FGIA Addresses Thermal Modeling, Highlights Seismic Testing Opportunity

The Fenestration and Glazing Industry Alliance (FGIA) has updated a guide outlining the considerations necessary when choosing proper glass for non-residential skylight and sloped glazing applications based on the best industry practices and technology. FGIA also has released a new publication, AAMA 515-19, Voluntary Procedure for Determination of Fenestration Surface Temperatures by THERM Finite Element Modeling, addressing aspects of the finite element (FE) thermal modeling process often used to predict interior surface temperatures on fenestration including non-residential windows, terrace and patio doors, curtainwall, storefront and entrances.

An overview of seismic testing of timber curtainwall was also held.

Skylights and Sloped Glazing

The document also describes the minimum requirements for sloped glazing as specified in the International Building Code (IBC). AAMA GDSG-1, Design Guide for Sloped Glazing and Skylights, an FGIA standard, was last updated in 1987, when it was first created.

Per the guide’s introduction, for many years, simple skylight units and factory clerestories utilized single lite wired glass. In more recent years, sloped glazing has grown into a prominent feature of modern architecture. Atrium enclosures, monumental metal framed skylights and canopies are now common. Today, other glass types such as laminated, fully tempered and heat-strengthened glass and sealed insulating glass units are widely used.

The performance and selection of glass have become major and critical factors. Changes in building code requirements, design practices, available glass products and industry standards are a result of the growing use of complex and large sloped glazing systems. In this guide, emphasis is placed on the importance of meeting product requirements for specification performance, energy conservation, daylighting and the safety of building
occupants.

THERM Document

Per AAMA 515, condensation will occur on any interior surface that falls below the dew point temperature of interior ambient air. Condensation can be unsightly, unsanitary and, over long periods of time, can damage adjacent building materials. This voluntary procedure helps designers determine what temperatures and film coefficients to use when running a project-specific condensation analysis.

Designers often use two-dimensional FE thermal modeling tools, such as Lawrence Berkeley National Laboratory’s (LBNL) THERM, to predict interior surface temperatures for standard or project-specific conditions. In other cases, thermocouple instrumentation is added to ASTM C1199 guarded hot box test units, or AAMA 501.9 thermal cycling tests of full-size mock-ups. For products with conductive framing, such as aluminum (with or without thermal barriers), caution is advisable in attempting to correlate FE modeling with testing, or in using FE modeling to predict variable test results.

LBNL’s THERM software is widely used to predict temperatures. This voluntary procedure is intended to make application of the software tool uniform between users, and to address some of the issues which arise in surface temperature prediction and condensation assessment:
• Conflicting or confusing project specifications;
• Model accuracy for aluminum framing;
• Repeatability and reproducibility of modeling and testing;
• Effects of substrates; and
• End-user expectations.

AAMA 515 outlines minimum requirements for FE thermal models used to predict surface temperatures of aluminum framing systems and is intended to be referenced in other industry standards, contract documents, proposals and marketing materials as needed.

AAMA GDSG-1, AAMA 515-19 and other AAMA documents available from FGIA, may be purchased from the online store at https://pubstore.aamanet.org/pubstore/.

Seismic Shake Table Test

A seismic shake table test of a timber frame building is scheduled to take place next year and will include several different glazing configurations. Dr. Keri Ryan, associate professor of civil engineering at the University of Nevada, Reno and the nonstructural testing lead, gave FGIA members an overview of the test in a webinar titled, “Opportunities for Seismic Shake Table Testing of Fenestration Products.”

The testing team will perform a shake table test of a ten-story mass timber building at the University of California San Diego’s large high-performance outdoor shake table. The table is currently undergoing upgrades which will transform it from a one lateral direction table into a multi-directional table. It’s projected to reopen in March 2021.

The test’s primary objectives are to validate that the performance of the structure meets the design specifications and to quantify the performance of select nonstructural components in the context of functional recovery and resiliency.

Ryan said the benefit of the proposed shake table testing is that it will allow her team to evaluate the complexities of dynamic shaking and how they impact the racking performance of building skins.

The testing team is interested in testing storefront, curtainwall and window wall systems in a variety of configurations, such as heat strengthened, tempered, laminated, insulating glass units, stick built, unitized, mechanically captured and structurally glazed.

Ryan and her team are calling for FGIA members to participate and collaborate in the test. FGIA also provided an overview of seismic testing of timber curtainwall.

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