Advanced Connection Systems for Architectural Glazing

Building envelope systems—especially the façade system—over high-rise buildings and structures consume approximately over 20 % or more of the total construction budget and are considered to be an economically significant attribute of the building. Architectural glass exterior systems, used as the entire building skin or part of its envelope, are considered to be one of the most influential building systems contributing to the proper function of the building. With the exception of a few guidelines in building design codes, there is currently a lack of design approaches provided for designers and engineers in appropriate selection of glazing details to effectively mitigate earthquake damage.

It would be difficult to find a material that matches the popularity of glass among engineers and architects. The great importance that glass has attained compared to other materials is associated with its ability to transmit light and to provide a transparent environment. Using this transparent environment and capturing the warmth and brightness of the sun inside a building was a major problem up to the beginning of the twentieth century. In the first half of the twentieth century, due to introduction of new materials to the building industry, such as steel and concrete, as well as more complex structural solutions, integration of glass into the building envelope was made increasingly possible and changed its position from small openings in the façade to considerably large surfaces covering most of the building envelope. In this chapter a brief history of utilization of glass into the building exterior systems is presented. Also different architectural glazing systems that are currently being used are introduced and described.

In this chapter, mechanical compatibility between the building envelope system and the building structure is discussed. Different levels of integration between these two systems are introduced and the problems arising from improper compatibility between them especially in architectural glazing systems are being discussed. The current provision that exist in building design codes for obtaining a compatible behavior and previous studies on achieving mechanical compatibility are presented.

As mentioned earlier, the basic cause of damage to the nonstructural elements of the building during an earthquake is deflections and displacements within the structural elements. In this chapter the behavior of the glass panels subjected to these displacements are investigated for different types of architectural glazing systems. For every system depending on the fixtures and their boundary conditions, the maximum allowable lateral force that may be exerted on the panel is derived using the theory of plates for the three cases of dry glazed systems, structural sealant systems and point fixed systems. Simplification has been made in order to achieve analytical solutions.

The use of advanced connectors in cladding systems has been proposed by many scholars and designers after post-earthquake surveys. Laboratory tests had shown that fixed elements of a cladding system are vulnerable to damage during an earthquake due to deformation accruing in the structure of buildings. The idea of using advanced connectors was to provide isolation between the envelope system and the structure and to dissipate seismic energy. Since light-weight cladding systems do not affect the dynamic behavior of the building, giving very little contribution to it, it is obvious that the energy dissipating approach on a building scale can only be carried out in heavy cladding systems. Goodno et al. (Ductile Cladding Connection Systems for Seismic Design NIST, Gaithersberg, 1998) provide a detailed study of different dissipating connection systems. But since energy dissipating mechanisms can also be used as a means of controlling the forces resulting from displacements, they still have the potential for being used in light cladding systems in order to provide a desirable level of isolation. Due to their simplicity, both in terms of analytical study and practical use and high control over the forces that are transmitted, friction damping connectors are proposed in this research as suitable connecting devices between the glazed envelope and the structure of the building.

One of the major contributions of this study is the introduction of a novel connection device that may be used in complex architectural glazing systems that utilization of the previously discussed connection systems is not applicable. In this newly proposed connection device, the friction mechanism is incorporated between spherical and cylindrical surfaces. In this chapter the development of the idea of the connection device is presented as well as the adjustments necessary for adapting it for different architectural glazing systems. Finally based on the Coulomb theory of friction, the governing equations that control the behavior of the connection device are presented.

Providing a desired level of isolation in mechanical terms means to limit the forces and moments acting from one system over the other. These limit forces will be based on the properties of the glazed envelope system and its load-bearing capacity. This evaluation needs to be done in two parts. First within the safety criterion which is to protect the glass panels and its components from failure during or after a severe situation like an earthquake, and second within the serviceability criterion which is, in general, to maintain the desired behavior of the envelope system after the incident in terms of air-tightness and water-tightness and prevent distortions in the envelope surface. To satisfy the safety conditions of a glazed system it is necessary to tune the friction damping device in a way that the forces transferred through it are kept below the maximum allowable forces, which can be handled by the glass panel based on the positions of the connection devices. It is both necessary to study this effect both over a single glass panel and within a group of connected glass panels. An analytical approach is presented for tuning the friction based on the behavior of one-panel window glasses. Then in order to check the results of the analytical solutions a numerical modeling will be performed. With the help of numerical modeling it is also possible to investigate more complex glass panel shapes, the effect of local stresses near the places of the friction damping devices and finally different placement of the connection device over the boundaries of the glass panel.

Although experimental studies have not been performed within the scope of this research, in this chapter a brief discussion is presented on the experimental tests that are suggested for studying the behavior of the proposed connection devices and their effect on curtain wall systems during seismic events. The aim of these tests will be first to study the behavior of the connection device itself and later to see the effect that it will have on envelope systems subjected to seismic actions. In order to study the mechanical behavior of the connection device a laboratory test apparatus is discussed that is especially conceived for the study of cladding connections. And for the study of the effects of the connection device based on the recommendations of American Architectural Manufacturing Associations (AAMA) (Association of American Architectural Manufacturers 2001), a test facility is proposed to perform two types of static and dynamic experiments on a mockup.