Of Retractable Roofs and Curved Steel

The 2014 North American Steel Construction Conference (NASCC) opens next Wednesday, March 26, in Toronto and runs through Friday, March 28.  It is the premier conference that deals with steel in construction.

Countless programs, seminars, and exhibits are offered at this well attended show.  Browsing through the Advance Program, I find a number of offerings that interest me.  One particularly stood out for me.

“25 Years of North American Retractable Roofs” reviews the history from the opening of Rogers Centre (then SkyDome) roof in 1989 through the construction of Montreal’s Olympic Stadium.  The presentation will be given by Mark Waggoner and Randy Braun of Walter P. Moore who will review the evolution of operable roof technology through a variety of completed projects.

This session reminded me that we at Chicago Metal Rolled Products curved 750 tons of steel rail to support the retractable roof at Miller Park, home to the Milwaukee Brewers.  Our customer was Mitsubishi Heavy Industries.

2100ft of heavy rail was rolled to a 600ft radius with a tolerance of +/- 1/4in.  The steel sections are about 9in wide, 6in tall and 30ft long.

Cross Section of Steel Rail for Miller Park
Bogey Wheels Ride on Rail Curved by Chicago Metal Rolled Products

At the NASCC session on retractable roofs, I’ll be anxious to learn what might be reasonable fabrication tolerances for such structures.  Mitsubishi originally wanted a radius and flatness tolerance on the curved rail of +/- 1/32in.  What was problematic, however, was that the rail produced in Luxembourg and shipped through the Great Lakes to Chicago could not be produced to that standard.  After a number of discussions, Chicago Metal and Mitsubishi agreed on a +/- 1/4 inch; Chicago Metal held +/- 1/8 inch.

The only fan-shaped convertible roof in North America, the $50 million, 7-panel retractable roof opens and closes like a fan in about 10 minutes.  The roof panels pivot mechanically on a fixed point behind home plate and 175ft above the playing field.

The roof is closed if game temperatures are expected to be below 60 degrees, or if rain or high winds are in the forecast.

The upcoming NASCC seminar on retractable roofs also reminded me of another project we contributed to.  Chicago Metal curved 410 tons of 12in square tubing to a variety of radiuses from 1000 to 1200 feet to frame the retractable roof at the University of Phoenix Stadium where the Arizona Cardinals play.

12in Square Tube for the Arizona Cardinals Retractable Roof

Across the width of the field span 256-foot-long lenticular trusses so-called because both the top and bottom chords are curved, creating a profile that resembles a convex lens.  Tube bending from Chicago Metal Rolled Products helped create the sixteen such trusses that are incorporated in the two retractable roof panels.

It is interesting to compare Miller Park with the University of Phoenix Stadium.  Miller Park is a baseball stadium; Phoenix a football stadium.  Of course both can have multiple uses.  Miller Park’s roof opens like a Japanese fan; Phoenix’s like a boat hatch.  More often than not, Miller Park will be shutting out the cold by closing its roof; Phoenix will be shutting out the heat.  A unique aspect of the Phoenix stadium is its ability to pull the grassy field out of the stadium exposing it to fresh air, water and sunshine.  A variety of activities can then be held on the remaining concrete floor inside.

I’m looking forward to attending this session and many others at 2014 NASCC.


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