The connection methods of steel structures include welding, ordinary bolt connection, and high-strength bolt connection, as follows.

(1) Welding

1. Commonly used welding methods for steel structures in construction projects: According to the degree of automation of welding, they are generally divided into three types: manual welding, semi-automatic welding, and automatic welding.

2. According to the connection parts of the welding joints, the fusion welding joints can be divided into: butt joints, corner joints, T-shaped and cross joints, lap joints, and plug welding joints.

3. Weld defects are usually divided into: cracks, holes, and other defects. 

(2) Ordinary bolt connection

1. Common ordinary bolts include hexagonal bolts, stud bolts and anchor bolts.

2. Holes can be made by drilling, punching, milling, reaming, boring and piercing. For larger diameter or rectangular holes, gas cutting can also be used. Gas cutting and hole expansion are strictly prohibited. Drilling and punching are one-time hole making (among which, the thickness of the punched plate should not exceed 12mm). Milling, reaming, boring and punching are secondary hole making methods, that is, the secondary processing of holes is carried out on the basis of primary hole making. The method of gas cutting is used for hole making. In actual processing, the diameter of the circular hole is generally within 80mm. When drilling cannot be achieved, gas cutting can be used for hole making; in addition, for oblong holes or special-shaped holes, the method of drilling first and then using gas cutting can be generally used. When punching is used for hole making, the thickness of the steel plate should be controlled within 12mm.

(3) High-strength bolt connection

1. High-strength bolts are usually divided into friction connection, tension connection and pressure connection according to the connection form, among which friction connection is the basic connection form widely used at present.

2. The treatment methods of the friction surface of the high-strength bolt connection usually include sandblasting (shot) method, pickling method, grinding wheel grinding method and wire brush manual rust removal method. The treatment process can be selected according to the requirements of the design anti-slip coefficient. The anti-slip coefficient must meet the design requirements.