The rigid joint design for steel column beams ensures both rigidity and shear resistance to ensure stable moment transmission. The key is to ensure the integrity of the joint structure, the continuity of the force transmission path, and the coordinated action of shear components. This allows the joint to both resist rotational deformation (ensure rigidity) and withstand shear impact (enhance shear resistance). Ultimately, this ensures uniform moment transmission, preventing excessive rotation due to insufficient rigidity or localized damage due to shear failure. Rigid joints are the key hub for force transmission between columns and beams. Bending moment transmission relies on the coordinated action of the axial force of the flange and the shear force of the web. Therefore, the design must be based on the principle of "strong flange rigidity for bending transmission and strong web shear resistance," combining structural optimization with material adaptation to create a joint system that balances rigidity and shear resistance.
The holistic design of the joint structure is the foundation for ensuring rigidity. The steel column and beam must be tightly connected through the flange and web to form a single load-bearing unit, minimizing rotational gaps. The connection between the beam flange and the column flange is the core component for transmitting bending moments. Full-penetration welds are typically used. The welds must cover the entire width and thickness of the flanges. This ensures that axial tension and compression are evenly transferred to the columns through the welds when the flanges transmit bending moments. This prevents localized deformation of the flanges due to discontinuous or insufficient weld strength, which could weaken the joint rigidity. Furthermore, the connection between the beam web and the column web must coordinate with the flange force transmission and be tightly secured using high-strength bolts or combined welds (bolts + welds). The bolts should be evenly distributed along the web height to prevent localized loosening of the web under shear forces, further restraining the joint's rotational potential. Some joints also incorporate cover plates (such as double or single cover plates) at the flange connection. These cover plates are connected to the flanges and columns via welds or bolts, creating a triple rigid connection: flange-cover-column. This significantly enhances the joint's resistance to rotation and ensures more stable moment transmission.
Strengthening shear resistance requires designing specialized components for areas where shear is concentrated at the node to prevent excessive shear from causing web buckling or connection failure. The web of a steel beam is the primary component bearing the shear force at the node. When the shear force is large, shear buckling is likely to occur due to the thickness of the web alone. Therefore, transverse stiffeners are required on both sides of the web. The stiffeners are arranged perpendicular to the web, welded to the beam flange at the top and the column flange or web at the bottom to support the web and prevent wavy deformation of the web under shear. For nodes with particularly large shear forces (such as nodes in industrial plants subject to dynamic loads), diagonal stiffeners are also installed. The diagonal stiffeners and the web form a triangular support structure that disperses the shear force borne by the web to the column flange, reducing local stress concentration in the web. In addition, the web thickness of the steel columns in the node area will be appropriately increased, or a slab will be added to the outside of the column web to enhance the column's ability to withstand shear forces from the steel beam. This will prevent localized sagging of the node under shear forces due to insufficient column web strength, which could affect overall load-transfer stability.
The continuous design of the force transmission path is key to balancing rigidity and shear resistance. The transmission of bending moments from the steel beam to the column must be uninterrupted and abrupt, avoiding stress concentration that weakens the node's performance. When bending moments are transmitted within the beam, the flanges bear the primary axial forces (tension and compression), while the webs bear the secondary shear forces. Therefore, the node design must adhere to this force transmission logic: the axial force from the beam flange is directly transmitted to the column flange via full-penetration welds, ensuring a straight, uninterrupted axial force transmission path. The shear force from the beam web is transmitted to the column web via bolt groups or combination welds. The number and arrangement of the bolt groups must be calculated based on the shear force to ensure that the shear force is evenly distributed throughout the column and avoid overloading local bolts. Some joints utilize a hybrid load-transmission configuration combining "butted flanges and lapped webs." The flanges utilize butt welds to ensure rigid bending transmission, while the webs are connected to the columns via lap plates. The length and width of the lap plates must be tailored to the shear force transmission requirements. This not only allows for smoother shear force transmission, but also enhances joint rigidity through the restraining effect of the lap plates, achieving synergistic bending and shear resistance.
Adapting material properties can further enhance joint rigidity and shear reliability. Ensure that the strength of the joint connection components is no less than that of the steel column beam material to avoid the "strong component, weak joint" phenomenon. The strength grade of the weld material must match the steel grade of the steel column beam. For example, welds made of high-strength steel require high-strength welding wire or rods to ensure that the welds do not fail before the component itself when transmitting axial and shear forces. The performance grade of high-strength bolts must be selected based on the load requirements of the joint, and the bolt preload must meet the design requirements. This preload ensures a tight fit between the bolts and the component, reducing gaps in the joint under load and enhancing rigidity. The steel strength and thickness of auxiliary components such as stiffeners and cover plates in the joint area must be compatible with the web and flange of the steel beam to avoid local deformation caused by insufficient auxiliary component strength, which could impact the overall performance of the joint. For example, the thickness of the stiffeners must be at least half the thickness of the web to ensure effective support of the web and prevent buckling.
Stress dispersion design in the joint area can prevent excessive local stress from compromising rigidity and shear resistance. Structural optimization is necessary to reduce stress concentration areas. The corners where the beam flanges meet the column flanges are prone to stress concentration. During design, the welds here are polished into a smooth, rounded arc shape, or a rounded transition plate is added at the corners to smoothly transfer stress from the flange to the column, avoiding stress concentration at sharp corners that could lead to weld cracking. For bolted joints, bolt holes must be placed away from stress concentration areas, and the distance between the hole edge and the component edge must meet regulatory requirements to prevent stress concentration around the bolt holes and steel tearing. Some joints also incorporate ribs (such as corner braces) at the intersection of the flange and web. These ribs connect the flange at one end and the web at the other. This rib partially transfers the axial force of the flange to the web, distributing the shear force on the web and reducing stress concentration at the joint, further enhancing the joint's rigidity and shear stability.
Precise control of the installation process is crucial for ensuring the designed performance of the joint. Strict construction controls are required to minimize the impact of installation deviations on rigidity and shear resistance. During joint installation, the alignment of the steel column and beam must be adjusted to ensure perfect alignment of the flange and web connection surfaces. This prevents misalignment that could lead to uneven weld stress or insufficient bolt preload. Full penetration welds must be welded in layers, with controlled temperature and speed for each layer to prevent deformation that could cause joint gaps and weaken rigidity. High-strength bolts must be tightened to the preset torque using a torque wrench to ensure uniform preload on each bolt and prevent loosening of some bolts, which could compromise joint shear performance. After installation, the nodes must be visually inspected and non-destructively tested (such as ultrasonic testing of the internal quality of welds) to check for weld defects, loose bolts, and other problems, to ensure that the rigidity and shear resistance of the nodes meet the design requirements and provide guarantees for the stable transmission of bending moments.
