Recently the investigation on the application of tensile steel for ship structures has been developed and several reports has been published. These papers concerned mostly on the application for a part of strucutural members of ships. This paper discussed the test results on two ship models under deck loads, one of these models is made of high tensile steel and others made of mild steel, and both are the strutures between two transverse bulkheads of a ship and similar to the actual ship. On the basis of the investigation herein, simple formulae are presented which can be used to obain the collapse load of beams or girders. A study of the behavior in the elastic range is also given and the effect of axial forces set up at large deflection are taken into account.