3-Dimensional Analysis for Grid Girder Construction of Wing Tank

Abstract

As the ratio of depth to length of cargo oil tanks of tankers up to 40, 000 deadweight tons approximates to 1, it is no way unreasonable to construct wing tanks with vertical webs only. In the case of the so called mammoth tankers, however, while they are made much greater in depth, tanks to be installed in most cases are limited to 12 meters in length, with the result that the tank depth often shows a ratio of 1.7 to the tank length. In such cases, the writer considers it better to use the grid girder construction made up of the main girder installed horizontally and the secondary members vertically.Since little has been studied about the grid girder construction in the past, the writer has worked out how to calculate the strength of the construction, as follows : 1. Calculate each rahmen by the Hardy-Cross method.2. Solve a simultaneous linear equation where the deflection at each joint is the unknown value. Having 4 or 6 unknowns, this equation is by far simpler than the 56 unknowns simultaneons linear equation by the slope deflection method.3. In calculating rahmens, shearing and the effect of the end bracket cannot be neglected.4. Although some problems, such as the effective breadth of the structural members, stress causea at the brackets, etc. are yet to be solved, the value found out by the method well agrees with that obtained in the tests conducted.