Volume 37, Issue 10, October 2002


New Research Says Two Lites are Not as Strong as One

Algor Inc., a Pittsburgh-based company that makes computer software and provides services for mechanical and civil engineers, reports that it has used its Finite Element Analysis (FEA) software to make what it says is an “astonishing discovery.” The study showed that two bonded window lites are not as strong as one lite that has the thickness of the bonded pair. This is according to an article that originally appeared in the June 6, 2002, issue of Machine Designing magazine.

“Designers had assumed that the strength of architectural laminated glass with an interlayer equaled 60 percent of the strength of monolithic glass of equivalent thickness,” said W. Lynn Beacon, associate professor of civil engineering at Texas A & M University in College Station, Texas, and
engineering consultant. 

Research funded by PVB manufacturers recently redefined the relationship so the strength factor has been increased to .75 in most building codes throughout the United States, said the article. Some PVB researchers now say the structural behavior of laminated glass is equivalent to the structural behavior of monolithic glass for most common applications, so a laminated-glass strength factor of 1.0 should be adopted.

Beason used Algor FEA software to analyze laminated and monolithic glass. He created two models of a 72 by 72 by ½-inch glass lite, one laminated and the other monolithic. “The maximum principal stress revealed in the Algor finite-element model for the laminated glass plate is about 25 percent greater than for the monolithic glass plate,” said Beacon. He adds that FEA results do not warrant the general use of a single-lite equivalency for the design of architectural grade laminated glass. In fact, he says that this could result in poor estimates of stresses and deflections for some common laminated glass situations, which could lead to broken windows.

“If a consensus can be reached regarding an appropriate design temperature, FEA results can be combined with glass-failure prediction formulations to develop rational design criteria for architectural-grade laminated glass in general use. In the interim it would be unwise to increase the laminated glass strength factor above .75 for architectural-grade laminated glass.” 

LBNL Study Finds Skylight Well Reduces Solar Heat Gain

A recent study by the Environmental Energy Technology Division (EETD) of Lawrence Berkeley National Laboratory has found that energy absorbed in a skylight’s well is carried upward by convection, resulting in stable temperature stratification of the well air. According to the study, heat is trapped in the air at the top of the well and can only reach the space below by thermal 

A report in the EETD’s newsletter stated, “results in the air at the top of the well [remain] at a higher temperature than outside air even on a very hot day. The heat transfer through the skylight is directed outward. The skylight/well combination rejects part of the solar gain that has entered through the skylight.”

In addition, tests found that approximately 25 percent of solar energy admitted by a skylight is rejected, so that only 75 percent can impose a cooling load on the space below. 

According to LBNL, the study’s findings will mean new issues to consider when designed buildings with skylights. For example, depending on the nature of the adjustment, heat rejected through the well walls may or may not add to the cooling load. LBNL says additional research will be necessary to develop a method for calculating trapped heat and the expected temperatures from the well geometry and incident solar flux on the skylight.

American Chemical Society Recognizes Two
James R. Moran of Solutia Inc. and Richard W. Rees, Ph.D, formerly with DuPont, were each honored by the American Chemical Society as a Hero of Chemistry on August 18 during a ceremony in Boston. Both developed safety glass innovations.

Moran was honored for his work in creating a laminated safety glass formed by bonding a Saflex® IIIG PVB interlayer between two lites of glass. The interlayer is designed to keep glass fragments within a window’s frame in the event of an explosion, storm or other type of blast.

Rees was recognized for his Surlyn® ionomer resins invention, a family of tough, clear plastics. DuPont’s SentryGlas® Plus interlayer is made from the resins and used in creating laminated safety glass.


Applied Films Corp. announced that it has received an order for a Terra-G system for the application of thin films primarily for the architectural and automotive glass market.



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