Zhuojin Pipe Fitting Co., LtdTemperature Difference Calculation for Steel Tube Concrete Truss Arch Bridges
Literature Overview
The paper by Liu Zhenyu, Sun Chao, and Chen Baochun, published in Highway Traffic Science (2010, Vol. 27, No. 12), addresses a critical practical problem in the construction of steel tube concrete (CFT) truss arch bridges: the determination of closure temperature and effective temperature values. The authors employed a finite element method validated against measured temperature field data from an actual bridge, providing a rigorous analytical framework for temperature-induced stress analysis in CFT truss arch structures.
Core Technical Points
Closure Temperature Determination
The study establishes that the atmospheric average temperature exerts the most significant influence on the calculated closure temperature of CFT truss arches. The recommended closure temperature is approximately the average air temperature over the 28-day period following concrete pouring, plus an offset of 3–5°C. Seasonal adjustments are prescribed: the lower bound (3°C) applies during winter closure operations, while the upper bound (5°C) applies during summer closure. This recommendation is grounded in the thermal expansion behavior of both the steel tube and the confined concrete, which exhibit different coefficients of thermal expansion (approximately 12×10⁻⁶/°C for structural steel and 10×10⁻⁶/°C for ordinary concrete).
Effective Temperature Range
Solar radiation plays an asymmetric role in the temperature field: its influence on the minimum effective temperature is negligible, whereas its effect on the maximum effective temperature is substantial. The maximum effective temperature approaches the annual maximum temperature of the locality, while the minimum effective temperature approximates the local minimum daily mean temperature.
Parametric Influences
| Parameter | Influence Level | Engineering Significance |
|---|---|---|
| Atmospheric average temperature | Very high | Primary determinant of closure temperature |
| Solar radiation | Moderate–High | Affects maximum effective temperature significantly |
| Chord tube diameter | Moderate | Larger diameters exhibit greater thermal gradients |
| Surface radiation absorptivity | Moderate | Dark coatings increase solar heat absorption |
| Arch plane orientation | Low | Minimal effect on temperature distribution |
| Wind speed | Low | Slight cooling effect, generally negligible |
Interpretation of Technical Details
From a steel pipe manufacturing and welding perspective, the thermal expansion mismatch between the steel tube and the internal concrete is of considerable importance. During the 28-day concrete curing period, the concrete undergoes hydration heat generation while simultaneously experiencing ambient temperature fluctuations. The steel tube, having already been fabricated and welded, is subjected to differential thermal stresses at the weld joints and at the tube-concrete interface. The closure temperature calculation directly impacts the residual stress state of the welded chord members at the time of structural closure.
The surface radiation absorptivity parameter is particularly relevant to pipe surface treatment. Black-painted steel pipes absorb more solar radiation than galvanized or light-colored surfaces, leading to higher effective temperatures and consequently greater thermal stresses. In practice, this means that the surface coating specification of the chord tubes should be considered during the temperature analysis phase, not merely as an aesthetic or corrosion protection choice.
Connection with Engineering Practice
In the fabrication of CFT truss arch bridges, the chord tubes are typically seamless or HFW welded steel pipes conforming to standards such as GB/T 8162 or ASTM A53. The welding joints in the chord members are the most vulnerable locations for thermal stress concentration. When the closure temperature is miscalculated, the resulting unanticipated thermal stresses can lead to:
- Fatigue cracking at weld toes under cyclic thermal loading
- Premature degradation of the weld HAZ under sustained compressive or tensile stress
- Differential deformation between the steel tube and concrete, potentially causing delamination at the interface
The recommended practice of adding 3–5°C to the 28-day average temperature accounts for the combined effects of solar heating on the upper chord, convective cooling on the lower chord, and the thermal lag of the concrete mass. Engineers should verify this offset against local climate data for the specific construction site, particularly in regions with large diurnal temperature ranges.
Key Questions and Reflections
A notable question arising from this study is whether the 3–5°C offset remains valid for larger diameter tubes or for tubes with different wall thicknesses. The study indicates that tube diameter has a moderate influence, but the interaction between diameter, wall thickness, and concrete fill ratio on the thermal gradient profile warrants further investigation. Additionally, the study focuses on the Fujian Province climate zone; extrapolation to regions with extreme temperatures (such as northern China in winter or tropical coastal areas in summer) requires site-specific validation.
Study Insights and Implications
This paper provides a practical and validated methodology for temperature-induced stress analysis in CFT truss arch bridges. For steel pipe suppliers and fabricators, the key takeaway is that the thermal behavior of the structure is inseparable from the geometric and surface characteristics of the steel tubes. Surface treatment specifications, tube diameter selection, and welding sequence planning should all be coordinated with the structural engineer's temperature analysis to ensure long-term structural integrity.