Zhuojin Pipe Fitting Co., LtdConstruction Technology of 132m Steel Tube Concrete Arch Bridge at Lashiwa Yellow River Bridge
Literature Overview
The paper by Wang Huidong and Zhang Hao, published in Railway Standard Design (Volume 24, Issue 9, 2004, pages 77-79), details the construction technology for a 132-meter steel tube concrete (SRC) arch bridge spanning the Yellow River at the Lashiwa Hydropower Station. This project represents a significant engineering challenge due to the large span, the complex geological and hydrological conditions of the Yellow River valley, and the requirements for high structural integrity and long-term durability. The paper focuses on key construction techniques including integrated hoisting and cable-tower systems, dynamic adjustment of the bare arch shape using tensioning jacks, and the two-stage closure of three arch ribs.
Core Construction Technologies
The construction of a large-span steel tube concrete arch bridge involves several critical technical challenges that must be addressed systematically. The primary structural system consists of three parallel steel arch ribs, each filled with concrete to create composite SRC members. The steel tubes serve as both formwork for the concrete and as structural reinforcement, providing a doubly curved compression member with excellent load-bearing capacity and ductility.
Steel Tube Segment Bending and Fabrication
The steel tube segments are fabricated through cold bending (cold forming) processes, which must be carefully controlled to avoid localized plastic deformation, wall thinning, or micro-cracking in the steel tube walls. The bending radius must be maintained at or above the minimum recommended value, typically R/D ≥ 10 for carbon steel tubes and R/D ≥ 15 for alloy tubes, where D is the tube diameter. The bending process introduces residual stresses that can affect the subsequent concrete filling and structural performance. Quality control during bending includes dimensional inspection using three-dimensional laser scanning, wall thickness measurement at critical locations (particularly the inner fiber of the bend), and visual inspection for surface defects.
| Construction Parameter | Specification | Quality Control Method |
|---|---|---|
| Steel tube diameter | 600-800 mm | Caliper measurement |
| Wall thickness | 12-16 mm | Ultrasonic thickness gauge |
| Bending radius ratio R/D | ≥12 | 3D laser scanning |
| Concrete grade | C50-C60 | Cube compressive strength test |
| Concrete filling density | ≥95% | X-ray or gamma-ray scanning |
| Arch rise | 28-32 m | Total station surveying |
| Closure temperature | 20±5°C | Thermocouple monitoring |
Integrated Hoisting and Cable-Tower System
The integrated hoisting and cable-tower system is a key innovation in this project. Traditional arch bridge construction often requires separate systems for lifting and cable-stayed support, leading to complex coordination and potential interference. The integrated system combines the hoisting functions with the cable-stayed tower structure, allowing for more efficient and controlled erection of the arch segments. This approach reduces the number of temporary structures required and improves the overall construction schedule.
The dynamic adjustment of the bare arch shape using tensioning jacks is another critical technique. Before the concrete is filled, the steel arch ribs are erected as bare steel structures. Due to the weight of the steel tubes themselves, the arch will deflect under its own weight, deviating from the designed shape. Tensioning jacks are applied at strategic points along the arch to counteract this deflection and bring the bare arch into the correct geometric profile. The dynamic adjustment process requires real-time monitoring of deflection using precision surveying instruments and iterative adjustment of jack forces until the target profile is achieved within acceptable tolerances (typically ±10 mm for a 132 m span).
Two-Stage Closure of Three Arch Ribs
The three arch ribs are closed in two stages to manage the structural transitions during construction. In the first stage, the two outer arch ribs are closed first, creating a stable structural frame. The inner arch rib is then closed in the second stage, after the outer ribs have been loaded with concrete and have achieved sufficient structural stability. This staged closure approach minimizes the risk of asymmetric loading and ensures that the structural forces are distributed gradually and predictably.
The closure operation must be performed at a specific temperature (typically the mean temperature of the construction period) to minimize thermal stresses in the completed arch. The closure joints are designed with temporary connection devices that can be released after the concrete has reached its design strength, allowing for thermal expansion and contraction without introducing additional stresses.
Engineering Practice Integration
From a steel pipe manufacturing and welding perspective, this project highlights several important considerations. The steel tubes used for the arch ribs must meet strict quality requirements, including chemical composition analysis, mechanical property testing, and non-destructive examination of the pipe body and welds. The longitudinal welds in the steel tubes, if present, must be fully radiographed (RT) or examined by phased array ultrasonic testing (PAUT) to ensure weld integrity. The welding procedure must be qualified according to relevant standards such as GB/T 19866 or AWS D1.1, with appropriate preheating and interpass temperature control to prevent cold cracking in the heat-affected zone.
The concrete filling process within the steel tubes presents unique challenges. The concrete must have excellent pumpability and workability to fill the tube completely without voids. Vibration and compaction methods must be carefully selected to ensure full consolidation, particularly at the top of the tube where air entrainment can occur. Post-filling inspection using X-ray or gamma-ray scanning is recommended to verify the density and detect any voids or honeycombing.
Study Insights and Implications
This project demonstrates the successful application of SRC technology to large-span bridge construction in challenging environments. The integration of advanced construction techniques, including the integrated hoisting system and dynamic shape adjustment, represents a significant advancement in bridge engineering practice. For engineers involved in similar projects, the key lessons include the importance of precise dimensional control during steel tube fabrication, the critical role of temperature-controlled closure operations, and the necessity of comprehensive quality assurance at every stage of construction. The staged closure approach for multiple arch ribs provides a practical solution for managing the complex load transitions during construction, and this methodology can be adapted for other multi-rib arch bridge projects.