Zhuojin Pipe Fitting Co., LtdTemperature Action Value and Temperature Effect Analysis for Through-Truss Steel Pipe Concrete Truss Arch Bridges
Literature Overview
The paper by Liu Zhenyu and Yu Jian, published in the Journal of Nanchang University (Engineering Science Edition) (2012, Vol. 34, No. 4, pp. 373-377), investigates the temperature action values and temperature effects for a through-truss steel pipe concrete (SRC) truss arch bridge. The research, conducted at Huaqiao University and the Yunnan Provincial Highway Science and Technology Research Institute, uses ANSYS finite element analysis combined with meteorological data to determine appropriate temperature action values (closure temperature and effective temperature) and analyze the effects of temperature changes on the arch foot solid web section stresses.
Temperature Action Values: Closure Temperature and Effective Temperature
Temperature is a critical environmental load for steel pipe concrete arch bridges, particularly for long-span structures where thermal expansion and contraction can induce significant stresses and displacements. The two key temperature parameters identified in this study are:
- Closure temperature (合拢温度) - The temperature at which the arch ribs are connected or closed during construction, establishing the reference temperature for the completed structure.
- Effective temperature (有效温度) - The temperature range that the structure actually experiences during service, accounting for non-uniform temperature distributions across the cross-section.
Key Temperature Findings
| Temperature Parameter | Value Relative to Meteorological Data | Engineering Implication |
|---|---|---|
| Closure temperature | Approximately 2°C above monthly average temperature | Affects initial stress state of completed structure |
| Minimum effective temperature | Approximately 5°C below daily minimum average temperature | Governs contraction effects and tensile stresses |
| Maximum effective temperature | Approximately 6°C above daily maximum average temperature | Governs expansion effects and compressive stresses |
The closure temperature being approximately 2°C above the monthly average temperature reflects the reality that closure operations are typically performed during warmer parts of the day, and the steel pipe concrete structure may retain some construction heat. This temperature difference, while seemingly small, can have significant effects on the long-term stress state of the structure.
The effective temperature range being wider than the meteorological data suggests that the actual temperature experienced by the structure is more extreme than the ambient air temperature, likely due to solar radiation heating the upper portions of the arch rib and the insulating effect of the concrete core.
Finite Element Analysis and Temperature Effect Evaluation
The ANSYS finite element model was used to analyze the effects of temperature changes on the arch foot solid web section stresses. The analysis revealed several important findings:
- Arch rib closure timing - From the perspective of reducing temperature-induced effects, the arch rib closure time should be selected during periods when the monthly average temperature approaches the annual average temperature. This minimizes the temperature differential between the closure temperature and the mean service temperature, reducing cyclic thermal stresses.
- Lateral rod temperature effects - The temperature changes in the lateral rods (diagonal and vertical members of the truss) have relatively small effects on the arch foot stresses. This is because the lateral rods are relatively slender members with smaller cross-sectional areas, resulting in smaller thermal forces.
- Solid web section temperature effects - The solid web section (实腹段) at the arch foot experiences significantly larger stress variations due to temperature changes compared to the truss members. This is attributed to the different structural configuration of the solid web section compared to the truss members, resulting in different thermal expansion behavior and constraint conditions.
Structural Configuration Effects on Temperature Response
The difference in temperature response between the solid web section and the truss members is a critical finding. The solid web section, being a continuous, massive concrete-filled steel pipe section, has:
- Higher thermal mass - Greater heat capacity leads to slower temperature changes but also larger accumulated thermal strains.
- Greater constraint - The connection to the abutment or foundation provides more constraint against thermal expansion, resulting in higher thermal stresses.
- Non-uniform temperature distribution - The large cross-section creates temperature gradients through the thickness, with the outer surfaces experiencing more extreme temperatures than the core.
The truss members, being slender and relatively exposed, experience more uniform temperature distributions and have less constraint, resulting in lower thermal stresses.
Engineering Practice Implications
The findings of this study have direct implications for the design and construction of steel pipe concrete truss arch bridges:
- Construction scheduling - The timing of arch rib closure is a critical construction decision that should be informed by temperature analysis. Closure should ideally occur when the ambient temperature is close to the annual average temperature to minimize long-term thermal cycling effects.
- Temperature load modeling - Designers should use effective temperature values that account for the non-uniform temperature distribution across the structure, rather than relying solely on meteorological data. The effective temperature range should be wider than the meteorological range to capture the actual thermal environment of the structure.
- Detail design considerations - The solid web section at the arch foot requires special attention in design due to its susceptibility to temperature-induced stresses. Adequate expansion joints, flexible connections, and stress-relieving details should be incorporated in this region.
- Monitoring and maintenance - Temperature-induced displacements and stresses should be monitored during the service life of the bridge, particularly during extreme weather events. Any unexpected thermal behavior should be investigated to ensure structural safety.
| Design Parameter | Recommended Approach | Rationale |
|---|---|---|
| Closure temperature | Target annual average temperature | Minimizes cyclic thermal stresses |
| Temperature load range | Use effective temperatures from FE analysis | Captures non-uniform temperature effects |
| Solid web section design | Include thermal stress relief provisions | Mitigates high thermal stresses |
| Truss member design | Standard thermal expansion considerations | Lower thermal stress sensitivity |
| Monitoring program | Include temperature and displacement sensors | Detect abnormal thermal behavior |
Study Insights and Conclusions
This research provides valuable insights into the temperature behavior of steel pipe concrete truss arch bridges, a structural type that combines the advantages of steel pipe concrete (high strength, good ductility, corrosion resistance) with the efficient load path of truss arch geometry. The finding that the solid web section is more sensitive to temperature effects than the truss members highlights the importance of considering structural configuration differences when evaluating thermal effects.
The proposed effective temperature values, derived from finite element analysis combined with meteorological data, provide a more realistic representation of the thermal environment experienced by the structure. This approach is superior to the simplified temperature models often used in code-based design, which may underestimate or misrepresent the actual thermal loads.
The recommendation to time the arch rib closure operation to coincide with periods of near-annual-average temperature is a practical and cost-effective strategy for reducing long-term thermal fatigue. This construction scheduling consideration should be integrated into the overall construction planning process for steel pipe concrete arch bridges.
This study contributes to the growing body of knowledge on the thermal behavior of composite steel pipe concrete structures and provides practical guidance for engineers involved in the design, construction, and maintenance of steel pipe concrete truss arch bridges. The findings underscore the importance of rigorous thermal analysis in ensuring the long-term performance and safety of these structures.