Temperature Field Distribution in Rectangular Steel Tube Concrete Sections in Severe Cold Regions

Literature Overview

The study by Tian Zhijuan and colleagues from Chang'an University, published in the Journal of Architecture and Civil Engineering in 2018, investigates the temperature field distribution in rectangular steel tube concrete (STC) sections under solar radiation in severe cold regions. Using Xining City as a representative location, the authors conducted on-site temperature monitoring of horizontally placed rectangular STC members with longitudinal stiffeners, and developed a finite element thermal analysis model using ABAQUS. The research addresses a critical but often overlooked aspect of STC structure design in cold climates: the thermal loading induced by solar radiation and environmental temperature variations.

Core Technical Findings

The experimental and numerical results demonstrate that the temperature field in rectangular STC sections is highly non-uniform under solar radiation, with significant temperature gradients developing across the cross-section. The steel tube temperature is directly influenced by the ambient temperature, with a slight lag in temperature change and temperature extremes that exceed the ambient temperature extremes. The concrete core temperature is indirectly influenced by the ambient temperature, exhibiting a more pronounced lag and lower temperature extremes compared to the steel tube.

The longitudinal stiffeners inside the rectangular steel tube increase the contact area between the steel and concrete, reducing the lag in concrete temperature change and decreasing the cross-sectional temperature gradient. This is an important finding for structural design, as reduced temperature gradients lead to lower thermal stresses and improved structural performance.

Finite Element Model and Validation

The authors simplified the three-dimensional temperature field to a two-dimensional model for computational efficiency, incorporating solar radiation, wind speed, and ambient temperature as boundary conditions. The ABAQUS finite element model was validated against the on-site measurement data, showing good agreement between the measured and calculated temperatures at both the steel tube and concrete measurement points. This validation provides confidence in the model's applicability for design purposes.

The solar radiation boundary condition is particularly important, as it introduces an asymmetric heat flux on the exposed surface of the STC member. The wind speed boundary condition affects the convective heat transfer coefficient, which influences the rate of heat loss from the member surface. The ambient temperature boundary condition provides the baseline thermal environment, with diurnal and seasonal variations that drive the thermal cycling of the structure.

Engineering Practice Implications

For steel pipe manufacturers, this research highlights the importance of surface finish and coating quality on the thermal performance of STC members. A high-quality protective coating can reduce solar radiation absorption and minimize the temperature extremes experienced by the steel tube, thereby reducing thermal stresses and extending the service life of the structure. The choice of coating material, thickness, and color should be considered in the design of STC members for severe cold regions.

From a welding perspective, the temperature gradients identified in this study can induce significant thermal stresses in welded connections and joints. The differential thermal expansion between the steel tube and concrete, exacerbated by the non-uniform temperature distribution, can lead to weld cracking, particularly in high-strength steel welds with limited ductility. Welding procedures should include preheating and controlled cooling rates to mitigate these thermal stresses, and post-weld inspection should include thorough NDT to detect any thermally induced defects.

Key Questions and Reflections

The study focuses on horizontally placed STC members, which are representative of bridge components and horizontal structural elements. However, the thermal behavior of vertically oriented STC members, such as columns, may differ due to the different solar radiation exposure patterns and the effects of thermal stratification. Future research should extend to vertical members and consider the combined effects of solar radiation, wind, and precipitation on the thermal performance of STC structures.

The simplification of the three-dimensional temperature field to a two-dimensional model is a pragmatic approach for design purposes, but it may not capture all the thermal effects in complex structural geometries. The interaction between the longitudinal stiffeners and the concrete core, while identified as reducing the temperature gradient, may introduce localized thermal stresses at the stiffener-concrete interface that are not captured in the simplified model.

Study Insights and Outlook

This research provides essential thermal data for the design of STC structures in severe cold regions, where thermal loading can be as critical as mechanical loading. The identification of the longitudinal stiffeners as a factor that reduces the cross-sectional temperature gradient offers a practical design strategy for improving thermal performance. Future work should integrate the thermal analysis with structural analysis to predict the combined effects of thermal and mechanical loading on the long-term performance of STC members. Additionally, the development of thermal-structural coupled finite element models that account for material property degradation due to thermal cycling will be essential for predicting the service life of STC structures in harsh environmental conditions.