Fragility curves for hail resistance of toughened glass

Damage to glazing installations including skylights in a windstorm, or hailstorm, can be very costly and disruptive. Many owners and stakeholders prefer to invest into a design that would give the desirable level of protection. However, no resources exist to guide the design of glazing panels in such a way to balance the costs of initial investment against the risk of damage and disruption to services resulted from a hailstorm. The knowledge gap is uncertainties over the probability of failure of toughened glass of known dimensions during a severe hailstorm of given intensity. This article presents the outcome of a study which was aimed at making accurate predictions of the probability of failure of both new and in-service (scratched) toughened glass. Fragility curves showing these predictions have been developed and validated. It is shown in the developed fragility curves that the risk of failure of 6 mm thick toughened glass failing in a very severe hailstorm was rather high. Increasing the thickness of glass by a mere 2 mm would reduce the predicted risks to a negligible level even when the effects of normal wear and tear during the service life of the installations have been taken into account. • A model for predicting failure of glass in an isolated impact of hail was developed. • The methodology was extended to predict failure probability in a hailstorm of given intensity. • Fragility curves representing hail resistance of toughened glass were developed. • Model accuracy has been validated experimentally through impact testing. • The developed model give more accurate and faster predictions than conventional methods.