Zhuojin Pipe Fitting Co., LtdSimulation Analysis and Model Testing of Construction Process After Main Arch Closure in CFST Tied-Arch Bridge
Literature Overview
The paper by Zhang Kebo, Yan Donghuang, and Yang Rihua (2008), published in World Bridges (Vol. 36, No. 1, pp. 57-60), presents a comprehensive study on the construction process simulation and model testing of the Yiyang Maocaojie Bridge, a CFST mid-rise tied-arch bridge. Funded by the Western Transportation Construction Science and Technology Project (2003318798201), this work addresses the critical phase of construction that occurs after the main arch closure, where the structural behavior transitions from a staged assembly to a complete system. The study combines 1:20 scale model testing with finite element simulation analysis to verify the accuracy of computational predictions and the feasibility of the construction methodology.
Core Technical Content and Construction Phase Analysis
The main arch closure represents a pivotal moment in the construction of a tied-arch bridge, as it transforms the structure from two independent cantilever arms into a continuous arch system. The post-closure construction phase involves several critical operations that can significantly affect the final structural performance:
| Construction Phase | Key Operations | Structural Concerns |
|---|---|---|
| Arch closure | Final welding, gap closure, stress release | Residual stress accumulation, weld distortion |
| Deck assembly | Bridge deck installation, load transfer | Differential settlement, load path transition |
| Tie rod tensioning | Post-tensioning of tie members | Stress redistribution, arch thrust control |
| Finishing works | Pavement, barriers, utilities | Dead load addition, serviceability |
Simulation Model Development
The authors established a detailed FE simulation model that accounts for the construction sequence, including the staged assembly of arch ribs, the progressive deck installation, and the post-tensioning of tie rods. The model incorporates the geometric nonlinearity arising from large deformations during construction, as well as the material nonlinearity of the CFST members. The 1:20 scale model test was designed to replicate the key construction phases and instrumented with strain gauges and displacement transducers to capture the structural response at critical locations.
Welding and Fabrication Considerations
From the perspective of steel pipe and welding technology, the arch closure operation is particularly demanding. The CFST arch ribs, typically fabricated from large-diameter steel tubes (commonly Φ800-Φ1200 mm for main arch ribs in bridges of this span range), require precise alignment and welding at the closure joint. The welding process at the arch crown or closure section must account for:
- Residual stress management: The pre-existing residual stresses from the tube manufacturing process (HFW or LSAW longitudinal welds) combine with welding-induced residual stresses at the closure joint, potentially creating unfavorable stress superposition.
- Distortion control: The closure weld must be executed with minimal angular and longitudinal distortion to maintain the designed arch profile, which is critical for the structural performance of the tied-arch system.
- Material matching: The weld metal must match or exceed the strength and toughness properties of the base steel tube material, particularly in low-temperature service environments.
- NDT requirements: The closure weld is typically classified as a critical weld requiring 100% UT or RT inspection, with acceptance criteria per relevant standards such as SY/T or GB/T.
Comparison of Simulation and Test Results
The authors report that the simulation results showed good agreement with the model test measurements, validating both the FE model formulation and the construction methodology. The key findings include:
- The stress distribution after arch closure was consistent between simulation and test, with maximum stresses occurring at the arch haunches and springings.
- The deformation profile during deck assembly matched predictions within acceptable tolerances, confirming the accuracy of the construction sequence simulation.
- The tie rod tensioning stage produced the expected stress redistribution, with the arch thrust being effectively balanced by the tie rod tension.
Engineering Practice Integration
This study provides valuable guidance for the construction planning and quality control of CFST tied-arch bridges. The integration of model testing with simulation analysis establishes a verification framework that can be adapted for similar projects. For welding engineers involved in the fabrication and field welding of CFST arch ribs, the following practices are recommended:
- Implement a weld sequence plan that minimizes cumulative distortion at the closure joint, using symmetric welding patterns and temporary fixturing.
- Perform pre-weld thermal analysis to predict the thermal cycle and residual stress distribution, enabling targeted post-weld heat treatment if necessary.
- Conduct full-scale weld coupon tests using the same welding parameters, consumables, and base material batches as the production welds, to verify mechanical properties and fracture toughness.
- Establish a construction monitoring system that compares real-time strain and displacement data with simulation predictions, enabling early detection of anomalies.
Study Insights and Reflections
The methodology presented in this paper—combining scaled model testing with construction sequence simulation—represents a rigorous approach to construction verification that is particularly valuable for complex steel-concrete composite structures. The 1:20 scale model, while not capturing all full-scale effects, provides a practical means of validating the FE model and identifying potential issues before full-scale construction. For the welding and fabrication community, this approach underscores the importance of considering the entire construction sequence, not just individual weld quality, in ensuring structural integrity. The arch closure weld is not merely a connection—it is the structural event that defines the final load path of the entire bridge system, and its quality directly influences the long-term performance and safety of the structure.
The key lesson for practice is that construction simulation must be performed with the same rigor as structural design analysis, and that the verification of simulation predictions through physical testing is essential for building confidence in the construction methodology. Engineers should invest in developing detailed construction simulation models early in the project, updating them as construction progresses, and using the simulation-test comparison as a quality assurance tool throughout the construction phase.