1 GLASS PROCESSING DAYS 2005 - www.gpd.fi Building Projects Case Studies The Laminated Glass Column E.J. van Nieuwenhuijzen, F.P. Bos, F.A. Veer Building Technology group, faculty of Architecture, Delft University of Technology, www.zappi.bk.tudelft.nl Keywords 1=glass 2=column 3=production problems 4=quality Abstract A transparent column, consisting of two glass tubes laminated with a clear resin, has been developed during several years of ZAPPI research. Intensive testing led to a lamination process for columns on a scale relevant to building structures with close to perfect results. Compression tests showed safe, gradual and controlled failure behaviour compatible with the ZAPPI safety philosophy. This prescribes safe failure behaviour of transparent structural components rather than using gross over dimensioning to achieve safety. The composition of the column and the results of compression testing are discussed. Introduction In 1999 the first results of the research into transparent columns was described by Veer and Pastunink [1,2]. This work was continued over the years and last year the research took place within the framework of the All Transparent Pavilion project (fig 1) [3]. The safety philosophy of this ZAPPI pavilion is that safety can be guaranteed by designing safe failure behaviour into transparent components and not by grossly over dimensioning the structure as is current practice. Safe failure behaviour means that a component shows, during a test with gradually increasing loading, clearly visible damage without a risk of total failure and thus shows endurable deformation before complete failure (fig 2). Thus ductile rather than brittle failure is the result. In the All Transparent Pavilion, the columns carry the vertical loads and are thus subjected to compressive forces. Proper design of the joints avoids bending loads. Research shows that because of buckling, torsion and commercial availability a tube is the best shape for this transparent column. The design of the column has to meet strict requirements for transparency, strength and safety. A laminate of glass tubes with a clear resin should fulfil these demands (fig 3). Both of the glass tubes can carry the load, the resin will slow down and arrest cracks while keeping the fragments of broken glass together after failure in such a way that they can still carry some compressive forces. While this concept works nicely for pure compression, bending loads can result in local peak stresses and tensional stresses, thus effecting the failure mechanism. Therefore bending should be avoided by using properly designed hinged connections at the top and bottom of the column. The laminated tubes are similar to the transparent columns produced commercially by Schott Rohrglas [4], but the structural concept is completely different. Schotts laminated glass tubes uses one core tube, a PVB layer as intermediary and two half tube shells that together form the outer tube. In contrast with the ZAPPI column, only the inner tube is the load bearing element. The shells essentially protect against impact damage. There is a risk that if the load carrying inner tube fragments the outer tube will simply slit apart along the seam with the whole structure collapsing. The structural goal of the column is that it can carry large compressive loads without failure. In the unlikely occurrence of any damage leading to failure, there should be enough time to if necessary remove the extra load that is causing the failure, to support the damaged column or to flee. Thus it is necessary that the column has a significant fraction of it’s total strength left after the first crack can be seen and that subsequent failure behaviour is gradual. In other words: once a first crack appears during an increasing load, the remaining load carrying capacity should be sufficient to carry all loads. The architectural and aesthetic goal of this research is to produce a completely transparent column on a scale that is relevant for normal building structures. Concept & production The concept is the earlier introduced idea of laminating two glass tubes with a clear resin,[1,2]. The resin functions to stop and slow down cracks during failure and to keep fragments of broken glass together after failure of the glass tubes. The damaged glass tubes can still carry loads until the complete cross-section at a particular height delaminates. The production method consists of placing one small diameter tube within a larger diameter tube and sealing the bottom. The small (0.8 to 2 mm) gap between the two tubes is slowly filled with a liquid resin monomer. After polymerisation of the resin, the laminated column is except for cleaning ready to be used in a building. Starting with small specimens in 1997, the behaviour of the resins during curing proved to be a repetitive difficulty for several years. Heat production, Figure 2 Intended failure of laminated glass column Figure 1 Original design of All Transparent Pavilion Figure 3 Cross section of laminated glass column