To accurately assess the temperature action and effect of steel-concrete composite girder bridges in plateau and cold areas, this paper investigated nearly 50 years of historical meteorological data from 26 meteorological observation stations in the Tibet region of China. Based on the most unfavorable extreme meteorological data at each meteorological station, a finite element model was used to analyze the temperature field of the composite girder. The most unfavorable values of temperature were obtained. The regional differences in temperature actions at different meteorological stations were analyzed, and the isotherm maps of the extreme values of the uniform temperature and thermal gradients were further obtained based on spatial interpolation methods in the ArcGIS program. The study shows that the uniform temperature is significantly affected by the climatic environment, and the isotherm maps provide a visual representation of the geographic distribution pattern of temperature extremes. The maximum and minimum uniform temperatures in Tibet range from 18.28 °C to 42.27 °C and from −41.07 °C to 4.71 °C respectively. The maximum regional difference of positive and negative thermal gradient reaches 11.32 °C and 7.69 °C respectively. The temperature effects calculated using the most unfavorable values of the isotherm map are all more unfavorable than the specification calculations. In particular, the tensile stress of the concrete under the positive thermal gradient reaches 2.91 MPa, which exceeds the standard value of the tensile strength of concrete. This is a significant risk factor for cracking. The compressive stress of the steel girder under a negative thermal gradient reaches 19.35 MPa, which represents a 136% increase compared to the specified value. This increase elevates the risk of instability in the steel girder.

Current bridge design codes specify combination coefficients for wind–temperature joint actions, yet few studies have addressed these for bridges in plateau canyon regions. This study investigates the joint actions and combination coefficients for Haihuang Bridge, which is in a plateau canyon region surrounded by mountains. Using long-term structural health monitoring data, trivariate normal copulas and Con-KRP were applied to estimate joint probabilities of wind speed and air temperature in different directions. The combination coefficients range from 0.68 to 0.92 for temperature actions and 0.56 to 0.75 for wind actions, obtained based on the principle that bivariate Con-KRP equals univariate Con-KRP. Significant differences in the joint actions are found in different directions. Furthermore, the combination coefficients in the plateau canyon region are much larger than those in the subtropical coastal plain region, indicating a need for further study on the regional difference.

Complex wind and temperature characteristics in the Yellow River basin (YRB) challenge the safety and durability of long-span concrete-filled steel tube (CFST) bridges greatly. To address this issue, it is important to accurately assess the joint actions of wind and temperature. In this paper, the joint actions of wind and temperature in eight typical YRB cities are analyzed. The joint distributions of wind speed and air temperature are developed with the Archimedean Copula, and the Kendall return period is used for occurrence probability estimations. Eight wind–temperature combinations are considered. Responses for these combinations are calculated and compared with specification actions. Results show significant wind–temperature variations in the YRB. When wind actions adopt the univariate representative values (URVs), the temperature actions are reduced by 20–40%; when temperature actions use URVs, wind actions experience a reduction by more than half of their URVs. The joint responses can sometimes exceed, but are mostly less than, the specification responses, with a maximum strength margin over 11 MPa. These efforts suggest that the proposed joint actions can expand the provisions in the General Specification and provide guidance for the design of long-span CFST bridges.

In order to accurately assess the temperature action and effect of steel-concrete composite girder bridges in plateau and cold area, this paper investigated nearly 50 years of historical meteorological data from 26 meteorological observation stations in the Tibet region of China, and numerical simulation of the temperature field of the composite girder was carried out by using the most unfavorable extreme meteorological conditions of each meteorological station as the boundary, respectively. The most unfavorable values of effective temperature and positive and negative vertical temperature gradients were obtained. The geographical variability of the temperature actions at different meteorological stations was analyzed, and the contour maps of the extreme values of the effective temperature and temperature gradient actions were further obtained by using the spatial interpolation method. The study shows that the effective temperature of the composite girder is significantly affected by the climatic environment, and the isotherm map can visualize the geographical distribution law of the effective temperature extremes of the concrete box girder. The maximum and minimum effective temperatures in Tibet range from 18.28 ℃ to 42.27 ℃ and from -41.07 ℃ to 4.71 ℃ respectively, with a geographic variability of 23.99 ℃ and 45.78 ℃ respectively. The maximum regional difference of positive and negative temperature gradient reaches 11.32 ℃ and 7.69 ℃ respectively. Referring to the Chinese specification and the European specification of the composite girder's temperature role in the value, the highest effective temperature and positive temperature gradient in most of the areas in Tibet is too conservative, and the lowest effective temperature and negative temperature gradient is not safe enough, which may lead to the composite girder bridges with cracking of the concrete deck slabs and the disease of the bearings and expansion joints.