Thermal resistance of framed windows: Experimental study on the influence of frame shading width

The presented experimental work investigates the performance of window glass panes exposed to radiant heat flux. Such performance is of interest, as the cracking and fallout of window glass panes during a fire strongly influences the fire duration and thereby the structural response and the safety of fire brigades and rescue services.

This study focuses mainly on investigating the influence of shading width on monolithic glass panes exposed to different radiation levels. The investigated shading widths and radiation levels were selected from a literature survey and commonly found shading widths used in domestic windows. In the study, 39 experiments were conducted on 400 × 400 × 4 mm monolithic float glass specimens set up in a window frame replica and irradiated by a gas-driven burner until cracking was observed. Three different radiation levels (5, 10, and 15 kW/m²) were investigated with four different shading widths (10, 15, 20, and 25 mm).

The results suggest that the shading width influences the time at which glass failure occurs at low radiation levels. However, for radiation levels of 10 and 15 kW/m², the shading width became insignificant due to the rapid increase in temperature gradients. The onset of failure by cracking was less than a minute for radiation levels of 15 kW/m². The results also indicated that a wider shading width influences the temperature difference between the exposed and shaded parts of the glass at the time of the failure so that a wider shading results in a slightly higher temperature gradient.