Apple Store - Glass Staircases
A unique and eye-catching feature of Apple's high-profile stores is the glass staircase, intended to attract visitors to visit the second (or even third) floor, which most retail shoppers avoid. Besides the visually interesting design, the stairways and their accompanying glass bridges are engineering and architectural marvels, and made possibly by recent advances in glass technology that allows its use in more demanding applications.
Over the years the staircase designs have evolved from simple stright-runs up to the second floor, and now include free-standing and wall-mounted, angled turns and spiral designs, and most recently a three-story version. [list of stores with glass stairs]
Perhaps not surprisingly, the staircase received a design patent in 2002 with Steve Jobs' name first, followed by several others. The staircase design itself received a design patent, and the complex glass and hardware system received a separate technical patent.
Download (pdf) a copy of the very complex technical text and diagrams as obtained directly from the U.S. Patent and Trademark Office.
The technical details are, of course, superfluous to the average visitor to an Apple store, where, "It's all about the experience." The stairs are irresistible --you must simply ascend them once you spot them. Your climb consists of gazing left-and-right at the elevated view of the store, and frequent stops to examine the stairs themselves. I find it necessary to hold the handrail, since the open design and semi-transparent glass provide a levitation effect.
Once you reach the top (or bottom at Fifth Avenue), you inevitably turn around to look at what you've just climbed, and to study the structure to see how it was all done. As you turn left or right, you again are drawn to look down/up at the stairs, both for the color and form, but also for the structure.
Going down the stairs is usually a slow endeavor, as you gaze downward at the glass and metal, and pause once again on the landing to look around. By the time you've reached the ground floor, you feel like you've actually been entertained.
If you take time to walk around the bottom of the stairs, you can't help but be impressed by the underlying structure of the staircase, including the custom-designed and manufactured hardware.
Some of the glass staircases are accompanied by a glass bridge that connects the two sides of the second floor opposite the staircase. At Fifth Avenue, the store entrance floor is glass, coverd by a glass cube. The glass bridge features a similar design and hardware.
The staircases were designed by structural engineer James O'Callaghan, who is now a partner with Brian Eckersley at Eckersley O’Callaghan Structural Design. The company's Web site has photos and details of the various Apple store staircases.
The stairs on the convergence of several technologies, including laminated glass production, and a panel construction that's called "point-supported."
Working with its retail store architectural firm Bohlin Cywinski Jackson, Apple designated an all-glass design for the stairs--both the steps (treads) and the supporting structure. In the first version at the SoHo store, the stairs would have to rise 4.6 meters over a length of 10 meters with a half landing, and 27 risers (at Regent Street the stairway is 33 ft. long and rises 20 ft.). The supporting side wall would continue up past the treads, and forms a glass balustrade, or side railing of the staircase. The final design of the staircase called for treads that were 2.1 meters wide for SoHo (2.45 at Regent Street).
During a 2005 glass industry conference, O'Callaghan told a session that Apple was looking for, "a very sharp aesthetic with a patterned surface to the tread similar to that found on chequer plate steel." He said there were two key reasons to use an all-annealed glass tread, both related to aesthetics and durability.
First, O'Callaghan said, the glass could be polished after the laminating process, significantly increasing the sharp appearance of the edge of the tread. Second, should the top sheet be clipped by foot traffic, the tread could remain in place for a reasonable amount of time without needing replacement, whereas a tempered glass sheet that failed would compromise the aesthetic.
Apple also specified a pedestrian bridge as an all-glass structure spanning the two second-floor sections of the high-profile retail stores.
As simply as the staircases appear to store visitors, an enormous amount of engineering and research went into their design. First, the materials themselves had to be selected and tested to meet load and fire safety requirements. Building codes require certain minimum weight loads for stairways, and in this case the design load was about 100 pounds per square foot (technically 4.5 kiloNewtons per square meter). The glass structures also had to meet certain fire code requirements that limit failure of the components when exposed to flame.
For Apple's stairs, the glass also had to provide significant seismic protection, since several installations would be in cities with frequent earthquake activity. Extensive finite element analysis (FEA) was performed, O'Callaghan told the conference attendees, to accurately predict global and local stresses in the panels and around the holes supporting the treads.
Much of the engineering was centered on the connections between glass panels, since that is where the majority of stress occurs. Special connection hardware had to be designed, and new testing methods had to be devised to evaluate them in the design. Unlike connectors for wood or metal, glass-to-glass connections must be engineered to an extremely tight tolerane,
Lastly, pedestrian bridges are subject to certain vibrations when in use. Through engineering and material selection, the stiffness and natural frequency of such bridges can be adjusted so that the vibrations caused by human impact aren't objectionable or annoying to the pedestrians. In this case, the tread design was intended to keep the natural frequency above 5Hz to maintain pedestrian comfort, Callaghan explained.
Once the individual glass designs were finalized, integration testing began. The treads and sidewalls were linked using hardware made of various metals. One component of the connecting hardware had to be built into the tread during manufacture of the glass. This created a requirement that the glass and metal components be thermally compatible to prevent them from expanding and contracting at different rates, which would, in turn, lead to cracking and tread failure. After several rounds of testing, the design team found that titanium hardware was the best selection.
During the industry conference, O'Callaghan recalled that other hardware materials did not heat and cool at the same rate as the glass during the manufacturing process. This resulted in several pieces cracking and otherwise failing. Even when the titanium design was finalized, the hardware-glass package was found to be very susceptible to temperature variations. O'Callaghan told the conference that during installation of one store's staircase, the interior was still open to the weather, and several treads cracked as the outside temperature went up and down. In later installations, he said later, stores were completely enclosed before the stairs were installed, eliminating any glass cracking.
Extensive tests were carried out on the final design, both by O'Callaghan and DuPont, using both actual materials, and so-called "Nastran" and "Lucas" FEA software, designed to calculate stresses and deformations in complex geometrical structures. The results of the FEA is color-coded diagram of the stress plotted at various points on the object.
When the design and manufacturing process was finalized, Depp Glass (NY) was selected to manufacture the staircase components, while the titanium hardware was manufactured by Tripyramid Structures Inc. (Mass.). The actual fabrication, installation and safety tests were performed by Seele GmbH & Co. (Gerthofen, Germany).
The staircases are constructed of 3-ply glass treads, bonded together with a Dupont SentryGlas Plus ionoplast interlayer [tech info]. The treads are tied through titanium hardware to the glass side panels. The treads are surface acid-etched to provide slip and privacy protection.
Specifically, the glass treads at the SoHo store consist of an 8mm extra clear Depp Glass Diamond Plate layer, a 0.060-inch DuPont SentryGlas Plus ionoplast interlayer, a 15mm extra clear Diamond Plate layer, another 0.060 DuPont SentryGlas® Plus ionoplast interlayer, and another 8mm extra clear Diamond Plate layer.
The tread is a total of 55mm thick, or about 2.1 inches.
The staircase vertical, laminated glass sidewalls were supplied by BGT Bischoff Glasstechnik GmbH (Germany). They consist of a center 15mm laminate, with 12mm layers on either side. The side glass panels range up to 5.8m high x 1.6m wide, which O'Callaghan said generally need to be craned in through the skylight roof during off peak hours.
The top surface of each tread has a diamond-pattern surface to provide some gripping so customers don't slip on the stairs.
Here is a diagram of the stair tread from the patent application filed by Apple in 2002.
You can see an entire laminated tread panel in this photo, showing the various layers, the blue-green color, the connecting hardware to the vertical sidewall glass (invisible in the photo), and the tread grip pattern.
O'Callaghan noted at the conference that the SoHo store staircase is gravity loaded at the base and carries the load of the treads to a base steel channel. However, The Grove retail store staircase has the treads supported between the glass walls which are, in turn, hung from the second floor. O'Callaghan told the group, "The magic of the Los Angeles hanging glass wall approach is emphasized by the manner in which the walls levitate clear of the floor from where the stair rises."
Two recent stores took the glass staircase to another level--a 180-degree twist. Both the Shinsaibashi and Shibuya stores in Japan feature a spiral glass staircase. Interestingly, the Shinsaibashi staircase spirals to the left, while the Shibuya staircase spirals to the right. The staircase is an engineering marvel, but also creates a strong attraction for visitors to ascend to the second floor. Glass maker Isoclima of Padova (Italy) supplied the curved and laminated balustrades, which are constructed of chemically tempered glass. The side panels are three layers of 10 mm glass, with two 1.52 mm-thick PVB interlayers. The 6-foot treads are 4-ply annealed and laminated glass. O'Callaghan told an interviewer that an earthquake two weeks after the stairway was installed did not damage.
The Staircase Team
Also check these:
One of several technical diagrams submitted by Apple in 2002 to the U.S. Trademark and Patent Office in support of its application for a patent on the glass staircase design.
North Michigan Avenue - The sign at the bottom of the stairs states, "Welcome to the Apple Store!" and then ironically asks, "Have you ever visited our second floor?" The sign explains that the theater, Genius Bar and Studio are located on the second floor. Notice the skylight over the stairs, lending a daylight cast to the interior and the stairs. Lights from the bottom illumiinate the glass.
This custom-built hardware connects two load-bearing glass panels at the San Francisco store with a third "fin" cross-support at right angles (rear).
This hardware attaches an individual step (tread) to the load-bearing side glass panel. Notice the multi-layed, laminated structure of the tread, and the special three-hold holes used to tighten and loosen the connector. The glass is blue here, since it's illuminated by an overhead skylight. Under artificial light it has more of a green cast.
One of several techncial diagrams submitted by Apple in 2002 to the U.S. Trademark and Patent Office in support of its application for a patent on the glass staircase design. This is a side view of the tread support hardware. The part on the left (#162) is the same one shown in the photo directly above. The glass side support wall is #154, the tread hardware is #184, and the glass tread itself is #158.