Geometric Nonlinear Analysis of Arch Rib Hoisting in Concrete-Filled Steel Tube Arch Bridges

Literature Overview

This paper by Zhang Mingyuan, Wang Xueguo, Jiang Zhixue, and Lu Zhe'an, published in the Journal of Wuhan University of Technology in 2003 (Vol. 25, No. 9, pp. 40-42), addresses the geometric nonlinear behavior during the hoisting (erection) of arch ribs in large-span concrete-filled steel tube (CFST) arch bridges. The study was supported by the Hubei Provincial Science and Technology Project (20011g0037) and was applied to the Nanlidu Bridge in Enshi Prefecture. As a senior engineer specializing in steel pipe fabrication, welding, and quality control, I recognize the critical importance of construction-stage analysis for CFST structures, where the steel pipe components are fabricated through welding and then filled with concrete.

Core Technical Content and Methodology

The authors developed a geometric nonlinear static analysis program specifically tailored for cable-beam-bar plane structural systems, which are characteristic of the temporary hoisting systems used in CFST arch bridge construction. The methodology encompasses:

Geometric nonlinear formulation: The analysis accounts for large displacements and rotations that occur during the sequential hoisting of arch rib segments, where the structural geometry changes significantly from the initial to the final configuration.
Forward iterative algorithm: Based on construction control theory, the forward algorithm was employed to simulate the step-by-step erection process, considering the progressive changes in load paths and internal force distributions.
Engineering application: The analysis was applied to the Nanlidu Bridge in Enshi Prefecture, providing construction control guidance for the actual hoisting operation.

Key Technical Findings

Technical Aspect	Description	Relevance to Steel Pipe Fabrication
Geometric nonlinearity	Large displacements during hoisting	Affects dimensional accuracy of welded segments
Analysis system	Cable-beam-bar plane structure	Represents the temporary hoisting system
Algorithm	Forward iterative method	Captures progressive construction stages
Engineering case	Nanlidu Bridge, Enshi Prefecture	Practical validation of methodology
Construction control	Real-time monitoring and adjustment	Requires precise welding and fabrication tolerances

Interpretation of Technical Points

The geometric nonlinear analysis is essential because, during the hoisting of CFST arch rib segments, the structure undergoes significant geometric changes. Each segment, when lifted and connected to the previously erected segments, induces secondary stresses and redistributes the internal force system. The steel pipe segments of the arch rib are typically fabricated through welding (longitudinal and circumferential welds) and must maintain tight dimensional tolerances to ensure proper fit-up during erection.

From a welding perspective, the following considerations are paramount:

Welding distortion control: The longitudinal and circumferential welds in the steel pipe segments must be designed and executed to minimize angular and longitudinal distortion. Pre-setting (camber) of the segments before welding is often necessary to compensate for expected welding-induced deformations.
Fit-up tolerances: During the hoisting process, segments must be aligned and connected with precision. The welding groove preparation and fit-up gap must comply with the requirements of GB/T 985.1 and the applicable welding procedure specifications. For CFST arch ribs, typical fit-up tolerances include a root gap of 2-5 mm and misalignment of no more than 1.5 mm.
Temporary support welding: The temporary hoisting connections (often bolted or welded) must be designed to withstand the geometric nonlinear effects identified in the analysis. These temporary welds may require post-weld heat treatment to relieve residual stresses before the permanent structural loading is applied.

Connection with Engineering Practice

In the fabrication of CFST arch rib segments, the following engineering practices are directly informed by the geometric nonlinear analysis:

Segmentation strategy: The number, length, and weight of individual segments must be determined based on the hoisting capacity and the geometric nonlinear response. Overly long segments may experience excessive bending during lifting, while too many segments increase the number of field welds and associated quality risks.
Welding sequence optimization: For the field-welded connections between segments, the welding sequence must be planned to minimize distortion. Symmetrical welding from the center outward, or alternating welds on opposite sides of the joint, are common strategies to control angular distortion.
Concrete filling sequence: The concrete filling of the steel pipe segments must be coordinated with the hoisting sequence. The analysis must account for the additional self-weight of the concrete as each segment is filled, which changes the load distribution during subsequent hoisting operations.
Quality assurance during erection: Each field-welded joint must be inspected using non-destructive testing (RT or UT) before the next segment is hoisted. The acceptance criteria for weld defects should be stringent, particularly for the circumferential welds that carry the primary bending and axial loads in the arch rib.

Key Questions and Reflections

How does the geometric nonlinear analysis account for the welding residual stresses and distortions in the fabricated segments? The idealized finite element model typically assumes perfect geometry, but in reality, welding-induced deformations can shift the neutral axis and alter the load distribution.
What is the impact of welding defects on the geometric nonlinear response? A lack-of-fusion defect or an undercut at a circumferential weld can create a local stress concentration that, under the large displacements predicted by the nonlinear analysis, may initiate crack propagation.
The analysis assumes elastic material behavior. However, during the hoisting process, local yielding may occur at weld joints due to stress concentrations. Should the analysis incorporate material nonlinearity in addition to geometric nonlinearity?

Study Insights and Implications

This paper provides a rigorous analytical framework for the construction-stage assessment of CFST arch bridges. The development of a specialized geometric nonlinear analysis program for cable-beam-bar systems demonstrates the need for construction-specific analysis tools that go beyond the capabilities of general-purpose structural analysis software.

For engineers involved in the fabrication and welding of CFST arch rib segments, the key takeaway is that the construction process itself introduces significant geometric nonlinearities that must be anticipated and controlled. This means that the fabrication tolerances, welding procedures, and erection sequences must be carefully planned in conjunction with the construction-stage analysis. The quality of each field-welded joint directly affects the structural integrity of the completed arch, and any weld defect that reduces the effective cross-sectional area or creates a stress concentration can compromise the load-bearing capacity predicted by the analysis.

The study also highlights the importance of construction monitoring. Real-time measurement of displacements, strains, and temperatures during the hoisting process should be compared with the analytical predictions, and corrective actions should be taken when deviations exceed acceptable limits. This integrated approach of analysis, fabrication, welding quality control, and construction monitoring is essential for the successful completion of large-span CFST arch bridges.