Transient temperature fields and thermal stress fields in glazing of different thicknesses exposed to heat radiation

Thermal performance analysis and cracking prediction of glazing elements are essential for fire safety evaluation of a building. This work investigated the transient temperature fields and the corresponding stress fields in glazing of different thicknesses with one side exposed to heat radiation. Based on the results of investigation, the criterion of critical temperature difference in cracking prediction was formulated. Glass samples of different thicknesses were tested under the same radiation exposure. Besides, a transient two-dimensional heat transfer model was presented to obtain the transient temperature fields in the glass samples. In addition, the temperature fields were loaded to ANSYS to obtain the thermal stress fields. It is found that in the initial heating period, the maximum stress was mainly caused by the temperature gradient component across thickness and the stress value was larger for thicker glazing; as time evolved, the maximum stress was gradually dominated by the temperature gradient component along the planar direction. Thus, for thick glazing under strong heat, thermal bending stress caused by temperature gradient across thickness should be calculated first to evaluate the cracking time, and the criterion of critical temperature difference is appropriate only if the thermal bending stress cannot reach the breaking value. For other conditions, cracks will result from the stress caused by the temperature gradient along the planar direction, and the criterion of critical temperature difference is applicable for cracking prediction of glazing in any thickness.