Field-assembled curtain walls

Utah State University’s Wayne Estes Training Center’s expansive, field-assembled curtain wall supports the aesthetic, sustainable, and practical appeal crucial to the ultra-competitive recruiting environment of college athletics.
Photo © Larry Ford and Tyson Bybee

Performance as specified
Regardless of whether the curtain wall will be provided as unitized or as stock length for field assembly, the manufacturer is responsible for designing and testing the product to rigorous industry standards. Detailed installation instructions in the form of manuals or project-specific shop drawings are critical to a successful installation.

The American Architectural Manufacturers Association (AAMA) 501, Methods of Test for Exterior Wall, is the first and most reliable indication for specification writers seeking to ensure curtain wall products meet a project’s required performance. Following AAMA 501, curtain wall manufacturers provide specifiers with test results or full test reports for review, which validates the curtain wall products perform as designed and in substantial accordance with the test procedures described in AAMA 501 and referred in ASTM standards.

Below is an example of an AAMA 501 testing sequence manufacturers would follow to validate their products’ performance for a typical stock length curtain wall used for low- to mid-rise projects. If project-specific testing is required, it is important to identify the test and sequence in the specification. Design professionals can refer to AAMA 501 for complete descriptions of all mandatory and optional tests and sequencing.

  1. Preload (ASTM E330, Standard Test Method for Structural Performance of Exterior Windows, Doors, Skylights and Curtain Walls by Uniform Static Air Pressure Difference): A positive differential (inward acting) of [50 percent design load], held for a minimum of 10 seconds, and then released. Wall and anchoring inspected.Allowable: No visible signs of failure.
  2. Air infiltration (ASTM E283, Standard Test Method for Determining Rate of Air Leakage Through Exterior Windows, Curtain Walls, and Doors Under Specified Pressure Differences Across the Specimen): Testing to be conducted at a static pressure differential of 300 Pa (6.24 psf).Allowable: Leakage not to exceed 0.3 L/s-m2 (0.06 cfm/sf) of fixed wall area.
  3. Static water penetration (ASTM E331, Standard Test Method for Water Penetration of Exterior Windows, Skylights, Doors, and Curtain Walls by Uniform Static Air Pressure Difference): Testing shall be conducted at a positive static pressure differential of 720 Pa (15 psf). Water to be applied to the exterior face for 15 minutes at a minimum rate of 3.4 L/m2 min (5.0 gal/sf h).Allowable: No visible water penetration to the interior.
  4. Dynamic water penetration (AAMA 501.1, Standard Test Method for Water Penetration of Windows, Curtain Walls and Doors Using Dynamic Pressure): Using dynamic pressure testing shall be conducted at 720 Pa (15 psf) with a minimum water application rate. Allowable: The collection of up to 15 ml (0.5 fluid oz) of water in a 15-minute test period on top of an interior stop or stool integral with the system shall not be considered water leakage.
  5. Uniform load deflection test (ASTM E330): Deflections measured with dial indicators. Structural loads will be applied for 10 seconds in the following sequence: +50 percent design load [preload]; +100 percent design load; –50 percent design load [preload]; and –100 percent design load.
    Design load is the design pressure (Pa) required for the curtain wall system and determined by the project’s basic wind speed, building height, exposure category, and importance factor, or by wind study. It is important to include the design loads (+/-) for typical and corner zone areas in the curtain wall specification.
    Allowable: L/175 for spans up to 4115 mm (162 in.) or L/240 + 6.4 mm (1/4 in.) for spans greater than 4115 mm, but less than 12.2 m (40 ft).
  6. Repeat air infiltration (ASTM E283).
  7. Repeat static water penetration (ASTM E331).
  8. Repeat water penetration (AAMA 501.1).
  9. Seismic movement at design displacement (AAMA 501.4, Recommended Static Test Method for Evaluating Window Wall, Curtain Wall and Storefront Systems Subjected to Seismic and Wind-Induced Inter-Story Drift): Three complete cycles performed in each direction. Horizontal movement shall be 0.010 times the greater adjacent story height, unless otherwise specified. Allowables include:one glass lite or up to 10 percent may break, but must be retained in glazed opening with no fallout; any damage shall be readily repairable onsite; post air-water performance can be attained with minor adjustments, and visible seals or gaskets may be repaired; no wall components may fall off and trim may be disengaged; and trim elements may be replaced. The above performance relates to standard occupancy seismic use group I. Specifiers can refer to AAMA 501.4 for pass/fail criteria for seismic use groups II and III.
  10. Repeat air infiltration (ASTM E283).
  11. Repeat static water penetration (ASTM E331).
  12. Thermal cycles (AAMA 501.5, Test Method for Thermal Cycling of Exterior Walls): Entire mockup should be subjected to three thermal cycles. Each cycle shall be maintained for two hours after establishing temperature of low exterior temperature of –18 C (0 F); high exterior temperature of 82 C (180 F); maintain interior temperature between 21 and 27 C (70 and 80 F); and application of positive and negative design loads during hot and cold cycles. Allowable: Components used within the system shall withstand thermal movements without buckling, distortion, cracking, and failure of glass joints seals or undue stress on the finished surfaces, materials, or fixing assemblies. The manufacturer may elect a lower exterior temperature of –29 C (–20 F) to relate the system’s thermal performance to those required at regions with colder temperatures.
  13. Repeat air infiltration (ASTM E283).
  14. Repeat static water penetration (ASTM E331).Uniform structural overload test (ASTM E330): Permanent deformation of the system shall be measured and recorded at 1.5 times design loads when held for 10 seconds (+75 percent positive design load; +150 percent positive design load; –75 percent negative design load; and –150 percent negative design load.)
    Allowable: No glass breakage or permanent damage to panels, fasteners, or anchors shall occur and permanent deformation to wall framing members shall not exceed 0.2 percent of their clear span.
  15. Seismic movement at 1.5 times design displacement test (AAMA 501.4): Three complete cycles shall be performed in the horizontal direction parallel to the main elevation at the intermediate simulation. Parallel horizontal movement will be 1.5 times the specified design displacement of left, zero, right, and zero making up one complete cycle. Allowable: At the conclusion of the test, there shall be no glass fallout and no wall component may fall off unless otherwise specified.
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