Lessons Learned from Failures of the Building Envelope in Windstorms

Lessons learned from failures of the building envelope in windstorms are encapsulated in three principal findings. the building envelope is crucial to the performance of buildings in windstorms. Windborne debris is decisive in shaping the performance of the building envelope. Design attention should be given to postimpact behavior of building-envelope systems. Reviews of damage documentation, insurance records, and computer simulations of building failures establish the importance of the building envelope to satisfactory building performance. These reviews also establish the decisive role of windborne debris in causing damage. the imperative for considering the postimpact behavior of building envelope systems is discussed, and innovative glazing products that meet new design criteria are presented. It is concluded that the building envelope should be given status equal to the principal structural frame in terms of design attention

Failure Strengths Of Laminated Glass

Laminated glass used in architectural glazing comprises two layers of glass connected by a thin interlayer of polyvinyl butyral. Previously reported nondestructive experimental stress analyses offer evidence that laminated glass behaves like monolithic glass of the same nominal thickness except when temperatures are high. This evidence has been augmented to include failure behavior by destructive tests of a large number of laminated-glass specimens. Test results reveal that failure strengths of annealed laminated-glass specimens are equal to failure strengths of annealed monolithic glass specimens of the same nominal thickness at room temperature and decrease to about 75% of monolithic-glass strength at 170° F (77° C). Further, heat strengthened, and fully tempered laminated-glass specimens exhibit failure strengths that are approximately three and five times, respectively, the strengths of annealed monolithic-glass specimens of the same nominal thickness, suggesting monolithic behavior of these types of laminated glass, as well. © ASCE

Design of Window Glass for Lateral Pressures

ASTM Standard E 1300-04 ( Standard practice for determining load resistance of glass in buildings ) outlines procedures for determining the strength of window glass products when the glass is subjected to uniform lateral pressure. This standard practice addresses each of the commonly used window glass products (monolithic glass, laminated glass, and insulating glass) that are fabricated from annealed, heat strengthened, and fully tempered glass plates, used singly or in combination. the procedures are based on principles of structural mechanics, are thorough, and are presented in clear and concise terms. Analyses of the basis for and the scope of these procedures lead to two interesting observations. First, the procedures are based on a very conservative definition of glass strength, and second, the procedures encompass certain technical refinements, design conditions, and product configurations that are outside of practical application, thus making the procedures appear overly complex to the user. Recommendations are offered for taking advantage of the inherent conservatism and discerning perspectives to make the procedures simpler and more practical. © ASCE

Effects of Accelerated Weathering on Architectural Laminated Glass in a Windstorm Environment

An experimental study was conducted to assess the serviceability and ultimate limit state behavior of a fully glazed architectural laminated glass system under accelerated weathering conditions. Glazed specimens included heat-strengthened laminated glass with a low-emissivity, metallic solar coating on one glass surface next to the polyvinyl butyral interlayer. The laminated glass units were anchored to the aluminum curtain wall frame with a perimeter anchor bead of medium-modulus structural silicone sealant. Accelerated weathering was performed in a manner similar to the provisions of ASTM E773-88 and E774-92. All specimens (weathered and unweathered) were then subjected to a severe windstorm simulation test, i.e., windborne missile impacts followed by an extensive positive/negative pressure spectrum. Results indicated that the accelerated weathering had demonstrable effects on both the PVB laminated glass and the structural silicone anchor bead. However, complete resistance to glass fallout during the pressure spectrum was achieved when the inboard glass ply remained unbroken after completion of the windborne missile impacts

Seal Forces In Structural Glazing Systems

Silicone sealants are used as structural connections between the two glass plates in an insulating glass (IG) unit and between the IG unit and the supporting mullion. These connections become an integral part of the entire glazing system, worthy of attention by structural design engineers. Since the behavior of IG units subjected to lateral pressures, such as wind, is highly nonlinear, von Karman plate equations are employed in the mathematical model developed here. Also, since the two thin glass plates are separated by a sealed air space, a complex interaction occurs between the trapped air space and the glass plates. In the model developed here, the connections between the two glass plates and between the plate and mullion are modeled as continuous springs along the boundaries of the IG unit. Stresses in the glass plates and forces that occur in the IG-unit seal and the structural seal are calculated as the IG unit is subjected to a lateral pressure. © ASCE

Postbreakage Behavior Of Heat Strengthened Laminated Glass Under Wind Effects

Results of a full-scale experimental investigation into the post breakage behavior of heat-strengthened laminated glass subjected to windstorm effects are presented. Two different interlayer constructions and two different glazing configurations are examined. The two interlayer constructions are a PVB polymer and a PVB/PET/PBV composite polymer. The two glazing configurations are a conventional dry glazed system and an unconventional system with a silicone anchor bead. Two test criteria are established that relate to effects of a severe windstorm. The first criterion addresses impact with windborne debris; the second defines a wind-load spectrum that represents a severe windstorm of a 4-hr duration. Three principal findings are presented. First, the ability of heat strengthened laminated glass to reject small missile impacts with small probabilities of breaking the inner glass ply is established. Second, heat-strengthened laminated glass with the silicone anchor bead performed significantly better than similar glass in a dry-glazed system. Finally, the heat-strengthened laminated glass with the PVB/PET/PVB composite interlayer performs significantly better than similar glass with PVB interlayer. © ASCE

Edge Strength of Window Glass by Mechanical Test

A mechanical test is described that can be used to measure the edge strength of annealed and heat-strengthened glass. The mechanical test apparatus stresses only one of the two edge-lines on the edge of a glass specimen. The testing concept employs the theory of unsymmetrical bending. The test device loads glass specimens in a manner that places tensile stresses on the tested edge-line while keeping the other edge-lines at zero stress or in compression. In annealed glass tests, the scored edge-line was found to be 20% weaker than the edge-line opposite the scored edge-line. Comparisons between the edge strengths of annealed and heat strengthened glass revealed that the mean edge strength of heat strengthened glass is larger than that of annealed glass by about 50%. © ASCE

Structural Behavior Of Architectural Laminated Glass

Experimental and theoretical investigations conducted over a 20-year time period by several investigators provide sufficient data and information to define, for practical engineering purposes, the behavior of architectural laminated glass under lateral pressures. Investigations included definitions of material properties, theoretical stress analyses, experimental stress analyses, and destructive tests involving monolithic, laminated, and layered glass plates of several geometries. The preponderance of data and information indicate that: (1) Architectural laminated glass behaves in a manner similar to monolithic glass of the same nominal thickness under short-term lateral pressures (representative of wind loads) at and below room temperature; (2) the temperature at which behavior changes from being similar to monolithic to significantly different from monolithic under short-term lateral pressures is not clearly defined, but is around 49°C (120°F); and (3) architectural laminated glass behaves in a manner similar to monolithic glass of the same nominal thickness under long-term lateral pressures (representative of snow loads) at temperatures of 0°C (32°F) and below. © ASCE

Comparison of the Hindin Proteins of Strongylocentrotus franciscanus, S. purpuratus, and Lytechinus variegatus: Sequences involved in the Species Specificity of Fertilization

Bindin is the sea urchin sperm acrosomal protein that is responsible for the species-specific adhesion of the sperm to the egg. Two new bindin cDNA sequences that contain the entire open reading frame for the binding precursor are reported: one for Strongylocentrotus franciscanus and one for Lytechinus variegatus. Both contain inverted repetitive sequences in their 3' untranslated regions, and the S. franciscanus cDNA contains an inverted repetitive sequence match between the 5' untranslated region and the coding region. The middle third of the mature bindin sequence is highly conserved in all three species, and the flanking sequences share short repeated sequences that vary in number between the species. Cross-fertilization data are reported for the species S. purpuratus, S. franciscanus, L. variegatus, and L. pictus. A barrier to cross-fertilization exists between the sympatric Strongylocentrotus species, but there is no barrier between the allopatric Lytechinus species