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transportation
BRIDGES
Old Railroad Span Gets a New Life Without Taking a Break
 
By Angelle Bergeron
Temporary jacking frame shifts load to new piers as permanent cap is created. Trains roll on through.
Angelle Bergeron / ENR
Temporary jacking frame shifts load to new piers as permanent cap is created. Trains roll on through.
Construction crews are working around the clock during a critical 18-day window to replace a center support pier and pivot mechanism on a swing bridge that carries 25 trains per day without interrupting service.

OCCI Inc., Fulton, Mo., is jacking up the 906-ft-long, steel-truss railroad bridge over the Ouachita River in Monroe, La., balancing it on shims and then replacing the main pier and power mechanism that spins the center spans. The critical phase of the six-month, $7-million job is scheduled to end Nov. 16, when crews are to have completed switching out the pivot mechanics and finished the new support pier.

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  • “We have to support the bridge temporarily, cut the top eight feet of pivot pier out, leave the bridge mid-air, then add support by sliding in a new cap,” says W.N. “Nick” Marianos, a structural consultant and engineering professor at the University of Missouri-Rolla. TransSystems Corp., Kansas City, is engineer of record, performing design and construction management.

    “It is somewhat of a design-build contract with OCCI, which has experience doing structural repairs of big things that move, like swing bridges, locks and dams and gates,” says Marianos.

    TransSystems has monitored the bridge since 1995. Ten years ago it found the brick and mortar central support pier of the 1880s-era bridge was gradually tilting. Eugene German, TransSystems’ project manager, says the cause is unknown. “After some time, it will likely keel over,” Marianos says. 

    The tilt is pushing the ends of the bridge out of alignment, requiring recurring maintenance. The situation prompted owner Kansas City Southern Railroad to rehabilitate the bridge. 

     TransSystems began devising a fix last fall. “Our parameters were to increase speed and reliability and not hinder navigation,” says John Dunsworth, TransSystems’ project engineer.

    Building a new bridge would have disrupted river traffic for four or five months, says German. With the rehab plan, OCCI only has to close the river for 18 days. It leased a tugboat to help pass critical barge traffic during the closure and coordinated train schedules with KCS to give it six- to eight-hour work windows between trains.

    To build a new center pier, OCCI drove four 8-ft-dia. drill shafts two upstream and two downstream of the old pier to 90 ft. The drill piers were filled with reinforced concrete and topped with a steel box girder fabricated by Missouri Fabricators Inc., a division of OCCI. “The box girder surrounds the old pier and is connected in between with steel diaphragms,” says Ted Kettlewell, OCCI executive vice president. 

    The contractor then jacked the 800-ton center span with 16 100-ton jacks, four on each of the vertical steel members bracing the center of the swing span, transferring the load to the box girder and the new piers. “We lifted that up with those little jacks,” Kettlewell says. “I think that’s really cool. Few people have actually taken a swing bridge apart and put it back together.”

    New piers, cap and pivot assembly give new life to 1880s bridge.
    OCCI Inc.
    New piers, cap and pivot assembly give new life to 1880s bridge.
    OCCI Inc.
    New piers, cap and pivot assembly give new life to 1880s bridge.

    To demolish the top 8 ft of the old brick pier, OCCI used what Kettlewell calls “a woodpecker,” a BROKK 330 electrically powered pneumatic hammer small enough to fit into the tight space under the bridge. OCCI created what is essentially the bottom slab for the pivot assembly tracks by pouring 14 in. of concrete into a 30-ft x 32-ft rebar-filled form. Both the upper and lower pivot assemblies were set on top of the rebar, and the entire product was placed atop a steel beam diaphragm on the new pier structure, immediately upstream.

    Then, over 12 hours during the night of Nov. 4-5, the contractor slid the new center pivot track assembly into place using 60-ton center-hold hydraulic jacks pulling at 3,500 psi, along with lots of patience and grease. The upper track was centered under the bridge and bolted on. At the same time, a crew working on the lower track hung anchor bolts, built a form around the rebar and bottom slab and shot 7⁄8-in. studs into the steel diaphragm of the box girder assembly to prepare to pour a 4-ft-deep slab of concrete that will unify the pier tops and box girder to complete the new cap.

    After Nov. 16, OCCI will finish by making minor steel repairs to the swing span and strengthening the bridge’s three approach spans. The project will upgrade the span to support “a Cooper E80 live load,” Marianos says. The code is a complex formula from steam locomotive days, but Marianos says the bottom line is that the old bridge “will safely carry modern rail loading.”

     


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