Solar Radiation Temperature Distribution in Circular Steel Tube Concrete Arch Ribs

Literature Overview

Peng Yousong, Qiang Shizhong, and Liu Yueshen from the School of Civil Engineering at Southwest Jiaotong University published this study in the journal "Bridge Construction" in 2006, Volume 36, Issue 6, pages 18-20. The paper addresses a critical but often overlooked aspect of steel tube concrete (STC) arch bridge engineering: the nonlinear temperature distribution within circular arch ribs caused by solar radiation. Using heat conduction theory combined with finite element methods, the authors developed an analytical model for solar radiation temperature distribution that accounts for solar radiation intensity, ambient temperature variation, geographic location, orientation, and geometric dimensions.

Core Technical Findings

The most striking finding is that the nonlinear temperature difference across the cross-section of a circular STC arch rib can exceed 20 degrees Celsius. This temperature gradient is not uniform and creates complex thermal stress states that can significantly affect the structural behavior of the arch bridge. The study demonstrates that temperature effects in STC arch bridges deserve serious attention in design and assessment, as the conventional assumption of uniform temperature across the cross-section is inadequate.

The finite element model considers the following key factors:

• Solar radiation intensity and spectral distribution
• Solar angle and incidence direction varying with time of day and season
• Geographic latitude and local climatic conditions
• Arch rib orientation relative to solar path
• Geometric dimensions including outer diameter, wall thickness, and concrete core diameter
• Thermal properties of steel and concrete materials

Thermal Analysis and Structural Implications

The temperature gradient across the arch rib cross-section creates differential thermal expansion between the sunlit and shaded portions. Since the steel tube and the concrete core have different coefficients of thermal expansion (approximately 12 x 10^-6 /°C for structural steel and 10-14 x 10^-6 /°C for concrete), the temperature difference induces complex interfacial stresses at the steel-concrete boundary.

The nonlinear temperature distribution means that the centroid of the temperature profile does not coincide with the geometric centroid of the cross-section. This eccentricity generates a thermal bending moment that can be comparable to or even exceed the thermal moment caused by a uniform temperature change. For arch bridges, this thermal bending moment is particularly concerning because it introduces additional secondary stresses that can accumulate over repeated daily temperature cycles.

Welding and Material Considerations

From a metallurgical and welding perspective, the temperature cycling caused by solar radiation has implications for the fatigue life of the steel tube. The daily temperature variation creates cyclic thermal stresses that, although individually small, can contribute to fatigue damage accumulation over the service life of the bridge. Welded joints in the steel tube, which are inherently more susceptible to stress concentration, should be evaluated for thermal fatigue resistance.

The thermal gradient also affects the bond interface between the steel tube and the concrete core. Differential thermal expansion can lead to progressive debonding at the steel-concrete interface, particularly at locations where the temperature gradient is steepest. This debonding reduces the composite action between steel and concrete, potentially leading to unexpected structural degradation.

Engineering Practice and Recommendations

For bridge engineers designing STC arch bridges, this study provides clear guidance on the need to incorporate solar radiation temperature effects into structural analysis. The design should include:

1. Nonlinear temperature distribution modeling rather than uniform temperature assumptions
2. Thermal stress analysis considering the combined effect of temperature gradient and temperature change
3. Fatigue assessment of welded joints under cyclic thermal loading
4. Monitoring of steel-concrete interface integrity during service life

The finite element model presented in this paper can serve as a basis for developing more sophisticated thermal-structural coupled analysis procedures. Engineers should calibrate the model with field temperature measurements to account for local environmental conditions, including wind speed, cloud cover, and surface coating properties that affect solar absorption.

Study Insights and Concluding Remarks

This paper represents a valuable contribution to the understanding of thermal effects in STC arch bridges. The finding of 20 degrees Celsius or more temperature difference across the cross-section is a wake-up call for engineers who may have previously assumed that temperature effects could be simplified to uniform temperature changes. The nonlinear temperature distribution creates a fundamentally different stress state that must be properly analyzed and accounted for in design.

For the steel pipe fabrication and welding industry, this research highlights the importance of considering service environment temperature cycling in the design of steel tubes used in bridge applications. Welded joints should be designed and inspected with awareness of thermal fatigue effects, and quality control procedures should include evaluation of weld integrity under cyclic thermal loading conditions. The integration of thermal analysis into bridge engineering practice is essential for ensuring the long-term safety and durability of STC arch bridges, particularly in regions with high solar radiation intensity.