Monitoring temperatures on a real box-girder bridge and energy budget analysis for basic information on bridge cooling and surface freezing

A prestressed concrete (PC) box-girder bridge was instrumented to enable monitoring of its surface and body temperature. The daily variations of temperature in the pavement and upper beam of the bridge were greater the deeper from the surface. During daytime on a fine day, bridge surface temperatures were higher than air temperatures, and at nighttime on a fine night, temperatures at the surface were lower than air temperatures. It is well known that sensible heat transfers depend on wind speed and surface temperature. The wind speed measured at the bridge and on the road revealed that the wind speed at the bridge was higher than at the road due to their topography. This wind effect during the daytime causes the surface temperature at the bridge to be lower than that at the road. Thus, the reason why only bridge surfaces may freeze while roads do not can be explained by the fact that the surface temperatures of bridges are usually lower than those of roads, which can be attributed to their energy budget patterns caused by the wind speed differences between bridges and roads.