Zhuojin Pipe Fitting Co., LtdInfluence of Concrete Construction Sequence on Dumbbell-Shaped Steel Pipe Concrete Arch Bridges
Literature Overview
This paper examines the effect of concrete pouring sequence within the arch ribs on the structural behavior of dumbbell-shaped steel pipe concrete arch bridges. A dumbbell-shaped arch cross-section consists of two separate steel tubes connected by a concrete web or diaphragm, forming a distinctive cross-section that provides high bending stiffness while maintaining structural efficiency. The construction sequence of concrete placement within and between the steel tubes can significantly influence residual stresses, deformation distribution, and the final load-bearing capacity of the arch.
Cross-Sectional Configuration and Construction Challenges
The dumbbell-shaped cross-section comprises two outer steel tubes (typically circular or elliptical) connected by a central concrete web. This configuration offers several advantages: high flexural rigidity due to the large section modulus, efficient use of steel material, and the ability to use high-strength concrete in the web zone. However, the construction of concrete within and between the steel tubes presents unique challenges, particularly regarding the sequencing of placement operations.
| Construction Phase | Description | Key Concern |
|---|---|---|
| Phase 1 | Concrete placement in bottom tube | Thermal gradient, hydration stress |
| Phase 2 | Concrete placement in web zone | Bonding to existing concrete, differential shrinkage |
| Phase 3 | Concrete placement in top tube | Weight distribution, arch thrust development |
| Phase 4 | Diaphragm and finishing concrete | Final composite action, residual stress relaxation |
Sequence-Dependent Structural Response
The order in which concrete is placed within the steel tubes and connecting web directly affects the development of arch thrust and the distribution of internal forces. If the bottom tube is filled first, the additional weight generates a sagging moment that must be resisted by the partially constructed arch. Subsequent placement of the web and top tube concrete then introduces additional weight at different locations, modifying the internal force distribution.
The paper demonstrates that sequential placement can lead to differential shrinkage between concretes placed at different times. Early-placed concrete undergoes more shrinkage by the time later-placed concrete reaches its final properties, creating internal stresses at the interface between concretes of different ages. These differential shrinkage stresses can be particularly problematic in the web zone, where the bond between the web concrete and the tube concrete is critical for composite action.
Residual Stress and Deformation Analysis
Finite element analysis combined with field measurements reveals that the construction sequence significantly influences the magnitude and distribution of residual stresses. When concrete is placed symmetrically (both tubes simultaneously), the arch experiences primarily axial compression with minimal bending. Asymmetric placement, however, introduces bending moments that can lead to permanent deformation of the steel tubes.
The study identifies several critical aspects:
- Thermal stresses from hydration of fresh concrete are highest in the first-placed zone, potentially causing local buckling of thin-walled tubes.
- Differential settlement between sequentially placed concrete zones can create cracking at the interface.
- The arch thrust line position shifts during construction, requiring temporary support systems to be designed for the worst-case sequence scenario.
Practical Construction Recommendations
Based on the analysis, the paper proposes optimized construction sequences that minimize residual stresses and ensure uniform composite action:
- Place concrete in both bottom tubes simultaneously to maintain symmetric loading.
- Allow initial setting and early-age strength development before proceeding to the web zone.
- Place web concrete in horizontal layers with controlled thickness to limit thermal gradient.
- Complete top tube concrete placement last, after the web has gained sufficient strength to transfer loads.
The use of low-heat cement, thermal insulation blankets, and controlled cooling rates are recommended to manage hydration temperatures. Additionally, the interface between sequentially placed concretes should be roughened and treated with bonding agents to ensure adequate shear transfer.
Engineering Significance
For bridge engineers designing steel pipe concrete arch bridges, understanding the construction sequence effects is essential for predicting long-term behavior. The residual stresses induced during construction can reduce the effective load-bearing capacity and influence crack initiation under service loads. Proper construction planning, informed by the sequence-dependent analysis presented in this study, can significantly improve the structural performance and service life of dumbbell-shaped SRC arch bridges.