Zhuojin Pipe Fitting Co., LtdOptimization Analysis of Prestressed Steel Concrete Composite Truss for Coal Conveying Bridges
Literature Overview
The research by Song Can, Yao Jitao, Yan Lei, and Zhao Huajing, published in World Information on Earthquake Engineering in 2016, addresses the structural optimization of prestressed steel-concrete composite trusses used in large-span coal conveying bridge upper corridors. Supported by the National Natural Science Foundation of China (Grant No. 51278401), this work introduces an innovative objective function called the equivalent deflection ratio and applies an improved full-stress method to optimize truss configurations for 70 m and 80 m spans.
Core Technical Methodology
The concept of the equivalent deflection ratio as an optimization objective function represents a significant methodological contribution. Traditional optimization approaches typically minimize either deflection-to-span ratio or steel tonnage independently, but neither alone captures the true economic efficiency of a prestressed composite truss. The equivalent deflection ratio integrates both structural performance and material economy into a single metric, enabling more rational design comparisons.
The improved full-stress method serves as the computational engine for this optimization. In this method, each truss member is designed to reach its allowable stress under the governing load combination, ensuring that no member is significantly under-stressed. The optimization variables include the form of web members and the arrangement of tension rods, which directly influence both the load path efficiency and the fabrication complexity of the truss.
Optimization Results and Comparative Analysis
The study evaluated multiple truss configurations and arrived at several key findings:
| Configuration | Span | Deflection-Span Ratio | Steel Tonnage | Economic Efficiency |
|---|---|---|---|---|
| Chevron web members | 70-80 m | Lower | Lower | Best overall |
| Multi-anchor external cable | 70-80 m | Reduced midspan deflection | Reduced | Significantly improved |
| Single-anchor configuration | 70-80 m | Higher | Higher | Less optimal |
The finding that chevron-shaped (inverted V) web members provide the best economic benefit is consistent with established truss design principles but is validated here through the more rigorous equivalent deflection ratio framework. The multi-anchor external cable arrangement further reduces midspan deflection and equivalent deflection ratio, demonstrating that prestressing cable layout is as critical as truss geometry itself.
Welding and Fabrication Considerations
From a steel pipe and welding engineering perspective, the optimization results have direct implications for fabrication planning. Chevron web members involve diagonal butt-welded or fillet-welded connections between steel pipe elements and chord tubes. The geometry of chevron members creates complex joint configurations at the apex where two diagonal members meet the bottom chord, requiring careful weld sequence planning to minimize distortion.
Key fabrication challenges include:
- Control of angular distortion at the chevron apex joints, where asymmetric heating patterns can cause significant out-of-plane deformation.
- Weld procedure qualification for multi-layer, multi-pass welding at thick-walled joint regions, particularly when using Q345 or Q420 grade steels.
- Fit-up tolerances for diagonal members connecting to chord tubes, where dimensional accuracy is critical for achieving full-stress utilization.
- Inspection of circumferential welds at truss panel joints, where residual stresses from multiple adjacent welds can accumulate and affect fatigue life.
The prestressing cables themselves require careful anchorage design, with attention to weld integrity at cable anchorage plates and the steel-concrete interface where bond development occurs.
Engineering Practice Integration
The improved full-stress method combined with the equivalent deflection ratio objective function offers a practical optimization framework that can be applied to other prestressed steel structures beyond coal conveying bridges. Engineers working on industrial conveyor structures, pedestrian bridges, or even offshore platform structures can adapt this methodology. The computational simplicity noted by the authors makes this approach accessible for preliminary design stages where rapid scheme comparison is needed.
However, the optimization framework does not directly account for welding cost, inspection time, or fabrication complexity, which are significant factors in real-world project economics. A complete design optimization should integrate the structural efficiency metrics from this paper with a fabrication cost model that includes weld volume, weld access requirements, and NDT coverage.
Reflections and Study Insights
This paper demonstrates that the optimization of prestressed composite trusses benefits greatly from a holistic objective function that captures both performance and economy. The equivalence between structural efficiency and economic efficiency, when properly weighted, leads to designs that are not only structurally sound but also practical to fabricate and inspect. The emphasis on external cable arrangement as a key optimization variable highlights the importance of prestressing system design in composite structures, a topic that deserves greater attention in current engineering practice.
The application of prestressed steel-concrete composite trusses to coal conveying bridges represents a specialized but important engineering domain where the combination of large spans, heavy loads, and dynamic loading demands rigorous structural optimization. The methodology presented here provides a transferable framework for similar applications across industrial infrastructure.