Whether it is a circular tube or a rectangular steel structure tube, its cross-section material is far from the neutral axis, and it is a closed cross-section with the shear center and centroid coincident, and its bending and torsion properties are obviously better than that of angle steel. Because the truss composed of steel tube members can save a lot of gusset plates and filler plates. It is said that compared with the traditional angle steel truss, steel pipe truss can save more than 20% steel, and for some structures (such as transmission towers), it can save as much as 50% steel. In addition, the unique seal of the pipe section makes it have good corrosion resistance. The joint structure of rectangular steel tube roof truss is simpler than that of circular tube, which is widely used in China. Therefore, this paper mainly introduces the design characteristics of rectangular steel tube roof truss.

At present, steel tube truss structures are mainly used in situations where they do not directly bear dynamic loads. In order to prevent local buckling of steel tube members, it is generally required that the ratio of outer diameter to wall thickness of circular steel tube is not more than 100, and the ratio of maximum outer edge size to wall thickness of rectangular steel tube is not more than 40. In principle, both hot-working pipes and cold-bending pipes can be used, but the yield strength of the materials should not exceed Q345 steel, the yield ratio should not exceed 0.8, and the wall thickness should generally be controlled below 25mm.

The height-span ratio of steel pipe roof truss can be selected in the range of115 ~110. The type and quantity of joints (such as choosing herringbone web system without vertical rods) and the specifications of pipes used should be minimized. In the steel tube truss structure, members are directly welded together to form joints. Common direct welded joints of rectangular steel pipes. Among the members intersecting at the same node, the one with the largest section size is usually called the main pipe (usually the chord), and the others are called the branch pipes. Branch pipes are not allowed to be inserted into the main pipe. The included angle between the main pipe and the branch pipe or between two pipes should not be less than 30. The end of branch pipe should be cut by automatic pipe cutter, and the groove should not be cut when the wall thickness of branch pipe is less than 6mm. The connection weld between the branch pipe and the main pipe shall be continuously welded along the whole circumference with smooth transition. Weld forms can be full fillet weld, fillet weld and butt weld. However, in the area where the included angle between the branch pipe wall and the main pipe wall is not less than120, butt weld or fillet weld with groove shall be adopted. The leg size of fillet weld shall not be greater than twice the wall thickness or 1.5 times (the branch pipe is a rectangular steel pipe).

In order to ensure the safety and normal work of the directly welded steel pipe structure, not only the components in the structure are not allowed to be damaged, but also the joints are not allowed to be damaged. Therefore, the main pipe and branch pipe in steel tube structure, as common axial stress members or compression (tension) bending members (when there is internode load), should not only meet the bearing capacity requirements of these members, but also the design value of axial internal force of branch pipe should not exceed the design value of joint bearing capacity. The bearing capacity of joints is closely related to the failure mode of joints.