Abstract
In the cyclic racking evaluation of curtain wall systems, physical testing with instrumentation is the standard method for collecting performance data by most design professionals. The resulting testing of full-scale mockups can provide many types of data, including load and displacement values at different stages of loading through failure. While this type of data is valuable for product/system development/fabrication and design, such data can also provide a means for simulation validation of the curtain wall cyclic performance under simulated earthquake loading. Once the simulation study is validated using the test results, then parametric studies by designers can be conducted with greater ease, ideally with commercial software packages, without the need for testing. For the results of this research study, a practical industry formulated finite element modeling (FEM) approach was used to predict the performance of the curtain wall mockups. Here, unitized four-sided structural sealant glazing (4SSG) curtain wall system mockups that incorporate a re-entrant corner were subjected to cyclic racking displacements per the American Architectural Manufacturers Association (AAMA) 501.6 Structural Sealant protocol. System performances, including displacements, were obtained from the FEM study and used to calculate the effective shear strain of the structural silicone and the drift capacity of the system. This paper describes the details of the techniques developed for FEM, the analysis results, and shows an example application of the numerical modeling approach for mockups with racking test results available. The goal of this modeling approach was to create and test methods that practicing consulting engineers can quickly conduct in their offices on common commercially available software often available to them.
Highlights
In regards to architectural glass curtain wall systems, there have been several studies using finite element modeling (FEM), in particular for point-supported glass systems [1,2,3] and for curtain wall performance under wind loading and debris impact mitigation [4]
The components of the 4SSG curtain wall system were modeled in the FEM as follows: (a) the aluminum frame consisting of transoms and mullions as frame elements, (b) structural sealant as area element type shell-thick, and (c) glass as either an area element type shellthick or as sets of diaphragm constraints applied to the nodes of the structural sealant that are shared with the glass
The FEM acts relatively linearly, which means that the influence of the links at R17 is not large enough to cause the non-linear behavior seen in the test data
Summary
In regards to architectural glass curtain wall systems, there have been several studies using finite element modeling (FEM), in particular for point-supported glass systems [1,2,3] and for curtain wall performance under wind loading and debris impact mitigation [4]. Limited work has been done to either experimentally measure or model glass failures caused by edge stresses in contact with mullions [9,10,11], but none of these studies considered seismic loading along the edges. Depending on whether or not glass panels have cut, ground, seamed, or polished finish will impact crack initiation during drift due to the flaws of each finish type, which differ in their severity and distribution [12]. Knowing these contributing factors, FEM is a challenge to engineers because crack initiation along glass edges is a function of glass-to-frame contact stresses and glass-edge finish conditions. In addition to its aforementioned successful use in predicting the wind resistance of a given glass panel, FEM has been used successfully to predict local stresses caused by wind-borne debris impact in glass [4,13,14,15], blast loading [16], modal analysis of laminated glass [17], glass tempering [18,19], and thermal and residual stresses in annealed glass and other settings for unique loadings [20,21,22]
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