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Protection Engineering Consultants (PEC) was engaged by the Air Force Research Laboratory (AFRL) to provide evaluation of the performance of window systems incorporating Herculite® XP glass and develop a fast running model to be used as a design tool enabling engineers to specify Herculite® XP glass for the Defense Acquisition Challenge (DAC). Herculite® XP glass is a high strength glass technology developed by PPG Industries with a residual stress about twice that of commercially produced FT glass. The research program included quasi-static tests of Herculite® XP glass at PEC, shock tube tests of punched windows (insulating glass units (IGUs) with commercial window frames containing Herculite® XP glass) at ABS Consulting, and two full-scale blast tests at AFRL on IGUs containing Herculite® XP glass in punched window and storefront configurations using commercially available window frames.

The DAC test program was used to validate a model capable of predicting glass failure for both static and dynamic loads. The GFPM developed by Beason and Morgan (1984) was chosen for its incorporation of load rate, empirical probability distribution (validated), and because it is the basis for the industry standard ASTM E1300 design methodology. However, the GFPM was only developed to accommodate AN glass and needed modifications to handle the increased strength of Herculite® XP glass.

The Glass Failure Prediction Model (GFPM) is the basis for ASTM E1300 which is used across the nation for window glass design. ASTM E1300 states that the model is valid only for annealed (AN) glass but, ASTM E1300 does incorporate heat strengthened (HS) or fully tempered (FT) glass through the use of multiplication factors. Rather than multiplication factors, this paper will address modifying the GFPM to incorporate these types of higher strength glass. Designers can then incorporate the model into common design methods such as single degree of freedom (SDOF) and finite element analysis (FEA) to analyze dynamic performance of glazing layups. To validate the modified GFPM, both static and dynamic testing of high strength glass was completed and comparisons to analysis predictions will be provided in the paper. The paper also illustrates how to use the modified GFPM in window design for both static and dynamic applications through the use of Single-degree-of-freedom Blast Effects Design Spreadsheet for Windows (SBEDS-W), a SDOF design tool to be released by the U.S. Army Corps of Engineers Protective Design Center (USACE PDC). Dynamic window analysis tools like SBEDS-W will be utilized more frequently due to the new threat-based requirements for windows and doors in the Unified Facilities Criteria (UFC) 4-010-01 DoD Minimum Antiterrorism Standards for Building (9 February 2012). Also, an understanding of the failure prediction capabilities of SBEDS-W is important for engineers performing the dynamic glazing analyses.

Read more in the full PEC TechNote by Kirk Marchand…

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