Precisely position both the truck-mounted cranes and the steel girders in adherence with the official survey on an interchange improvement jobsite
Barnhart Crane & Rigging Co.
Manhattan Road & Bridge Co.
The I-430/I-630 interchange improvements in Little Rock, Ark., are upgrading an existing cloverleaf intersection and providing better access to nearby streets and collector-distributor roads from westbound I-630, which ends at Shackleford Road, the next north-south road located west of I-430.
The Arkansas State Highway and Transportation Department wants the $124 million project - the biggest publicly funded one in state history - to be completed by the end of 2014.
The roughly $88 million Phase III of the project includes a new overpass for westbound I-630 over Shackleford Road, a rebuilt I-430 overpass to accommodate the new I-630 overpass and two flyover ramps: one going from I-430 south to I-630 east and one from I-630 west to I-430 south.
The improvements to the original interchange from the early 1970s were deemed necessary because it now carries more than 180,000 vehicles per day, considerably more than it was designed to handle.
Arguably the most important part of improvements to an interchange at Interstates 430/630 is four new or reconstructed ramps that are being added to an existing cloverleaf interchange. The project requires the erection of massive steel girders. Truck-mounted cranes must be positioned precisely to ensure that their reach does not exceed their rated lifting capacity, and the girders themselves must be positioned in adherence with the official survey. Ensuring the precise positioning of both the trucks and girders necessitates precise surveying work.
In summer 2012, telescopic truck-mounted cranes operated by Barnhart Crane & Rigging Co., Memphis, Tenn., picked these girders, varying in length from 50 to 200 feet-plus and weighing 15 to 60 tons, at two points and placed them onto concrete columns or jacks, depending on the section. For obvious public safety reasons, traffic was diverted when girders were erected above existing lanes, and work was scheduled outside of rush hour whenever possible.
For one girder erection sequence that constructed the flyover ramp from southbound I-430 to eastbound I-630, Manhattan Road & Bridge Co. of Tulsa, Okla., and Barnhart were scheduled to complete the work in 20 days. Three shifts of nine hours ran continually during this period. In late July, as the girder sections were being joined from both ends, traffic was alternately rerouted to a service road in either direction when the work was being done above the existing northbound and southbound I-430 lanes.
Due to these tight schedules, ensuring that the cranes were located at an optimal relative position to reach the girders’ officially surveyed X, Y and Z locations - and pick the girders at strategically plotted locations that allowed the cranes to lift within their rated capacity - was critical. The task of marking points for the cranes’ locations fell to Phillip King, surveyor for Manhattan, who used a Topcon Positioning Systems GPT-7500 total station to do it.
Jim Jolly, general superintendent for general contractor Weaver-Bailey Contractors, El Paso, Ark., noted the importance of crane positioning in the context of the overall project. “That’s the biggest issue with the girder erection - making sure that the cranes are in the right spot so they don’t have to be moved around,” he said. “What Phil has been doing is very important, in my mind. The cranes have to reach out, and they can’t get overloaded. If they get too close, they can’t hit it. It’s got to be perfect.”
Jolly pointed overhead to a splice with 60 large bolts connecting two girder sections. Ensuring that the girders were also lifted into their proper locations was also critical, he pointed out. “Like that splice up there - look at how many bolts there are,” he said. “If the next girder section doesn't line up, think about how long it would take to fix the last splice in the sequence. That’s what makes the surveying so critical: one mistake can cost thousands and thousands of dollars.”