Barges Carry Concrete to Work Site in Construction Of Longest Cable-Stay Span Bridge in North America
Barges Carry Concrete to Work Site in Construction Of Longest Cable-Stay Span Bridge in North AmericaScheduled to open to traffic in 2005, the $531 million Cooper River Bridge is destined to become the longest cable-stay span bridge in North America.
The 1,546-foot, cable-stayed span will hang from twin, diamond-shaped towers overlooking the historic harbor of Charleston, S.C. The towers will reach gracefully upward more than 575 feet and support a road deck almost 200 feet above the mean high tide mark. Bridge designers envision the towers becoming a signature icon for Charleston.
Begun in July, 2001, the bridge is owned by the South Carolina Department of Transportation and is the largest, single project in the history of that state’s DOT. It will replace two functionally obsolete truss bridges, linking Charleston with the nearby town of Mount Pleasant via US Highway 17.
The main span of the new bridge is suspended by 128 individual cables between the support piers, which can hold more than one million pounds, or 500 tons each.
The design of the diamond-shaped towers incorporates the latest in seismic engineering considerations. Along with eight north/south traffic lanes, each 12 feet wide, the roadway will include a 12-foot pedestrian/bicycle lane.
A combination of public input, engineering requirements and the expertise of the world’s leading bridge and lighting designers were melded to create the stylish and functional structure.
When completed, more than 305,000 cubic yards of concrete will have been placed. Almost everything from the drilled shafts that support the main bridge pylons, to the 2.5-mile bridge deck and approaches are being pumped by equipment from Putzmeister. The equipment includes rented concrete boom pumps of every size from Pioneer Concrete Pumping Services’ fleet in Charleston. Pioneer Concrete is the exclusive pumping contractor for the project.
In addition to the rented pumps, crews are using a 55-meter and two, 38X-meter Putzmeister boom pumps sold to Palmetto Bridge Constructors (PBC), the general contractor. PBC is a joint venture of Tidewater-Skanska, of Virginia Beach, Va., and HBG Flatiron, of Longmont, Colo.
Brian Ballard, project superintendent for PBC said, “We consider Putzmeister the Cadillac of pumps. Because we put a lot of concrete through the equipment, we rely on their dependability and state-of-the-art technology. We chose Pioneer Concrete for their solid reputation and 24-hour local service and support for both the equipment we purchased and the equipment we’re renting. They go out of their way to service us and, therefore, we’ve been extremely satisfied.”
PBC poured 670 cubic yards of concrete, or the equivalent of 70 ready-mix trucks, to fill each of the 22 drilled shafts that support the bridges two diamond towers. Each of the shafts are 10 feet in diameter and extend 237 feet below the high water mark. Because it was impossible to drive 70 trucks out onto the Cooper River, barges were used to transport concrete to the construction site.
Concrete trucks brought the concrete to the water’s edge and poured it into the first of three hopper systems. Each funnel-shaped hopper can carry 125 cubic yards. The concrete in the land hopper flowed onto a specially designed conveyor belt and into a hopper set on a floating barge. ROTEC Industries, Elmhurst, Ill., manufactured these stationary conveyors.
Seven hopper loads of concrete were carried by barge out into the river channel to fill each of the drilled shafts that support the main bridge pylons. The hopper on the barge was brought to the drilled shafts, where a second conveyor belt was used to transport the concrete from the barge into a third hopper. The third hopper was fixed on a barge at the drilling site. From the fixed hopper, concrete was carried by another conveyor belt into a Putzmeister 55-meter boom pump, which filled the drilled shaft.
About seven hours were required to fill one shaft with an average of 100 cubic yards of concrete placed per hour.
Two of the bridge project’s largest pours to-date each required 36 hours of round-the-clock pumping using larger sized Putzmeister models – the 52Z and the 55-meter. These models were needed to pump the second stage placements of 4,150 cubic yards of concrete for each of the tower footings. The completed footings each contain approximately 6,000 cubic yards of concrete and are 80 feet wide, 110 feet long, and 18 feet thick at their widest point. In much the same way concrete was placed for the drilled shafts, it was necessary to bring the concrete hoppers to the middle of the harbor, convey the concrete using a conveyor and discharge into the pump for these large footings. Constructed in two stages, the concrete placement for both of the footings was completed in two weeks.
Along with filling the drilled shafts and cofferdams with concrete, a 55-meter Putzmeister pump is being used to pour concrete bridge columns and pier caps. The long reach of the boom pump is needed because of extreme heights involved.
The Cooper River Bridge project is so large that placing more than 1,000 yards of concrete daily is commonplace. And it is not uncommon to see up to five concrete pumps working at any given time. Construction remains on schedule.
Owner: South Carolina Department of Transportation
Engineer: Parsons Brinckerhoff, New York
Design/build: Tidewater-Skanska, Virginia Beach, Va., and HBG Flatiron,
Longmont, Colo. formed Palmetto Bridge Constructors (PBC) with assistance from Parsons Brinckerhoff
Ready-mix supplier: Wando Concrete, Charleston, S.C.
Pumping contractor: Pioneer Concrete Pumping Services, Charleston, S.C.
PBC Equipment: One Putzmeister 55-meter and two 38X-meter concrete boom pumps along with ROTEC Industries stationary conveyors with delivery hoppers
Pioneer Equipment: Putzmeister 52Z-meter, 46X-meter, 42X-meter, 36-meter, 32Z-meter and