Volume 7 Issue 5 May 2006
Fenestration Anchoring Systems
by Larry Livermore
When windows and sliding glass doors are tested in the laboratory for performance class and grade at a specific design pressure per AAMA/WDMA/CSA 101/I.S. 2/A440, the tests are performed with specific anchorage systems and fastening arrangements used to attach the product to a wooden test buck.
However, these products are often installed with anchoring schemes and hardware different than those used when they were tested. In the real world, the actual anchorage systems as well as the substrates to which they are attached are many and varied. The various mullions, transoms or subframe systems can require vastly different anchoring types and spacing, or the installation might require multiple fasteners concentrated at mullions, muntins or meeting rails. This may also differ greatly from the as-tested product.
Lab vs. Real-World Conditions
So, how is one to know that the installed product will perform in the same manner as it did in the laboratory?
This becomes an even more important issue in high wind zone areas, particularly coastal hurricane zones. Jurisdictions in Florida and Texas have led the way by focusing on the fenestration anchorage system as a critical element in structural strength. Other states are following suit. Until now, no industry consensus document has existed concerning the requirements for analyzing alternative anchorage systems and validating that they will perform equal to, or better, than the system tested.
AAMA has addressed this situation by developing a new guideline (AAMA 2501-06) for analyzing various anchoring systems, entitled Voluntary Guideline for Engineering Analysis of Window and Sliding Glass Door Anchorage Systems. The guidelines, scheduled for May release, enables the user to confirm that the product anchorage system provides a load resistance with appropriate safety factors equal to or greater than the project design pressure and supports the product in a manner equivalent to that tested.
The recommended procedure follows six steps:
1. Propose an anchorage system;
2. Establish the maximum design load per attachment;
3. Determine the forces acting on the attachment;
4. Select an attachment system to resist the forces so determined;
5. Confirm that the product frame can resist the forces at the attachment points; and
6. Report the required anchorage and/or fastener quantity, spacing, type, material, strength, embedment, edge distances and other appropriate parameters.
Working with Engineers
The calculations must be signed and sealed by a registered Professional Engineer (PE). In order to perform the calculations, the engineer requires the following information:
Dimensions of the installed product at the rough opening;
Profiles and material properties of the frame, parts and anchors;
Required design pressure rating for the installed system;
Details and material specifications for the wall conditions surrounding the door or window opening.
Design capacities of the fasteners for the surrounding wall conditions;
Building movements relative to the product frame anchorage; and
Anchorage configuration used for testing of the product for performance grade certification.
Door and window manufacturers will benefit from this consensus document by pointing out that if their product is anchored in ways other than that used in product testing, the method must be used to validate equivalent or better performance. This has obvious liability implications. Specification writers will also benefit by being able to reference a specific approach rather than simply requiring PE review.
The new guidelines are intended for reference by architects and specifiers, not as a comprehensive how to for engineers. However, a companion Technical Information Report (TIR) is already under development to provide more details on what the PE should look for, rules of thumb and analytical methodology. The two documents should work together to provide a complete reference for verifying the performance of virtually any fenestration anchorage system.
Larry Livermore serves as technical standards manager for the American Architectural Manufacturers Association in Schaumburg, Ill. He may be reached at firstname.lastname@example.org.
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