Steel Tube Arch Installation Methods and Construction Control

Literature Overview

This paper by Du Diansuo, Wang Ketai, and Li Zhitao (1998), published in Railway Standard Design (Vol. 18, No. 8, pp. 15-17), presents the installation methods and construction control procedures for the 3168-meter steel tube arch of the Tianjin Development Zone Rainbow Bridge main span. The paper is authored by engineers from the 18th Engineering Bureau of the Ministry of Railways, Unit 5, reflecting the practical engineering experience of a major construction project.

Core Technical Content

Project Background

The Tianjin Development Zone Rainbow Bridge features a steel tube concrete (STC) arch with a total length of 3168 meters. This is a substantial structure that required careful planning of the installation sequence, temporary support systems, and construction control procedures to ensure structural integrity during and after construction.

Installation Methodology

The installation of the steel tube arch involves several key phases:

1. Prefabrication: Steel tube segments are fabricated in workshops according to the design dimensions and tolerances. The segments are typically fabricated from HFW or LSAW welded steel pipes per the relevant standards.
2. Transportation: The prefabricated segments are transported to the construction site, with careful attention to preventing damage to the steel tube surfaces and weld seams.
3. Erection: The segments are lifted into position using cranes or temporary lifting equipment. The erection sequence is critical to maintaining the structural stability of the arch during construction.
4. Splicing and welding: Adjacent segments are spliced together using field welding procedures. The welding process must be carefully controlled to minimize residual stresses and distortion.
5. Concrete infilling: After the steel tube arch is erected and the temporary supports are in place, the concrete core is poured to complete the STC arch.

Construction Control

Construction control involves monitoring the geometry and stresses of the arch during installation to ensure that the actual construction state matches the design intent. Key control parameters include:

• Arch elevation: The vertical position of the arch crown and haunches must be within specified tolerances.
• Arch chord length: The horizontal distance between the arch springing points must be accurate.
• Segment joint alignment: The angular and positional alignment of adjacent segments must be within tolerance.
• Temporary support loads: The loads on temporary supports must be monitored to ensure they remain within design limits.

Technical Analysis

Steel Pipe Fabrication Requirements

The steel tube arch segments are fabricated from large-diameter steel pipes, typically in the range of 500-1500 mm in diameter with wall thicknesses of 10-30 mm. The fabrication process must comply with relevant standards such as:

The weld quality of the steel tube segments is critical to the structural integrity of the arch. Longitudinal welds in HFW or LSAW pipes must be inspected using non-destructive testing (NDT) methods such as radiographic testing (RT) or ultrasonic testing (UT) per GB/T 3323 or ISO 17636.

Field Welding Considerations

The field splicing welds between adjacent segments are subject to additional challenges compared to workshop welds:

• Environmental conditions: Wind, rain, and temperature variations can affect weld quality.
• Accessibility: Limited access to the weld joint can make preparation and inspection difficult.
• Residual stress: Field welds may introduce higher residual stresses due to the constrained conditions.

The welding procedure specification (WPS) for field welds must be qualified through weld procedure qualification testing (WPQT) per ISO 15614 or GB/T 19948. The welders must be certified per ISO 9606 or GB/T 15169.

Construction Control Procedures

The construction control procedure for the steel tube arch installation follows a systematic approach:

1. Pre-construction survey: Establish reference points and control benchmarks.
2. Segment alignment: Use total stations and theodolites to align segments within tolerance.
3. Stress monitoring: Install strain gauges and displacement sensors to monitor structural response.
4. Temporary support adjustment: Adjust temporary supports based on monitored data to maintain the arch geometry.
5. Post-construction verification: Verify the final geometry and stresses against design values.

Study Insights and Reflections

This paper provides valuable practical insights into the construction of large-span steel tube concrete arches. The construction control procedures described are essential for ensuring that the as-built structure matches the design intent, which is critical for the long-term performance and safety of the bridge.

From a welding engineering perspective, the field splicing welds represent a critical quality control point. The weld quality directly affects the structural integrity of the arch, and any weld defect can lead to premature failure under service loads. The welding procedure must be carefully controlled, with rigorous pre-weld inspection, in-process monitoring, and post-weld NDT.

The paper also highlights the importance of temporary support systems in arch construction. The temporary supports must be designed to carry the full weight of the arch during construction, including the self-weight of the steel tube segments and the construction loads. The supports must be monitored throughout the construction process to ensure they remain within their design capacity.

For engineers involved in similar projects, this paper serves as a practical reference for the planning and execution of steel tube arch installation. The construction control procedures described can be adapted for different arch geometries and spans, with appropriate modifications to the monitoring parameters and tolerance criteria.