The Ben Sawyer Bridge, built in 1945, is a swing bridge on SC 703 in Charleston County that spans the Intracoastal Waterway and connects Mount Pleasant and Sullivan’s Island. As a local icon that represents simpler times, still pleases aesthetically and has been tossed around by Hurricane Hugo, it was decided that the Ben Sawyer Bridge would be rehabilitated so that its appearance and current right of way remain the same.
PCL Civil Constructors, Inc., Tampa, Fla., began construction of the Ben Sawyer Rehabilitation project in February 2009. The $31.5-million design/build contract, approved by the South Carolina Department of Transportation (SCDOT), is funded by federal money from the Federal Highway Administration. Hardesty & Hanover LLP, New York, N.Y., is providing the bridge and seismic design as well as design management. Parsons Brinkerhoff PCL (PB Americas Inc.), New York, N.Y., is providing construction management services.
The project consists of replacing the approach spans to the bridge, replacing the steel superstructure on the swing span and replacing the electrical and mechanical systems.
According to Kimwood Partenheimer, Parsons Brinkerhoff’s consultant to SCDOT and resident construction engineer, “The new bridge will be similar to the existing bridge in design and height with slightly wider traffic lanes.” The lanes and the sidewalk are being widened to improve safety for vehicles and pedestrians alike.
Keeping Similar Dimensions
To be exact, the bridge will remain close to its 1,154-ft. (351.7 m) length, but it will have the wider 14-ft. (4.26 m) traffic lanes instead of 11 ft. (3.35 m). Also, one side of the bridge will have a 5.5-ft. (165 cm) wide sidewalk as opposed to the original 2.5-ft. (75 cm) sidewalks on each side of the bridge. When the bridge was built in 1945, rivets were commonly used but rivets are no longer acceptable for construction. In order to preserve the aesthetics of the original Ben Sawyer Bridge, the contractor will be using rounded head bolts that will actually look like rivets.
“It will look like the old bridge,” Partenheimer explained, “except it will be brand-spanking new.”
The bridge deck for the new swing span is composed of lightweight concrete and steel grating. The approach span deck and sidewalk will be made with conventional reinforced concrete deck using lightweight concrete. The swing span’s improved sidewalk will contain solid aluminum deck panels and a steel railing system, which will be similar in appearance to the existing bridge.
Also similar to the existing bridge is the new control house, which will be located above the roadway at the same location and will be an octagonal design reminiscent of the original control house. However, the new space will be larger to allow for maximum views for the controller, a new bathroom and new electrical equipment space.
Watching Out for the Wildlife
The project site consists primarily of marsh, also known as wetlands. In fact, the steel and concrete swing span, which traverses navigable water, is only 245 ft. (75 m) long. The bridge construction consists of a north abutment, six approach spans, the swing span, six more approach spans and a southern abutment. The approach spans carry the bridge over the marsh, which is more tidal water, and the swing span carries the bridge over the navigable water, which is the Intracoastal Waterway.
In order to lessen the impact on the environment and to reduce costs, the new bridge is being rehabilitated on the existing alignment and using existing concrete pier foundations. New seismic isolation bearings, however, will be mounted on the existing concrete piers. There will be no need for a new right-of-way, and there will be just a slight shift in the road’s center line. Another environment precaution is that the contractor is not allowing any type of fill to be placed in the wetlands area during construction. Additionally, the new swing span is being constructed off-site at the Naval Shipyard in North Charleston, which also will reduce impacts to the wetlands
An access trestle is being used during construction to minimize environmental impact and allow the daily tides to pass through the construction zone. If by chance any marsh areas are impacted by the access trestle, the contractor will return the marsh to its original contours, re-vegetate where needed, and monitor the site’s progress subsequent to construction.
The trestles are a main component of this project. Four temporary work trestles were completed in June. The two eastern trestles are being used to assist crews that are installing the new bridge fender system. The two western, or harbor side, trestles are used by crews placing pilings between the trestles and the existing bridge. The replacement bridge approaches will be built upon these temporary pilings.
In addition to the four trestles, workers are making use of temporary approach spans/trestle combinations on both east and west sides. For example, east side workers are using the temporary trestles for moving equipment needed for construction of the fender system. Once the fender system is complete, PCL Civil Constructors will convert the trestles to temporary approach spans. The combination span/trestles also will be used to build the new approach structures.
Sleight of Hand
At some point, there will be a seven-day closure of the bridge to all types of traffic, which is when the contractor will replace the east and west approaches, the swing span, approach slabs and the approach roadway. During this 24-hour workday schedule, a barge will bring in the steel superstructure, which will be lifted into place over the existing bridge pieces. Using a jack, lift and roll system, the existing bridge will then be rolled onto the eastern trestle, which will allow workers to roll the new replacement approaches into place. Partenheimer described it as a parallel movement: “Move both of them at the same time to the east-shifting bridges to the east.”
The actual date of the seven-day closure, according to Partenheimer, will not be known “until the day it happens.” “Maybe sometime in early November — can’t zero in on a date yet,” he said.
Before June 22, the bulk of the work on the project was on the temporary trestles and temporary approaches. Now, permanent work is underway on the fender system. Subcontractor, Freck Enterprises, Cocoa, Fla., is using the eastern trestle to install the new bridge fender system. The fender system is designed to protect the concrete pier that supports the swing bridge span from being accidentally struck by boat traffic. Freck will drive new timber piles and add two rows of 8 by 12 in. (20 by 30 cm) horizontal strakes. Once these items are in place, the old fender components located directly behind the new timber will be removed. Also, when the strakes are in place, Freck will be able to install the rest of the support structure for the fender system, which includes access decking for maintenance personnel.
To assist with removing and replacing the fender system, Freck has brought in a 50-ton (45 t) Bucyrus Erie 30 Super B crawler crane on a 30 by 120 ft. (9 by 36 m) barge. This crane/barge combination will support workers removing the existing timber piles, supports and decking, and constructing new timber piles, supports and decking. The Intracoastal Waterway will not be closed for Freck’s work, but the width of the channel will be reduced.
“PCL is still in the process of completing the work on the temporary approach spans located on the west side of the existing bridge,” stated Partenheimer. “These final preparations are being made in anticipation of the first girders arriving on the project July 21.”
Once these girders arrive in July, the contractor will install them on the west side, as well as work on beams, rebar and the concrete for the new deck. Twelve girders in all will be shipped via tractor trailer from the supplier in Florida.
Currently, besides the actual field work, the final design plans are being finished along with a number of “shop drawings.” Partenheimer added, “Fabrication of electrical, mechanical and structural components is ongoing at several locations in Florida, Alabama and Pennsylvania.”
PCL will be self-performing most of the construction. In addition to Freck, subcontractors will be used for earthwork, construction signage and asphalt paving. No decision has been made yet on whether or not a subcontractor will be hired to place the reinforcing steel in the bridge decks.
So far, PCL has used a vibratory hammer and a diesel hammer to drive the temporary pipe piles that support the temporary trestles and temporary approach bents. Presently, PCL has two Manitowoc 4000 150-ton (135 t) crawler cranes situated on the north and south trestles. The contractor also is utilizing a JLG rubber-tired 4WD fork lift to offload deliveries of timber, and there are two 60-ft. (18 m) personnel lifts being used, a JLG and a Genie.
After the seven-day closure period, the demolition phase will begin. During this time, workers will finalize construction activities and dismantle the old swing span for removal. Everything should be wrapped up in time to meet the completion date of May 2, 2010. CEG
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