Solar Radiation Gradient Temperature Effects on Concrete Filled Steel Tube Arch Ribs

Literature Overview

This paper by Guo Zengwei, Zhang Yali, Yang Yifan, and Zhou Shuixing from Chongqing Jiaotong University investigates the gradient temperature effects on Concrete Filled Steel Tube (CFST) arch ribs under solar radiation, based on field measurements from the Qianwei Minjiang Special Bridge in Sichuan Province. Published in the Journal of Chongqing Jiaotong University (Vol. 42, No. 5, 2023, pp. 16-24), the study was supported by the National Natural Science Foundation of China (Grant No. 51878106) and multiple Chongqing municipal research programs. The research involves real-time surface temperature monitoring, thermal-mechanical coupled finite element modeling considering the steel-concrete interface contact state, and analysis of gradient temperature and stress distribution patterns.

Core Technical Findings

The study reveals that the radial temperature distribution within the CFST cross-section under solar radiation is extremely non-uniform. Within the depth range of D/8 from the steel tube top (where D is the diameter), the temperature gradient results are approximately 5 degrees Celsius higher than the recommended values in JTG D60-2015 and approximately 8 degrees Celsius higher than those in TB 10092-2017. At the D/2 location (the center of the cross-section), the temperature is only about 50 percent of the value recommended by TB 10092-2017.

The steel-concrete interface stress exhibits a "tension-compression" alternating pattern within a 24-hour cycle. Peak tensile stress reaches 0.8 MPa at 14:00 and 15:00. The study recommends that design and construction measures should ensure that the internal concrete develops expansion compressive stress exceeding 0.8 MPa to prevent debonding between the steel tube and concrete.

Key Technical Parameters and Standards Comparison

Process and Standards Analysis

The findings have significant implications for the design of CFST arch bridges, particularly in regions with intense solar radiation such as Sichuan Province. The existing design standards JTG D60-2015 and TB 10092-2017 appear to underestimate the temperature gradient effects in the upper portion of the CFST cross-section and overestimate the temperature at the center. This discrepancy can lead to inaccurate thermal stress predictions and potentially inadequate design for thermal effects.

The steel-concrete interface stress analysis reveals a critical engineering concern: the alternating tension-compression stress cycle at the interface can lead to progressive debonding over time, particularly in the presence of moisture ingress and corrosion. The recommendation to develop expansion compressive stress exceeding 0.8 MPa in the internal concrete provides a practical design target for construction quality control. This can be achieved through controlled concrete placement, appropriate shrinkage compensation measures, and careful management of the concrete curing process within the steel tube.

From a quality control perspective, the thermal-mechanical coupled analysis should be incorporated into the design verification process for CFST arch bridges. Construction practices should include temperature monitoring during concrete placement in solar-exposed conditions, with particular attention to the summer season when peak temperature gradients occur. The interface bond quality should be verified through non-destructive testing methods such as ultrasonic testing after construction completion.

Engineering Practice Integration

For practical engineering applications, the findings suggest that CFST arch rib design should incorporate site-specific temperature gradient data rather than relying solely on standard recommended values. The construction sequence should account for thermal effects, with concrete placement preferably scheduled during cooler periods or with active cooling measures during hot conditions. The steel tube surface finish and surface treatment should be optimized to promote thermal contact with the concrete, reducing the interface stress concentration.

The study's recommendation for pre-compression development in the internal concrete can be implemented through controlled concrete mix design with expansion agents, careful compaction to ensure full contact, and appropriate curing protocols. Regular monitoring of the steel-concrete interface condition during the service life of the bridge should be incorporated into the maintenance plan, with particular attention to the upper portion of the arch rib where temperature gradients are most severe.

Key Questions and Reflections

An important question is how the temperature gradient effects interact with other environmental factors such as wind loading, humidity variation, and freeze-thaw cycling to influence the long-term performance of the CFST arch rib. The study focuses on a specific location in Sichuan Province, and the findings should be validated for other geographic regions with different solar radiation characteristics. Additionally, the effect of paint coatings and surface treatments on the steel tube on temperature absorption and gradient distribution warrants further investigation, as these are common in bridge construction practice.

Study Insights and Implications

This research provides critical insights into the thermal behavior of CFST arch ribs that challenge existing design standard assumptions. The significant deviation between measured temperature gradients and standard recommended values necessitates a reassessment of thermal design practices for CFST arch bridges, particularly in high-solar-radiation regions. The identification of the steel-concrete interface stress pattern and the recommendation for pre-compression development offer practical construction guidance that can be implemented through existing quality control protocols. The study underscores the importance of field measurement in validating theoretical models and standard assumptions, and highlights the need for site-specific thermal analysis in CFST bridge design.