Innovative Lifting Frame Launches Beams from Existing Structure

Conventional bridge building means and methods generally call for cranes to lift heavy girders into place. For the 1,000-foot-long bridge carrying U.S. 21 over the Catawba River in York County, S.C., KCI (through our recent acquisition of Triplett-King & Associates Inc.) helped contractors develop a cutting-edge lifting frame to launch beams from the existing structure, eliminating the need for barge-mounted cranes.

This was the first time we were asked to design a system for launching girders transversely off the old bridge. We had no previous projects to go by.

Andrew M. Craig, PEPractice Leader

Andrew M. Craig, PE

The South Carolina Department of Transportation (SCDOT) originally contracted KCI to provide project management, alternatives analysis and structural design, and later construction inspection services, to replace the bridge on a new alignment just upstream. During design, engineers determined that the existing structure was unable to support the load associated with cranes and heavy girders, and subsequently approached several area contractors who indicated that a combination of barges and cranes was the most viable construction methodology.

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Although originally set for replacement on the same alignment, KCI engineers determined that moving the structure upstream would save more than $1.5 million in mobilization costs and significantly reduce impacts to the more than 20,000 motorists that cross the bridge every day. www.AerialPhotosElite.com

Not among that initial group, the Lane Construction Corporation (then REA Contracting LLC) was selected to build the structure and approached KCI with an alternate to using barge-mounted cranes in setting the heavy concrete beams. Because of the extremely low water levels in the Catawba, they were concerned that without significant coordination for water release at the upstream dam, many of the approximately 100 barges required would bottom out on the rocky river bottom, sustaining significant damage.

This totally took the water elevation out of the equation. Instead of having to put barges out there and hope to get water to cover all the rocks, they were able to control their own destiny and invented a system to set the beams.

John G. Huskins, SCDOT Resident Engineer

To improve safety, minimize environmental impacts and remove the uncertainty associated with using barges, the contractor looked toward the existing bridge via a lateral launching lifting frame as a means of bypassing the need for cranes. According to Lane project manager Troy M. Carter, PE, the idea came from retired construction project manager Rick Bahnson, who had shared a photograph of a Washington, D.C., project that had used a similar concept on a much smaller scale.

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The 3-D model allowed engineers to consider numerous load cases including modeling a girder as a moving load along the rail beam to determine critical positions, wind loads, collision loads from the trolley impacting the bumper stops, and out-of-tolerance loading creating a “pull” on the frame. A distinguishing feature of the lifting frame, the cable-stay-type brace towers almost 50 feet above the bent caps as it supports the 30-foot cantilevered rail beam from above.

The first order of business was to analyze the existing structure to ensure that a truck carrying the heavy concrete beam would not create an overload situation. Engineers then worked with Lane bridge superintendent Emilio Valentin to determine steel member sizes and types that met their preferences while providing the strength required. Visual analysis 3-D software was used to model the structure and analyze various load cases.

Clamped to bent caps on the new substructure, the lifting frame is a steel structure that cantilevers over the existing bridge. A trolley runs along the large beam with hoists on each side to pick up a girder from the delivery truck and carry it over the water before being lowered onto the new pier. Following the beam as it travels along the trolley to its final position, four light-weight man baskets provide a stable platform for workers to operate the two hoists and trolley system.

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A fully-threaded rod allows each man basket to be raised or lowered to ensure workers are at the optimum height to operate the hoist and trolley system.

Adjustable bolts were added to allow for field control of the cantilevered arm, which must remain level during trolley operations. “When you pick up a girder, the whole system wants to deflect downward at the end, leaving the trolleys with an uphill climb,” said KCI design engineer Andrew M. Craig, PE. “The adjustable bolts allowed us to counteract this downward deflection and provide a level rolling surface for the trolleys.”

KCI was also challenged with finding the most effective way to advance the frame further down the new bridge as construction continued. A track and roller system was developed to allow the 100,000-pound frame to ride on the newly placed girders.

Each span of the new bridge consists of 11 beams, and the team quickly realized their goal of setting an entire span over the course of three and a half nights. Overall, the lifting frame played a big part in successfully placing almost 90 concrete girders with no impact to the Catawba River below.

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SCDOT would not allow additional anchors to be embedded in the permanent structure. Instead, the team used a clamped-type connection fitted around the concrete cap.

“The lifting frame is a controlled system,” said Carter. “It’s almost boring to watch, but we’re placing beams without cranes or barges. It’s safer and eliminates environmental impacts.” By bringing the concept into reality, Lane and KCI have proven that a lateral launching system can place beams as efficiently as traditional construction methods.

The design was absolutely flawless. Even from the first span it went like clockwork. Everything worked as prescribed. It was amazing and the most economical means of placing these girders.

C. Russell CarrollSenior Inspector

C. Russell Carroll

The cutting-edge system is safe, lightweight and mobile, and can be used on other projects with similar circumstances, including limited access and environmental concerns. “Part of the beauty of this system is that it’s not just a one-shot deal,” said SCDOT resident engineer John G. Huskins. “They had plans drawn up and were meticulous about marking and labeling so once it was disassembled for storage, it could be put back together again.”

Craig and KCI Practice Leader James D. Fitz Morris, PE, have presented the lifting frame concept for several branches of the American Society of Civil Engineers as well as the industry organization’s annual South Carolina Statewide Conference. The project was recently recognized with an Engineering Excellence Award from the American Council of Engineering Companies of South Carolina.