Design Considerations

Heat Strengthened Glass with Ceramic Enamel Frit



Photo of Stephen M. Morse, Ph.D.

Stephen M. Morse, Ph.D.

Assistant Professor

Michigan Tech University

Photo of Kayla Natividad, Ph.D.

Kayla Natividad, Ph.D.

Pilkington North America

Photo of H. Scott Norville, P.E., Ph.D.

H. Scott Norville, P.E., Ph.D.

Professor, Department of Civil, Environmental, and Construction Engineering

Texas Tech University



Window glass design using ASTM E 1300 entails determining glass thickness(es) and types so that the window glass construction load resistance magnitude equals or exceeds the design load magnitude over a specified time interval. A typical spandrel glass configuration consists of an insulating glass unit witdurabilityh an interior heat strengthened lite that has a full flood ceramic enamel frit application. Numerous thermally induced fractures in heat strengthened lites with full flood coverage ceramic enamel frit in spandrel glass configurations have occurred in the recent past. These thermally induced fractures led to investigations concerning the load resistance of heat treated (both heat strengthened and fully tempered) glass with and without ceramic enamel frit. The authors conducted initial investigations using small beam specimens in four-point bending. Following that, they tested full size heat strengthened glass lites with and without ceramic enamel frit.

The investigations have indicated that a full flood application of ceramic enamel frit can reduce the load resistance of heat strengthened glass by as much as 40%-50%. ASTM E 1300 provides no guidance to determine the load resistance of heat strengthened glass that has a surface treatment that reduces its load resistance. In fact, a literal reading of its scope indicates that ASTM E 1300 cannot be used to facilitate thickness selection of glass with a surface treatment that reduces its load resistance. This would include a full flood application of ceramic enamel frit. Based upon their work in investigating heat strengthened glass load resistance, the authors advance recommended reductions to design values of glass load resistance for heat strengthened glass lites with ceramic enamel frit.


ASTM E 1300-16 (2016) defines load resistance (LR) as the magnitude of the constant uniform load acting on a glass lite for a duration of 3 seconds that will result

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An application of ceramic enamel frit alters the LR of HS glass. The change in LR associated with ceramic enamel frit depends on many factors including but not limited to

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Glass Strength Distributions

ASTM E 1300-16 defines glass LR in terms of a lateral load with constant magnitude over a 3 second duration, P3, that corresponds to a probability of breakage of

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Comparisons of Experimentally Determined New HS Glass Load Resistance with ASTM E1300 Design Load Resistance Determined by the Simlified Method

The surface flaw parameters facilitate the construction of LR charts based upon the experimental failure data. Figure 3 presents a chart similar to non-factored load (NFL) charts in ASTM E

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Design Example: LR of a Spandrel Insulating Glass Unit by the Simplified Method

Consider an IG unit with rectangular dimensions 965 mm x 1930 mm. The design wind load (3-second duration) that the IG unit must resist is 7.00 kPa. We would like

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Design Recomendations

These recommendations may seem draconian but limited data exist concerning the LR of HS glass with ceramic enamel frits. The charts in Figures 4-7 concern one color of frit from

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Discussion and Conclusions

Glass, whether AN, HS, or FT, fractures under the action of tensile stress in combination with other factors. This is true whether the tensile stress is induced by temperature variations

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Rights and Permissions

ASTM. “Standard Practice for Determining the Load Resistance of Glass in Buildings.” ASTM E 1300-16, West Conshohocken, PA (2016).

Bergers, M., Natividad, K., Morse, S.M., and Norville, H.S. “Full scale tests of heat strengthened glass with ceramic frit,” Glass Structures and Engineering, Springer, (2016). 1(1): 261-276.

EN 1863-2. “Glass in Building – Heat Strengthened Soda Lime Silicate Glass – Part 2: Evaluation of Conformity/Product Standard” BSI, Brussels, BE (2004).

Krohn, M., Hellmann, J., Shelleman, D., Pantano, C., and Sakoske, G. “Effect of enameling on the strength and dynamic fatigue of soda-lime-silica float glass," Journal of the American Ceramic Society, (2002). 85(10): 2507-2514.

Maniatis, I., and Elstner, M. “Investigation on the mechanical strength of enamelled glass.” In Glass Structures & Engineering; Springer: Switzerland, (2016). Vol. 1, Issue 1, p. 277.

Morse, S. M. and Norville, H.S. "An analytical method for determining window glass strength," Proceedings, Glass Performance Days 2011. Tampere, Finland. June 18-20.

Natividad, K., Morse, S.M., and Norville, H.S. “Tests of heat treated glass with full coverage ceramic frit,” Journal of Architectural Engineering, ASCE, 23(3), (2017). 8 pp.