ON FIELD-MEASURED VERTICAL TEMPERATURE GRADIENT OF BOX GIRDER IN STEEL BRIDGES

To investigate distribution of the vertical temperature gradient of a closed steel box girder under solar radiation, specifications in four major codes on the vertical temperature gradient of a main girder or steel box girder in China and other countries are first compared. Then, temperature measurement is carried out inside a steel box girder bridge. It was found that under the effect of hot weather and strong solar radiation, the temperature rose rapidly on the deck overlay and reached its maximum at around 14:00, while the maximum temperature of the deck was recorded at around 16:00. Notable temperature differences between the deck and bottom plate occurred from 14:00 to 18:00, with the maximum value of 16.8℃ presented at around 14:30. It was also found that the positive vertical temperature gradient showed nonlinear distribution, and the girder top had a larger positive temperature difference but a minor negative temperature difference. A suggested pattern of vertical temperature gradient was fitted using a four-broken-line, which is in line with specification in the Eurocode 1.