moment of inertia in the lower part which in turn helps the rigidity of the tub 39 s lower part as well as aids in the distributing of forces over a greater area thus when the arch 39 s curvature increases in height over the tub 39 s 11 cylindrical wall 34 radial height decreases understanding that the upper portion of the tub 11 does not require high rigidity therefore being able to economize material with this design as well as allowing for coherent distribution of dynamic and static forces the arch as can be discerned can be formed in different curvatures and configurations the preferred curvature shall depend on the particular design of each tub depending on variations of the ear 39 s 35 design the presence or lack of belts or cylindrical reinforcements 37 and in case of the actual configuration of these on the design of the mold itself are among other factors which can alter the shape or curvature of the arch 39 which is built with the best possible shape to ensure the best distribution of forces on the tub 39 s 11 cylindrical wall 34 now turning attention to the belts or cylindrical reinforcements 37 shown in fig1 a 2 5 6 7 8 it can be seen that said belt or cylindrical reinforcements 37 can be developed preferably in the tub 39 s lower part 11 surrounding the cylindrical wall 34 the reinforcements 37 are ribs in rectangular or trapezoidal transverse sections which protrude in radial shape from the cylindrical wall 39 s 34 exterior surface this allows for a greater moment.