Zhuojin Pipe Fitting Co., LtdPBL-Stiffened Rectangular Steel Tube Concrete Truss Arch Bridge Design
Literature Overview
This paper by Long Gang, Liu Yongjian, Zhu Weiqing, and Feng Bowen, published in Highway Traffic Science and Technology (2017, Vol. 34, No. 12, pp. 51-58), presents the design and structural analysis of a novel PBL-stiffened rectangular steel tube concrete (SRC) truss arch bridge. The research was supported by multiple funding sources including the National Natural Science Foundation of China (51378068, 51508027), the Ministry of Transport Construction Science and Technology Program (2013 318 812 410), the Shaanxi Provincial Natural Science Foundation (2016JQ5104), and the China Postdoctoral Science Foundation (2015M582587). The study addresses a critical practical problem in SRC bridge engineering: the debonding and void formation at the steel-concrete interface under solar radiation and cyclic loading.
PBL Stiffener Concept and Structural Innovation
The PBL (Profiled Steel Bar) stiffener is a transverse rib element inserted between the steel tube wall and the concrete infill to enhance interfacial bonding and mechanical interlock. The innovation presented in this paper is the systematic integration of PBL longitudinal ribs within the rectangular SRC arch ribs of a truss arch bridge, creating a new structural form designated as the PBL-stiffened rectangular SRC truss arch bridge.
| Component | Function | Design Consideration |
|---|---|---|
| PBL longitudinal rib | Enhance steel-concrete interfacial bonding | Spacing, height, and welding quality |
| Rectangular steel tube | Primary load-bearing element | Wall thickness, tube geometry |
| Concrete infill | Compressive load sharing, fire protection | Mix design, placement quality |
| Truss system | Lateral stability, load distribution | Member sizing, connection design |
| Arch rib | Primary compression member | Axial force, bending moment |
The PBL stiffener addresses two critical failure mechanisms identified in existing SRC bridge practice: debonding at the steel-concrete interface under thermal cycling caused by solar radiation, and void formation due to incomplete concrete filling in large cross-sections. Both mechanisms compromise the composite action between the steel tube and the concrete, leading to reduced structural capacity and accelerated deterioration.
Structural Analysis and Force Distribution
The finite element analysis was conducted at two levels: the overall bridge level and the local detail level. The overall analysis evaluated the force distribution across the lower arch ribs, the truss-arch composite system, and the key structural components under various loading conditions.
The force distribution analysis revealed several important patterns:
| Structural Component | Force Distribution Pattern | Design Implication |
|---|---|---|
| Lower arch rib | Maximum axial compression near crown, decreasing toward arch feet | Crown region requires highest section capacity |
| Arch rib at crown | Minimum axial pressure, increasing toward arch feet | Arch feet experience maximum axial force |
| Arch feet | Maximum axial pressure and shear force | Foundation design critical |
| Web members (腹杆) | Transfer forces between lower rib and arch rib | Connection design critical |
| Nodes near crown | Complex stress state with high web forces | Detailed local analysis required |
The web members serve as the primary load transfer elements between the lower arch rib and the arch rib, connecting the entire truss structure into a unified load-bearing system. The nodes near the crown, where web member forces are largest, exhibit complex stress states that require detailed finite element modeling to accurately capture local stress concentrations and deformation patterns.
PBL Stiffener Performance and Interface Behavior
The local finite element models of typical nodes and arch rib segments revealed the effectiveness of PBL stiffeners in improving structural performance:
| Performance Aspect | Without PBL Stiffener | With PBL Stiffener | Improvement |
|---|---|---|---|
| Force transfer length at nodes | Longer | Significantly reduced | Improved load distribution |
| Stress concentration at nodes | Severe | Reduced | Enhanced fatigue resistance |
| Node deformation | Larger | Smaller | Better serviceability |
| Steel-concrete debonding under solar radiation | Significant | Substantially reduced | Improved durability |
| Void formation risk | Higher | Lower | Better composite action |
The PBL stiffener reduces the force transfer length at nodes, which means that the load is distributed over a shorter distance, resulting in higher local stresses but a more efficient load path. This reduction in transfer length is accompanied by a decrease in overall node deformation, improving the serviceability performance of the structure.
The thermal analysis of the steel-concrete interface under solar radiation demonstrated that the PBL stiffener significantly mitigates debonding and void formation. The mechanical interlock provided by the PBL rib creates additional resistance to relative displacement between the steel tube wall and the concrete, maintaining composite action even under the differential thermal expansion caused by solar heating. This is particularly important for bridges in regions with large diurnal temperature variations, where thermal cycling can cause progressive interface degradation over the bridge's service life.
Engineering Practice and Quality Control
The construction of the PBL-stiffened SRC arch bridge requires careful attention to several quality control aspects:
- PBL rib welding to the steel tube wall must be performed in accordance with qualified welding procedures, with full penetration welds to ensure complete mechanical interlock. The weld quality directly determines the effectiveness of the PBL stiffener.
- Concrete placement must ensure complete filling of the tube interior, with particular attention to the regions between PBL ribs where voids are most likely to form. High-performance concrete with good workability and low shrinkage is recommended.
- The truss member connections must be designed to accommodate the complex force states identified in the analysis, with particular attention to the nodes near the crown where web member forces are largest.
- The overall bridge geometry and alignment must be verified during construction to ensure that the assumed force distribution patterns are achieved in practice.
The bridge under construction in Xining, Qinghai Province, demonstrates that the PBL-stiffened rectangular SRC truss arch bridge form meets functional requirements, achieves environmental harmony and aesthetic appeal, maintains reasonable stress levels throughout the structure, and satisfies safety requirements. The integration of PBL stiffeners represents a practical engineering solution to a well-recognized durability problem in SRC bridge construction.
This research contributes a novel structural concept with demonstrated analytical support and practical implementation. The PBL stiffener approach offers a scalable solution that can be applied to various SRC bridge configurations, and the detailed finite element analysis methodology provides a template for evaluating similar structural innovations in future projects.