Paul A. Kremer

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.

Seismic Performance of Two-Side Structural Silicone Glazing Systems

This paper presents the results of the first phase of an experimental research program on simulated seismic performance of structural silicone glazed (SSG) curtain wall systems. Full-scale, two-side SSG mockups made up of three side-by-side glass panels were tested under cyclic racking displacements to determine serviceability and ultimate behavior responses. Variables were glass type (annealed and fully tempered) and panel configuration (monolithic, laminated, and insulating glass). In the experiments carried out, damage states such as gasket deformation/pullout, sealant failure (e.g., adhesion/cohesion, etc.), glass cracking glass and fallout were identified and their corresponding drift levels were determined. The extent of damage to silicone sealant was determined through air leakage tests.

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.

Dynamic strains in architectural laminated glass subjected to low velocity impacts from small projectiles

An experimental validation of a mechanics-based finite element model for architectural laminated glass units subjected to low velocity, two gram projectile impacts is described. The impact situation models a scenario commonly observed during severe windstorms, in which small, hard projectiles, such as roof gravel, impact windows. Controlled experiments were conducted using a calibrated air gun to propel a steel ball against simply supported rectangular laminated glass specimens. Dynamic strains on the inner glass ply were measured using foil strain gages and a high speed data acquisition system. Impact speed, interlayer thickness, glass ply thickness, and glass heat treatment conditions were varied. Dynamic strains predicted by the finite element model were in close agreement with those measured in the laboratory.

Seismic Performance of Stick-Built Four-Side Structural Sealant Glazing Systems and Comparison With Two-Side Structural Sealant Glazing and Dry-Glazed Systems

A research project was undertaken to study the simulated seismic performance of mock-ups of a full-scale, four-side structural sealant glazing (SSG) system. “Stick-built” mock-ups were subjected to cyclic racking displacements in accordance with the American Architectural Manufacturers Association (AAMA) 501.6 test method. Although the test method focuses on glass fallout, drifts associated with serviceability damage states, such as sealant adhesive or cohesive failure, and glass cracking were also identified during the conduct of the tests. Damage to sealant joints was tracked as a function of drift level using visual and video inspections of weather-seals and structural-seals and air-leakage tests. Data from this study are compared with data collected from similar studies on comparable two-side SSG and dry-glazed mock-ups. Contact with panels diagonally above and below a given glass panel at panel corners was found to be the likely cause of initial sealant damage, glass cracking, and glass fallout as opposed to glass-to-frame interactions for two-side SSG and dry-glazed curtain-wall constructions. Thus, modified corner geometries and/or joint dimensions can be used to delay (i.e., shift limit states to higher drift levels) or avoid these damaging panel interactions. Mock-up specimens were also instrumented extensively so that real-time glass-panel translation and rotation, and weather-seal deformation measurements could be recorded. A summary of these measurements is presented and discussed in the context of their follow-up use for informing the development of damage prediction models for SSG curtain walls during seismic loadings. The study shows that stick-built curtain walls with four-side SSG configuration are expected to have higher drift capacity compared to two-side SSG and both are expected to have higher drift capacity compared to dry-glazed configurations.

Resuspension of biological particles from indoor surfaces: Effects of humidity and air swirl

Human exposure to airborne particles can lead to adverse health outcomes such as respiratory and allergic symptoms. Understanding the transport mechanism of respirable particles in occupied spaces is a first step towards assessing inhalation exposure. Several studies have contributed to the current knowledge of particle resuspension from indoor surfaces; however, few published studies are available on resuspension of biological particles from indoor surfaces. The objective of this study is to investigate the impacts of humidity and air swirl on resuspension of biological particles from floor and duct surfaces. Controlled laboratory experiments were conducted under varying degrees of humidity and airflow conditions. Resuspension rates of five types of particles (quartz, dust mite, cat fur, dog fur, and bacterial spore-Bacillus thuringiensis as an anthrax simulant) were determined for two types of floor surface (carpet and linoleum) and a duct surface (galvanized sheet metal). The results show that the particle property of being hydrophilic or hydrophobic plays an important role in particle resuspension rate. Resuspension rates of hydrophilic dust mite particles increase up to two orders of magnitude as relative humidity (RH) decreased from 80% to 10% at 25°C. However, resuspension rates of cat fur and dog fur particles that are hydrophobic are within the measurement error range (±15%) over 10-80% RH. With regard to resuspension of bacterial spores (Bacillus thuringiensis) from a duct surface, the resuspension rates are substantially affected by air swirl velocity and particle size. However, no discernible increase in particle resuspension was observed with duct vibration.

Fragility Curves for Architectural Glass in Stick-Built Glazing Systems

Fragility functions are presented for 15 glazing system configurations in support of Applied Technology Council efforts to develop a performance-based seismic design approach for building performance assessment. The study includes seismic evaluation of curtain wall and storefront systems in terms of probability and the consequences of damage, including economic and life safety consequences. Defined damage states consist of gasket degradation, initial glass cracking and crushing, and glass fallout. Alternatives are offered to the provided prototype fragilities for configurations with differing glazing characteristics, which account for varying glass-to-frame clearance, aspect ratio, and glass panel dimensions. Issues related to applying laboratory-based fragility data to actual glazing systems in the field are addressed.

Development of Finite-Element Modeling Approach for Lateral Load Analysis of Dry-Glazed Curtain Walls

This paper presents a finite-element modeling option to provide an analytical approach for a seismic analysis of dry-glazed curtain-wall systems. In this modeling approach, Ansys finite-element software was used to model the glass panel, aluminum glazing frame, perimeter rubber gaskets, rubber setting and side blocks, glass-to-frame clearances, and glass-to-frame contact once the clearance was overcome by in-plane drift. The results of the finite-element modeling of the curtain-wall system were compared with full-scale laboratory test results. The effect of some of the parameters such as gasket friction and aspect ratio were evaluated. The study showed that finite-element modeling is a viable approach for analytical evaluation of curtain walls. The modeling can function to predict the drift associated with glass-panel cracking. Further refinement of the modeling approach developed can increase the accuracy of the prediction.

Racking Test Evaluation of Unitized Curtain Wall Systems Using Glazing Tapes

Results of cyclic racking tests on EN-WALL 7250 unitized curtain wall system mockups are presented. Mockups had overall dimensions of 180 in. wide by 156 in. high and were comprised of nine glass panels adhered to aluminum framing with 3M™ VHB™ structural glazing tape structural seals and structural sealant weatherseals. Racking tests followed the AAMA 501.6 protocol to characterize the performance of the system. Tests were carried out in a step-wise manner in order to stop the test after each drift increment to inspect the mockup for any damage. A complete description of the unitized system design is presented along with test observations

Development of Failure Prediction Models for Structural Sealant Glazing Systems under Cyclic Racking Displacement Conditions

A research project was undertaken recently at Penn State University to study the simulated seismic performance of “Structural Sealant Glazing” (SSG) used to adhere glass panels to common curtain wall framing systems. In the most common type of SSG curtain wall construction, referred to as “two-side” SSG, two glass panel edges (typically opposing vertical edges) are adhered to the support framing using structural sealant, while the other glass panel edges are mechanically fastened to the support framing. In this study, full-scale two-side SSG curtain wall mock-ups consisting of three, side-byside glass panels were subjected to cyclic racking displacements to characterize their performance and to identify sealant and glass component failure modes under serviceability and ultimate racking displacement conditions. Attempts were also made to develop kinematic-based models to predict failure states (e.g., structural sealant failure) of the SSG curtain walls. This paper discusses the details of the predictive model and its evaluation on the basis of comparisons with mock-up test data. The model developed appears to give good estimates of the observed sealant failure drift. Conclusions and recommendations regarding appropriateness and limitations of the predictive model are provided.