Designing Structural Laminated Glass

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.