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ASTM Standard E 1300 in the Past Decade
By: A. William Lingnell, P.E.

During the initial article A Brief Review of the Background History and Use of the ASTM Standard E 1300 for Glass Analysis in the December 2011 issue, it was referenced that a continuation of the history of the ASTM E 1300 standard would venture into the changes and updated additions of the standard that have occurred in the new millennium since year 2000. This article will delve into the work that has occurred since 2000.

In 2000, charts were made bigger, and more legible, allowing easier interpolation between load lines. Conversion factors were added for load durations other than 60 seconds and 30 days. Related to this was the addition of how to combine loads of different durations. One of the most important additions to the 2000 revision was an effort assist evaluation of even more complex designs not covered in the standard. Examples of this are point supported glass, non-rectangular shapes, and edge supported conditions other than four edge. It was recognized that engineers and designers were analyzing these types of designs, but with no consensus set of maximum values for edge stress and surface stress. The addition of tables addressing these values in the appendix of E 1300 was a major contribution for standardization.

Several major changes occurred in the 2002 version of the standard. For one, in that same year the industry began changing how wind speed and pressure (Windload) were addressed in the US. Previously, Windload was averaged over 60 second duration. In 2002, the American Society of Civil Engineers agreed to change their standard on determining design loads (ASCE 7) from 60 seconds to a 3 second gust. After much debate and discussion about this topic within the ASTM task group, it was decided to rework all twelve of the existing load chart, making adjustments for 3 second load duration.

In addition, there had been extensive work by DuPont showing that the factors for laminated glass currently used in E 1300 were too conservative. This work resulted in establishment of separate load charts for laminated glass.

Previously, the document assumed that glass was always supported on 4 sides. In the 2002 revision, charts were added to address design loads in 1, 2, and 3 side support conditions. With this revision the document expanded to 59 pages. There were 42 load charts, 5 tables of factors, and 13 procedures covering various glass constructions. There was much concern about complexity and the need for a computer program to keep track of the logistics required to obtain a result. Unfortunately, ASTM as an organization does not promote the writing of sanctioned computer software, although others were free to do so.

Editorial changes and revised glass type factors were made in the 2003 version of the standard. Prior to 2004, only polyvinyl butyral (PVB) interlayers for laminated glass were recognized. In order to accommodate other interlayer materials, the 2004 revision included a procedure for establishing equivalency to PVB. The basis for equivalency was to provide evidence through a standardized test (ASTM D 4065), that the non-PVB interlayer had an equal or greater lower bound Young’s Modulus of 1.5 MPa, and a shear modulus of 0.4 MPa.

In 2007, definitions for the designation of laminated glass were revised. Since there are many layup combinations of laminated glass with varying glass ply thickness and interlayer thickness, and a "designated" laminated glass thickness was necessary for determining which load chart is appropriate. In this update the load charts were adjusted once again this time to accommodate larger size glass plates in thicker glasses. Sizes as large as 120" x 250" (3050 mm x 6350 mm) and larger could now be evaluated.

The most recent version of the standard at this writing is the 2009 edition. This revision added a procedure for analyzing triple glazing. This procedure again assumed load share is proportional to stiffness of the plate and determined load share factors based on the cube of the thickness. Also added was a procedure for determining the "effective thickness" of laminated glass. This procedure is provided for use in independent stress analysis for design situations not covered in the main document of E 1300. There is committee work going on at present to add to and improve the standard further. Stay tuned for the next version that is expected to release in 2012.

 

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