Zhuojin Pipe Fitting Co., LtdExperimental Study on Calculated Closure Temperature for Steel Tube Concrete Arch Bridges
Literature Overview
This 2010 paper by Lin Chunhao, Zheng Jialian, and Huang Haidong, published in the Journal of Guangxi University (Natural Science) (Vol. 35, No. 4, pp. 601-609), investigates the temperature effects during the formation process of steel tube concrete (STC) arch ribs in bridge construction. The research was supported by the National Western Transportation Construction Science and Technology Project (200431881426) and the Guangxi University Research Fund Project (X091013). The study addresses a critical construction engineering issue: how to determine the calculated closure temperature for STC arch bridges, which significantly affects the structural behavior and stress state after construction.
Research Background and Significance
In the construction of STC arch bridges, the arch ribs are typically erected as empty steel tubes first, and then concrete is poured into the tubes to form the composite STC section. The concrete hydration heat generates significant temperature changes within the arch rib during the curing process. These temperature effects influence the residual stress state and the final geometry of the completed arch. The calculated closure temperature is a key parameter used in structural analysis to determine the stress state corresponding to the construction completion condition.
Construction Process Stages
| Stage | Description | Temperature Effect |
|---|---|---|
| Empty tube erection | Steel tubes assembled to final geometry | Ambient temperature |
| Tube closure | Final joint welded to close the arch ring | Closure temperature |
| Concrete pouring | Concrete poured into closed tube | Hydration heat generation |
| Hydration heat peak | Maximum temperature reached | Peak temperature effect |
| Temperature stabilization | Temperature returns to ambient | Residual temperature stress |
| Construction completion | All construction activities finished | Final stress state |
Experimental Program and Instrumentation
The experimental study employed a single circular tube section STC arch rib as the test specimen. The experiment covered the complete process from empty tube closure to the formation of the STC arch rib. Continuous temperature monitoring was conducted to capture the temperature field evolution and associated structural responses throughout the entire process.
Instrumentation and Data Collection
| Instrument Type | Purpose | Measurement Frequency |
|---|---|---|
| Thermocouples | Measure temperature at various locations | Continuous |
| Strain gauges | Measure strain in steel tube and concrete | Continuous |
| Displacement transducers | Measure geometric deformation | Continuous |
| Pressure sensors | Measure internal pressure during concrete pouring | Continuous |
Key Experimental Findings
The experimental results revealed important patterns in the temperature field and structural response during the STC arch rib formation process:
- Temperature field evolution: The hydration heat caused a significant temperature rise in the concrete, with the peak temperature occurring several days after pouring. The temperature distribution was non-uniform across the section, with higher temperatures in the concrete core and lower temperatures in the steel tube wall.
- Steel tube residual temperature stress: The hydration heat had a relatively small effect on the residual temperature stress in the steel tube. This is because the steel tube, being a thin-walled component, experiences relatively uniform temperature changes, resulting in minimal differential thermal strain.
- Concrete residual temperature stress: The hydration heat had a significant effect on the residual temperature stress in the concrete. The temperature gradient between the concrete core and the steel tube wall creates differential thermal strain, leading to substantial residual stresses in the concrete.
- Geometric deformation: The temperature effects caused measurable deformation of the arch rib, including changes in the arch rise and chord length. These deformations must be accounted for in the structural analysis.
Determination of Calculated Closure Temperature
Based on the experimental data, the authors proposed a methodology for determining the calculated closure temperature for STC arch bridges:
- Structural temperature: The atmospheric average temperature 7 days after concrete pouring can be used as the structural temperature at the time of arch rib formation. This accounts for the temperature stabilization period following the hydration heat peak.
- Section temperature forces: The residual temperature forces in the cross-section, calculated after the hydration heat has dissipated, should be used as the corresponding section temperature forces in the structural analysis.
- Analysis approach: The calculated closure temperature and the associated temperature forces are used as initial conditions in the structural analysis to determine the final stress state of the completed bridge.
Methodology Summary
| Step | Description | Key Parameter |
|---|---|---|
| 1 | Measure atmospheric temperature 7 days after pouring | T_ambient |
| 2 | Calculate residual temperature forces after hydration heat dissipation | N_T, M_T |
| 3 | Use T_ambient as calculated closure temperature | T_closure = T_ambient |
| 4 | Use N_T and M_T as section temperature forces | Initial conditions |
| 5 | Perform structural analysis with initial conditions | Final stress state |
Engineering Practice Implications
The findings have direct implications for the design and construction of STC arch bridges:
- Design considerations: The calculated closure temperature should be determined based on the proposed methodology rather than using the temperature at the time of tube closure. This distinction is important because the hydration heat significantly modifies the temperature state after concrete pouring.
- Construction monitoring: Temperature monitoring during the concrete curing period should be conducted to verify that the actual temperature field matches the predicted values. Any significant deviation should trigger a reassessment of the calculated closure temperature.
- Stress analysis: The residual temperature stresses, particularly in the concrete, should be included in the structural analysis to accurately predict the long-term stress state and serviceability performance.
- Quality control: The concrete mix design should consider the hydration heat characteristics to minimize excessive temperature rise and thermal cracking. Low-heat cement or supplementary cementitious materials may be specified for large-volume pours.
Study Insights and Reflections
This research provides valuable experimental evidence for the determination of calculated closure temperature in STC arch bridges. The finding that hydration heat has minimal effect on steel tube residual stress but significant effect on concrete residual stress is particularly important for design engineers, as it highlights the need for careful consideration of concrete temperature stresses in STC structures. The proposed methodology of using the 7-day post-pouring atmospheric temperature as the structural temperature is practical and easy to implement in construction practice. However, the study should be extended to consider the effects of seasonal temperature variations, wind-induced temperature gradients, and the long-term thermal creep behavior of concrete. The work represents a significant contribution to the understanding of temperature effects in STC bridge construction and provides a practical tool for engineers to determine the calculated closure temperature with confidence.