Temperature Field Measurement of Steel Tube Concrete Truss Arch Under Solar Radiation

Literature Overview

The paper by Chen Baochun and Liu Zhenyu, published in China Journal of Highway and Transport in 2011, presents field measurement results of temperature distribution in the chords of a steel tube concrete truss arch bridge under solar radiation. This research addresses a practical engineering problem: the thermal effects of solar radiation on steel tube concrete (SRC) truss arch structures. The authors installed temperature measurement points on the arch rib cross-sections and deployed a small weather station to collect meteorological data. The study analyzes the temperature distribution patterns in the upper and lower chord tubes and evaluates the temperature-induced stresses using finite element analysis. The findings provide valuable guidance for thermal design of SRC truss arch bridges.

Core Technical Findings

The research reveals several important patterns in the temperature distribution of SRC truss arch chords under solar radiation:

The key conclusion of this research is that the temperature distribution and average temperature of each chord tube in the truss arch are similar to those of a single circular tube. This finding simplifies the thermal analysis significantly, as engineers can apply established thermal models for single SRC tubes to each chord tube in the truss arch configuration. Furthermore, the temperature difference between different chord tubes is small, and the resulting temperature stresses are also small, suggesting that thermal effects between chords can be neglected in practical calculations.

Temperature Field Analysis Methodology

The field measurement approach employed in this study involves:

1. Temperature measurement point layout: Thermocouples are installed at strategic locations on the arch rib cross-sections to capture the temperature distribution across the chord tube walls and within the concrete core.
2. Meteorological data collection: A small weather station is deployed near the bridge to record ambient temperature, solar radiation intensity, wind speed, and other relevant meteorological parameters.
3. Data correlation: The measured temperature data is correlated with meteorological parameters to identify the dominant factors influencing the temperature distribution.
4. Finite element thermal analysis: A finite element model is developed to calculate the average temperature of each chord tube and the resulting temperature stresses.

The temperature distribution in the chord tubes under solar radiation can be understood through the following mechanisms:

• Direct solar heating: The sun-facing surfaces of the chord tubes experience direct solar radiation, leading to elevated surface temperatures.
• Heat conduction through the tube wall: Heat conducts from the heated outer surface to the inner surface of the steel tube and into the concrete core.
• Radiation exchange between chord tubes: In the truss arch configuration, chord tubes can exchange thermal radiation with each other, partially compensating for differential solar exposure.
• Convection heat transfer: Air convection around the chord tubes dissipates heat to the ambient environment.

Engineering Practice Implications

The findings of this research have direct implications for the thermal design of SRC truss arch bridges:

1. Simplified thermal modeling: The temperature distribution in each chord tube can be modeled using established single-tube thermal models, avoiding the need for complex three-dimensional thermal analysis of the entire truss arch.
2. Negligible inter-chord thermal stresses: The small temperature differences between chord tubes mean that thermal stresses arising from differential expansion between chords are insignificant and can be neglected in structural design.
3. Chord-web thermal interaction: The temperature difference between chord tubes and web members is also small, meaning that thermal stresses from this interaction are negligible in practical calculations.
4. Thermal design focus: The primary thermal design consideration should be the temperature gradient across the chord tube cross-section, which induces bending stresses in the tube wall.

Key Questions and Reflections

While the findings of this research provide valuable practical guidance, several questions merit further consideration:

• Seasonal variations: The study appears to focus on specific measurement periods. How do the temperature distribution patterns vary across different seasons, particularly between summer and winter conditions?
• Cloud cover effects: The influence of cloud cover on the temperature distribution is not explicitly addressed. Cloud cover can significantly reduce solar radiation and alter the temperature distribution patterns.
• Long-term thermal fatigue: Although the temperature stresses between chords are small, the cyclic nature of daily temperature variations may contribute to thermal fatigue over the service life of the bridge. This aspect warrants further investigation.
• Wind effects: Wind can enhance convective heat transfer and alter the temperature distribution. The interaction between wind and solar radiation on the thermal response of the truss arch should be considered in comprehensive thermal analysis.

Study Insights and Reference Value

This research provides practical, measurement-based guidance for the thermal design of SRC truss arch bridges. The key insight is that the thermal behavior of truss arch chords under solar radiation is largely predictable from single-tube thermal models, and the inter-chord thermal effects are negligible. This simplification is valuable for practical engineering design, as it reduces the complexity of thermal analysis while maintaining adequate accuracy. For bridge engineers, this research supports the adoption of simplified thermal design approaches for SRC truss arch structures, provided that the temperature gradient across individual chord tubes is properly accounted for.