Why Window Glass Fails

Despite the focus on the wind loading in the determination of glass thickness, damage surveys conducted following recent disasters have revealed that wind pressure does not cause glass breakage factor such as wind borne debris, excessive building motion and blast pressures have been documented as the cause of widespread glass breakage the designers of window glass at the affected project did not anticipate these factor. A major consequence of the glass breakage was a breach in the building envelope that resulted in damage to property and personal injury.

A substantial amount of glass breakage occurred in a relatively small area in downtown Houston Texas during Hurricane Alice. The density of broken window glass lites can be readily observed from the density of the plywood replacement panels. It is highest at a level near the elevation of the roof line of an adjacent building. The breakage density decreases with change in elevation from rooflines of adjacent building. This suggests strongly, if not conclusively, that the window glass broke as the result of wind-borne debris , such as roof gravel, carried by the wind from the adjacent building. Close-up photo of broken windows revel from the fracture origin and pattern that breakage was caused by impact rather than by the wind certainly wind was a factor in that it carried the debris but it was a factor in that it carried the debris but it was not the ultimate cause of breakage

140512_FLASH_1949Flood-LancasterAveWindow glass broke during explosions results from uniform pressure loading of high magnitude and short duration. in explosions, wind  has nothing to do with glass breakage. Glass breakage is also common in areas subjected to earthquakes Breakage occurred almost at the onset of shaking in a department store near Union Square in san francisco during the loam prieta earthquake of October 17, 1989. Again wind had nothing to do with the breakage other building affected by the earthquake show evidence of racking movements that could resulted in but fortunately did not glass breakage

Spontaneous glass breakage often occurs at project glazed with fully tempered glass Nickel sulfide contamination , a leading cause of  spontaneous  breakage of tempered glass, apparently cannot be eliminated completely by glass manufacture and this problem has caused sufficient concern that one manufacture has adopted a policy restricting the use of tempered glass for most architectural glazing application

All this case show that window glass breaks as the result of varying causes must of which have no relationship to wind loads Architect or engineers cannot possibly be expected to amount for all possible  events that might break window they are designing . one of the designers main goals , though should be to product designs that minimize damage and injury in the event of window glass breakage

Glazing shopee can help you select glass based on site conditions. Write to glazingshopee@gmail.com

Author: Dr H Scott Norville