Tube & Pipe
Tuesday | 16 October, 2012 | 10:30 am

Spine of steel

By Nick Wright

Tubular steel skywalk links new Hilton with convention center in Ohio capital

October 2012 - Skywalks, the enclosed corridors bridging a gap between two structures, don’t draw much attention. They’re functional, typically following the form and design of the buildings they connect. However, a new skywalk that recently went up in Columbus, Ohio, incorporates tubular steel in a way that has enlivened what is an otherwise pedestrian path.

Straddling N. High Street in downtown Columbus’ lively Short North district is a 100-foot-long skywalk, supported by a 4-foot-diameter steel tube, connecting the Greater Columbus Convention Center with the new Hilton Columbus Downtown. The 532-room Hilton is scheduled to open in October.

It’s a refreshing design. The existing skywalks in Columbus are large, external diagonalized trusses, fairly opaque and unassuming. Architecture firm HOK, Chicago, sought to open the occupants’ view from inside to out, as well as maximize the view along High Street.

“By developing a single overhead structural tube, that a series of discrete lightweight structural ribs hang from and are glazed on all four sides, we were able to achieve that goal,” says Todd Halamka, senior vice president at HOK. It includes minor amounts of stainless steel and aluminum, he says.

From the spine-like steel tube hangs a series of hollow structural steel pipe ribs, 64 in all, that secure the skywalk’s glass and support the elevated walkway. The ribs and 366 glass panels are secured with a custom toggle system that clamps to the inner lites of the insulated glass units with recessed edge channels, according to Tobias Karnagel, director of operations at New Haven, Conn.-based Roschmann Steel & Glass, the project’s contractor. The firm is the U.S. arm of Germany-based Roschmann Group, which constructs the gamut of enclosure systems, like millionless glass-fin systems and stainless steel curtain wall systems.

The S355 grade (equivalent to ASTM A500 grade C) steel pipe was sourced from Turkey and fabricated in 10-foot sections, later welded into three sections, according to Karnagel. Those three sections were shipped in 40-foot containers. Then, the sections were welded together in Columbus and shipped to the job site in its full length. The pipe alone weighs about 75,000 pounds.

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Rehearse and perform
The installation of the skywalk was no small feat (click for a time-lapse video). The designer's initial strategy of working over busy High Street would have meant expensive third shift and weekend labor on top of disruptive road closures. Roschmann's revised strategy called for a bolted assembly, rather than welded, to eliminate any potential field welding. Thus the skywalk was assembled, glazed and sealed onsite completely before being lifted into place. The preassembled walkway, gaskets and cross bracing were assembled in Germany.

“Only at the two splice locations the tension rods had to be installed in the field,” says Karnagel.

High Street did close on the Friday evening before the “big lift,” according to Roschmann. Turner Smoot acted as the hotel’s construction manager. After two 550-ton mobile cranes hoisted a 100-foot crane boom as a dry run, the skywalk was lifted, set and lowered onto structural steel supports on either side of the street. The coordinated two-crane lift, called a “tandem pick,” shared the weight of the skywalk, which totals about 290,000 pounds. Although the Hilton was built with an opening in its facade for the skywalk, the convention center had a hole cut out to accommodate it, fitted with a connector link.

The Short North neighborhood in Columbus is known for its 17 metal arches that span one mile of N. High Street. They form a gradual gateway, transitioning from the restaurants, shops and bars to the convention center and eventually downtown, which fills the skywalk’s southern view. The angled, cascading glass pattern of the skywalk, in this case an inverse arch, is a contextual response to those arched frames, says Halamka. It brings a “subtle reference” to context of place. MM 

 

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