Control of Car Decks Welding Deformation in RO-RO Ships

Abstract

Lashing rails are used in RO-RO ships to lash cars to car decks during transportation. These rails are firmly fillet welded to decks to avoid damage by car tires during loading and unloading. These rails are welded to decks after the deck is completely assembled and welded. Due to their small height, the effect of lashing rails welding tendon farce is additional compressive stress and shrinkage in deck plating, and additional sagging of deck structure. Local plate deflection between longitudinal stiffeners also considerably increases. Correction of this deformation is difficult and consumes work hours and calendar time.

In this work, Alternative welding sequences are numerically investigated. Back heating, treatment of gaps and misalignments occurring during welding and alternative supporting methods during welding are considered. The best sequence is selected based on comparison of welding deformation caused by each sequence.

To reduce compressive stress and local deformation in deck plate, mechanical straitening of deck platting after welding the lasing rails is numerically considered. This technique can only be applied when lashing rails are welded first. Reduction of tendon force and transverse bending is numerically predicted and checked against physical testing of mechanical straitening of a deck plate with lashing rails welded to it. Such reduction is incorporated in the prediction of deck structure welding deformation. Its effect on overall as well as local deformation of the deck is assessed.