Theoretical confirmation of temperature gradient characteristics in concrete bridges through refined thermal analysis

Bridge temperature gradient models are critical for assessing temperature effects, with their shape and magnitude remaining a central concern in the engineering community. Existing thermal modeling exhibits limitations in accounting for radiative heat exchange between a bridge and its environment, particularly in distinguishing thermal contributions from sunlit versus shaded ground areas. To address this gap, this study innovatively develops an algorithm that dynamically tracks changes in radiative view factors from bridge surfaces to ground shadows. Through refined thermal analysis of a conventional concrete box girder using one-month measured weather data, key findings include: 1) The shape of vertical temperature gradient (VTG) shows the closest alignment with both exponential curves and 5th-order parabolas specified in bridge design codes, with a marginally better fit for the former; 2) The VTG "zero" point typically occurs at around 1.2 m girder depth; 3) Bridge orientation induces significant VTG variations up to 3.4 °C, with east-west alignments exhibiting maximum gradients while north-south orientations showing minimum values in the Northern Hemisphere; 4) Notably, the diurnal temperature range exerts greater influence on VTG than solar radiation, potentially challenging the conventional consensus that solar radiation is the dominant factor.