Bärande konstruktionselement av glas : Dimensionering och utformning av glaspelare

The use of glass as building material has increased for many years and has over the past decade also been used in structural elements. The main feature of glass is that it is transparent and therefore allows light. This also means that an expanded use of the material would provide a great opportunity to create modern architecture. There are no standards for the design of glass components in Sweden, but there are current efforts to develop standards for this in Europe, so called Eurocodes.Some of the properties of glass is that it’s a durable material that can withstand moisture and other types of attacks and it is fragile to temperature changes. The type of glass used in construction is float glass, i.e. glass produced by the mass flowing on a tin bath and slowly cooling down. Thus, the dimensions of the material is very thin, it is then also easy to swing. Therefore, sound insulation ability is not satisfying. In order to get thicker dimensions of the glass several layers of glass can be laminated together by using a transparent intermediate layer that is usually polyvinyl butyral, PVB.The structural characteristics are that glass is a brittle material that has a high strength under compression, about 890 MPa, and rather low tensile or bending strength, 45 MPa. Tempered glass has a higher tensile strength, 120 MPa. The tempering process is done by reheating the glass followed by a faster cooling. A compressive stress is then formed on the surface and the breakage of the glass happens first when the maximum tensile stress is exceeded. The strength of glass is also dependent of what the surface of the glass looks like, damage on the surface can cause a breakage.The design of connections between glass and other materials is very important to avoid stress concentrations in the glass. A hole made in the glass implies loss of strength which should be considered if connections with bolts are intended. The area in contact with other materials can preferably be staggered to reduce stress concentrations.A structural glass column could add value for a room, when compared to using a non-transparent traditional building material. To get a more stabile construction a glass column should consist of several sheets of glass glued together.For the design of glass columns, in which glass sheets are either laminated together or glued together by other means the shear deformations that may arise in the adhesives must be taken into account. This is done by taking into account that the materials have different Young’s modulus and shear modulus. The report shows various methods to take this into account in the calculation process. The methods give similar results, but they also show that introduction of simplifications means that the design is not on the safe side.The resistance of a glass column is relatively good compared to other materials, the limiting glass is thin, and brittle fracture. It’s therefore important to incorporate some type of back up into the design of the glass pillar. A good solution can be to glue together multiple sheets of glass.More research is needed on this subject, both to develop standards for the calculation of glass element strength and develop formulas that make the design easier.For the glass to make a breakthrough as a construction material, it must not only appear standards for the design, but it also must be cheaper to choose glass as a material, perhaps by pre-fabricated glass elements.Validerat; 20111116 (anonymous