Zhuojin Pipe Fitting Co., LtdPrestressing Technology and Structural Analysis of Steel Tube Concrete Tie-Arch Bridge
Literature Overview
This 1999 paper published in Bridge Construction (Vol. 29, No. 3) documents the prestressing technology and structural behavior of the Nanjing Qixia Bridge, a large-span wide-deck steel tube concrete (SRC) tie-arch bridge with a main span of 86.5 m. Authored by Liu Zhao, Meng Shaoping, Lu Wenhua, and Liu Borun from Southeast University and Nanjing Railway First Engineering Company, the study addresses a relatively novel structural concept at the time, combining the composite action of steel tubes filled with concrete in arch ribs with a prestressed tie beam system.
Core Technical Content
Bridge Configuration and Design Philosophy
The Qixia Bridge represents an early Chinese application of steel tube concrete technology in long-span tie-arch bridges. The structural system relies on the arch ribs transferring vertical loads into horizontal thrust, which is resisted by a prestressed concrete tie beam acting as a self-equilibrating system. The use of SRC arch ribs rather than conventional reinforced concrete or steel arches provides several engineering advantages:
- Higher axial compressive capacity per unit cross-sectional area due to the confining effect of the steel tube on the concrete core
- Improved ductility and post-yield behavior compared to plain concrete arch ribs
- Reduced construction time owing to the formwork-free nature of the steel tube
- Enhanced corrosion resistance of the structural steel tubes when properly coated
Prestressing Construction Technology
The prestressing of the tie beam is critical to the overall structural performance. The study describes a multi-stage prestressing sequence that must be carefully coordinated with the erection of the arch ribs. Key aspects include:
- Pre-tensioning of the tie beam before arch rib installation to establish initial compressive stress
- Gradual release of temporary supports as arch rib segments are erected
- Monitoring of prestress losses during and after construction
- Coordination between prestressing operations and welding of the SRC arch rib segments
| Construction Phase | Structural Behavior | Key Control Parameter |
|---|---|---|
| Tie beam prestressing | Self-equilibrated compression in tie beam | Prestress force accuracy (±5%) |
| Arch rib erection (segment by segment) | Progressive load transfer from temporary supports to tie beam | Arch rib axial force distribution |
| Full span completion | Full composite action activated | Residual stress in tie beam |
| Long-term service | Creep and relaxation of prestress | Deflection and stress monitoring |
Structural Analysis and Monitoring
The authors conducted both analytical and experimental evaluation of the bridge during construction. The measured stresses in the tie beam were compared against theoretical predictions to assess structural safety at each construction stage. The study highlights that:
- The composite action between the steel tube and concrete core in the arch ribs significantly increases the bending stiffness beyond what either material alone would provide
- The prestressing force in the tie beam must account for secondary effects arising from the eccentricity of the arch rib centroid relative to the tie beam
- Wide-deck SRC tie-arch bridges exhibit unique torsional and lateral stability characteristics that differ from narrow-deck counterparts
Engineering Practice Insights
From a steel pipe manufacturing and welding perspective, this project demands particular attention to the fabrication quality of the SRC arch rib tubes. The steel tubes forming the arch ribs are typically large-diameter spiral-welded or longitudinally-welded steel pipes (commonly 400–600 mm in diameter, with wall thicknesses of 10–16 mm). The following quality considerations are paramount:
- Weld seam integrity: The longitudinal or spiral weld of the arch rib tubes must achieve full penetration with no lack of fusion, undercut, or porosity. Visual testing, magnetic particle testing (MT), and ultrasonic testing (UT) are essential. The weld metal must be compatible with the parent steel grade (typically Q345 or Q390 structural steel per GB/T 1591).
- Tube geometry: Ovality and out-of-roundness must be controlled within tight tolerances (typically ≤ 1% of diameter) to ensure uniform concrete confinement. Excessive ovality leads to uneven concrete cover and premature local buckling of the steel tube.
- Concrete placement: The concrete core must be placed under controlled conditions to avoid voids or honeycombing, which would compromise the composite action. Superplasticized concrete with good pumpability and self-compacting properties is preferred.
- Segment joint welding: When arch rib segments are fabricated in manageable lengths and joined on-site, the field welds must achieve full-strength butt joints. Preheating to 100–150°C is typically required for wall thicknesses above 12 mm to prevent cold cracking in the HAZ.
Key Reflections
This study demonstrates that the successful implementation of SRC tie-arch bridges requires not only advanced structural analysis but also meticulous attention to fabrication and construction quality. The prestressing technology described here has since been refined and applied to bridges with spans exceeding 100 m in China. For steel pipe manufacturers, the demand for large-diameter, high-quality structural steel tubes for bridge applications continues to grow, requiring robust quality systems covering raw material certification, welding procedure qualification, and non-destructive testing protocols in accordance with standards such as SY/T 5257 and ISO 3183.