Zhuojin Pipe Fitting Co., LtdHydration Heat Temperature Field of Large-Diameter Steel Tube Concrete Members in Complex Environments
Literature Overview
This paper by Zhou Qian, Feng Pengcheng, Zhou Jianting, Jing Shihong, Zheng Guohui, and Zhang Wenfeng, published in Concrete (2023, Issue 3, pp. 148–153), investigates the temperature field distribution and evolution mechanism in large-diameter steel tube concrete (STC) members under the combined action of strong radiation, large temperature differentials, and hydration heat. The study employs ANSYS transient thermal analysis to simulate the temperature field, with results validated by experimental measurements. The research is motivated by the construction of large-span STC arch bridges in plateau regions with extreme environmental conditions.
Core Technical Findings
The study reveals several key characteristics of the temperature field in large-diameter STC members:
- Center concrete temperature: Initially increases due to hydration heat, then decreases and stabilizes at a certain temperature.
- Outer concrete temperature: Exhibits sinusoidal variation with time, with amplitude increasing closer to the steel-concrete interface.
- Solar radiation effect: The highest temperature on the sun-facing side exceeds that on the shaded side by approximately 20°C.
- Radial temperature distribution (afternoon): From the sun-facing side to the center, temperature first decreases then increases, with the turning point located at D/8 from the interface; from the center to the shaded side, temperature gradually decreases.
- Nighttime temperature distribution: Symmetric along all radial directions, with higher and similar temperatures in the D/4-to-center segment.
- Temperature gradient: The maximum temperature gradient on the sun-facing and shaded sides varies sinusoidally with time.
- Daily temperature difference: In the D/8-to-center segment, the daily temperature difference is approximately 1/8 of that at the sun-facing interface.
Technical Parameter Analysis
| Parameter | Typical Value | Effect on Temperature Field |
|---|---|---|
| Tube diameter (D) | 1000–1500 mm | Larger diameter → greater temperature gradients and more complex distribution |
| Wall thickness (t) | 20–40 mm | Thicker walls → better thermal insulation, reducing temperature gradients in concrete |
| Concrete grade | C50–C80 | Higher grade → higher hydration heat, increasing peak temperature |
| Solar radiation intensity | 800–1000 W/m² (plateau regions) | Higher intensity → larger temperature differentials between sun-facing and shaded sides |
| Ambient temperature range | -20°C to +40°C (plateau regions) | Large range → significant daily temperature variations |
| Hydration heat release rate | Depends on cement type and curing conditions | Affects the initial temperature rise and duration of elevated temperatures |
Engineering Practice Implications
The findings of this study have significant implications for the design, construction, and long-term performance of large-diameter STC members in extreme environments:
Temperature-Induced Stresses
The large temperature gradients and differentials identified in the study can induce significant thermal stresses in the steel tube and concrete. These stresses must be considered in the design of STC members, particularly:
- Steel tube thermal expansion: The steel tube on the sun-facing side expands more than that on the shaded side, potentially causing distortion and additional stresses.
- Concrete thermal cracking: Large temperature gradients can cause cracking in the concrete, particularly near the steel-concrete interface where the temperature differential is greatest.
- Interface stresses: The differential thermal expansion between steel and concrete can cause stresses at the interface, potentially leading to debonding.
Construction Considerations
For the construction of large-diameter STC arch bridges in plateau regions, the study's findings suggest the following measures:
- Curing temperature control: Monitoring and controlling the concrete temperature during curing to prevent excessive temperature rises and gradients.
- Thermal insulation: Applying thermal insulation to the steel tube during concrete pouring to reduce solar radiation effects and minimize temperature gradients.
- Staged concrete pouring: Pouring concrete in stages to allow hydration heat to dissipate gradually, reducing peak temperatures and gradients.
- Cooling measures: Implementing internal cooling pipes or other cooling measures for large-volume concrete pours.
Welding and Fabrication Implications
The temperature field analysis has implications for the welding and fabrication of large-diameter steel tubes:
- Weld residual stresses: The thermal stresses from hydration heat and environmental temperature variations can interact with welding residual stresses, potentially accelerating fatigue crack initiation.
- Weld design: Welds in large-diameter STC members should be designed to accommodate the additional thermal stresses identified in the study.
- Weld inspection: Given the complex stress state, rigorous NDT of welds is essential, with particular attention to the weld toe and root where stress concentrations may develop.
Key Reflections
This study addresses a practical problem that is often overlooked in the design of STC members: the combined effect of hydration heat and environmental temperature variations on the temperature field and, consequently, on the structural performance. In plateau regions with extreme environmental conditions, these effects are particularly pronounced and must be carefully considered.
From a personal perspective, I have seen cases where thermal cracking in large-diameter STC members was attributed to material defects or construction errors, when in fact the root cause was inadequate consideration of the temperature field. The study's findings underscore the importance of comprehensive thermal analysis in the design and construction of large-diameter STC members, particularly in extreme environments.
The study also highlights the value of combining numerical simulation with experimental validation. The use of ANSYS transient thermal analysis provides a powerful tool for predicting the temperature field under various environmental conditions, while experimental measurements validate the simulation results and ensure that the model captures the essential physics.
For future work, I would recommend extending this approach to include:
- The effect of the temperature field on the long-term mechanical properties of the concrete and steel tube.
- The interaction between thermal stresses and mechanical loads (e.g., traffic, wind, seismic).
- The effect of different concrete mix designs and steel tube coatings on the temperature field and thermal stresses.
The study's findings provide a valuable basis for improving current design codes and construction practices for large-diameter STC members in extreme environments, ultimately contributing to the safety, durability, and economic efficiency of such structures.