Support for point support: Engineering, advice crucial but not always easy to get

Although it has been around for several years, many U.S. contract glaziers still view point-supported glazing or spider glazing as a highly specialized application. It’s use in the U.S. construction market represents only a fraction of that in Europe, where the application of structural glass within building design has become the norm rather than the exception. Unfortunately, most U.S. glaziers and architects steer clear of specifying structural glass walls or canopies due to the lack of suppliers offering good quality professional advice and support. As with any products such as these, however, there are many companies willing to supply only hardware with no consideration to the design, suitability or application of the products in the buildings. Even more concerning is the kind of engineering support these companies offer to the specifiers or end users. Much of it is based on criteria set for products with either totally different performance characteristics or rules substantially out of step with the capabilities of today’s modern high-performance materials.

Typically, when point-supported glazing is called for, contract glaziers get presented with plans from the specifier that do not directly identify a company’s system or components, but tend to offer a generic design concept.

This approach, unfortunately, opens the doors for those who purely trade on commodities rather than fully engineered packaged solutions. The glaziers ultimately end up with all involved being more reticent to get involved in future projects. The architect concentrates on the building’s aesthetic image and function, and relies on glass installers and general contractors to come up with solutions and deliver products to job sites. In view of this, a contractor attempting to undertake a structural glass project might wish to consider the following rules before bidding a job that involves point-supported glass.

Only use companies with engineers familiar with structural glass design. We [Custom Hardware Manufacturing Inc.’s Architectural Glass Systems division] often have contractors show us plans for a proposed wall or canopy system and those plans call for a particular glass makeup. It is dangerous to assume that the parts can just be purchased from any hardware supplier and the structure built to the architects’ or building engineers’ plans because the detail is there. These projects must be engineered. Many, but not all, suppliers offer engineering or specification services similar to CMHI’s.

Not all hardware is the same. Differences in quality, size of the glass fittings and their locations on the glass play a role in how the glass reacts to the loads imposed. Therefore, once the glass is engineered, never substitute one fitting for another.

Gather the necessary information prior to getting bids. Besides the blueprints, the supplier should ask for the required wind and snow loads, and the specifications, if any, that pertain to the system. Some hardware suppliers might not ask for this information, so they should be willing to supply the necessary engineering specifications for their hardware such as testing results and design limits. Structural glass engineers require this information.

Case in point
Since CHMI Architectural Glass Systems’ inception in 2002, we have had to re-invent the way we sell and promote our products several times. Our first approach to market was from a hardware-only standpoint, similar to the business model used to promote the company’s product lines. In most cases, however, we found the subcontract glazier preferred the single-source total-package solution incorporating glass, engineering and ancillary steel hardware over and above sourcing these elements separately themselves.

In acknowledging this message from our customers, we quickly set about modifying our business model to offer the one-stop shop service they required. Design, engineering and fabrication of all project-related metallic elements along with the supply of the spider fittings and rotules was consolidated in-house at CHMI. Our engineering design team then restructured to provide customers with the necessary information they required to source the glass from their local suppliers.

This approach was then extended to the architectural community as we quickly realized that by educating the architects and becoming involved in the specification and design process much earlier we could ensure correct product specification. Both of these fundamental shifts in philosophy have helped us to fulfill a niche in the market not offered previously. We are between the hardware supplier and the specialty-glazing firms, and we help promote the proper construction of point-supported glass structures.

References
Advanced Structures Inc., www.asidesign.com
Custom Hardware Manufacturing Inc. Architectural Glass Systems, www.chmi.com
C.R. Laurence Co., www.crlaurence.com
DHD International Inc., www.dhdinternational.com
Dorma Glas, www.dorma.com/glas
Eckelt, Trulite, www.eckelt.at, www.trulite.com
Epco Architectural Hardware Inc., www.epcocorp.com
Novum Structures LLC, formerly Mero Structures, www.mero.com or www.novumstructures.com
Nuova Oxidal Srl, www.nuovaoxidal.com
Paragon Architectural Products LLC, www.glassengineer.com
Pilkington Planar, W&W Glass LLC, www.wwglass.com
Ronstan Architectural Rigging Systems, www.ronstan.com/arch/contact.asp
Stella Custom Glass Hardware Inc., www.stellassemblies.com

Bibliography
William S. Coddington, a Perrysburg, Ohio, consultant, searched the Glass Processing Days archive for articles about point-supported glass design. Here's what he found; the papers are available at www.glassfiles.com.

1997
Glass as a Structural Element, M. Chaunac and F. Serruys

1999
The Analysis, Design and Testing of an Asymmetric Bolted Glass Roof Panel, Antony Smith
Architectural Glass as a Structural Element in Japan, Satoru Wakul
Construction Details for Structural Glass Assemblies, Tim Macfarlane
The Design of a Tall, Ground-Based Glass Wall, Stabilized by Laminated Glass Fins, Graham Dodd
Glass Design Strength and the Performance Concept, Ray V. Foss
Structural Glass Architecture, Hugh Dutton

2001
Composite Action Between the Members in Glass-Covered Structures, Paavo Hassinen
Designing Glass Holes for Bearing,  Benjamin Fay
Glass Strength of Annealed and Tempered Structural Glass in the Area of Drilled Holes, Jens Schneider
Structural Transparency and Architecture, Werner Sobek
FEM New Ways in Glass Design and Engineering, Dirk Bohmann

2003
Calculation of Point Bearings for Glass as Load-Bearing Element in the Development of Single Direction Cable Supported Glass Walls, Tim Macfarlane
Influence of Various Support Conditions on the Structural Behavior of Laminated Glass, Holger Graf
Look No Frames, John Colvin
The Properties of Glass and Their Influences on Construction, Dieter Balkow
Safe Post Breakage Behavior of Point Fixed Glazing Systems, Jean-Clément Nugue
Structural Engineering, Barbara Siebert

2005
Constructing with Glass, Ian Ritchie
Design Rules for Glass Panes Fixed by Embedded Point Fittings, Tobias Hermann
New Generation of Point Fixings, Barbara Siebert
Not Just Glass Fins: MIT Brain & Cognitive Science Project, Neil McClelland
Structural Bearing in Holes in Glass,  Brian Eckersley

In addition, Coddington notes that the Glass Association of North America's Glazing Manual, 2004 edition, discusses the Structural Performance of Glass on p. 35, and GANA has a 2005 information bulletin on Point Supported Glass at www.glasswebsite.com.