Zhuojin Pipe Fitting Co., LtdCalculated Closure Temperature Determination for Steel Tube Concrete Arch Bridges Based on Test Research
Literature Overview
The paper by Lin Chunjiao, Zheng Jialian, and Huang Haidong, published in the Journal of Guangxi University (Natural Science Edition) in 2010, presents experimental research on the temperature effects during the formation process of steel tube concrete (STC) arch ribs. The study investigates the structural temperature field and temperature effects under the action of concrete hydration heat, and proposes a method for determining the calculated closure temperature of STC arch bridges.
The research is supported by the National Western Transportation Construction Science and Technology Project and Guangxi University Research Fund. The experimental work was conducted on a single circular tube section STC arch rib, covering the process from empty steel tube closure to the formation of the complete STC arch rib.
Experimental Program and Temperature Field Analysis
The experimental setup involved continuous monitoring of the temperature field and structural response during the STC arch rib formation process. The monitoring covered the critical period from steel tube closure through concrete pouring and curing, capturing the temperature evolution and associated structural effects.
| Monitoring Parameter | Measurement Method | Time Interval |
|---|---|---|
| Steel tube temperature | Thermocouples embedded in steel tube | Continuous |
| Concrete temperature | Thermocouples at multiple depths | Continuous |
| Structural displacement | Displacement transducers | Continuous |
| Ambient temperature | Meteorological station | Hourly |
| Concrete hydration heat | Calorimetric measurement | Continuous |
The temperature field analysis reveals several important characteristics:
- Initial temperature rise: Immediately after concrete pouring, the concrete temperature rises rapidly due to hydration heat. The steel tube temperature increases more gradually due to its thermal mass and the heat transfer resistance at the steel-concrete interface.
- Temperature differential: A significant temperature differential develops between the concrete core and the steel tube, particularly during the early stages of hydration. This differential creates thermal stresses within the composite section.
- Temperature stabilization: After approximately 7 days, the concrete temperature stabilizes as hydration heat generation decreases. The steel tube temperature continues to equilibrate with the ambient temperature, creating a residual temperature field.
- Residual temperature effects: The stabilized temperature field creates residual thermal stresses and deformations that persist in the structure, affecting the long-term structural behavior.
Calculated Closure Temperature Methodology
The paper proposes a methodology for determining the calculated closure temperature of STC arch bridges based on the experimental findings:
- Structural temperature: The average ambient temperature during the 7 days following concrete pouring is adopted as the structural temperature at the time of arch rib formation.
- Temperature internal forces: The residual temperature internal forces at the end of the hydration heat period are used as the corresponding section temperature internal forces for structural analysis.
This approach simplifies the complex time-dependent temperature field into a single equivalent temperature condition that can be used in structural analysis. The methodology is based on the key finding that hydration heat has a minimal effect on the residual temperature stress in the steel tube, while having a significant effect on the concrete.
| Parameter | Value/Method | Rationale |
|---|---|---|
| Structural temperature | 7-day average ambient temperature | Captures the stabilized temperature condition |
| Steel tube residual stress | Negligible | Steel tube temperature equilibrates quickly |
| Concrete residual stress | Significant | Concrete retains hydration heat effects |
| Time of measurement | 7 days after pouring | Hydration heat largely dissipated |
| Analysis method | Equivalent temperature load | Simplifies time-dependent effects |
Engineering Practice Implications
The proposed methodology has several important implications for the design and construction of STC arch bridges:
- Design accuracy: Using the calculated closure temperature provides a more accurate representation of the structural temperature condition than using the ambient temperature at the time of steel tube closure. This improves the prediction of internal forces and deformations in the completed structure.
- Construction planning: The methodology highlights the importance of monitoring the ambient temperature during the critical 7-day period following concrete pouring. Construction schedules should account for temperature variations that could affect the calculated closure temperature.
- Structural analysis: The equivalent temperature load approach allows for the inclusion of temperature effects in standard structural analysis procedures, without requiring complex time-dependent thermal analysis.
- Quality control: The methodology provides a basis for verifying the structural temperature condition during construction, enabling comparison between predicted and measured values.
Key Insights and Reflections
The most significant finding of this research is the differential effect of hydration heat on the steel tube and concrete components of the STC section. The steel tube, due to its high thermal conductivity and relatively small thermal mass compared to the concrete volume, equilibrates with the ambient temperature relatively quickly. In contrast, the concrete core retains the effects of hydration heat for a longer period, creating significant residual temperature stresses.
This differential behavior has important implications for the design of STC arch bridges. The residual temperature stresses in the concrete can affect the long-term structural performance, including the development of cracks, the distribution of internal forces, and the overall structural stiffness. The proposed methodology of using the 7-day average ambient temperature as the calculated closure temperature provides a practical and accurate approach to accounting for these effects.
The research also highlights the importance of considering temperature effects in the construction sequencing of STC arch bridges. The temperature condition at the time of concrete pouring can significantly affect the structural behavior, and this effect should be accounted for in the design calculations. The proposed methodology provides a systematic approach to incorporating temperature effects into the design process.
A limitation of the current methodology is that it assumes the temperature effects can be represented by a single equivalent temperature condition. In reality, the temperature field is spatially and temporally variable, and the equivalent temperature approach may not capture all the nuances of the thermal behavior. However, for practical engineering purposes, the simplified approach provides a reasonable balance between accuracy and computational efficiency.
Summary
This experimental study provides valuable insights into the temperature effects during the formation of steel tube concrete arch ribs and proposes a practical methodology for determining the calculated closure temperature. The key finding that hydration heat has minimal effect on steel tube residual stress but significant effect on concrete residual stress guides the development of the equivalent temperature load approach. The proposed methodology of using the 7-day average ambient temperature as the structural temperature provides a practical and accurate tool for incorporating temperature effects into the design of STC arch bridges. Engineers should adopt this methodology to improve the accuracy of structural analysis and ensure the long-term performance of STC arch bridge structures.