According to the bending tests¹⁾ in still water of welded tanker “Neverita”, it was found that bending stress in the longitudinal bulkheads is very low and has great discrepancies from beam theory. The author thought that this phenomenon is due to shear-lag in bulkhead plate and analyzed by theory of shear field the stress distribution of the box-shaped beam with two longitudinal bulkheads (Fig.1) stiffened by stringers and especially, on the case which the bending rigidity of the box-beam is very large compared with that of longitudinal-bulkheads and the author obtained the general solution (22) of static equilibrium equation (3) or (20) for the boundary conditions of (4), (6) & k²_??_0 and the following results by the numerical example for the case of 11 stringers:
(1) The inefficient action of longitudinal bulkheads is due to shear-lag.
(2) The quantity K=(Gbt/EF) (L/H)² has the great influence on the shear-lag phenomena, where Gbt, shear rigidity of the bulkhead; EF, extensional rigidity of stiffeners; L, H, length and depth of the bulkhead. When K is small, shear-lag occurs intensely, but when K is large, its stress distribution obeys approximately the usual beam theory as shown in Fig. 5 6, 7, 8