Miller Park stadium gets a lift

15 April 2008

Enerpac had another stadium lifting job at the back end of last year in the USA. The roof-opening mechanism of Miller Park, home of baseball team Milwaukee Brewers, was malfunctioning because one of the bogie guide rollers, on which the five movable roof sections travel, had shattered.

The day after the season finished the engineers, ironworkers and millwrights moved in to replace all 10 bogies (powered carriages). The 12,000 tonne roof is designed in a fan shape, with each of the movable sections pivoted at its home-plate end and riding on two bogies at its wide (outfield) end 183 m away.

The 6.7 m-long bogies were fitted with pairs of double-flanged wheels to ride on an eight inch wide circular track. The two double-flanged wheels on each bogie were arranged to ride the single track in an in-line fashion, with guide rollers following single tracks mounted on both sidewalls of the main track bed. The original-equipment bogies proved inadequate for their massive burden. A drawback was their cylindrical wheel-faces, with the outside of the wheel naturally wanting to travel further than the inside on the arc track, which is believed to have contributed to the problem.

The wheels on the replacement bogies were designed with spherical rolling surfaces, to allow for minor bogie tilt, and the wheel axles are turned such that the bogie naturally follows the curved track. In addition, the new bogie design employs four wheels arranged in two pairs, instead of the previous two-wheel design.

Replacing the bogies required the roof to be jacked up. This meant that not only jacking platforms but also jacking brackets to lift against had to be designed, fabricated, and installed.

Lateral movement during the lifting process also had to be taken into account. Working 183 m from the pivot ends of the roof panels, thermal expansion and contraction were significant, and wind effects (which famously brought down the “Big Blue” Lampson Transi-Lift crawler crane during stadium construction in 1999) could not be ignored.

The stadium roof sections were jacked in ten separate lifts, one for each bogie replacement. Each time, the roof was lifted by 102 mm to 152 mm, the old bogie driven out under its own electric power, a new bogie rolled in, and the roof lowered back into place on a spindle bearing. A 500 tonne crane moved bogies to and from ground level.

The weight lifted ranged up to about 800 tonnes, so a capacity safety margin was provided by using four Enerpac 300 tonne, 700 bar, 300mm stroke hydraulic cylinders for each lift. The cylinders were connected to a common manifold fed by an Enerpac 700 bar 9.3 kW electric pump.

The jacks had lock rings to guarantee load holding, and a locking valve was used in the pump-to-manifold feed line. The locking valve incorporates a check valve with a manually controlled pilot operator.

The 300 tonne hydraulic jacks were a single-acting load-return type. To provide positive pull-down, the Enerpac pump setup included a valve with a venturi feature to deliver negative pressure when needed.

The hydraulic system was assembled and tested before being put into service. To provide for lateral movement during lifts, the jacks rested on a 38 mm thick steel plate, then a sheet of Teflon, and then a sheet of polished stainless steel.

Total cost of the project, for which the main contractor was Price Erecting, was close to $15 million.

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