Now light steel structure and steel grid are widely used in all kinds of buildings in our country. Because of its wide use, it promotes the development of modern industry in our country to a certain extent. In the production process of light steel and space truss, welding structure is widely used. Many practice and research found that the welded structure has its own regularity, if not correctly grasp, the use of welded structure will be limited, and even cause great loss of people's lives and property.
1. Welded joint
In the welding structure, generally can choose different ways of welding joints, some joint methods are unique to the welding process, some are used for riveting or bolt joint sleeve. Generally speaking, the former can better meet the requirements of welding structure operation function. The common welded joints are butt joint, T joint, corner joint and lap joint.
Butt joints: butt joints with different plate thicknesses are different. Generally, thin plate can choose crimping joint or single side weld without groove. Single side weld joint with backing plate without groove can be selected for plate thickness addition, but double side weld butt joint without backing plate is recommended. In order to ensure the penetration, butt joint can be welded after single side or double side groove. The groove shape includes V-shape, U-shape, X-shape and K-shape.
For the submerged arc active welding process, the same butt joint mode as manual arc welding can be selected, but the dimension parameters on the groove have certain changes, as shown in the figure below.
T形接頭：同樣有開坡口和不開坡口等方式，在該類接頭中選用不開坡口角焊縫施焊類型為廣泛，一般可選用等角或不同焊腳尺度的角焊縫。 角接頭：其特性介于對接接頭和T形接頭之間，接頭中焊縫可接近于對接焊縫和角焊縫。 搭接接頭：這種焊縫由鉚接或螺栓接頭轉化而來。搭接接頭中一般要用角焊縫施焊，它能夠是旁邊面焊縫、瑞面焊縫或是聯合焊縫、塞焊也是搭接接頭焊接辦法之一。
T-joint: there are also beveling and non beveling methods. In this kind of joint, non beveling fillet weld is widely used. Generally, fillet weld with equal angle or different leg size can be used. Fillet joint: its characteristics are between butt joint and T-joint, and the weld in the joint can be close to butt weld and fillet weld. Lap joint: this kind of weld is transformed from riveted or bolted joint. Generally, fillet weld is used in lap joint. It can be side face weld, side face weld, joint weld or plug weld. It is also one of the welding methods of lap joint.
Weld is formed by different ways of welding, mainly divided into butt weld (plane butt and curved butt) and fillet weld.
According to the external shape of the weld, it can be divided into convex and plane shape, while the fillet weld can also choose concave weld besides the above two kinds. Through a lot of weld forming experiments, it is found that the convex weld on the surface seems to strengthen the weld and increase the cross-sectional area of the weld. In practice, the convex weld is bad for the operation of the joint and can not increase the tensile strength of the welding section. This is because the convex weld causes the distortion of the force transmission line under the action of load. Stress concentration occurs at the transition from weld to base metal, resulting in fracture of the joint between weld and base metal. In order to improve the operation function of butt weld, the weld shape can be selected, which is conducive to the uniform transmission of stress line and the reduction of stress concentration. For the fillet weld, the concave weld can be selected. The appearance of the weld makes the weld form a smooth transition to the base metal, which can effectively reduce the stress concentration, so it can greatly improve the operation function of the welding joint.