Effect of Temperature Load on Cable Deviation Angle During Suspended Assembly of Steel Tube Concrete Arch Bridges

Literature Overview

This paper, published in Central South Highway Engineering in 2004, investigates the influence of temperature loads on the deviation angle of stay cables during the suspended assembly and closure process of steel tube concrete (STC) arch bridges. The authors, affiliated with Guangxi University, employed a combination of千斤顶 (jack) and steel strand inclined suspension techniques for bridge assembly. The study derives an analytical expression for the cable deviation angle under temperature variation and concludes that the effect of temperature on cable force direction is negligible, allowing engineers to treat the cable force direction as constant during temperature changes.

Core Technical Findings

The fundamental concern in suspended assembly of STC arch bridges is the precise control of cable tension and geometry during the closure phase. The stay cables (扣索) transfer loads from the arch ribs to temporary supports or towers, and their deviation angle directly affects the distribution of forces in the arch system. The authors derived a mathematical expression relating the temperature change to the deviation angle of the stay cables.

The key conclusion is that temperature-induced changes in cable deviation angle are extremely small under practical construction conditions. This means that during the closure process, engineers can safely assume that the direction of cable force remains unchanged even when ambient temperature varies. This simplification has significant practical implications for construction monitoring and cable force adjustment procedures.

Technical Parameters and Assumptions

Interpretation of the Analytical Approach

The derivation of the cable deviation angle expression involves considering the thermal expansion or contraction of both the cable and the supporting structure. The cable itself undergoes axial deformation proportional to the temperature change and its coefficient of thermal expansion. The supporting structure, typically a steel or concrete tower or temporary support, also deforms under temperature loads. The net effect on the cable's geometric angle depends on the relative deformations of these components.

The authors' conclusion that the deviation angle change is negligible is physically reasonable. Steel cables have a relatively low coefficient of thermal expansion (approximately 12×10⁻⁶/°C), and the geometric stiffness of the cable-support system dominates over the thermal deformation effects. In practical terms, the axial elongation of a cable due to a 20°C temperature change is on the order of a few millimeters per meter of cable length, which produces a negligible change in the cable's inclination angle.

Engineering Practice Implications

This finding directly addresses a common concern in bridge construction monitoring. During the closure phase of arch bridges, engineers must precisely control cable forces to ensure that the arch ribs assume their intended geometry. If temperature effects were significant, construction schedules would need to be tightly controlled to specific temperature windows, which is impractical and costly. The conclusion that temperature effects on cable deviation angle are negligible provides engineering confidence that cable force adjustments can be made without excessive concern for ambient temperature fluctuations.

However, it is important to note that while the deviation angle change is negligible, the cable force magnitude itself can still be affected by temperature through the thermal expansion of the cable. The distinction is critical: the direction of the force is stable, but the magnitude may vary. Engineers should still monitor cable forces during temperature changes, particularly for long-span bridges where cumulative thermal effects on force magnitude may become significant.

Practical Recommendations for Construction Monitoring

1. During the closure phase, cable force measurements should be taken at consistent times of day to minimize temperature-related force variations.
2. The deviation angle of stay cables can be assumed constant for the purpose of force component calculation, simplifying the analysis.
3. Temperature compensation in cable force monitoring should focus on force magnitude rather than force direction.
4. For bridges with spans exceeding 300 meters, a more detailed thermal analysis may be warranted, as cumulative effects could become non-negligible.

Study Insights and Reflections

From my experience in steel pipe and structural fabrication, the principle demonstrated here—that geometric stability of a system can be maintained even when thermal effects are present—is well-established in pressure vessel and piping design. The key insight is the separation of effects: thermal expansion primarily affects axial force magnitude, while geometric constraints maintain directional stability. This separation of concerns is a powerful analytical tool that simplifies complex construction scenarios.

The study's practical value lies in its ability to reduce construction complexity. By establishing that temperature does not significantly affect cable deviation angle, the authors have effectively removed one variable from the construction control equation, allowing engineers to focus on more critical parameters such as cable force magnitude, arch rib geometry, and closure sequence. This is a classic example of how rigorous analysis can simplify engineering practice by identifying which factors truly matter and which can be safely neglected.

The research was supported by the National Natural Science Foundation of China and regional research funding, reflecting the importance of STC arch bridge technology in Chinese infrastructure development. The findings remain relevant for contemporary bridge construction, where STC arch bridges continue to be widely used for their favorable strength-to-weight ratio and constructability.