Non-Uniform Temperature Field of Steel Tube Members Under Solar Radiation

Literature Overview and Thermal Analysis Importance

This study investigates the non-uniform temperature distribution within steel tube structural members subjected to solar radiation, a phenomenon that has received relatively limited attention in structural engineering practice despite its potential to significantly influence member performance and service life. Solar radiation creates a complex thermal environment on exposed steel tube surfaces, with temperature gradients developing not only along the length of the member but also through the wall thickness and around the cross-section perimeter.

The research significance is particularly important for steel tube structures in hot and arid regions, where solar radiation intensities can exceed 1000 W/m² during peak hours. The resulting temperature differentials between sun-exposed and shaded surfaces can reach 30-50°C, creating thermal stresses that may contribute to fatigue cracking, distortion, and accelerated corrosion. For welded steel tube structures, these thermal effects interact with welding residual stresses, potentially initiating or propagating cracks at critical locations.

Core Technical Findings and Temperature Distribution Patterns

The numerical and experimental results reveal that the temperature field within a steel tube member under solar radiation is highly non-uniform, with maximum temperatures occurring at the directly sun-exposed outer surface and minimum temperatures at the shaded inner surface. The temperature gradient through the wall thickness is relatively small due to the high thermal conductivity of steel, but the gradient around the cross-section perimeter is significant due to differential solar absorption.

The temperature distribution pattern shows that the maximum temperature differential occurs between the directly sun-exposed surface and the opposite shaded surface. For a square steel tube oriented with one face perpendicular to the sun direction, the temperature difference between the sun-facing and opposite faces can exceed 40°C during peak solar radiation periods. This differential creates a bending moment due to thermal expansion, which can be comparable to or exceed the self-weight bending moment for slender members.

Thermal Stress Analysis and Welding Implications

The non-uniform temperature field generates thermal stresses within the steel tube member. For a fully constrained member, the thermal stress can be calculated as σ_th = E·α·ΔT, where E is the elastic modulus, α is the thermal expansion coefficient, and ΔT is the temperature differential. For structural steel with E = 206 GPa, α = 12×10⁻⁶/°C, and ΔT = 40°C, the thermal stress reaches approximately 98.9 MPa, which is a substantial fraction of the yield strength of Q345 steel (345 MPa).

The interaction between thermal stresses and welding residual stresses is of particular concern. Welding residual stresses in the heat-affected zone of longitudinal and circumferential welds can reach values approaching the yield strength. When superimposed with thermal stresses from solar radiation, the combined stress state may exceed the yield strength locally, initiating microplastic deformation that accumulates over repeated daily thermal cycling. This mechanism can contribute to thermal fatigue cracking, particularly in the heat-affected zone where the material properties are already compromised by the welding thermal cycle.

Mitigation Strategies and Engineering Recommendations

Several engineering measures can mitigate the adverse effects of solar radiation on steel tube members. Surface coating with high-reflectivity paint can reduce solar absorptivity from 0.7 to 0.2, decreasing peak surface temperatures by 15-20°C. Internal insulation of hollow steel tube members with reflective foil or aerogel blankets can reduce the temperature gradient across the wall thickness. For critical welded connections, thermal stress relief treatment after welding can reduce residual stresses to below 50 MPa, providing additional margin against thermal fatigue.

The study also highlights the importance of considering solar radiation effects in structural design codes. Current design standards primarily account for wind and seismic loads but give insufficient attention to thermal effects from solar radiation. For steel tube structures in hot climates, thermal analysis should be incorporated into the design process, particularly for slender members and welded connections where thermal fatigue is a credible failure mechanism.

Study Reflection and Practical Insights

As a welding engineer, I find this research particularly relevant because it connects thermal phenomena with welding residual stress management. The daily thermal cycling caused by solar radiation represents a low-amplitude, high-cycle fatigue mechanism that can interact with welding-induced residual stresses and microstructural changes in the heat-affected zone. This interaction is analogous to the thermal fatigue mechanism observed in power plant components and pressure vessels, where cyclic temperature changes cause crack initiation and propagation over extended service periods.

The practical implication is that welding residual stress relief should be considered not only for structural safety under static loading but also for long-term durability under thermal cycling. For steel tube structures in hot and arid regions, post-weld stress relief treatment, combined with appropriate surface coatings and thermal analysis during design, represents a comprehensive approach to ensuring long-term structural integrity. This research provides valuable quantitative data that can inform design decisions and maintenance strategies for steel tube structures exposed to significant solar radiation, ultimately contributing to improved safety and extended service life of critical infrastructure components.