Frequently Asked Questions (FAQ)

# Welding Methods for Steel Structures

# Welding Methods for Steel Structures The common welding method used in steel structures is **arc welding**, including **manual arc welding**, **automatic or semi-automatic arc welding**, and **gas-shielded welding**, etc. **Manual arc welding** is the most widely used welding method in steel structures, with simple equipment and flexible operation. However, working conditions are poor, production efficiency is lower than that of automatic or semi-automatic welding, and weld quality varies greatly, depending to a certain extent on the skill level of the welder. **Automatic welding** features stable weld quality, few internal defects, good ductility and impact toughness, and is suitable for long straight welds. **Semi-automatic welding**, with manual operation, is suitable for welding curved or arbitrarily shaped welds. Automatic and semi-automatic welding shall use welding wires and fluxes compatible with the base metal. Welding wires shall comply with national standards, and fluxes shall be determined according to welding process requirements. **Gas-shielded welding** uses inert gas (or CO₂) as the shielding medium to isolate molten metal from air and maintain a stable welding process. It has concentrated arc heating, high welding speed and deep penetration, so weld strength is higher than that of manual welding. It also provides good ductility and corrosion resistance, making it suitable for welding thick steel plates. ## I. Weld Types According to the relative positions of connected members, welded connections can be divided into four types: **butt joint, lap joint, T-joint and corner joint**. The welds used in these connections include two basic types: **butt welds** and **fillet welds**. In practical applications, selection shall be made based on the stress conditions of the connection, combined with fabrication, installation and welding conditions. ## II. Weld Details ### 1. Butt Welds Butt welds transfer force directly and smoothly without significant stress concentration, thus providing good mechanical performance. They are suitable for member connections under static or dynamic loads. However, due to high quality requirements and strict gap requirements between workpieces, they are generally used for shop-fabricated connections. ### 2. Fillet Welds **Types of fillet welds**: According to the relationship between their length direction and the external force, fillet welds can be divided into side fillet welds parallel to the load direction, front fillet welds perpendicular to the load direction, diagonal fillet welds oblique to the load direction, and wrap-around fillet welds. **Cross-sectional forms of fillet welds**: They are divided into **standard type, flat-slope type and deep-penetration type**. The standard fillet has a leg ratio of 1:1, approximately an isosceles right triangle, with severe stress concentration due to sharp force flow deviation. For structures directly subjected to dynamic loads, to ensure smooth force transmission, front fillet welds should adopt the flat-slope type with a leg ratio of 1:1.5 (long leg along the internal force), and side fillet welds should adopt the deep-penetration type with a ratio of 1:1.