Enhancing the shear resistance of the connection points between columns and beams in heavy-duty racking square steel frames requires comprehensive measures from multiple perspectives, including structural design, material selection, connection techniques, and auxiliary reinforcement measures, to ensure the rack maintains structural stability and safety when carrying heavy cargo.
The connection points between columns and beams are the core load-bearing points of heavy-duty racking square steel frames, and their shear resistance directly affects the rack's overall load-bearing capacity. Common connection methods include hook-and-loop, snap-on, pin-and-clip, welding, and bolting. The snap-on and bolting methods are widely used in applications requiring high structural stability due to their ability to effectively control three-dimensional forces. The snap-on method creates a stable mechanical structure through the three-dimensional engagement of the connectors at the ends of the beams with the pre-recorded holes in the columns. The bolted method enhances the shear stiffness of the joints through the combined shear and tensile-compressive action of high-strength bolts.
In terms of material selection, columns and beams are typically constructed from high-strength cold-rolled steel plates or hot-rolled steel sections, whose yield strength and tensile strength directly influence the shear performance of the joints. At the connection points, steel materials of similar or higher quality than the main structure should be selected to avoid stress concentration due to differences in material properties.
The impact of the connection process on the shear resistance of the joint cannot be ignored. When welding connections, ensure that the weld quality meets specification requirements to avoid defects such as lack of fusion and slag inclusions that reduce shear strength. For pressure-bearing high-strength bolt connections, the bolt preload and torque coefficient must be strictly controlled to ensure uniform stress distribution across the bolt group. Regarding bolt arrangement, avoid cross-sectional weakening caused by too small bolt spacing, while also preventing stress concentration caused by too large bolt spacing. For example, the distance from the center of the bolt to the edge of the component should not be less than three bolt diameters, and the minimum spacing between two bolts should not be less than five bolt diameters.
Auxiliary reinforcement measures can further enhance the shear resistance of the joint. For example, adding stiffeners at connection nodes can improve shear stiffness by increasing the moment of inertia of the section. Using wedge-shaped cover plates can enhance the shear resistance of beam-column joints without reducing beam strength and stiffness. For rigid connections between box-shaped or circular columns and beams, external stiffeners can be used, making the joint strength significantly greater than the steel beam. Furthermore, the rational arrangement of diagonal braces and cross braces can create a stable triangular structure, effectively distributing horizontal shear forces and enhancing the rack's overall resistance to lateral displacement.
In terms of structural optimization, shear capacity can be increased by increasing the cross-sectional area of the connection nodes. For example, in the case of crane beam reinforcement, increasing the cross-section by welding thick steel plates to the web and flange plates significantly increases the load-bearing capacity. For heavy-duty rack square steel frames, locally thickening the columns and beams at the connection nodes or adding longitudinal stiffeners can reduce shear deformation. At the same time, attention must be paid to the thickness design of the joint area. If the thickness does not meet the specification requirements, the column web in the joint area should be partially thickened or welded to prevent structural failure due to shear failure.
Installation quality control is critical to ensuring the shear resistance of the joint. During column installation, verticality should be calibrated with a spirit level. The vertical deviation of a single column should be controlled within a reasonable range to prevent additional bending moments caused by column tilt. When installing beams, ensure that the hooks or connectors are accurately inserted into the column holes and that the safety pins or locking bolts are inserted to prevent the beam from falling due to forklift collisions during loading and unloading. Furthermore, the tightness of the connectors should be regularly checked, and loose or damaged bolts and pins should be promptly replaced to ensure that the joint maintains a stable load-bearing state.
