Zhuojin Pipe Fitting Co., LtdConstruction Process Control of Steel Tube Concrete Tied Arch Bridges
Literature Overview and Background
The article by Xiang Yingming, published in Railway Construction (2010, Vol. 50, No. 10), addresses the construction process control of a steel tube concrete tied arch bridge on the Shashen Railway in Fujian Province, China. The main span of 96 m makes this a significant engineering challenge, particularly because the structure is a through-type tied arch bridge carrying the railway track below the arch. Steel tube concrete arch bridges combine the high compressive strength of the confined concrete core with the ductility and formwork efficiency of the steel tube, but their construction sequence introduces complex temporary loading conditions that must be carefully managed to prevent permanent deformation, residual stress accumulation, and geometric deviation from design intent.
The core challenge lies in the fact that the structural behavior during construction differs substantially from the as-built condition. During erection, the arch ribs are not yet fully constrained by the tie rods and deck systems, meaning the temporary support system bears significant loads that must be gradually transferred to the permanent structure. Any error in the sequence of load transfer can result in excessive deflection, cracking of the concrete core, or even instability of the arch rib segments before they are interconnected.
Key Technical Points of Construction Control
The construction of a 96 m steel tube concrete tied arch bridge typically follows a staged erection sequence. The following table summarizes the critical stages and their associated control objectives:
| Stage | Key Activities | Primary Control Objective | Typical Monitoring Parameters |
|---|---|---|---|
| Foundation and Pier Construction | Pier cap and bearing pad installation | Verticality and plan position accuracy | Vertical deviation within ±5 mm/m; bearing pad flatness within 1 mm |
| Arch Rib Segment Fabrication | Steel tube rolling, welding, pre-fabrication | Weld quality and geometric accuracy | Weld NDT (UT/RT) pass rate ≥95%; segment dimensional tolerance ±2 mm |
| Arch Rib Erection | Segment lifting and temporary connection | Alignment and temporary support stability | Arch crown deflection ≤ L/800; horizontal deviation ≤ L/500 |
| Concrete Infilling | Pumping concrete into steel tube | Uniform concrete density and void-free filling | Concrete slump flow 200-260 mm; filling rate controlled to avoid voids |
| Tie Rod and Deck Installation | Tensioning tie rods, installing deck | Load transfer from temporary to permanent system | Tie rod tension within ±5% of design value; deck deflection ≤ L/1000 |
| Final Adjustment | Cable tension adjustment, bearing pad leveling | Final geometric accuracy and stress distribution | Residual stress within allowable limits; final deflection within ±5 mm |
The critical control point during arch rib erection is the management of the temporary support system. For a 96 m span, the arch rib is typically erected in segments from both sides toward the crown. The temporary support must be designed to carry the self-weight of the erected segments plus construction loads, and its removal must be sequenced to avoid sudden load redistribution. The author emphasizes that the entire construction process requires full-process monitoring, which means continuous measurement of deflection, stress, and temperature at multiple locations throughout the arch ribs and temporary supports.
Monitoring Methods and Deformation Management
The monitoring strategy described in the article follows a systematic approach that integrates multiple measurement techniques. Deflection is measured using total stations and precision levels at designated cross-sections along the arch rib, typically at the springing, quarter-span, and crown positions. Stress monitoring employs strain gauges bonded to the steel tube outer surface at critical locations such as the arch rib joints and the connection to the pier caps. Temperature monitoring is essential because thermal gradients across the arch rib cross-section can induce secondary stresses that are comparable to or even exceed those from construction loads.
The deformation management approach uses a predictive-analytical method where a finite element model of the construction sequence is updated with measured data at each stage. If the measured deflection deviates from the predicted value by more than 10 percent, the construction sequence is paused and the cause is investigated. This is a direct application of the Plan-Do-Check-Act cycle in construction engineering: the plan is the construction sequence with predicted deformations, the do phase is the actual construction, the check phase is the comparison of measured versus predicted values, and the act phase is the adjustment of subsequent construction steps based on the analysis.
A key insight from the literature is that the concrete infilling stage introduces the most significant risk of deformation deviation. The concrete, while still in a semi-plastic state, exerts lateral pressure on the steel tube, and if the filling rate is too rapid or the concrete mix is too fluid, the steel tube can bulge outward. This outward bulge is permanent and cannot be corrected after the concrete hardens. Therefore, the concrete filling process must be controlled in terms of both rate and consistency, with frequent inspection of the steel tube outer profile during and after filling.
Engineering Practice Integration
From a steel pipe manufacturing and welding perspective, the quality of the steel tube segments used in the arch ribs is paramount. The steel tubes for such applications typically conform to GB/T 8163 or similar standards, with typical specifications of Q345 or Q420 grade carbon-manganese steel, outer diameters ranging from 600 mm to 1200 mm, and wall thicknesses of 12 mm to 20 mm. The welding of arch rib segments, typically performed using submerged arc welding (SAW) or flux-cored arc welding (FCAW), must meet full-penetration requirements with 100 percent ultrasonic testing and radiographic testing of all longitudinal and circumferential welds.
The residual stress from welding can affect the initial stress state of the arch rib and must be accounted for in the construction sequence modeling. In practice, post-weld stress relief by controlled heating or vibration is sometimes applied to critical joints, though this is not always feasible in the field. The weld heat-affected zone (HAZ) of the steel tube, particularly for Q420 and higher grades, must be evaluated for potential impact toughness degradation, especially if the structure is in a cold climate region.
The monitoring data collected during construction should be archived and made available for the long-term performance evaluation of the bridge. This data provides a baseline against which future deformations due to traffic loading, temperature cycling, and material aging can be assessed. The integration of real-time monitoring with structural health monitoring systems represents a natural extension of the construction control methodology described in the article.
Summary and Implications
The literature provides a clear demonstration that the construction of steel tube concrete tied arch bridges is a highly sensitive process where geometric accuracy, load sequence management, and material quality control are interdependent. The full-process monitoring approach advocated by the author is not merely a regulatory requirement but a technical necessity for ensuring that the as-built structure achieves its designed performance. For engineers involved in steel pipe supply for such projects, the implications are direct: the steel tube segments must be manufactured and welded to exacting standards, and any dimensional or weld quality deviation will propagate through the construction sequence and may compromise the final structural integrity. The methodology described can be extended to other steel tube concrete structures, including bridges, towers, and industrial chimneys, where the construction sequence and load transfer mechanisms present similar challenges.