RuMoer #63
Extreme Forces
Most adhesive candidates were discarded already in the early stages of research due to their coloration, insufficient shear strength or too high flexibility. Eventually, visual prototypes and structural tests directed the research to a photo-curing family of clear adhesives especially designed for glass to glass bonding, with high shear stiffness and good long and short term compressive behaviour. Visually, the adhesive has a similar refraction index to glass and does not discolour when exposed to sunlight. Another important feature is its photo-catalytic curing which allows for fast construction: it takes less than a minute for the adhesive to cure under UV-radiation, acquire its full structural capacity and become moisture- and water- resistant. Series of 4-point bending tests on 1.2 m long glass beam specimens, each comprising 3 arrays
of glass bricks, proved the monolithic behaviour of the system when bonded by this adhesive. All specimens acted as one single rigid unit under loading by failing with a straight, clear-cut in the middle (fig.3). However, the structural tests also revealed that the chosen adhesive reaches its optimum (and desired) bond strength when applied in a layer of a mere 0.3 mm thickness. The low viscosity and effectively zero ideal thickness of the adhesive together with the inelastic nature of glass generated several implications concerning its homogeneous application that resulted in exceptionally strict allowable tolerances regarding not only the brick’s dimensions but also the overall façade. Not only the size of each brick unit, but even each layer of the construction of the glass wall had to be confined within a tight dimensional precision of a quarter of a
Figure 3: The failure pattern of the glass beams tested under 4 point bending demonstrates the monolithic behaviour of the system under loading
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Academic article