Finite Element Simulation of Multi-Scale Flange Sleeve Intersection Joints in Steel Tube Towers

Literature Overview

This paper by Jin Shu, Li Jingyu, Niu Yanhong, Wang Lei, and Tian Li presents a finite element analysis of a novel joint configuration for large-span steel tube transmission towers. Published in 2016 in Volume 42, Issue 3 of Sichuan Building Science Research (pages 17–22), the study addresses a critical structural engineering challenge: the connection of branch members to main members in large-span steel tube towers where conventional joint types exhibit deficiencies in strength, stiffness, and constructability.

The authors propose a new joint type termed the "flange sleeve intersection joint" (法兰套管相贯节点), which combines the advantages of welded intersection joints, insert plate connections, and flange connections into a unified design that overcomes the limitations of each individual approach.

Technical Background and Problem Statement

Large-span steel tube towers for power transmission lines require robust joint connections between main members (vertical or near-vertical tubes) and branch members (horizontal or angled tubes). The three conventional connection methods each possess distinct disadvantages:

The proposed flange sleeve intersection joint integrates a sleeve (套管) with flange interfaces into the intersection geometry, creating a hybrid connection that offers:

• Improved stress distribution at the intersection zone
• Enhanced constructability through field-bolted flange connections
• Reduced welding complexity compared to pure intersection welds
• Better fatigue performance due to controlled stress concentrations

Finite Element Analysis Methodology

The study employed ABAQUS, a leading finite element analysis software, to perform elastic-plastic analysis of the proposed joint at different scales. The multi-scale approach is particularly important because steel tube tower joints vary significantly in size depending on the tower height and span length. Key aspects of the analysis include:

1. Geometric modeling: Accurate representation of the sleeve geometry, flange dimensions, and intersection penetration details
2. Material modeling: Elastic-plastic constitutive behavior accounting for steel yield and strain hardening
3. Contact modeling: Proper definition of contact interfaces between sleeve and tube surfaces, and between flange bolted connections
4. Loading scenarios: Simulation of realistic load combinations including dead load, wind load, and ice load

The elastic-plastic analysis reveals the load-bearing capacity, deformation characteristics, and failure mechanisms of the joint under various loading conditions. The multi-scale parametric study identifies how geometric proportions (sleeve length, sleeve thickness, flange dimensions, tube diameter-to-thickness ratio) influence the joint's structural performance.

Key Technical Findings

The finite element results provide valuable insights into the structural behavior of the flange sleeve intersection joint:

• Stress distribution: The sleeve geometry effectively redistributes stress concentrations that would otherwise develop at the intersection penetration in conventional welded joints. The stress flow through the sleeve is more uniform, reducing peak stress levels.
• Failure mechanism: The analysis identifies the critical failure modes, which typically include local yielding of the main tube at the intersection, plastic hinge formation in the sleeve, and potential bolt failure at the flange interface.
• Load capacity: The joint demonstrates adequate strength margins under design load combinations, with the sleeve providing additional load path continuity.
• Deformation behavior: The joint exhibits acceptable deformation characteristics, with the flange bolted connection providing controlled flexibility that accommodates thermal expansion and load-induced deformation.

Engineering Practice Implications

For transmission tower design engineers, this research offers a practical alternative to conventional joint types. The flange sleeve intersection joint is particularly advantageous in scenarios where:

• Field welding is impractical or prohibited due to safety or quality concerns
• Inspection of welded intersections is difficult due to access limitations
• Tower components must be transported in modular sections and assembled on-site
• Fatigue resistance is a critical design consideration for long service life

The design of the sleeve thickness and length requires careful consideration based on the finite element results. Too thin a sleeve fails to redistribute stresses effectively, while an excessively thick sleeve adds unnecessary weight and cost. The optimal sleeve geometry balances structural performance with economic efficiency.

Quality Control and Inspection Considerations

From a welding and quality control perspective, the flange sleeve intersection joint reduces the demands on field welding quality. The primary welds (sleeve to tube) can be performed in a controlled shop environment, while field connections rely on bolted flange interfaces that are more readily inspectable and verifiable. This shift from field-welded to shop-welded connections aligns with industry best practices for ensuring structural integrity in critical infrastructure.

The bolted flange connections require attention to bolt preload control, surface preparation, and corrosion protection. Proper torque control during assembly is essential to ensure the designed frictional resistance and bearing capacity. Regular inspection of bolt tightness and flange surface condition should be incorporated into the maintenance program.

Study Insights and Outlook

The multi-scale finite element analysis approach demonstrated in this study provides a robust methodology for evaluating novel joint configurations before physical prototype testing. This computational approach, combined with targeted experimental validation, accelerates the development of new joint types while reducing development costs. Engineers should consider similar computational workflows when evaluating alternative joint designs for steel tube structures, as the insights gained from parametric studies can directly inform design optimization and code development.