Designing Structural Laminated Glass

How the Interlayer Properties Affect Post Breakage Performance



Photo of Vaughn Schauss

Vaughn Schauss

Manager, Technical Consultancy Americas




Laminated glass with standard PVB has long been used for safety and security due to its ability to adhere the broken glass fragments together. As the boundaries of glass design keep growing, especially in structural applications, a new classification of stiff interlayers has been developed. With higher shear modulus values, these stiff interlayers provide greater coupling of the glass lites, allowing for stronger and sometimes even thinner laminates. However, these interlayers are viscoelastic in nature, and temperature and load duration play a vital part in their performance. When designing with structural laminates, it is critical that the proper shear modulus values be used to calculate glass strength using tools such as the effective thickness method or finite element method software, at least for pre-breakage conditions. This becomes complicated when considering post breakage strength. Currently, destructive testing is the only reliable method to test for post-breakage strength. To investigate the role of interlayer, two overhead applications were tested. The first testing was performed on laminated glass skylights that were point supported. The laminates were conditioned to 50°C and then impacted with a 100 Kg soft bodied impactor. Different interlayers were tested; however, only the laminate with the Ionoplast interlayer passed the test. In addition to the skylight testing, another test program was initiated to study the effect temperature has on the interlayer’s post breakage strength. Point supported laminated glass canopies were tested with three different interlayers: standard PVB, stiff PVB, and Ionoplast. The samples were conditioned to three different temperatures, -20°C, +21°C, and 50°C. After the top lite of glass was broken, 100 Kg blocks were loaded onto the canopy. At 50°C, only the Ionoplast laminate could sustain the 100 Kg load. In addition to the canopy testing, laminates made with stiff interlayers were subjected to wind load testing at different pressures. The laminate deflection was measured, and then the samples were impacted and subjected again to the same wind load pressures. Before the laminates were impacted, the deflection measurements were essentially identical. However, after impact, a large difference in deflection measurements was observed, with the stiff PVB laminate deflecting more than the Ionoplast laminate, even at 28°C.


Laminated glass has a significant advantage over monolithic glass. When monolithic annealed or heat-strengthened glass breaks, the glass will shatter into large, dangerously sharp pieces. The pieces may fall out

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Interlayer Properties

When designing laminated glass, there are a few tools to verify the laminate will meet the required loads. One of these tools is ASTM E1300 Standard Practice for Determining Load

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Post-Breakage Performance

In addition to allowing for designs with thinner glass, stiffer interlayers also provide improved structural performance in the event of accidental glass breakage. This is especially important when considering minimally

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At lower temperatures like -20°C, standard PVB was stiff enough to hold the 400 Kg, even after the laminate was broken. However, as the temperature increased, the structural properties of

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Rights and Permissions

Consumer Products Safety Commission, CPSC 16 CFR 1201. “Safety Standard for Architectural Glazing Materials,” 2012.

ASTM E1300-16, “Standard Practice for Determining Load Resistance of Glass in Buildings,” ASTM International, West Conshohocken, PA, 2016,

OSHA (Accessed September 11, 2017).

Haldimann, Matthias, Andreas Luible, Mauro Overend. “Structural Use of Glass, Volume 10 of Structural Engineering Documents.” IABSE, 2008.

pr DIN 18008-6:2015-02 (D), “Glass in building - Design and construction rules - Part 6: Additional requirements for walk-on glazing in case of maintenance procedures,” German Institute for Standardization, 2015.

ASTM E1886-13a, “Standard Test Method for Performance of Exterior Windows, Curtain Walls, Doors, and Impact Protective Systems Impacted by Missile(s) and Exposed to Cyclic Pressure Differentials,” ASTM International, West Conshohocken, PA, 2013,

ASTM E1996-14a, “Standard Specification for Performance of Exterior Windows, Curtain Walls, Doors, and Impact Protective Systems Impacted by Windborne Debris in Hurricanes,” ASTM International, West Conshohocken, PA, 2014,

The Florida Building Code, TAS 201-94, “Impact Test Procedures,” 2014.

The Florida Building Code, TAS 202-94, “Criteria for Testing Impact & Nonimpact Resistant Building Envelope Components Using Uniform Static Air Pressure,” 2014.

The Florida Building Code, TAS 203-94, “Criteria for Testing Products Subject to Cyclic Wind Pressure Loading,” 2014.

ASTM E2751 / E2751M-17a, “Standard Practice for Design and Performance of Supported Laminated Glass Walkways,” ASTM International, West Conshohocken, PA, 2017,