Temperature Difference Calculation Values for Steel Tube Concrete Truss Arches A Study Note

Literature Overview

The paper by Liu Zhenyu, Sun Chao, and Chen Baochun (2010), published in Highway and Transportation Research, addresses a critical but often overlooked aspect of steel tube concrete truss arch bridge design: the determination of closure temperature and effective temperature values used in structural analysis. The authors employed a finite element method validated against measured temperature field data from an actual bridge, conducting extensive parametric analysis to derive practical temperature value recommendations for Fujian Province. This work is particularly significant because temperature-induced stresses in steel tube concrete truss arches can govern the design of connection welds, chord tube thickness, and overall structural integrity, yet field engineers frequently rely on oversimplified or regionally inappropriate temperature assumptions.

Core Technical Content and Key Findings

The study investigates two primary temperature parameters: the calculated closure temperature (合龙温度) and the effective temperature extremes (最高/最低有效温度). The closure temperature is the reference temperature at which the arch ribs are assumed to be stress-free during the closure operation, and any deviation between actual closure temperature and this calculated value induces secondary stresses throughout the structure. The effective temperatures represent the thermal loading extremes that the structure must withstand during its service life.

The key findings can be summarized as follows:

• Atmospheric mean temperature has the greatest influence on the calculated closure temperature, which is approximately equal to the average ambient temperature within 28 days after concrete pouring plus an offset of 3 to 5 degrees Celsius.
• For winter closure operations, the lower offset value (3 degrees Celsius) should be adopted; for summer closure, the higher offset value (5 degrees Celsius) is recommended.
• Solar radiation has minimal effect on the minimum effective temperature but exerts a significant influence on the maximum effective temperature, which approaches the local annual maximum temperature.
• The minimum effective temperature approximates the local minimum daily mean temperature.
• Chord tube diameter and the radiation absorption coefficient of the steel tube surface have notable effects on thermal response.
• Changes in arch plane orientation and wind speed have relatively minor influences.

Technical Parameter Analysis

The following table summarizes the key temperature parameters and their recommended values for Fujian Province based on the study:

Implications for Welding and Connection Design

From a welding and connection design perspective, the temperature values derived in this study have direct consequences for the fatigue life and residual stress management of welded connections in steel tube concrete truss arches. The chord tubes in truss arches are typically fabricated from seamless or longitudinally welded steel pipes conforming to standards such as GB/T 8163 or API 5L, and their welded joints (particularly butt welds at tube splices and gusset plate connections) are subjected to cyclic thermal stresses superimposed on mechanical loads. If the effective temperature range used in design is underestimated, the resulting thermal stresses may exceed the design assumptions, leading to premature fatigue cracking at weld toes and in the heat-affected zones (HAZ) of butt welds.

The finding that solar radiation significantly elevates the maximum effective temperature is particularly important for field engineers who may assume that shade-covered or nighttime construction conditions govern thermal design. In reality, the daytime solar heating of steel tubes with high absorption coefficients can produce local temperature differentials that induce substantial bending moments at rigid connections. This has implications for welding procedure qualification, as the preheat and interpass temperature specifications in welding procedure specifications (WPS) must account for the thermal environment during construction, not merely the final service temperature range.

Engineering Practice Integration

In practice, the recommendations from this study should be incorporated into the following engineering activities:

1. During the finite element analysis phase, the thermal loading model should use the region-specific closure and effective temperature values rather than generic national code defaults, which may not reflect local climatic conditions accurately.
2. Welding inspection protocols for truss arch chord tubes should include thermal stress assessment as part of the fitness-for-service evaluation, particularly for bridges in regions with large annual temperature swings.
3. The closure operation itself should be scheduled to minimize the temperature differential between the calculated closure temperature and the actual ambient temperature at the time of closure, thereby reducing initial residual stresses in the arch ribs and their welded connections.

Key Questions and Reflections

A critical question arises from this study: how do the recommended temperature values interact with the material properties of the steel tubes and the concrete infill? The thermal expansion coefficient of steel (approximately 12 x 10^-6 per degree Celsius) and concrete (approximately 10 x 10^-6 per degree Celsius) differ, and the differential thermal expansion between the steel tube and the concrete core generates interfacial stresses that may affect the bond between the two materials and the performance of internal welds in built-up sections. The study does not explicitly address this coupled thermal-mechanical interaction, which represents an area where further research could enhance design reliability.

Additionally, the study focuses on Fujian Province, which has a subtropical maritime climate. The applicability of the derived temperature values to regions with continental climates, high-altitude locations, or areas with extreme seasonal variations requires careful adaptation. Engineers working on projects in northern China, for example, should not directly apply the Fujian-specific values without conducting region-specific parametric analysis.

Study Insights and Practical Implications

The most valuable contribution of this paper is the emphasis on region-specific temperature parameter determination rather than reliance on generic code values. For engineers involved in the fabrication and welding of steel tube concrete truss arch components, this means that the welding quality assurance plan should include thermal stress considerations specific to the project location. The 3 to 5 degree Celsius offset for closure temperature is a practical and actionable parameter that can be directly incorporated into construction scheduling and welding inspection checklists. The finding that chord tube diameter and surface absorption coefficient significantly affect thermal response suggests that surface treatment options such as protective coatings with low absorption coefficients should be evaluated as part of the overall design optimization for thermal performance, which in turn reduces the demand on welded connections and extends their fatigue life.