Effects of Air Tightness Tests on Steel Thin-Wall Box Structures with Circular and Rectangular Cross Sections

In this paper, the effects of air tightness tests on steel box structures with rectangular or circular cross sections typical of port cranes (legs, arms, and crosspieces) are analyzed. Legs and arms are generally made with elements with profiles having a square or rectangular cross section, while the diagonal struts are made with profiles having circular cross sections. To verify the air tightness of these elements, a necessary requirement to protect them from corrosion if they are not protected with other protection techniques, air tightness tests are performed. These tests, in the framework of durability tests, must be carried out while maintaining the structure elasticity well below the yield limit of the material. The tests must therefore be carefully designed regarding the choice of the air pressure to be injected into the box structures to verify their tightness and the way the air is put into the structures. As shown in the present work by means of an experimental investigation supported by numerical analyses, the choice of the test pressure depends on the shape of the element to be tested and in particular on the shape of the cross section of the profile. To this end, by means of laboratory tests on small-scale models and numerical simulations in the nonlinear field, the actual induced stress state of the internal pressure on the watertight box structures is shown, indicating the values of the pressures, which produce local yields or ruptures.