the loads on the supports to differ significantly and the real pressure distribution subjects the lower supports to much higher loads then the upper ones. It is common with gaps between the supports in the doors and the corresponding ones in the hull. These gaps considerably affect the load distribution on the supports.