Exploring the effects of post-tensioning an all glass column of the bundled type to enhance slenderness and promote safe failure behavior

Abstract

The long and slender structural member, the elastic column, fails due to buckling. Buckling is a predictable, and visible, mode of failure allowing for timely repairs or replacement. This is no longer true when we look at long and slender columns made out of glass as glass is a brittle material. At the moment the critical buckling force is reached the column does not deform as much but suffers from explosive brittle failure, because of this it is unpredictable and extremely dangerous. As a result of this brittle failure behavior we apply safety factors twice as high when designing with glass compared to other construction materials, leading to excessively large, heavy and costly elements. Research focused on creating load bearing glass colums has been conducted and has led to a few preceding glass columns. These columns did lack either mechanical or architectural desirability though. New research is being conducted into producing a glass load bearing column by laminating solid rods together, this research is very promising but is still limited by the boundaries generated as a result of this immense safety factors. Increasing the cross-sectional properties of such a column does increase the column’s resistance to buckling, but again leads to excessively large structural elements with increased weight and cost. But what if we can, rather than accepting the consequences of the high safety factors, reduce the safety factors by increasing the mechanical behavior during buckling, transforming the brittle and explosive failure into a more gradual and ductile failure. This thesis researches the potential of post-tensioning a bundled glass column in an attempt to transform the explosive brittle failure into a ductile mode of failure. In order to verify this behavior a total of six slender glass columns have been produced with a length of 2400 millimeters, three of these where loaded with around 3000 kilograms of prestress and all six were destructively tested. A prestressed member appears to be a more flexible element than a similar non-prestressed member and has post-breakage load bearing capabilities.