Volume 39, Issue 6, June 2004
Close to the Edge
ASTM International Subcommittee Working to
Draft Test Method and Standard for Glass Railings
by Julie Schimmelpenningh
remember hearing that phrase from my mother so many times when I was young that it’s now burned into my brain. It is ironic that today I am chair of an ASTM International subcommittee that is creating test methods and specifications for a material that will allow a person to see the edge, walk up to the edge, in some cases gaze over the edge, yet still provide almost invisible protection and deterrence.
A Unique Application
Glass handrails, balusters and guards are being used almost everywhere today. They serve as a divider, edge deterrent or safety guard against changes in elevation where an individual or object could fall over the edge. The use of glass in these applications is unique—while it is typically chosen to provide a sense of freeness and openness to a space, this virtually invisible product is expected to perform just as wood, metal or concrete would. Performance of Railing Systems and Rails for Buildings (E06.56) is a subcommittee to ASTM E 06 on Performance of Buildings, and task group 08 is working to develop a test method and specification for glass railing systems and rails for buildings.
Test Method and Specification
After identifying a need in the marketplace, the task group was formed in early 2000 and development of the documents was initiated. The committee reviewed documents dealing with similar subject matter and decided to use the ASTM metal railing documents1 as a basis for the glass railing standards. These methods and specifications have been applied to other materials, but no documents have existed for glass until now. The current documents are in the process of becoming ASTM International consensus standards. Minor changes to the documents are slated during the next round of committee balloting, which upon approval should move the documents into publication.
This article briefly discusses the contents of those documents. It should be noted, however, that these documents have not yet been published.
The test method and specification as they stand today do not contain contradictory requirements from those cited in the International Building Code (IBC) section 1607.7, “Loads on Handrails, Guards, Grab Bars and Vehicle Barriers.” The glass requirements also coincide with those from section 2407, “Glass in Handrails and Guards.”
The test method describes procedures for assessing the static strength, impact performance and post breakage retention characteristics of railing systems, guards and balustrades. It applies to systems having glass as the major structural component or the infill panel(s) in one-, two-, three- and four-side support systems as used in various applications.
The test methods are limited to concentrated and linear loads with additional impact testing similar to CPSC 16 CFR part 1201. Designations of the systems are separated by glass; in-fill panels versus structural panels. The location of load placement is the first test performed on the railing system. The impact procedures follow, and the test method is completed by providing, directions on interpretation of the results. These test methods address the capability of glass railing systems to continue functioning as a barrier that provides a mechanism to account for potential fall-through after impact or glass breakage.
The complementary document to the test method is the “Standard Specification for the Performance of Glass in Permanent Glass Railing Systems, Guards and Balustrades.”
Like the test method, this specification is essentially derived from the metal railings specification with modifications that make it applicable to glass. While the criteria provides for normal and anticipated building uses, it does not account for abuses to the systems.
Design requirements are outlined in the specification that describes railing heights and resistance to penetration, hand rail design and offset limits. It should be noted that these are the basic height requirements only; several exceptions and exemptions exist and the specifier should reference and ensure compliance with the building code prior to installation.
Classifications of system type and performance level are also outlined in the specification. Level one relates to basic, level two relates to safety and level three and four relate to enhanced performance.
The overall pass/fail criterion for structural performance requires glazing retention to occur and the glass to be unbroken at the completion of each test. For the shot bag and pendulum impact, the criteria requires the system to be retained after impact in the framing system such that a 75-mm (3 inches) solid steel sphere will not pass through any part of the system using a force applied horizontally of 18 N (4.0 pounds).
The products evaluated by this specification have the potential to be subjected to a wide variety of forces and impacts that could cause breakage and lead to the possible fall-through hazards if the glazing vacates the frame. This specification outlines a test methodology that takes into account various impacts ranging from a sharp blow of a knee to a blunt object impact to a full-body impact. Although not every form of impact or force can be accounted for in a standard document, this specification provides a means of establishing a level of retention that may help glazing in railing systems perform its intended function of protection and fall-through prevention. Once a system has been tested successfully, there are permissible variations and substitutions of glazing products outlined in the specification that provide flexibility for manufacturers.
These documents intentionally were prepared to comply with the minimum current code requirements and should not exclude any products permitted for use today. The documents do provide a mechanism that will allow designers to specify enhanced performance should there be a concern about fall through during the time span between breakage and replacement.
Railings can be a breathtaking application for glass systems, provided they are engineered, specified and installed correctly. They offer an excellent means of allowing us to watch a ball game, take in an opera or be shielded from the splashing of a sea animal exhibit—all with minimal visual obstruction. As we get more and more comfortable with glass railing systems performing in our environments, they may one day allow that mischievous child to walk up to the edge of a landing, mush his nose into the glass and get that fluttery sensation in the pit of his stomach, without hearing those words: “Get away from the edge, you’re going to fall!”
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