Dynamic Racking Research Articles

Unitized curtain wall systems joint performance with re-entrant corners under seismic racking testing

Understanding damage mechanisms and associated facility challenges for curtain wall systems with different boundary conditions is critical in their performance evaluation and selection during the design stage of a building's lifecycle, in particular if vulnerable to earthquake effects. While many different styles and configurations exist, limited research has been conducted on unitized four-sided structural sealant glazing (4SSG) with re-entrant corners under dynamic racking testing conditions. As such, this paper details a study on full-scale unitized 4SSG curtain wall system mockups featuring a re-entrant corner and subjected to cyclic racking displacements. Racking tests were carried out in accordance with the American Architectural Manufacturers Association (AAMA) 501.6 protocol. Glass fallout, sealant adhesive or cohesive failure, and glass cracking failure modes were identified as limit states and corresponding drift levels were determined. Results of these tests on full-scale specimens are presented here and some of the challenges in data collection and accuracy when using a racking facility are discussed.

Numerical modeling of the seismic racking behavior of box culverts in dry cohesionless soils

In this study, dynamic behavior and lateral earth pressures on box shaped culverts buried in dry cohesionless soils were investigated through validated numerical analyses. Two dimensional plane strain finite difference models of 4m-high box culverts with different wall flexibilities were analyzed using FLAC-2D Finite Difference Code. The effect of relative flexibility on the dynamic racking displacements of the structure was investigated by modifying dynamic shear modulus of the cohesionless soil and structural attributes of the models. Shear strains, horizontal accelerations and wall deformations as well as lateral dynamic earth pressures at various points on the culvert were investigated through the numerical analyses. Results of the numerical analyses were validated with those of a previous centrifuge modeling study. Racking deformations of the numerical culvert models are found to be in agreement with the centrifuge test data. Dynamic lateral pressures acting on the side walls increase as the wall flexibility ratio decreases. Dynamic force on the sidewalls of the box culvert may reach up to 2.8 times the at-rest lateral earth load for the stiff prototype, whereas for the flexible prototype, this value is only 1.6 times the static earth load.

Architectural Glass Panels with Rounded Corners to Mitigate Earthquake Damage

The concept of employing architectural glass panels with modified corner geometries and edge finish conditions to improve their resistance to earthquake damage has been developed recently. To accomplish this, material is removed at glass panel corners (e.g., by rounding the glass corners) and glass edges are finished in the modified corner regions to minimize protrusions and edge surface roughness. The concept is applicable to a wide variety of architectural glass types and glazing frame types. Full-scale dynamic racking tests have shown that corner radius and glass edge finish conditions near the reshaped corner regions have significant influences on glass cracking and glass fallout drift resistances of monolithic architectural glass panels used in curtain walls.

Dynamic Racking Crescendo Tests on Architectural Glass Fitted with Anchored Pet Film

Results are presented of a pilot study conducted recently at the Pennsylvania State University Building Envelope Research Laboratory (BERL) to investigate the response of curtain wall mock-ups glazed with 6 mm (14 in.) annealed monolithic architectural glass panels fitted with anchored applied film under simulated earthquake conditions. Three common film-to-frame anchoring methods were evaluated: (1) structural silicone adhesive [13 mm (12 in.) triangular cross section] application along the entire glass panel perimeter; (2) an aluminum bar extrusion to anchor the film to the frame horizontal along only the top of the glass panel; and (3) two aluminum bar extrusions to anchor the film to the frame verticals along the two vertical edges of the glass panel. Serviceability (glass cracking) and ultimate (glass fallout) limit-state data were collected during in-plane dynamic racking tests. Other performance characteristics, such as cohesive failure of the structural silicone adhesive, loss of film-to-glass adhesion, film tearing, damage to aluminum anchor bars, pullout of the filmed glass unit from the frame glazing pockets, and eventual entire unit fallout, were also recorded. These preliminary tests indicated that anchorage type can demonstrably influence both the serviceability (initial glass cracking) and ultimate (glass fragment fallout and entire unit fallout) limit states of “unweathered” filmed glass panels. In this study, the structural silicone anchor provided the best serviceability limit-state performance of the three anchor methods tested, and the top anchor provided the best entire-unit glass fallout resistance.

Seismic Behavior of Curtain Walls Containing Insulating Glass Units

In-plane dynamic racking crescendo tests were performed on full-scale curtain wall mock-ups dry glazed with six different insulating glass unit (IGU) configurations and one laminated glass unit configuration. The tests were conducted to determine the serviceability and ultimate limit state behaviors of these configurations tested under simulated earthquake-induced lateral drifts. All IGU configurations tested were manufactured with an annealed monolithic pane and a laminated pane with an argon fill and an anodized aluminum spacer between the panes. Several parameters were varied in the laminated pane of each configuration including glass lite thickness and glass type in the laminated pane (annealed, heat strengthened, and fully tempered), and PVB interlayer thickness for the laminated pane. Properties of the annealed inside pane were not varied. For each configuration, average drift values for the occurrence of glass cracking in each IGU pane, glass fallout from the monolithic pane, and pullout and fallout of the entire glass unit are reported. Relevant damage to the aluminum framing is also reported. Results of these tests can be used to assess the seismic resistance of similarly glazed architectural glass panels in practice and to improve the design of asymmetric IGU configurations for use in seismic regions.

Employing glass panels with rounded corners to mitigate seismic damage in architectural glass wall systems

Racking motions during an earthquake can lead to serviceability failure (e.g., glazing gasket pullout. sealant damage. glass edge damage and glass cracking) or even ultimate failure (in the form of glass fallout that presents a threat to life safety) in conventionally glazed wall systems - even those that meet current building code provisions for nonstructural elements. A new approach to mitigation of seismic risk in conventionally glazed wall systems with architectural glass panels has been developed at the Building Envelope Research Laboratory (BERL) at The Pennsylvania State University. The essence of the approach is to modify the rectangular geometry of architectural glass panels at the corners through rounding. A pilot study at BERL has shown that rounding the corners of architectural glass panels can increase the drift capacity of the panels significantly and that maximum effectiveness is achieved by employing rounded corners with a 1 in. radius of curvature along with beveled and polished glass edges. Results of these inplane dynamic racking tests performed on full-scale mock-ups of curtain wall sections glazed with architectural glass panels of different glass types. employing various radii of curvature at the corners, various glass edge conditions. and varying glass-to-frame clearances are presented.

Dynamic Racking Performance of an Earthquake-Isolated Curtain Wall System

Dynamic racking tests, coupled with air leakage tests, were performed on fullsize specimens of a new, Earthquake-Isolated Curtain Wall System and a widely used, conventional curtain wall system (used as an experimental control). Dynamic racking tests simulated seismic movements that could be imposed upon a curtain wall system as a result of interstory drifts. Air leakage tests were performed as an indicator of serviceability performance of both curtain wall systems during the dynamic racking tests. The Earthquake-Isolated Curtain Wall System demonstrated strongly superior performance in terms of both serviceability (glass cracking and air leakage) and life safety (glass fallout). The conventional system exhibited vulnerability to annealed monolithic glass cracking and glass fallout at dynamic racking drift indices of 1.9% and 3.1%, respectively. No glass damage was observed in the earthquake-isolated system up to the dynamic racking displacement limit of the test facility, which corresponded to a drift index of 4.9%. Air leakage rates through vision panels in the conventional system remained constant up to a drift index of 1.9%, after which the air leakage rates increased rapidly. In contrast, air leakage rates through vision panels in the earthquake-isolated system remained unchanged up to the 4.9% drift index capacity of the test facility.

Seismic Test Methods for Architectural Glazing Systems

An ongoing effort is being made at the University of Missouri-Rolla to develop standard laboratory test methods and codified design procedures for architectural glass under seismic loadings. Recent laboratory work has yielded some promising results regarding the development of an appropriate seismic test method for architectural glass, as well as identifying ultimate limit states that quantify the seismic performance and damage thresholds of various glass types. Specifically, a straightforward “crescendo-like” in-plane dynamic racking test, performed at a constant frequency, has been employed successfully. Two ultimate limit states for architectural glass have been defined: (1) a lower ultimate limit state corresponding to major glass crack pattern formation; and (2) an upper limit state corresponding to significant glass fallout. Early crescendo tests have yielded distinct and repeatable ultimate limit state data for various storefront glass types tested under dynamic racking motions. Crescendo tests will also be used to identify and quantify serviceability limit states for architectural glass and associated glazing components under dynamic loadings. These limit state data will support the development of rational design procedures for architectural glass under seismic loadings.

Dynamic racking tests of curtain wall glass elements with in-plane and out-of-plane motions : R. A. Behr, A. Belarbi & J. H. Culp, Earthquake Engineering & Structural Dynamics, 24(1), 1995, pp 1–14

Dynamic racking tests of curtain wall glass elements with in-plane and out-of-plane motions : R. A. Behr, A. Belarbi & J. H. Culp, Earthquake Engineering & Structural Dynamics, 24(1), 1995, pp 1–14

Dynamic racking tests of curtain wall glass elements with in‐plane and out‐of‐plane motions

AbstractThis project was conducted to investigate the breakage and fallout behaviour of various types of architectural glass elements in a dry‐glazed curtain wall system under in‐plane and out‐of‐plane dynamic motions. The project was a follow‐up to an earlier project that focused exclusively on in‐plane dynamic racking performance of curtain wall glass elements. The recent data indicated that adding out‐of‐plane motions caused significantly higher amounts of glass breakage and subsequent glass fallout in most glass types that were found during the in‐plane tests to be prone to glass fallout. Specifically, 1/4 in (6 mm) annealed monolithic glass, 1/4 in annealed monolithic glass with a 0·004 in (0·10 mm) PET film (not anchored to the mullions), and 7/16 in (11 mm) fully tempered laminated glass exhibited comparable or higher fallout rates than the already substantial fallout rates that were observed during the in‐plane only racking tests. Unanchored window film was found to be ineffective in resisting post‐breakage glass fallout under dynamic racking motions. In contrast, 1/4 in (6 mm) annealed laminated glass and 7/16 in (11 mm) heat‐strengthened laminated glass exhibited no glass fallout during the out‐of‐plane tests, just as they exhibited no fallout during the in‐plane tests. Out‐of‐plane test results also showed that 3/8 in (10 mm) heat‐strengthened monolithic glass exhibited no fallout, while 3/8 in annealed monolithic glass exhibited very negligible glass fallout. The addition of torsional motions was not found to induce glass fallout in those glass types that resisted glass fallout in previous tests performed without torsional motions.

Dynamic in‐plane racking tests of curtain wall glass elements

AbstractAttention has been paid recently to the potentially serious life safety and economic loss issues related to the seismic performance of ‘architectural,’ or ‘non‐structural’ building elements such as glass lites in curtain wall systems. In response, a pilot study was undertaken at the University of Missouri‐Rolla to investigate the dynamic racking performance of a 15·6 × 12·0 ft (4·56 × 3·68 m) section of curtain wall containing three 5 × 6 ft (1·52 × 1·84 m) glass panels. The curtain wall system was a ‘wide mullion’ design that had generous 1 in (25 mm) clearances between glass edges and the aluminium glazing pocket. Dynamic racking tests were performed totally in plane; no out‐of‐plane or torsional motions were included. Various types of glass specimens were tested, including annealed, heat‐strengthened and fully tempered glass in monolithic and laminated configurations. Dry glazed and two‐side structural silicone curtain walls were tested. Test results for dry glazed specimens showed that annealed and heat‐strengthened laminated glass experienced no fallout whatsoever. By contrast, annealed monolithic glass experienced frequent fallout in both small and large shards. Fully tempered monolithic glass experienced dicing, which resulted in occasional fallout of entire glass lites. Loss of rigidity in fully tempered laminated glass (when both glass plies were broken) occasionally caused entire lites to fall out. Polyester film (not anchored to the mullions) was applied to annealed monolithic glass; it prevented small shards from falling out, but sometimes contributed to entire lite fallout after the onset of severe glass cracking. Annealed laminated glass units with two‐side structural silicone glazing exhibited only very minor glass damage and no glass fallout.