Solar Radiation Temperature Field of Steel Tube Concrete Arch Truss Considering Shielding Effects

Literature Overview

This paper by Lin Chunjiao, Huang Jiaxiang, and Li Xiang, published in China Journal of Highway and Transport in 2020, investigates the solar radiation temperature field distribution in the chord tubes of a truss-type steel tube concrete (SRC) arch bridge on the Sichuan-Tibet Railway. Funded by the Sichuan Science and Education Program (Grant No. 2018GZ0052), the study uses numerical methods to simulate the temperature field in the upper and lower chord tubes during summer and winter solar radiation conditions, taking into account the shielding effects between the chord tubes.

Core Technical Content and Thermal Analysis

The temperature field distribution in steel tube concrete arch bridges is critical for structural design because temperature gradients induce thermal stresses that can affect the structural integrity and serviceability of the bridge. The truss-type section introduces geometric complexity because the upper and lower chord tubes have different orientations relative to the sun, resulting in different solar radiation absorption patterns and shielding interactions.

The key findings from the numerical analysis are summarized below:

Parameter	Upper Chord Tube	Lower Chord Tube
Temperature Field Pattern	Follows solar radiation variation	Follows solar radiation variation
Linearity	Nonlinear with solar radiation	Nonlinear with solar radiation
Shielding Effect	Minimal	Significant
Maximum Steel Tube Temperature Location	Always on sun-facing side	Varies with shielding
Concrete Temperature Variation	Stable, primarily affected by ambient temperature	Stable, primarily affected by ambient temperature
Steel Tube Temperature Sensitivity to Solar Radiation	High	High (outer side), Low (inner side)
Concrete Sensitivity to Solar Radiation	Low	Low

The observation that the concrete temperature inside the steel tube is relatively insensitive to solar radiation is an important finding. This is because the steel tube acts as a thermal barrier, and the concrete mass provides thermal inertia that dampens temperature fluctuations. The steel tube surface temperature can vary significantly with solar radiation, but this temperature gradient does not fully penetrate to the concrete core.

Engineering Practice and Design Implications

For engineers designing steel tube concrete arch bridges, the following design considerations emerge from this study:

Separate temperature values should be used for the upper and lower chord tubes in thermal stress analysis. The shielding effect between the chord tubes creates significant differences in the temperature field, and using a single temperature value for both would lead to inaccurate stress predictions.
The nonlinear temperature variation with solar radiation requires time-dependent thermal analysis rather than steady-state analysis. The peak temperature does not necessarily occur at solar noon because of the thermal lag in the steel tube and concrete.
The outer side of the lower chord tube experiences more significant temperature variation than the inner side due to direct solar radiation exposure. This creates a through-thickness temperature gradient in the steel tube wall that induces bending stresses.
The concrete temperature is primarily governed by the ambient air temperature rather than solar radiation. This means that the thermal expansion of the concrete is driven by the diurnal and seasonal temperature cycles, while the steel tube experiences additional thermal cycling from solar radiation.
The difference in thermal expansion between steel and concrete creates interfacial shear stresses that can affect the bond quality and long-term durability of the SRC section.

Study Insights and Reflections

This study addresses a practical engineering problem that is often overlooked in bridge design. The assumption of uniform temperature distribution across the bridge cross-section is common in practice, but this assumption can lead to significant errors in thermal stress calculations, particularly for complex sections such as truss-type SRC arches.

The shielding effect between the chord tubes is a geometric phenomenon that depends on the bridge orientation, the sun position, and the time of day and year. For bridges located at high latitudes or in mountainous regions, the shielding effect can be particularly pronounced because the sun angle is lower and the terrain can create additional shading. Engineers should conduct site-specific solar radiation analysis to determine the actual temperature field distribution.

For practical design, I recommend the following additional measures:

Use finite element thermal analysis with time-dependent solar radiation loading to determine the temperature field distribution at critical locations and times.
Incorporate the temperature field into the structural analysis to determine thermal stresses and their interaction with mechanical loads.
Consider the use of thermal expansion joints or sliding connections to accommodate differential thermal expansion between the upper and lower chord tubes.
Apply thermal coatings or insulation to reduce the solar radiation absorption on the steel tube surfaces, particularly on the upper chord tube where the temperature is highest.
Conduct field measurements to validate the numerical predictions and calibrate the thermal models for specific bridge applications.

In conclusion, this study provides valuable insights into the solar radiation temperature field of truss-type SRC arch bridges. The findings confirm that the upper and lower chord tubes experience significantly different temperature fields due to shielding effects, and that the concrete temperature is relatively insensitive to solar radiation. Engineers should use these results to refine thermal stress analyses and improve the design of SRC arch bridges for serviceability and durability under thermal loading.