Glass Strength for Impact and Blast Loading

Abstract

Glass strength is highly influenced by strain rate. This material behaviour is well known in structural glass design and implemented in various standards. The strength of architectural glass is determined by component tests with a defined strain rate of 2 N/(mm²s), providing favourable terms for testing. As typical effects of actions on facades result in lower or higher strain rates, a strain rate factor must be implemented in structural design standards. Standard load cases as dead load, snow, climate and wind inducing low strain rates have been determined with sufficient accuracy by analytical models and extensive component testing. In difference, extensive experimental studies under higher strain rates are missing to cover accidental design situations as impact and blast. Here, only few test series are documented with a small number of test specimens, so that a statistical evaluation was not possible. Therefore, experimental tests are presented in this study, investigating the glass strength of annealed glass, heat strengthened glass and fully tempered glass under low-speed and high-speed conditions. To obtain statistical reliable experimental data, 160 glass specimens were tested, having stress rates in the relevant specimen center zones of 2 N/(mm²s) and 1,400 N/(mm²s). The surfaces of most specimens were pretreated with corundum to reduce the variation of glass surface bending strength. Further to verification of conducted tests by theoretical damage accumulation (risk integral method), load duration factors for impact and blast load design are proposed up to 1.12 for fully tempered glass and 1.4 for heat strengthened glass. On the basis of this results and other research, sufficient data are available to adapt load duration factors for impact and blast in structural design codes.