AAMA Analysis January/February 2020July 21st, 2021 by Nathan Hobbs
Sizing Up: AAMA 2502 Expands to Include Larger Designs
By Glenn Ferris
The most direct way to verify compliance of fenestration products with the code-mandated North American Fenestration Standard (NAFS) is via a certification label that’s based on laboratory tests—including those that assess structural integrity under wind pressure loading. However, there are special cases, such as project-specific or one-of-a-kind designs, where it can be prohibitively expensive and time-consuming to test and certify non-standard configurations. In many cases, local codes provide the option for window suppliers to obtain an engineering evaluation of the product instead of requiring additional tests—notably the Florida Building Code, which pioneered the approach in 2003 with its product approval system.
To eliminate confusion and multiple interpretations for what constitutes “accepted” practice, AAMA developed in 2007 a standardized process for engineering evaluation of doors and windows, in the form of AAMA 2502, Comparative Analysis Procedure for Window and Door Products. Essentially, AAMA 2502 sets forth engineering design rules by which products that differ from the size of the test unit can be qualified for code compliance of structural performance without further testing. These rules can also assist manufacturers in the product design effort.
To obtain code compliance, structural analysis computations along with detailed drawings and test data for doors and windows are typically compiled in the form of an analysis report that is signed and sealed by a registered professional engineer (P.E.). AAMA 2502 provides a procedure to document positive and negative design pressures different from those used with the tested size. This landmark guidance document has been updated and expanded for 2019, including the addition of guidance for:
• Analysis of unit sizes larger than those tested; and
• Figuring deflection and stress limits in addition to those tested.
Engineering Design Rules are specified for use in the structural analysis of product framing subjected to bending under uniform loading, such as those induced by wind. They apply to single span, simply supported beams, setting forth engineering calculation methods for load distribution and magnitude, section properties, strength, connections and deflection.
Also new to the 2019 edition of AAMA 2502 is a consideration of framing member deflection, typically expressed as a fraction of the length of its span “L,” e.g. L/175. To determine the maximum deflection of a member subjected to bending from uniform loads, the applicable deflection formula(s) for both symmetrical and asymmetrical cases of simply supported beams are provided.
By encompassing products larger than the test size and providing guidance for figuring deflection, the applicability of AAMA 2502 is increased, as it can now be utilized to support a larger range of unit sizes. In recognition of this increased value, the ICC Committee Action Hearings last August approved recognition of AAMA 2502-19 as a reference standard in the next edition of the International Building Code (IBC). It will be cited as an alternative to existing code requirements to permit engineering analysis of alternate sizes based on physical testing of a baseline assembly, rather than testing each alternate size.
Glenn Ferris is technical standards specialist for the Fenestration and Glazing Industry Alliance.
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