Stability Analysis of Steel Tube Concrete Single Tower Double Cable Plane Cable-Stayed Bridge

Literature Overview

The paper by Dong Jun et al. (2022), published in Construction Technology (Vol. 51, No. 9, pp. 60–64), investigates the structural stability of a steel tube concrete (SRC) single tower with a double cable plane cable-stayed bridge system, using the Xixian Huai River Bridge as the engineering case study. The authors employed ABAQUS finite element software to model the tower behavior during cable installation, comparing numerical results with on-site measurements to validate the simulation approach.

Core Technical Content

The study focuses on the stress distribution and deformation behavior of the SRC tower during the sequential tensioning of stay cables. The key assumptions include treating the pier and the zeroth block as rigid bodies, modeling stay cables as extremely high-stiffness solid steel members, and fixing the tower base with zero displacement and rotation in all three directions (x, y, z). These simplifications are critical for isolating the tower's structural response from the complex interaction with the main girder and foundation system.

The primary finding is that stress concentration occurs predominantly at the tower base connection zone, where both the steel tube and the core concrete exhibit elevated stress levels. As cable forces increase progressively during construction, the tower undergoes lateral offset deformation; however, this deformation does not compromise the overall structural stability of the bridge. The numerical simulation results for stress evolution and tower-top displacement closely track the measured construction data, confirming the reliability of the model.

Technical Parameters and Modeling Approach

The finite element model adopts a construction-stage analysis approach, which is essential for cable-stayed bridges where the final structural behavior is highly dependent on the construction sequence. The assumption of cables as extremely stiff solid members simplifies the nonlinear cable behavior but may introduce deviations when cable sag effects are significant. In practice, engineers should consider whether the sag stiffness model would yield more accurate results for long-span cables.

Engineering Practice Integration

From a quality control and safety monitoring perspective, the study recommends embedding stress sensors in the stress concentration zone at the tower base. This is a practical and cost-effective monitoring strategy that aligns with the PDCA cycle in construction management: the Plan phase involves sensor placement design, the Do phase covers sensor installation during construction, the Check phase monitors real-time stress data, and the Act phase enables corrective measures if stress levels exceed design thresholds.

For welding and fabrication considerations relevant to SRC towers, the connection between the steel tube and core concrete at the tower base is a critical detail. The welding of stiffening plates, cross-diaphragms, and connection nodes must be carefully controlled to avoid introducing additional stress concentrations. The HAZ properties of the base welds should be verified through ultrasonic testing (UT) and hardness surveys to ensure they do not become preferential locations for crack initiation under the high stress concentrations identified in this study.

Key Questions and Reflections

The study raises an important question regarding the validity of the fully fixed boundary condition at the tower base. In reality, the foundation may exhibit some rotational flexibility, particularly under asymmetric cable loading during construction. A parametric study varying the rotational stiffness at the base would provide more robust design guidance. Additionally, the paper does not address the long-term durability of the SRC interface under cyclic loading from wind and traffic, which is a concern for the service life of cable-stayed bridges.

The finding that tower offset deformation does not affect overall bridge stability is reassuring but should be interpreted cautiously. The analysis likely considers only the construction stage; the operational stage with dynamic traffic loads and wind effects may present different stability challenges, particularly for the single tower configuration which inherently lacks the lateral redundancy of a double tower system.

Study Insights and Implications

This research provides valuable construction-stage monitoring guidance for SRC cable-stayed bridge towers. The identification of the tower base as the critical stress concentration zone has direct implications for inspection protocols and sensor deployment strategies. For steel pipe fabrication and welding engineers, the emphasis on base connection integrity reinforces the need for rigorous welding quality assurance at all structural nodes, particularly where composite action between steel and concrete is relied upon for load transfer.