The properties and structural use of toughened glass
Recent architectural trends have increased significantly the use of glass in buildings not only as non-structural facade elements but also as important load carrying structural elements, i.e. as integrated load carrying elements in facades or as distinct structural elements such as columns – elements for with materials such as steel and concrete traditionally are used.

Glass has many excellent mechanical properties which make it a perfect choice for structural use: high compressive strength, good stiffness to weight ratio, good resistance to aggressive environments and good long term performance. Glass however is extremely brittle and this brittleness poses serious limitations in its structural use. The brittleness makes glass extremely vulnerable to the presence of small defects in the surface which in turn makes its tensile properties unreliable. Further, the brittleness prevents any inelastic deformations before failure which is usually a requirement in structural safety.

Development of on one hand toughened and heat treated glass and on the other laminated glass has pushed the structural applicability of glass significantly. Toughening of glass introduces residual compressive stresses in the surface and the edges of glass elements, stabilizing the micro-defects present in these areas. Heat treatment of glass introduces these residual stresses to a lesser degree, while laminating of glass typically combines various types of glass, hardened, heat treated or just plain float glass in such a way that ductility and integrity at failure is achieved. Combining these techniques for controlling the effective glass properties with innovative ways of designing joints and connections a new world of structural opportunities has been opened using glass as a structural material.

There is still however a lack of material specification tools, relevant test methods, structural design methodologies and standards. This makes the design procedure for structural use of glass cumbersome and often the designer has to resort to full scale destructive testing of key structural elements. The present project should be seen as a step towards establishing a design methodology for joints in hardened glass including bolted friction and bolted pin connections. Ultimately the results should allow for development of a methodology for material property specification and testing.