Zhuojin Pipe Fitting Co., LtdTemperature Field and Effect Analysis of Large Steel Tube Concrete Composite Arch Ribs
Literature Overview
The research by Zhou Liming, Tang Pengfei, Pan Dong, and Mao Jianping (2023), published in Concrete, Issue 8, examines the temperature field distribution and thermal effects in large-scale steel tube concrete (CFT) composite arch ribs throughout the structural lifecycle from concrete curing to long-term service. This study is particularly significant for bridge engineering applications where CFT arch ribs are commonly used for large-span structures. The research was supported by the National Natural Science Foundation of China (51878186, 51868007), the National Key R&D Program (2019YFC1511103), and the Guangxi Transportation Industry Key Science and Technology Project.
Full-Scale Monitoring and Temperature Field Characteristics
The researchers conducted real-time temperature monitoring of a full-scale CFT structure from the beginning of concrete hardening through the post-construction period. This comprehensive monitoring approach provides valuable empirical data that complements finite element analysis.
The temperature field characteristics observed during the study can be summarized as follows:
| Monitoring Period | Temperature Phenomenon | Engineering Significance |
|---|---|---|
| Hydration peak phase | Maximum internal temperature differential | Risk of thermal cracking and debonding |
| Post-peak 10 hours | Critical period for debonding initiation | Requires enhanced insulation measures |
| Solar radiation exposure | Surface temperature variation up to 15°C | Significant impact on thermal stress distribution |
| Long-term service | Cyclic thermal loading | Fatigue considerations for composite interface |
A key finding is that the internal surface temperature differential within the CFT section is prone to cause debonding phenomena, particularly approximately 10 hours after the hydration heat peak. This critical period requires careful thermal management through insulation measures to prevent interface damage that could compromise structural integrity.
Finite Element Analysis and Thermal Effects
Following the experimental monitoring, the researchers established a finite element model to analyze the effects of temperature-induced stresses and deformations. The model incorporated the following thermal and mechanical properties:
| Component | Thermal Conductivity | Coefficient of Thermal Expansion |
|---|---|---|
| Steel tube | 50 W/(m·K) | 12 × 10⁻⁶ /°C |
| Concrete | 1.7 W/(m·K) | 10 × 10⁻⁶ /°C |
| External concrete jacket | 1.7 W/(m·K) | 10 × 10⁻⁶ /°C |
The finite element analysis revealed several important thermal effect patterns:
- Radial temperature distribution: The temperature distribution across the CFT section cross-section follows a parabolic nonlinear pattern, with lower temperatures at the outer surfaces and higher temperatures at the center. This is consistent with the lower thermal conductivity of concrete compared to steel.
- Asynchronous strain-temperature response: The surface strain of the CFT structure does not vary synchronously with temperature changes. This asynchronous behavior is attributed to the viscoelastic properties of concrete and the differential thermal expansion between steel and concrete.
- External concrete jacket effects: After the external concrete jacket is cast, at the peak of hydration heat, the internal concrete stress reaches approximately 3 MPa, while the steel tube stress reaches approximately 36 MPa. The external concrete jacket stress remains below 2 MPa even after complete hardening.
Engineering Implications and Design Recommendations
The study provides several critical insights for the design, construction, and maintenance of CFT composite arch ribs:
- Construction sequencing: The timing of external concrete jacket placement relative to the internal concrete hydration cycle is critical. Placing the jacket during the peak hydration period may induce excessive stresses in the steel tube.
- Thermal insulation: During the hydration phase, particularly 10 hours after the peak, enhanced insulation measures are necessary to minimize internal surface temperature differentials and prevent debonding.
- Solar radiation management: The 15°C surface temperature variation caused by solar radiation has a significant impact on thermal stress distribution. Reflective coatings or shading devices may be warranted for structures in high-radiation environments.
- Long-term monitoring: Given the asynchronous strain-temperature response, long-term structural health monitoring systems should account for thermal effects to avoid misinterpreting thermal strains as damage indicators.
Study Insights and Concluding Remarks
This comprehensive study bridges the gap between experimental observation and theoretical analysis in understanding the thermal behavior of large-scale CFT structures. The finding that steel tube stresses can reach 36 MPa during the hydration peak of the external concrete jacket is particularly noteworthy, as it highlights the potential for significant residual stresses that may affect the long-term structural capacity. The parabolic temperature distribution pattern and the asynchronous strain-temperature response provide important boundary conditions for refined finite element models used in structural design. Engineers involved in CFT bridge construction should incorporate these thermal effects into their design calculations and construction protocols to ensure the durability and safety of these critical infrastructure components throughout their service life.