Uniform Load Data
Design professionals should review and adhere to all applicable national, state and local building codes and regulations when selecting glass design load factors.
Additional Factors
+ Type of Exposure
+ Building Height
+ Orientation
+ Wind Gusting
+ Shape
+ Safety Glazing Requirements
Tempering Considerations
Low-E, blue, green, grey, and bronze have heat-absorbing characteristics and retain heat as part of the absorption process. Texas Tempered Glass produces reflective glass, with the coating on the second surface of heat-absorbing glass, absorbs increased amounts of solar energy and may require heat-strengthening or tempering to reduce the possibility of thermal breakage.
Uniform Load/ Glass Strength
The wind load building are exposed to is neither static nor uniform. It is the design professional’s responsibility to translate a project’s specified wind or design loads into uniform static loads of a 60 second duration equivalent.
Heat strengthened and fully tempered glass will withstand greater uniform loads than annealed glass. Deflection characteristics, however, are the same for identical thickness of annealed, heat strengthened or annealed substrates.
Thermal Stresses
When glass is exposed to sunlight, solar energy is absorbed, causing the glass temperature to rise. The rate at which glass temperature rises is dependent on the type and thickness of glass used. If the glass is not properly thermally isolated from the glass framing system, or if it is glazed directly into a high heat capacity material such as concrete, the temperature of the glass may be significantly lower than the that of the center portion of the glass.
Glass, like most materials, expands with increased temperature levels. The hotter center portion of the glass expands more than the cooler glass edges, creating thermally-induced stresses at the edges. Thermal stresses are normally greatest at the center of each edge, diminishing toward the corners. Higher thermal stress may cause glass breakage and the ability of the glass to resist breakage, due to both thermal and mechanical stresses, depends on the edge strength of the glass.
Under abnormal conditions where thermal stress increases breakage risks, resistance to thermal stress of a lite of glass can be increased by tempering the glass. Tempering the glass also improves the glass's ability to withstand higher uniform loads.
Low-emissivity ( low-e ) Glass
Low-E glass may have various combinations of metal, metal oxide and metal nitride layers of coatings that are nearly invisible to the eye.
Energy savings through its ability to reflect long-wave infrared energy low-e coated glass reduces winter heat loss and summer heat gain through the glass, and provides high levels of visible light into the building The combination of thermal control and reduction in interior lighting requirements reduces energy consumption for residential and commercial buildings.
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