In a delicate operation that has been compared to pulling off a tablecloth without breaking any china, contractors at Milwaukee's Miller Park have completed the replacement of pivot bearings for the stadium's operable roof. The system is undergoing final testing and is expected to be fully operational for the start of the baseball season on March 28.
Although bearings are routinely replaced on moveable bridges, Miller Park's pivot system was not designed with bearing replacement in mind, say engineers involved with the repair. The project required a jacking system that would be able to lift high loads and could be installed in the limited space surrounding each pivot point, says Paul Skelton, a partner at Hardesty & Hanover LLP, New York City.
|INSIDE AND OUT Roof panels move on pivots behind home plate. (Photo top courtesy of LZA Technology, bottom courtesy of Southeast Wisconsin Professional Baseball Park District)|
The space for accessing the roof's five bearings was so tight that execution of the project was like "working with 100 people in a phone booth," says Robert DeScenza, executive vice president in the Chicago office of LZA Technology. LZA and Hardesty & Hanover designed the approximately $5-million repair.
The stadium's roof has been a source of contention since July 1999, when three ironworkers were killed during a roof truss lift (ENR 7/26/99 p. 12). Problems with the roof's operation, which are not believed to be connected to the accident, surfaced in the summer of 2001, the stadium's first season. Opening and closing the roof caused a grinding noise originating from the pivot area above home plate, where the five pie-slice-shaped panels, each weighing about 2,500 tons, rotate on spherical thrust bearings.
The stadium's owner, the Southeast Wisconsin Professional Baseball District, hired LZA and Hardesty & Hanover to investigate the problem and recommend a fix. The district continued to operate the roof on a limited basis while the two firms installed three separate systems to measure the stress in critical structural members and to monitor power output from the bogies that travel along rails at the outfield walls. If stress or power output had exceeded acceptable levels, roof operation would have been automatically halted. "If the bearings locked up, it could have had an impact on the integrity of the whole system," says DeScenza.
Although roof operation was never halted, its performance continued to deteriorate during the 2002 season to the point where the pivot noise could be heard from the outfield stands.
Last fall, the engineers found that bearings were moving on the wrong surfaces and recommended complete replacement (ENR 10/7/02 p. 12). The roof's builder, Mitsubishi Heavy Industries of America Inc., Waukesha, Wis., recommended its own fix that would have involved machining the existing pivots and bearings, at a cost of less than $1 million. "Had our proposal not been effective, we would have gone on to replacement," says Mary Cannon, Mitsubishi spokesperson.
The district maintains that Mitsubishi will eventually be required to pay for the replacement under the terms of its warranty agreement. "We did the only responsible remedy and feel confident that Mitsubishi will ultimately end up paying for the work" says Mike Duckett, the district's executive director. But Mitsubishi maintains that the warranty is now void since other firms performed the work.
In early January, the contractor began the process of replacing the existing bearings, which had steel-on-steel mating surfaces, with new assemblies that included roller bearings.
The project required installation of permanent work platforms to access the five pivots located on three different levels. Workers added structure to support the jacks and reinforcement to accommodate the stresses induced locally during the jacking process.
Stiffeners were added to some roof truss members and to the bottom of each so-called "tub," the steel plate enclosure of each truss at the pivot point. Three-ft-deep box beams, or brackets, were welded to the sides of the tub to accept the jacks. Similar box beams were also welded to the fixed structure to support the jacks from below. "All of these elements had to be purposefully designed not to have an impact on the roof when the pivot rotates," says Christopher Pinto, LZA project director.
|(Drawings courtesy of LZA Technology)|
The amount of welding required, tight spaces and brutal winter conditions were the main challenges for the contractor, says Bruce Wall, senior project manager for National Riggers and Erectors Inc., Plymouth, Mich. To prevent the welds from cracking in the sometimes sub-zero temperatures, the steel was preheated to between 350°F and 400°F. At times, as many as eight welders were working in the six feet of platform that surrounds each pivot. "People were practically welding on top of each other," says Wall.
The process required jacking each panel as many as five times, according to Wall. Panels were lifted first to remove the original bearings and machine the underside of the tubs and support structure. They were also raised and lowered several times to accommodate fitting of shims and alignment of bearing bolt holes.
To facilitate future replacement, which members of the design and construction team say is "highly unlikely," the components used to support the jacks and the new stiffeners will remain. Also, the new bearings are bolted in place, unlike the original bearings, which were secured with fillet welds.
The original bearings and lubricants have been packaged for inspection by Mitsubishi and the district. Attorneys are now developing protocols for forensic analysis.
Some observers expect that any legal action resulting from the bearing replacement will be rolled into existing claims. In 2001, the district filed a $5-million suit against Mitsubishi, charging mismanagement of the roof construction.
Mitsubishi filed a countersuit against the district and the stadium's general contractor, HCH Miller Park Joint Venture, led by Indianapolis-based Hunt Construction Group. It contends that delays and other problems beyond its control added $87 million to the original $46-million contracted price of the roof. Both the suit and the counterclaim are still pending. Hunt, which is also construction manager for the current bearing replacement project, declines comment.
The pivot replacement is one of three roof repair jobs under way at the stadium. The other two projects, both intended to stop water ' during storms with heavy rains and high winds, involve replacing flaps between roof panels and caulking work. By the Brewers' first exhibition game against the Minnesota Twins later this month, "fans will be able to focus not on leaks and squeaks but on brats, beer and baseball," says Duckett.
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