Northwestern University is creating new medical facilities in downtown Chicago including the Northwestern Medicine Outpatient Care Pavilion. With a variety of new buildings designed with state-of-the-art facilities, the need arose to provide a means of transportation from one building to another. In comparable situations, facilities have been connected by underground tunnels and skywalks to divert foot-traffic from sidewalks. Cambered steel beams are often the structural members of choice for skywalks.
To connect two of the medical facilities at Northwestern, the architects and engineers specified cambering two W44 x 335# beams — the largest 44in sections produced. One was to be 95ft long weighing 31,825lbs; the other 97ft long weighing 32,495lbs. Both were to have a 3in camber. The beams are cambered so that under load they–and the bridge–will be flat and straight.
One way of cambering beams is to roll the structural member through a three-roll bender (also called an “angle roll,” a “section bender,” or a “pyramid roll”). This type of machine assures a constant curvature throughout the arc segment. Another way of cambering beams is to do a point camber with a cambering machine. This method applies pressure via hydraulic cylinders to one or more points along a beam to induce camber. This method can result in a camber without a constant curvature. The second method is often acceptable; the first was specified by the engineers on this project.
Our customer, a structural steel fabricator, does point cambering in-house, but bending this size beam was beyond the company’s capacity. And the customer wanted the camber rolled into the beam. Both structural steel fabricators and steel service centers often subcontract cambering to Bender/Rollers who specialize in curving steel.
In this particular case, our customer called on bid time, May 15, 2013, to see if we could camber these huge beams. We said, yes. When it came time to order the beams from the mill, the customer called again to confirm that we could camber these beams. Again, we said, yes. We were awarded the order; we received the 95ft beam on August 7 and the 97ft beam on August 12 (both from Nucor-Yamato Steel via flatbed); and we shipped the cambered beams to the customer on August 19. The medical buildings and skybridge will open in 2014.
Chicago Metal Rolled Products had previously curved W44 x 290# beams the “easy way” (against the weak or y-y axis) for another pedestrian bridge at Northwestern’s medical campus.
