The Challenges of Writing a Structural Standard for Glass

Abstract

Glass has been used as a prized construction material for centuries.  Typically it has been used as a window infill, initially designed empirically where thickness available was adequate for the sizes available.  As technology has proceeded, the size of glass available has increased by orders of magnitudes and standards have been written to guide the design in windows.  Glass remains unique amongst the construction materials, that failure and replacement is considered an acceptable price to pay for the transparency of glass. The same logic has, however, limited the use of glass as a ‘structural’ material, despite the numerous built examples of it performing adequately. If it is acceptable for glass to break and collapse in some circumstances and not others, how does a standard define that boundary?  The challenges for standardization are both numerical and philosophical. The means of forcing glass to behave with a robust manner with failure mechanisms that incorporate redundancy and retention generally comes through lamination.  But the question is what to require when?  Additionally, the performance of the glass in the composite is stress-time dependent and the stress itself is load-time-temperature dependent.  This paper describes the philosophical and numerical challenges to writing a structural glass standard, the concepts of glass importance factor, post-failure loads and durations and progress that has been made in the drafting of an ASTM Guide to the Design of Structural Glass.