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Curtain wall design commonly uses insulating glass units for vision and spandrel glazing to provide better visual harmonization of building facade glass. Risks with this design approach include higher thermal stresses, especially when low-emissivity coatings are used on insulating glass units in spandrel areas. Ceramic enamel frit – commonly used to opacify spandrel glass – is known to induce a bending strength reduction of up to 50 percent. The ability of ceramic enamel frit coated glass to resist thermal stress is similarly reduced. Multiple incidences of thermal stress related fracture have occurred with heat-strengthened, ceramic enamel frit opacified spandrel glass. An increased chance of spontaneous breakage, by nickel sulfide inclusions, may occur if ceramic enamel frit opacified spandrel glass is fully-tempered to withstand the thermal stresses that it is exposed to.
Silicone spandrel glass coatings have been examined as a solution to prevent the strength reduction in heat-treated glass when ceramic enamel frit is applied as an opacifier. Four-point bending tests were used to investigate the flexural strength of coated heat-strengthened and fully-tempered glass. Ball drop testing was used to investigate the impact resistance of coated fully-tempered glass. Silicone coatings have no adverse effect on the flexural strength or impact resistance of the substrate and, in some instances, improve it. Therefore, silicone opacifiers do not reduce the resistance to thermal stress of heat-treated glass. These coatings also provide fallout protection in accordance with ASTM C1048 (ASTM, 2012). This suggests using a silicone opacifier on heat-treated spandrel glass could greatly reduce the risk of fracture resulting from thermally induced tensile stress, flexural stress, and impact related glass breakage in addition to reducing risk of injury from fallout if breakage occurs.
In the world of façade glass, there are two types of glass: vision, and spandrel. Vision glass is transparent to provide viewing areas for occupants and daylight for the interior
Study and procedure details about the two different experiment methods are defined below – what tools, software or models were implemented, how results were measured, etc.
Four-Point Bending Test
Four-Point Bending Test
All specimen fracture origins lay between the load points on the beam specimens, that is, within the area of constant bending moment and flexural stress. No fracture
Four-point bending test results indicate OPACI-COAT® coatings have a positive impact on the flexural strength of HS glass, and have little to no impact on the strength of FT glass
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