Precisely engineered

20 March 2008

The 104 girders vary from 40 to 140 feet in length with widths ranging from 12 to 16 feet. They weig

The 104 girders vary from 40 to 140 feet in length with widths ranging from 12 to 16 feet. They weigh from 40 to just over 100 tons

When completed, the automated people mover (APM) system at the Hartsfield-Jackson Atlanta International Airport will transport airport passengers from the main terminals to a new car rental facility and parking lots about 1.5 miles away. Archer Western, a division of The Walsh Group, designed, engineered and is constructing the new system that will run on two parallel tracks and will offer passengers a 10 minute round-trip.

The $130 million design-build contract is slated for completion in 2009, with work well underway as contractors fabricate, cure, haul and place the elevated concrete girders that comprise the system. For the heaviest of the 104 concrete tub girders that will make up the elevated track of the APM, Starrette Trucking contracted wiTheRMC to design a nine-axle trailer and dolly system for precision hauling.

“We have been working with Starrette for many years, building their, Paul Gill, mechanical designer at Elk River Machine Company (ERMC), based in Elk River, MN. “They have bought our five- and six-axle steerables as well as some of our three-axles. For the APM job at the airport, they needed a nine-axle to haul the heaviest girders.”

Starrette, based in Augusta, GA, has hauled bridge and concrete beams for DOT projects throughout the Southeast, and has been a mainstay at the Atlanta airport for several years hauling concrete beams for the construction of the new runway and related construction. When the company secured the contract for the people mover project, it knew that a specialized dolly and trailer system was needed to haul the heavy tub girders.

The girders vary from 40 to 140 feet in length and widths range from 12 to 16 feet. They weigh from 40 to just over 100 tons. In looking at the specs, Gill says he worked with the Georgia DOT, at first trying to get approval to be able to haul the girders on two six-axle trailers, using a double lane approach.

concrate tub girders are halued from the concrete fabrication plant to the construction site at Atlanta Hartsfield-Jackson Airport using a specially built ERMC nine-axle trailer anddolly system designed for hauling the girders

“But the bridges that needed to be crossed would not allow for some of those weights,” says Gill. “We would need to spread out the weight on nine axles. Th is was our first ever nine-axle.”

Load and go

To assure that the new trailer would be versatile enough to use for other jobs, it was designed so that it can be reassembled into one six-axle and one three-axle trailer.

“We bought the big rig for the tub girders at the airport,” says Larry McKenzie, project manager with Starrette Trucking. “We can also use this equipment to haul a Florida U beam from Savannah, GA to Orlando, FL, with the rigs grossing out to 348,000 pounds. The intent was to use it for these larger jobs and then if we weren't pulling the big beams we could we need.

The new nine-axle Hydra-Steer trailer features dual steering and enhances ERMC's proven “load and go” skid steer method with new single-frame steering capability. The new steering improves the versatility during extremely heavy loads and back hauling. The hydraulic load equalizing frame maintains proper axle loads during travel. Spreads on this trailer are 16 feet with five-foot axle spacing.

Plus, McKenzie praises the Hydra-Steer's hydraulic accumulator that helps equalize the axles, leveling them out from the back to the center to the front. McKenzie said they bought their first ERMC trailer back in the mid 1980s, and some are still in service.

The 104 girders vary from 40 to 140 feet in length with widths rangingfrom 12 to 16 feet. They weigh from 40 to just over 100 tons

Fabricated in Atlanta, each Fabricated in Atlanta, each girder on the APM is different, custom poured as a specific piece of the puzzle that will form the elevated track. Working closely with the engineering group, Gill and his team designed the Hydra-Steer so that securement for each girder would be simple and safe.

“We worked with all the mensions and the concrete ompany was able to case sleeves the product so that every piece pre-designed for the trailer with st plates for drop-in I-bolts that line up with the trailer,” explains Gill. “It is really quite impressive if you look close at the flanges and the way the widths change the center of gravity is different wiTheach piece. They pre-mark them so that when we set it on the trailer the center of gravity is correct, some will sit off-center but they are always level.”

McKenzie said they also attach chains to the I-bolts for extra securement.

The hauling part of the job should be complete by mid summer, with about 75% completed in late April. They generally pick up two to four girders a day, depending on weather, traffic and the like. “We have done four in a day, that was a good day,” he says. “A good day is three and a mediocre day is two. It all depends on the product being ready and other variables.”

The tub girders have to dry and cure for a certain amount of time before being moved.

At the concrete plant, the girders are loaded on the trucks using a gantry type concrete loading crane. At the airport construction site, two Manitowoc Model 999 crawlers lift the girders off the trailers and place them.


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