Mechanical Performance of Prefabricated Square Steel Tube Flange Connection Nodes

Literature Overview

This study, published in Industrial Construction (2017, Vol. 47, No. 8, pp. 139-144) by Liu Xuechun et al. from Beijing University of Technology and the Beijing Engineering Research Center of High-rise and Long-span Prestressed Steel Structures, investigates the mechanical performance of flange connection nodes for prefabricated multi-story steel structures. The research is supported by the National Natural Science Foundation of China (51678010) and the Beijing Natural Science Foundation (8172009). Using ABAQUS finite element analysis software, eleven flange node columns with different flange thicknesses, bolt edge distances, and bolt hole diameters were analyzed under combined tension, bending, and shear loading conditions.

Finite Element Model Configuration and Parameters

The flange connection represents a novel all-bolt splicing method for box columns in prefabricated multi-story steel structures. Unlike traditional welded connections, flange connections offer advantages in prefabrication, including ease of assembly, reduced on-site welding, and potential for disassembly and reuse. The connection involves flange plates attached to the column ends, which are bolted together to form the joint.

Core Technical Findings

The finite element analysis reveals that flange thickness is the primary factor influencing the bearing capacity, stiffness, and prying force of flange connections. Thicker flanges provide greater resistance to bending and shear, resulting in higher bearing capacity and stiffness. The prying force, which is the additional tensile force developed in the bolts due to the flexure of the flange plates, increases with flange thickness but is also influenced by the bolt edge distance.

The bolt edge distance affects the magnitude of the prying force. A larger edge distance allows for greater flange plate flexure before the bolt bearing resistance is mobilized, which can increase the prying force. Conversely, a smaller edge distance limits the flange plate deformation, reducing the prying force but potentially increasing the bearing stress at the bolt holes. The bolt hole diameter, surprisingly, has no significant effect on the mechanical performance of the flange connection nodes.

Prying Force Analysis and Design Considerations

Prying force is a critical phenomenon in bolted flange connections that can significantly affect the connection performance. When the flange plates flex under load, the bolts experience additional tensile forces beyond the direct shear and tension loads. This prying force can reduce the effective bolt capacity and potentially lead to premature connection failure if not properly accounted for.

The finite element analysis provides detailed insight into the distribution of stresses and deformations within the flange connection. The stress concentrations at the bolt holes, the flange plate bending moments, and the bolt tension distribution are all captured in the nonlinear analysis. The results can be used to develop design equations and guidelines for flange connection sizing.

The finding that bolt hole diameter has no significant effect on mechanical performance is practically important, as it provides design flexibility in bolt hole sizing. This means that bolt holes can be sized based on fabrication tolerances, bolt fit requirements, and installation practicality without concern for their effect on connection strength.

Engineering Practice and Quality Control

For prefabricated steel structures using flange connections, the following quality control measures are important: flange plate thickness must be precisely controlled during fabrication to ensure the designed bearing capacity and stiffness. The bolt edge distance must be maintained within specified tolerances to control the prying force. Bolt hole dimensions should be fabricated according to standard tolerances, with attention to hole position accuracy for proper bolt engagement.

The welding of flange plates to column ends requires careful attention to weld quality. The welds must be designed and executed to transfer the full connection loads without premature failure. Weld inspection methods such as ultrasonic testing (UT) or magnetic particle testing (MT) should be employed to detect any weld defects. The bolted connections require proper torque control during assembly to ensure the designed clamping force and friction resistance.

The parametric study of eleven specimens provides a comprehensive understanding of the flange connection behavior under combined loading. The results can be used to develop design charts and simplified calculation methods for practical engineering applications. The nonlinear finite element analysis captures the complex interaction between the flange plates, bolts, and column sections, providing a reliable basis for connection design.

Study Insights and Implications

This research provides valuable insights into the mechanical behavior of flange connections for prefabricated steel structures. The identification of flange thickness as the primary design parameter and the finding that bolt hole diameter has no significant effect offer practical guidance for connection optimization. The prying force analysis highlights the importance of considering this phenomenon in connection design, as it can significantly affect bolt sizing and connection performance. The finite element approach used in this study provides a reliable tool for analyzing complex flange connection behavior, enabling engineers to optimize connection designs for specific loading conditions and structural requirements. The results contribute to the advancement of prefabricated steel construction by providing validated design data for a novel connection type that offers significant advantages in construction efficiency and quality control.