Bending Pipes for The Trellis at Chicago's Millenium Park

Bending Pipes for The Trellis at Chicago’s Millennium Park

Five full years before its completion, Chicago Metal Rolled Products consulted with the engineers at Skidmore, Owens and Merrill (SOM) about bending pipes for the Pritzer Pavilion trellis at Millennium Park.

At 625 feet long, 325 feet wide and 60 feet at its highest point, a complex web of 12,14,16,18, and 20-inch diameter curved and intersecting pipe was to cover an area greater than 4 football fields and to hold speakers for a computerized, sound system entertaining an audience of 11,000.

Architect Frank O. Gehry’s design called for 570 tons of pipe curved in two planes with multiple radii. Chicago Metal suggested that each arch be curved in one plane and that the radii—ranging from 100 to 1000 feet-- change at each arch’s four nodal junctions. The architect agreed and chose to tilt each arch a little to the side. This early involvement and teamwork reduced costs and facilitated construction without compromising aesthetics.

Millennium Park Images

Chicago Metal used a 3-roll bending machine with a capacity of 200 in³ section modulus, one of a few machines in the country with tooling for bending pipes cold. Adapting to an accelerated schedule—an “X-node” was expedited to continue construction on the stage--the company delivered everything on time.

And, of course, the whole fabrication required AESS (architecturally exposed structural steel) quality. For example, SOM specified that the pipe have no scratches that your fingernail would hang up on. The precise bending of Chicago Metal Rolled Products made the difficulty of shop-fitting 130 curved and welded TYK joint connections “a snap”!

The trellis had to connect to the steel-clad, curvaceous ribbons which adorn the stage and which are so characteristic of Gehry’s architecture. The general contractor, Walsh Construction, and the erector, Danny’s Construction, both remarked that “the trellis pieces went together so well.” Working together, all parties helped create an architecturally significant structure that is a tribute to the versatility, economy, and beauty of steel construction. They didn’t curb their enthusiasm; they curved it.