Study on the Temperature Field Evolution and Temperature Gradient Pattern of Concrete-Filled Aluminum Tube Members under Natural Environmental Conditions

Concrete-filled aluminum tubes (CFAT) have shown considerable potential for application in bridge structures with high durability requirements, particularly in coastal environments. However, it remains unclear whether the existing temperature gradient provisions for concrete-filled steel tubes (CFST) are directly applicable to CFAT members. To address this issue, over one year of natural exposure monitoring was conducted to obtain the temperature field of unobstructed CFAT members and the corresponding meteorological parameters. A validated numerical model was then employed to compare the temperature fields of CFAT and CFST members under representative sunny and rainy conditions, and to investigate the effects of tube diameter and wall thickness on the cross-sectional temperature gradient. The results show that, compared with CFST members of the same size, CFAT members exhibit a more uniform cross-sectional temperature field, with peak temperatures on sunny days approximately 3–6 °C lower. This indicates that the existing CFST temperature gradient provisions should not be directly applied to CFAT members. Parametric analysis further shows that, for a constant diameter, increasing wall thickness reduces the peak temperature, whereas for a constant wall thickness, increasing diameter increases the peak temperature and decreases the center temperature, although this influence gradually weakens with increasing diameter. Based on these results, a three-segment temperature gradient pattern for unobstructed CFAT members was proposed, together with recommended temperature gradient values and slope change point positions. The proposed results can provide a basis for the thermal action representation and design parameter selection of CFAT members under similar environmental conditions.