Linear Shape Control Technology for CFST Arch Bridges

Literature Overview

This study by Yao Changrong and Li Yadong from Southwest Jiaotong University addresses the construction control of CFST arch bridges, specifically focusing on linear shape control technology. Published in the Journal of Highway and Transport Research and Development in 2006, the research discusses the relationships between different linear shapes during the construction process and proposes methods for calculating and controlling the hoisting linear shape of CFST arch rib segments. The study is particularly relevant to the suspended assembly construction method commonly used for CFST arch bridges.

Construction Background

CFST arch bridges are typically constructed using the suspended assembly method, in which steel tube arch rib segments are hoisted and connected at the crown or springing points, progressively extending toward the opposite side. During this construction process, the arch rib is not in its final structural configuration, and the linear shape (geometric profile) of the partially assembled arch differs from the design linear shape. Controlling the linear shape during construction is critical to ensuring that the final arch geometry meets design requirements and that the structural behavior under service loads is as intended.

Key Technical Content

Linear Shape Relationships During Construction

The study discusses the relationships between several types of linear shapes that exist during the suspended assembly construction process:

1. Design linear shape: The theoretical geometry of the arch rib as specified in the design drawings, typically a parabola, circular arc, or other mathematical curve.
2. Construction linear shape: The actual geometry of the partially assembled arch rib during construction, which differs from the design shape due to construction loads, temperature effects, and structural deformations.
3. Hoisting linear shape: The geometry of each arch rib segment as it is hoisted into position, which must be controlled to achieve the desired construction linear shape.
4. Final linear shape: The geometry of the completed arch rib after all segments have been assembled and the construction loads have been removed.

Hoisting Linear Shape Control Method

The authors propose a method for calculating and controlling the hoisting linear shape of CFST arch rib segments. This method takes into account the deformation of the partially assembled arch under construction loads, including the weight of the segments being hoisted, the weight of the completed segments, and any additional construction loads such as wind loads. By predicting the deformation of the partially assembled arch, the method determines the target position for each hoisted segment such that, after assembly, the arch rib approaches the desired construction linear shape.

Technical Parameter Considerations

Engineering Practice Implications

From a steel pipe fabrication and welding perspective, the linear shape control of CFST arch bridges has several important implications.

Steel Tube Fabrication Accuracy

The accuracy of the steel tube segments is critical to the overall linear shape of the arch. Each segment must be fabricated to precise dimensional tolerances, particularly in terms of length, curvature, and cross-sectional geometry. For steel tubes bent to form the arch segments, the bending process must be carefully controlled to achieve the required curvature without introducing excessive residual stresses or geometric imperfections. The welding of tube segments to form complete arch rib segments must also be controlled to minimize angular misalignment and dimensional deviations.

Weld Quality and Construction Loads

During the suspended assembly construction process, the partially assembled arch rib is subjected to significant construction loads, including the weight of the segments being hoisted and the weight of the completed segments. These loads induce bending moments and axial forces in the partially assembled arch, which can cause deformation. The weld joints between segments are critical load-bearing elements during construction, and their quality directly affects the structural behavior of the partially assembled arch. Poorly executed welds can lead to premature joint failure or excessive deformation under construction loads.

Thermal Effects on Linear Shape

The steel tube arch ribs are subject to thermal expansion and contraction during construction. The coefficient of thermal expansion of steel is approximately 12 × 10⁻⁶ per degree Celsius, which means that a 100-meter-long arch rib can expand or contract by approximately 12 millimeters for every 10-degree temperature change. This thermal deformation must be accounted for in the linear shape control method to ensure that the final arch geometry meets design requirements. The temperature at the time of segment hoisting and connection must be recorded and used in the calculation of the target hoisting position.

Study Insights and Reflections

This study provides a practical methodology for controlling the linear shape of CFST arch bridges during suspended assembly construction. The proposed method for calculating and controlling the hoisting linear shape is applicable to other similar bridge structures, as noted by the authors. For steel pipe engineers involved in CFST arch bridge construction, the study highlights the importance of precise steel tube fabrication and welding quality control. The linear shape of the completed arch depends not only on the construction control method but also on the accuracy of the individual steel tube segments and the quality of the weld joints connecting them. Future research could focus on integrating real-time monitoring of the construction process with the linear shape control method, enabling adaptive adjustments to the hoisting positions based on measured deformations rather than predicted deformations alone. This would improve the accuracy of the final arch geometry and reduce the risk of construction-related structural issues.