Long Road

Williamsburg Bridge Rehab Epic Close to End

A multicontract journey for the rehabilitation of the 103-year-old Williamsburg Bridge crossing the East River is edging toward completion as work continues on the eighth and final contract.

by Adrian MacDonald

After more than two decades of reconstruction work, the Williamsburg Bridge connecting Brooklyn and Manhattan is finally nearing the day when it no longer will wear layers of scaffolding.

Virtually every component of the 1903 structure, long neglected until the multiyear rehabilitation effort begun in the late 1980s, has been replaced or rehabilitated.

"The bridge was built for the pre-traffic era," said Hasan Ahmed, director of the city Department of Transportation's bureau overseeing the East River bridges. Now, the span is among the most heavily traveled in the city, with 100,000 vehicles on eight traffic lanes and 110,000 passengers each day on two subway lines.

While seldom spoken of in the reverent tones reserved for the famous Brooklyn Bridge to the south, the Williamsburg is structurally the strongest of the four East River crossings that the city agency oversees, said Terry Daly, senior vice president for Koch Skanska of Carteret, N.J., the contractor on the eighth and final phase of the rehabilitation effort. The city agency also maintains the Manhattan, Brooklyn, and Queensboro bridges.

Despite the Williamsburg's robust structure, it had fallen into disrepair over the years. There were even designs for a replacement bridge before the state Department of Transportation, which oversaw the bridge until about 1989, let the first rehabilitation contract in 1987.

The state oversaw the first three contracts, before the city transportation agency took over and issued four additional contracts in the ensuing years that totaled $741 million in construction costs and involved a rehabilitation of the cable suspension system; reconstruction of roadways, piers, and columns; and replacement of subway tracks, signals, and power systems.

Work on the $173 million final contract began in early 2003 with Koch Skanska, a unit of Skanska USA Civil of Whitestone, N.Y., tasked with strengthening the bridge's main steel support structures.

While Koch Skanska achieved substantial completion earlier this year, steel repairs, smaller seismic upgrades, and reconfiguration of lanes and dividers to introduce a new traffic flow system will keep the contractor busy for another year.

The Williamsburg is unique among suspension bridges worldwide because it has suspender cables only on the main span between the towers. Its outer end spans independently rely on supporting piers - an oddball design that has required various fixes over the years, including work in the current final contract. A more conventional design would use suspension cables for the whole bridge.

The uniqueness lies in a miscalculation by the original engineers, who chose to support the end spans independently in an attempt to save money, Daly said.

But when the original bridge construction finished, its designers realized the end spans weren't strong enough. They added two more intermediate piers - forfeiting the anticipated savings, Daly said.

"If you took away the rest of the bridge, each end span would stand alone as a bridge unto itself," he added.

The final contract's extensive work on those piers could have taken only eight months instead of the planned 4.5-year schedule if the city had the luxury of closing the bridge, Daly said. But the flow of vehicle and train traffic has been maintained throughout.

"Anywhere outside New York City it's cheaper to close the bridge," Ahmed said. "But here you have the user cost. Closing the bridge just isn't an option."

The contractors also didn't have the luxury of time. Unlike previous contracts on the bridge that offered bonuses for contractors to complete work ahead of schedule when tasks involved all-day lane closures, the final contract only involves offpeak closures - and thus no incentives. But all contracts, including the current one, apply penalties if the team does not hit project milestones on schedule.

"There were seven different liquidated damage penalties in the contract and no incentive bonuses," Daly added.

advertisement

Shoring Up with New Steel Work

The final contract has focused on the steel support structures in the main towers, end-span piers, and stiffening trusses. It also has miscellaneous work such as adjusting and upgrading cables, painting trusses, and renovating "comfort stations" on the pedestrian walkway.

Rehabilitating the main towers was a primary chore. Over the course of a century of increasing loads, stress on the tops of the towers - which support the main suspension cable - had bent them inward toward the bridge center, Daly said.

While it would have been cheaper to replace the towers, that would have required closing the span, Ahmed said. Instead, the engineering team devised a way to strengthen the towers with steel plates.

The design placed the steel plates on the river-facing side of the main towers to compensate for the compression load. It also called for "pre-loading" the steel by having the installers curve each plate outward in the center by 4 to 6 in., then bolt them incrementally from the outside toward the middle.

"That helps engage some of the compression load earlier," Daly said.

Koch Skanska custom-cut every plate for its location, using wood templates. To get the plates into place, the team had a crane lift them in pairs weighing about 3,000 lbs. to a hoist and delivery track system built on the side of the towers. The plates had to match 21,000 existing rivet holes.

Another major feature was work on the intermediate piers. The design team found it could completely replace these piers without disrupting traffic by cautiously removing only a few steel members at a time. However, the bridge's unusual design required special attention to the main bearings, which are located under the roadway inside the main towers.

"Koch Skanska does a lot of bridge bearing work, and this is definitely the most complicated bearing we've ever worked on," Daly said.

The bearings and main river piers for the end spans are located in the same towers that anchor the suspension cables for the center span, Ahmed said.

To support the bridge structure during the process of replacing the original bearings and river piers with larger and stronger ones, ironworkers constructed a temporary jacking tower around each pier inside the main towers. The temporary tower allowed crews to jack up the bridge surface just enough to "see daylight" and replace the bearing, said Douglas Reese, resident engineer on the project with Greenman-Pedersen of Babylon, N.Y.

"The drawings only give theoretical load numbers for the bearings," he added. "But the actual load differs. You measure as you go. We have gauges on all the temporary jacks to measure pressure in the jack and determine the actual load at the bearing location."

The new multirotational pot bearings have sliding capability, which can counter seismic movement in the bridge joints, Reese said.

Many Tasks Beyond Heavy Lifting

While ironwork formed the heavy part of the final contract, the single biggest task in terms of budget was a $50 million repainting effort on two stiffening trusses, Daly said. The 2,800-ft. long steel support trusses run the length of the bridge on either side with X-shaped members.

Daily said the painting job required sandblasting of existing lead paint and dust containment to meet environmental regulations through a complex network of tarps on scaffolding and a vacuum system that created negative air pressure in the work area. The system had 11 compressors with a combined capacity of 18,000 cu. ft. of air per minute.

The containment system also required closing lanes on either side of the truss, cutting the bridge's traffic capacity in half.

"The trusses are built tight to the road," Daly said.

The city gave the contractor 176 days to blast and repaint both trusses, with a liquidated damage penalty of $50,000 for each day it fell behind schedule. The team ran a 24-hour, 7-day-a-week schedule, and ultimately finished nine days early.

Key Players

Owner: New York City Department of Transportation

General Contractor: Koch Skanska, Carteret, N.J.

Resident Engineer: Greenman-Pedersen, Babylon, N.Y.

Designer: Parsons Transportation Group, New York

Engineering Consultant: Siefert Associates, Naugatuck, Conn.

Steel Fabricator: Michelman-Cancelliere Iron Works, Bath, Pa.

Steel Erector: Northeast Structural Steel, Yonkers, N.Y.

Electric Contractor: Welsbach Electric, College Point, N.Y.