High Bridge Construction: Digitally Controlled Hydraulics Facilitate Placement of Large Trusses
More than a century old, the Union Pacific Railroad’s Kate Shelley High Bridge across the Des Moines River has reached a stage where a “slow order” limits train speeds to 25 mph. The aging double-track bridge, built in 1901, is presently being replaced by a new $43 million double-track high bridge designed for train speeds up to 70 mph. “This is the type of major investment in replacement infrastructure that railroads must make,” comments Bill Wimmer, Union Pacific vice president, Engineering, in a press release.
The new bridge
The engineering firm, HDR Engineering Inc. of Omaha, Nebraska, describes the bridge design as consisting of steel deck plate girders (trusses) supported by concrete column bents. There are 20, 110-foot spans and five, 70-foot spans. The spans rest on 25 piers, five of which are boxed/braced. The Des Moines River is no longer used as a shipping channel, so a longer main span is not required. Not including approaches, the new bridge is 2550 feet long and 185 feet high.
Constructing the new bridge alongside the old one presented a challenge for contractor OCCI, Inc. of Fulton, Missouri. Hundred-ton span trusses rest on piers that in some cases are in excess of 150 feet tall. “Using a crane to lift the trusses into place isn’t feasible because of the terrain below the bridge level,” says Dave Fennewald of OCCI, noting that the river valley is flanked by two steep hillsides.
The solution developed by OCCI utilizes a cantilevered support system enabling a self-propelled gantry crane to place the mile of girder spans. Operation of the propane engine-powered gantry is fully hydraulic. The “rails” on which the gantry crane rides are a pair of 350-foot long box beams. No flimsy structure here—“The box beams weigh 900 lb per lineal foot,” comments Fennewald.
The role of digitally controlled hydraulics
The gantry and movable box beam launching arrangement is self propelled by means of a novel digitally controlled hydraulic system provided by Enerpac. The system employs eight, 50-ton clamping cylinders distributed along the supported length of the box beams, and a pair of 88-ton, five-foot stroke launching cylinders.
For each 70-foot or 110-foot span, the clamp, pull, unclamp, reset launching cylinder sequence is repeated until the cantilevered box beams reach the next pier. “OCCI wanted to automate the process to eliminate the need for human decisions as much as possible,” says Mike Chudy of fluid power distributor John Henry Foster, which has worked with OCCI over the years. The result was a decision to use Enerpac’s Synchronized Lifting System.
The key to all this is a fully integrated, PLC-controlled hydraulic clamping and launching system. “The system has sufficient versatility to be used in other applications in the future,” says Chuddy. He explains that a single package contains both the 10,000 psi hydraulic power and controls used for the clamping cylinders and a 3000 psi, high-flow system using proportional valves for the launching cylinders. The integrated package also contains the electronic controller, complete with a touch-screen interface (photo 6). Power is supplied at 460 volts by an on-site generator.
Could the hydraulics have been handled without the digital control system? The answer is “Yes, but…” The “but” means that without integrated control, numerous workers would have to be stationed for each box beam launch. Those workers would not all be within sight of each other. Add in the possibility of an instruction being misunderstood by a worker, and the advantages of the synchronized system become obvious.
Trusses and deck
One of the 52 trusses is shown in photo 6, ready to be hoisted into place by the gantry crane, photo 7 shows freshly placed trusses, and photo 8 shows the concrete deck panels.
With scheduled cutover in mid-2009, the new Boone High Bridge will help the Union Pacific meet expected long-term growth in freight volume.
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Who Was Kate Shelley?
Fifteen-year-old Kate was part of a central Iowa farm family when on the night of July 6th 1881 heavy rains caused flash flooding of the nearby Honey Creek. A wooden railroad bridge crossed Honey Creek, and a pusher locomotive had been sent out to check track conditions. The bridge had been washed out, and the train went into Honey Creek.
Kate heard the crash, grabbed a lantern, and went to the creek. She shouted to the two survivors of the four-man crew that she would get help. But a more pressing crisis also motivated Kate to get help. Within about an hour, a passenger train was scheduled to cross the now non-existent Honey Creek bridge. The passengers on that train might die if it wasn’t stopped.
Kate started across a bridge over the Des Moines River toward a nearby train station to give her warning. The going was difficult because the bridge was not fully planked, and then her lantern failed, so she crossed the bridge on her hands and knees with only lightning for illumination. Then she ran another half-mile to the station. She made it in time, and the passenger train was stopped in Ogden, Iowa with 200 passengers aboard.