Cross-Sectional Temperature Field Analysis of Rectangular Steel Tube Concrete Columns Under Solar Radiation

Literature Overview

This paper by Zhou Ting and colleagues from Tianjin University, published in the journal Industrial Construction in 2016, investigates the thermal behavior of rectangular steel tube concrete columns in super-tall buildings during the construction phase. These columns are subjected to direct solar radiation, which can cause significant temperature gradients across the cross-section. The research was supported by the Tianjin Municipal Commission of Housing and Urban-Rural Development Science and Technology Project (2015-3). Understanding these temperature gradients is essential because non-uniform temperatures can induce thermal stresses that affect the structural performance and construction quality of the columns.

Core Technical Content and Findings

The study focuses on the construction stage of super-tall building structures, where rectangular steel tube concrete columns are typically exposed to direct sunlight for extended periods. The authors analyzed the temperature field distribution across the cross-section, the temperature variation patterns on the steel tube walls and core concrete, and the temperature differential patterns.

Key findings from the analysis include:

The analysis revealed that the maximum temperature difference between the core concrete and the four steel walls can reach 35.6°C, while the maximum temperature difference between the east and west steel walls can reach 25.6°C. These temperature gradients are substantial and can generate significant thermal stresses in the steel tube walls and at the steel-concrete interface.

Thermal Behavior Analysis

The temperature field distribution across the rectangular steel tube concrete column cross-section is governed by several factors:

• Solar radiation intensity and direction, which determine the boundary conditions on the exposed surfaces.
• The thermal conductivity and diffusivity of the steel tube walls and the core concrete, which determine how rapidly heat penetrates into the section.
• The geometry of the cross-section, including the wall thickness and the overall dimensions.
• The ambient temperature and wind conditions, which affect convective heat loss from the shaded surfaces.

The study found that as the cross-section dimensions increase, both the extreme temperatures and the cross-sectional temperature differences increase, but this trend diminishes when the side length exceeds 1000 mm. This suggests that for very large cross-sections, the core concrete acts as a thermal buffer, and the additional dimensions beyond 1000 mm do not significantly exacerbate the temperature gradient problem.

Engineering Practice Implications

The findings have several practical implications for the design and construction of super-tall buildings with rectangular steel tube concrete columns:

1. Thermal stress calculations should be included in the structural analysis of these columns, particularly during the construction phase when solar exposure is most significant.
2. Construction scheduling should consider solar exposure, with critical concrete pouring operations planned for times of reduced solar radiation.
3. Temporary shading measures should be considered for exposed columns during hot weather to reduce thermal gradients.
4. The thermal expansion of the steel tube walls relative to the core concrete should be accounted for in the design of construction joints and temporary supports.
5. For columns with side lengths greater than 1000 mm, the thermal gradient problem is less severe relative to the section size, but absolute temperature differences remain significant.

Study Insights and Reflections

This paper addresses an often-overlooked aspect of super-tall building construction: the thermal effects of solar radiation on steel tube concrete columns. While thermal effects are well-understood in operational conditions, the construction phase presents unique challenges because the structure is not yet complete and may have different boundary conditions than the final design. The temperature differences of up to 35.6°C between the core concrete and the steel walls are substantial enough to generate thermal stresses that could compromise the integrity of the concrete or cause premature cracking at the steel-concrete interface. The finding that the temperature gradient effect diminishes for larger cross-sections is practically useful for structural designers, as it suggests that the thermal problem is more critical for smaller columns. Engineers should consider incorporating thermal analysis into the construction planning phase for super-tall buildings, particularly in regions with high solar radiation intensity. The study also highlights the importance of considering non-uniform temperature fields in structural analysis, as the assumption of uniform temperature across a section can lead to significant errors in stress prediction.