Zhuojin Pipe Fitting Co., LtdTemperature Field Measurement Study of Steel Tube Concrete Truss Arch under Solar Radiation
Literature Overview
This paper by Chen Baochun and Liu Zhenyu, published in the China Journal of Highway and Transport in 2011, presents a field measurement study of the temperature field in a steel tube concrete truss arch bridge under solar radiation. The research was supported by the Fujian Provincial Basic Research Program (Major Project, No. 2003F007) and conducted at Fuzhou University and Huaqiao University. The study involved installing temperature measurement points on the arch rib cross-sections and deploying a small weather station to collect meteorological data, providing a comprehensive understanding of the temperature distribution and temperature-induced stresses in steel tube concrete truss arch bridges.
Technical Background and Significance
Steel tube concrete (SRC) truss arch bridges combine the compressive strength of concrete with the tensile strength and ductility of steel tubes, offering an efficient structural system for medium and long span bridges. However, the temperature field in SRC structures is complex because the steel tube and the concrete core have different thermal properties. The steel tube, being a hollow section exposed to solar radiation on its outer surface, experiences significant temperature gradients that can induce thermal stresses in both the steel tube and the concrete core. These thermal stresses, when combined with mechanical loads, can affect the structural performance and durability of the bridge.
The truss arch configuration adds another layer of complexity because the bridge consists of multiple chord tubes and web members arranged in a truss configuration. The temperature distribution in each chord tube depends on its orientation relative to the sun, its exposure to solar radiation, and its thermal interaction with adjacent members. Understanding the temperature field is essential for accurate structural analysis, fatigue assessment, and serviceability evaluation.
Key Technical Findings
The field measurement results reveal several important patterns in the temperature distribution of the SRC truss arch chord tubes. The following table summarizes the key findings:
| Observation | Description | Engineering Implication |
|---|---|---|
| Parallel to sun rise-set direction | Upper and lower chord tubes have similar temperature distributions | Temperature effects on upper and lower chords are comparable |
| Perpendicular to sun rise-set direction | Left and right chord tubes have similar temperature distributions | Symmetric temperature effects on paired chords |
| Temperature distribution shape | Approaches that of a single circular tube | Simplified analysis using single tube model is acceptable |
| Average temperature difference between chords | Small | Temperature-induced stress differences between chords are minor |
| Temperature difference between chord and web members | Small | Thermal stress effects between chord and web members are negligible |
The most significant finding is that the temperature distribution and average temperature in each chord tube of the truss arch are close to those of a single circular tube. This means that the complex truss configuration does not significantly alter the thermal behavior of individual chord tubes, and the temperature analysis can be simplified by treating each chord tube as an independent circular tube exposed to solar radiation. This simplification greatly reduces the computational effort required for temperature analysis while maintaining acceptable accuracy.
Temperature Stress Analysis
The finite element analysis of temperature-induced stresses, based on the measured temperature distributions, reveals that the temperature stresses in the chord tubes and web members are relatively small. The average temperature difference between different chord tubes is small, and the temperature difference between chord tubes and web members is also small. These small temperature differences result in thermal stresses that are negligible compared to the mechanical stresses induced by traffic loads, self-weight, and other service loads.
The following table compares the magnitude of temperature-induced stresses with mechanical stresses for a typical SRC truss arch bridge:
| Stress Component | Typical Value | Relative Magnitude |
|---|---|---|
| Temperature-induced stress in chord tube | Small (order of MPa) | Negligible compared to mechanical stress |
| Mechanical stress from traffic load | Large (tens to hundreds of MPa) | Dominant stress component |
| Mechanical stress from self-weight | Moderate (tens of MPa) | Significant but secondary |
| Thermal stress from chord-web temperature difference | Very small | Negligible |
Engineering Practice Implications
The findings of this study have direct implications for the design and analysis of SRC truss arch bridges. First, the temperature field in individual chord tubes can be modeled using the simplified single circular tube approach, which reduces the complexity of the thermal analysis. Second, the temperature-induced stresses are small enough to be neglected in the structural analysis for most practical purposes. This means that the thermal effects do not require special consideration in the design of SRC truss arch bridges, simplifying the design process. Third, the temperature measurement methodology developed in this study can be used for monitoring the thermal performance of existing bridges and validating analytical models.
For quality control during construction, the thermal properties of the materials should be verified. The steel tube material should have consistent thermal conductivity and coefficient of thermal expansion, and the concrete core should be properly placed to ensure good thermal contact with the steel tube. Any voids or gaps between the concrete and the steel tube can create thermal insulation, leading to larger temperature gradients and potentially higher thermal stresses.
Study Insights and Reflections
This paper provides valuable experimental data on the temperature field of SRC truss arch bridges, which is essential for validating analytical models and improving design practices. The finding that the temperature distribution in chord tubes can be approximated by the single circular tube model is a significant simplification that reduces the computational burden of thermal analysis. However, it is important to note that this simplification is valid for the specific bridge geometry and environmental conditions studied. For bridges with different geometries, such as those with closely spaced chord tubes or those in shaded environments, the thermal interaction between members may be more significant. Additionally, the study focuses on solar radiation effects, but other thermal sources such as internal temperature changes due to concrete curing, ambient temperature fluctuations, and wind effects may also contribute to the temperature field. A comprehensive thermal analysis should consider all relevant thermal sources and their interactions. The results presented here provide a solid foundation for the thermal design of SRC truss arch bridges, and the simplified analysis approach recommended in this paper should be adopted in design guidelines where applicable.