Isotherm maps of temperature gradient for CFST in China: Statistical evaluation using long-term meteorological data

Bridge codes tend to employ generalized temperature gradient specifications derived from historical extremes. These provisions neglect site-specific environmental interactions that critically influence thermal behavior. The varied environments increase the uncertainty of temperature gradients. This study develops geospatially refined temperature gradient models for concrete-filled steel tube (CFST) bridges through isotherm maps. Long-term historical meteorological data from 839 stations in China were collected, and missing solar radiation data were supplemented using the Bahel model. A “layer-by-layer” method for temperature gradient isotherm maps is proposed. Long-term simulations of the temperature field at 91 radiation stations were carried out based on meteorological data. Meanwhile, the formulas for predicting the temperature gradients based on meteorological parameters were established. Then, Peak over threshold model based on the generalized Pareto distribution was used to calculate the temperature gradient loads at each meteorological station with a 100-year return period. Finally, the spatial interpolation method was used to draw the isotherm contour maps of temperature gradients. The results show that the temperature gradients of CFST bridges in China vary significantly across different regions. The regional differences can reach up to 17.91°C. Therefore, the specified values of temperature gradient for CFST bridges may lead to non-conservatism in design for most regions in China. Compared to the current specification, the temperature gradient isotherm maps presented in this paper offer enhanced geographic resolution. This will contribute to the more refined design of CFST bridges in China and serve as a valuable supplement to the Chinese specifications.