Sunlight induced temperature field in concrete filled steel tube study

Background and test significance

This paper is useful to steel tube engineers because it treats a steel tube as a thermally loaded shell rather than only as a structural member, and it quantifies how solar heating creates nonuniform through thickness and circumferential temperature fields.

Concrete filled steel tube members can also be viewed as steel pipe products with internal concrete restraint, so the measured thermal response is relevant to outdoor storage, erection, solar preheating, and residual stress relaxation after welding.

Key findings from the paper

Observation	Engineering meaning
Temperature peaks occur at different times around the tube	Surface points respond earlier than inner points, and the phase difference is significant.
Temperature variation becomes slower toward the centre	Heat conduction through the tube wall and concrete damps the thermal wave.
The centre point is influenced by all directions but dominated by the strongest direction	Local solar exposure can control the overall thermal history of the cross section.

The important point is that the temperature field is not a simple uniform rise, because the peak temperature at each surface point lags behind the solar exposure and the centre point integrates heat from all directions, with the strongest direction dominating the response.

Engineering implications for steel tube and weld fabrication

For pipe and fitting work, this type of test reminds us that solar heating can produce differential expansion between the hot sun side and the shaded side, which may distort long tubes, alter fit up, and complicate dimensional inspection.

When the tube is filled with concrete, thermal expansion mismatch and concrete restraint can create additional stress, so temperature mapping should be considered before flame straightening, local heating, or post weld heat treatment.

For welders, the data support a practical rule that outdoor preheat or drying should be evaluated by measuring the metal temperature at several clock positions, not by relying on ambient temperature alone.

In summary, the paper provides a clear experimental basis for treating sunlight as a nonuniform heat source, and it should influence how engineers plan temperature measurement, heat treatment, and dimensional control for exposed steel tubes.