Overall Hoisting Construction Method for Steel Pipe Concrete Tied-Arch Bridge

Literature Overview

This paper by Li Shuguang from Guangzhou Tunnel Development Company, published in the Central-South Highway Engineering journal in 2002, documents the first domestic application of single-arch-rib hoisting for the Guangzhou Jiefang Bridge, a steel pipe concrete tied-arch bridge. The work focuses on the construction workflow of the upper structure, specifically addressing the challenges of erecting steel tube arch ribs without wind bracing during assembly. From a steel pipe fabrication and welding perspective, this case study is particularly valuable because it highlights the practical demands placed on pipe segment fabrication, field welding, and structural integrity verification during the critical hoisting phase.

Core Technical Content

The Jiefang Bridge project introduced a pioneering approach to arch rib erection by lifting individual steel tube ribs as complete units rather than assembling them in place with temporary bracing. This method places extreme demands on the fabrication quality of the steel tube segments, the precision of welding joints, and the structural stability of the rib during the vulnerable pre-concrete-infill period. The construction sequence involves fabricating steel tube segments in a controlled workshop environment, transporting them to the site, hoisting them into position, welding segment connections, and only then pouring concrete into the steel tubes to form the composite arch rib.

Steel Tube Fabrication and Welding Requirements

The steel tubes used as arch ribs must meet stringent dimensional tolerances and weld quality standards because any deviation in geometry or weld integrity can lead to catastrophic failure during the single-rib hoisting operation. The following table summarizes the key fabrication parameters that are critical to the success of this construction method:

Hoisting Phase Structural Behavior

During the hoisting of a single arch rib without wind bracing, the steel tube acts as a pure flexural member carrying its own weight and any dynamic loads from wind or crane operations. The tube is in a "open-section" condition with no concrete infill, meaning it relies entirely on the steel tube's own bending stiffness, which is significantly lower than the composite stiffness achieved after concrete filling. The bending moment distribution during hoisting is asymmetric and can produce local buckling stresses in the thin-walled tube sections. Engineers must verify that the steel tube can withstand the maximum bending moment at mid-span during the lift without exceeding the allowable stress or experiencing local panel instability.

The welding joints between segments are particularly vulnerable during this phase because they represent the weakest cross-section in the rib. Full-penetration butt welds with 100% radiographic inspection are mandatory, and the weld heat-affected zone must be stress-relieved to prevent hydrogen-induced cracking under the combined effects of residual stress and operational loads. The weld metal composition must match or slightly exceed the base metal strength to ensure that the weld itself is not the failure initiator.

Construction Sequence and Quality Control

The construction workflow can be broken down into the following critical stages, each requiring specific quality control measures from a steel pipe and welding standpoint:

1. Workshop fabrication: Steel tubes are cut, formed, and welded into segments under controlled conditions with full NDT coverage.
2. Transportation: Segments are transported with proper support points to prevent denting or deformation of the tube cross-section.
3. On-site hoisting: The crane lifts the segment into position with precision alignment of the connection flanges or butt joints.
4. Field welding: Segment joints are welded in the field with careful control of preheat temperature, interpass temperature, and post-weld heat treatment.
5. Concrete infill: After the rib geometry is verified and all welds pass inspection, concrete is pumped into the steel tube to form the composite section.

A key lesson from this project is that the single-rib hoisting method demands a significantly higher level of fabrication quality than conventional assembly-in-place methods. The margin for error is smaller because the structure must be self-supporting during the lift, and any weld defect or geometric deviation can lead to loss of structural stability during the most critical phase of construction.

Engineering Practice Insights

From a practical standpoint, this construction method has profound implications for the steel pipe supply chain and welding operations. The requirement for full-penetration welds with 100% NDT inspection increases fabrication costs by approximately 20-30% compared to partial-penetration welds with spot inspection. However, this cost premium is justified by the reduced risk of catastrophic failure during the hoisting phase. The project also demonstrates that the absence of wind bracing during rib erection is feasible only when the steel tube geometry is optimized for bending resistance, which may require thicker walls or more frequent stiffening rings than would be needed in a braced configuration.

The Jiefang Bridge project set a precedent for subsequent steel pipe concrete arch bridges in China, establishing that single-rib hoisting is a viable construction approach when fabrication quality is rigorously controlled. The key takeaway for practicing engineers is that the steel tube is not merely a formwork for concrete but a structural member that must independently bear significant loads during construction phases, and its fabrication and welding quality must be correspondingly elevated.