Completed in 1936, New York City's Triborough is a mature bridge now undergoing a multi-year, multi-million dollar reconstruction project to ensure many more years of service to the eight lanes of traffic that throng it daily. The giant bridge connects the boroughs of Manhattan, the Bronx and Queens, with its three arms meeting on Randall's Island.
The Triborough Bridge and Tunnel Authority (TBTA), part of the Metropolitan Transportation Agency, is responsible for the Queens Midtown Tunnel, as well as the Verrazano, Throgs Neck, Whitestone and Marine Parkway bridges--all means of access and egress between boroughs within the city. The TBTA has its own maintenance and engineering divisions, and supports its work by collecting tolls on the bridges and tunnels.
Serving the Queens
For manageability, the TBTA bid and let the massive reconstruction project in a number of sections. Contract TB 64A covers a complete deck replacement on the suspended span of the main line of the bridge, which encompasses the suspended span from Wards Island to Queens. The suspended span involves 250,000 sq ft of new orthotropic deck with multicoat aggregate-filled polysulfide epoxy overlay--some 392 panels averaging 101/2 x 60 ft and weighing about 15 tons apiece. Anchorage and viaduct decking adds up to an additional 250,000 sq ft of precast panels.
The general contractors for contract TB 64A redecking of the suspended span and Queens Viaduct portion is a joint venture between American Bridge Corp. and Koch Skanska. They construct and rehabilitate bridges and other support structures for transportation agencies. Both companies have extensive orthotropic deck experience, Koch with the Throgs Neck Bridge and George Washington bridges in NYC and the Ben Franklin Bridge in Philadelphia, and American Bridge with NYC's Williamsburg Bridge.
The job was bid in November 2000. American Bridge/Koch Skanska won the bid with an original contract amount in the neighborhood of $147 million and received a notice to proceed in December 2000. Construction began in March 2001, with change-out of suspended cables and procurement of new deck materials.
All structural steel for the viaduct and the orthotropic steel plates came from Hyundai Corp. in Korea. The first shipment arrived at Port Newark in January 2002 and the fourth and final shipment arrived in October 2002. From Port Newark, the orthotropic deck panels were trucked to Bridgewater Protective Coatings Inc., Bridgewater, N.J.
Dressing in layers
Specifications required the orthotropic panels to be sandblasted and then protected with a multicoat aggregate-filled polysulfide epoxy overlay riding surface. Both American Bridge and Koch have their own steel fabrication facilities, but for work of this complexity it was preferable to employ a company with broad experience in working with epoxies and other high-tech coatings.
Bridgewater Protective Coatings Inc. was selected to do the work--a $2.8 million contract for the 392 deck plates--because of its extensive experience in coating application. The company has excellent facilities to receive a large order and process it quickly, including blasting equipment, a 100,000-lb gantry crane for material handling in the yard and a 40,000-lb indoor crane capacity. BPC was able to provide temporary storage for up to 200 panels as they came through from Korea, and applied the coating six panels at a time.
The company was familiar with the specified coating system, having applied this and other test coatings to the prototype project in 1997 for another segment of the Triborough undertaking, which led to contract TB 64A.
The epoxy was supplied by Transpo Industries, New Rochelle, N.Y., and the aggregate by 3M.
BPC employed the Low Modulus Polysulphide Epoxy Overlay T-48 coating for the Triborough Bridge. The resin comes in two components--T-48A resin and T-48B hardener. Thorough and complete mixing of these two components is vital for uniform curing and performance. Parts A & B were mixed together in a 2:1 volume for 2-3 minutes using a Jiffy mixer powered by a low-speed (400-650 rpm) electric drill until the blend was uniform.
The epoxy overlay was applied in a three-coat, 3/8-in. application. The first coat of resin was applied using notched squeegees or rollers at the rate of 40-50 sq ft per gal on the prepared surface. Immediately after the resin application, a very light broadcast was applied to break any air bubbles that may have formed during the priming process. A heavy broadcast then was applied after 15-20 minutes until refusal. Standard basalt was used as a cover aggregate.
After the first coat was set, the second and third coats were applied at a rate of 20-25 sq ft per gal. Broadcast aggregate was applied at approximately 11/2 lb per sq ft.
Ease of use
The contractor began removing and replacing the existing deck in May 2002. Where applicable, installation of precast deck speeds up construction. The bridge carries eight lanes of traffic, and only one lane can be closed at a time. Precast panels, with structural steel framing cast into the concrete riding surface, are relatively easy to put in place while maintaining seven lanes of traffic.
For improved drainage, the suspended span of the bridge is being elevated using the new orthotropic deck. The new deck plate will be 4 in. higher than the existing roadway at the curb-line; at the center of the span it will be 8 in. higher than the existing deck.
Three overhead DeMag cranes are used for changing out the deck panels on the suspended span. The 30-ton-capacity cranes span the eight lanes--more than 95 ft--allowing excellent flexibility in moving the deck panels and accessing the job. One is employed on each back span and one on the main span of the bridge.
The replacement project is set in eight stages starting from the Queensbound side of the bridge and working across to the Bronxbound side. The scheduled completion date of April 2004 may be accelerated by combining stages. The contractor has already been successful in combining stages 1 and 2 while keeping seven lanes open for traffic, and hopes to combine 3 and 4. Stages 1 and 2 were completed in January 2003, with all work accomplished during a daylight shift, 7 a.m. to 3:30 p.m.
