Analysis of Hybrid Construction Method for Steel Tube Concrete Arch Bridges

Literature Overview

The paper by Tang Jishun, Hu Tao, Chen Yuanjiu, and Wu Xuwei from Southwest Jiaotong University, published in Sichuan Building Science (Vol. 43, No. 6, 2017), proposes and analyzes a hybrid construction method for steel tube concrete (CSTC) arch bridges that combines scaffolding erection for the arch foot sections with cable-sling hanging method for subsequent segments. The research employs Midas/Civil finite element software to evaluate the structural behavior and final geometry accuracy of this hybrid approach compared to the conventional cable-sling hanging method alone.

Construction Methodology

Conventional Cable-Sling Hanging Method

The traditional approach for CSTC arch bridge erection involves:

1. Erection of temporary cable-sling support system from towers or anchor blocks
2. Sequential lifting and positioning of steel tube arch segments from the crown toward the arch feet
3. Connection of segments via field welding or bolted splices
4. Concrete infilling of the steel tubes after geometry verification
5. Release of cable-slings in a controlled sequence

Limitations of the conventional method:

• Difficulty in achieving precise geometry at the arch foot sections due to limited access and support flexibility
• High stress concentrations at the arch foot during construction
• Limited ability to correct accumulated geometric errors

Proposed Hybrid Construction Method

The hybrid method introduces a strategic modification:

Scaffolding Erection for Arch Foot Sections

The scaffolding method for arch foot segments provides:

• Direct vertical support eliminating reliance on cable-sling tension
• Greater geometric precision through survey-controlled positioning
• Reduced construction stress at the arch foot
• Easier access for welding and inspection of critical connections
• Ability to verify geometry before proceeding with subsequent segments

Finite Element Analysis Results

Internal Force Distribution Comparison

The Midas/Civil analysis reveals that the internal force distribution in the completed arch is largely consistent between the two construction methods:

Geometric Accuracy (Line Shape)

The most significant advantage of the hybrid method is improved final geometry:

• The arch foot sections, constructed on scaffolding, achieve closer agreement with the design line shape
• Cumulative geometric errors from cable-sling deflection and segment positioning are minimized
• The transition from scaffolding-erected sections to cable-sling-erected sections requires careful coordination but is achievable with proper interface design

Construction Phase Stress Analysis

During the construction process, the hybrid method exhibits:

• Lower peak stresses in the arch foot segments compared to the conventional method
• More uniform stress distribution during the sequential erection process
• Reduced temporary support requirements at the arch feet
• Potentially lower requirements for temporary reinforcement of the arch foot section

Engineering Practice Considerations

Interface Design Between Construction Methods

The transition zone between scaffolding-erected and cable-sling-erected segments requires careful engineering:

1. Connection detail: The interface joint must accommodate differential movement between the two construction phases while maintaining structural continuity.
2. Welding sequence: Field welds at the interface should be executed after both adjacent segments are in their final positions to minimize residual stress.
3. Temporary supports: Adequate temporary bracing is required at the interface during the transition period.
4. Survey control: Precise surveying at the interface ensures geometric continuity between construction methods.

Welding Quality Requirements for CSTC Arch Bridges

The fabrication and erection welding of CSTC arch bridges demands rigorous quality control:

Material and Manufacturing Specifications

Study Insights and Reflections

This research presents a practical and well-justified improvement to CSTC arch bridge construction methodology. The hybrid approach addresses a recognized limitation of the conventional cable-sling method—poor geometric control at the arch foot sections—without fundamentally altering the established construction workflow for the majority of the arch. The finding that internal force distributions are comparable between methods while geometric accuracy is improved with the hybrid approach makes a compelling case for adoption in projects where line shape precision is critical. The study's limitation is the absence of experimental validation through physical model testing or full-scale construction monitoring, which would provide additional confidence in the analytical predictions. For practicing bridge engineers, the key takeaway is that construction method selection should be evaluated not only on structural efficiency but also on geometric accuracy, constructability, and long-term durability implications. The hybrid method represents a pragmatic optimization that leverages the strengths of both scaffolding and cable-sling approaches while mitigating their respective weaknesses.