Statistical evaluation of vertical and lateral temperature gradients in concrete box-girders

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Atmospheric thermal loads are considered as one of the effective loads on bridge structures. The thermal actions in bridge superstructures are considered in most of the recent bridge design specifications. In this study, a concrete girder segment was cast in place in an open field to simulate the actual atmospheric exposure case of bridge girders. Inside and close the surfaces of the webs and flanges of the girder 62 thermocouples were distributed to measure the concrete temperatures in different sectional locations. In addition, the experimental field was provided with a compact weather station that records the three main influential atmospheric loads, which are the solar radiation and the temperature and speed of the field’s air. The experimental data from all sensors were recorded for a one-year that considers the variation of loads in the four seasons. The effective maximum temperature gradients, both vertically (along the depth of webs) and horizontally (along the width of flanges), were statistically correlated to the atmospheric loads and their derivatives. Nonlinear correlations were introduced to estimate the maximum gradients with determination coefficients of 0.92 to 0.96. The maximum errors between the experimental and predicted temperatures for the whole investigated period were in general less than 3.0 °C. The obtained correlations for the lateral gradients were more complicated than for the vertical gradient due to the effect of other parameters like the day index, which is related to the striking angle of solar radiations.