Germany Engineers Recognize SentryGlas® "Coupling Effect" for Higher Structural Loads
Neu-Isenburg, November 2011. The Deutsche Institut für Bautechnik (German Institute for Building Technology) in Berlin has granted general approval for the use of laminated safety glass made with DuPont™ SentryGlas® interlayer in construction on the basis of its structural coupling effect.
With immediate effect in Germany, the interlayer, which is five times stronger and over 100 times stiffer than a standard PVB interlayer, can now be included as a load-bearing element when calculating the load capacity of laminated glazing. This means that the cost-saving benefits of laminated safety glass made with SentryGlas® - including high safety at reduced glass thickness and therefore lower weight, as well very high edge stability, can now be accessed without requiring time and cost-intensive case-by-case approval.
The general approval of laminated safety glass on the basis of its structural coupling effect has been granted for laminates whereby at least two flat plies of glass have been laminated together using SentryGlas® interlayer. The glass plies can be made from:
- Float glass,
- Fully-tempered glass,
- Fully-tempered and heat-soaked glass,
- Heat-strengthened glass or
- Coated glass
According to the technical ruling, the resulting laminated safety glass panels may be used for linear supported glazing or impact-resistant glazing. The structural coupling effect is considered - beyond these three requirements - upon verification of the load-bearing capacity of vertical glazing under windload and horizontal loading caused by people or snow.
According to a report, carried out by Professor Jens Schneider, Fachgebiet Statik des Instituts für Werkstoffe und Mechanik im Bauwesen at Darmstadt Technical University, a shear modulus of up to 100 MPa should be used as parameters for SentryGlas®, depending on temperature and load. Considerably lower values are to be used for high glass temperatures, but even in such cases, load-bearing behavior is close to monolithic. Further details can be requested from DuPont.
"Many constructors and architects in Germany have already benefited from the considerable weight, performance and, ultimately, cost benefits of laminated safety glass with SentryGlas® interlayer for specific projects," comments Ingo Stelzer, technical specialist for SentryGlas® interlayers at DuPont in Neu-Isenburg, Germany. "Yet they have often been required to gain case-by-case approval for the project, an additonal step that involves considerable expense. A recent example is provided by the renovated glass facade at the headquarters of the Fraunhofer Gesellschaft in Munich, where the original panels of toughened safety glass were replaced with laminated safety glass. The existing supporting structure could be retained without the need for reinforcement, thereby helping to keep renovation costs down. As of now, the many advantages of laminated safety glass with SentryGlas®, which include high edge stability, transparency and post-breakage stability, are accessible to many day-to-day projects in the private, communal, and industrial sectors, amongst others, without any additional administrative hurdles. They can be used for the design of balustrades, facades and overhead installations that combine light weight with high levels of safety."
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Recent general approval for the use of laminated safety glass made with DuPont™ SentryGlas® interlayer in construction, based on its structural coupling effect, enables significant reductions in thickness. For a laminate consisting of two plies of float glass, each 8 mm thick and measuring 1.5 m by 2.5 m and laminated with 1.52 mm SentryGlas® interlayer, a deflection of 53 mm and a maximum tensile stress of 29 MPa is calculated based on a linear load of 1 kN/m from a height of 1 m and without allowing for the shear modulus of the interlayer (previous circumstances). This is significantly higher than the permissible glass stress of 18 MPa according to German building codes. When allowing for a shear modulus of 65 MPa (applicable to interior applications), the results and well within the permissible limits at 10 mm deflection and 12 MPa glass stress. Even when using a shear modulus of only 4 MPa (applicable to exterior applications in direct sunlight), the results hardly change and are well within the limits.
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