Structural Analysis of Annealed Glass Windows

Brandon Erickson, P.E., S.E., Structural Engineer
Case Synopsis: The plaintiff, a teenage boy, was preparing for practice with his high school wrestling team when he suffered a serious injury to his arm. The injury occurred while he and his teammates were moving wrestling mats, which were rolled and stacked in the school cafeteria when not in use. In the course of endeavoring to move the top-most rolled mat, the plaintiff’s arm broke through one of the adjacent windows causing permanent damage to his arm.
Expert Analysis: In his deposition the plaintiff claimed to have only “touched” the glass window, which then reportedly shattered and broke, allowing his arm to be cut on the shards of glass as it passed through the plane of the broken window. An examination of the window wall revealed that the glass used in the windows was annealed, not tempered glass (often referred to as safety glass). Plaintiff’s counsel argued the presence of safety glass would have prevented injury to his client. The school’s defense counsel argued that notwithstanding the presence of annealed glass, the window would not have broken under the conditions described by the plaintiff, suggesting that instead the plaintiff was “roughhousing” while leveraged against the window to move the mat. Defense counsel requested a structural engineering analysis of the window system to quantify the force required to cause the glass panes to break.
Fortunately, the remaining original windows in the cafeteria wall were still intact and available for diagnostic testing. A custom-designed and constructed testing mechanism was conceived and employed to quantify the breaking strength of the windows. All elements were precisely replicated to the same conditions that occurred during the incident, including a prosthetic hand and testing apparatus to move it with similar force and angle. Prior to conducting the physical tests on the windows, engineering calculations were performed to predict the force at which the windows would break. The calculations were based upon the material properties of the glass chards collected from the broken window, which was deemed identical to the unbroken windows that were tested. These calculations served as a means of comparison with the forthcoming test data, and aided in the development of the testing mechanism to ensure it was capable of delivering sufficient force to the windows. Continue reading “Structural Analysis of Annealed Glass Windows”