Fourteen contracts will be let before rehabilitation of this 98-year-old suspension bridge becomes complete.

by Jamey A. Barbas, Jay A. Patel, and Frank X. Progl

The bridge has a 1,600-ft. main span supported by four main cables and two 596-ft. side spans independently supported on three intermediate towers. The New York City bridge carries eight traffic lanes, two heavy rail transit tracks, and a pedestrian footwalk, and is a major truck route between Manhattan and Long Island. A major reconstruction of the transit structure has recently been completed. This project involved an unusual transit shutdown and successful early completion.

The New York City Department of Transportation awarded the Design and Construction Support Service contracts to the Parsons Transportation Group - Steinman. The reconstruction of the transit structure, called Contract 6, is the third major rehabilitation contract of the Williamsburg Bridge. Contract 6 follows the rehabilitation of the cable suspension system (Contract 4) and the rehabilitation of the south roadways on the main bridge with a new steel orthotropic deck and total replacement of the long approaches of the south roadways (Contract 5). The rehabilitation of the north roadways is currently underway (Contract 7), and a final Contract 8 is in the process of design and will primarily include tower rehabilitation.

For Contract 6, extensive input was received from the New York City Transit during the design stage, and the New York State Department of Transportation provided quality assurance oversight for steel fabrication and erection. The construction inspection was performed by GPI. The contract was awarded to the joint venture, Koch/Nab, for $130 million.

Two BMT transit tracks carry the J, M, and Z subway trains across the Williamsburg Bridge. Approximately 90,000 people per day use these trains, which are a vital link in the city’s transportation network. The main challenge of this contract was to perform all the work that required a shutdown of subway service within a five-month window. The cost of the work scheduled to be performed during shutdown exceeded $80 million.

Various measures were successfully implemented to provide alternative transportation to the subway riders during the transit shutdown. Frequent bus service across the bridge between the Marcy Ave. station in Brooklyn and the Essex St. station in Manhattan was available. Additional buses also provided connections at the Marcy Ave. station to the A and C and the L and G subway lines in Brooklyn, which provide alternative routes into and out of Manhattan. An extensive public information campaign, similar to the one successfully implemented at the closure of the south roadways in Contract 5, minimized disruption to transit riders as much as possible.

Due to the critical nature of the project, many special features were specified to help ensure that the construction schedule would stay on track. A penalty of $100,000 per day, and an equally large incentive was provided for the on-schedule completion of the transit shutdown work. Additional measures were included in the contract requirements to minimize the chance of delays during this critical time. Such measures included a partial payment for steel and transit equipment pay items as soon as shop drawings were approved (as an incentive for their early completion), the requirement for a large portion of the steel and long-lead system components to be delivered to the site as a condition to allow the shutdown to take place, and a requirement for two independent surveys of the existing steel structure on the suspension bridge and the anchor bolts on the existing piers, to minimize fit-up problems during erection.

The contractor completed the milestone work 35 days ahead of schedule, thereby returning train service to the public over a month early and collecting an incentive of $3.5 million.

On the approaches, the new transit substructure consists of single concrete pier stems with steel box pier caps. The concrete pier stems were constructed during Contract 5 to accelerate the reconstruction of the bridge. The foundation, stem construction, and architectural detailing of these piers are similar to the ones used for the south approach structure. Steel pier caps were secured to the concrete stems by tensioning anchor bolts installed during the stem construction. Using steel pier caps allowed for a shorter shutdown duration than concrete pier caps would have.

The superstructure is composed of four parallel steel girders, each located below a rail, on simply supported spans ranging between 87 and 131 ft. The girders have constant depth ranging between 6.5 and 7.5 ft. The new open deck consists of timber ties and bolted splice rails. Access platforms were provided underneath the girders to facilitate inspection and maintenance.

In the main bridge, the existing stringers and pedestals were replaced in kind. However, to avoid the stringer cracking pattern noticed during the inspections of the original structure, the new stringers are aligned closer to the rails. The floor-beam rehabilitation consists of the addition of web reinforcement plates. The connection of the vertical hangers that transfer the loads from the floor-beams to the main trusses through overhead transverse trusses were retrofitted by installing additional splice plates and replacing deteriorated rivets with H.S. bolts and adding new H.S. bolts to extend its fatigue life.

As an add-on to Contract 6, the truss bearings at the intermediate towers will also be replaced. The new bearings feature a single large roller to minimize longitudinal forces transmitted to the towers. The rollers and the upper and lower bearing plates have helical gear teeth to prevent them from becoming misaligned or falling off in case of extreme uplift, and to incorporate some lateral force resistance.

Although major improvements to the existing bridge were made throughout the design, the substandard width of the roadways and substandard clearances between train tracks could not be altered at the tower locations, where the roadway passes through the existing tower legs. The horizontal train clearances between the two sets of rails and between the rails and roadway traffic on the bridge are therefore tighter than normally designed for new NYCT construction and required innovative solutions to overcome the existing substandard structural clearances. Certain measures, however, were used to maximize the safety of highway and transit way alike.

While modern safety roadway barriers installed during the previous contract were wider than needed at the time, safety niches and additional protective channels were specially designed to maintain or improve the existing clearing up room for NYCT maintenance personnel.

Signal, power, and communications cables, previously supported by messenger cables, are now enclosed in tamper-resistant cable trays hidden at debris shield level between the track girders. Ladders provide maintenance access from track level.

Tighter clearances meant that the contact rails for the two tracks are too close together to step between them and too far apart to step over them safely. New crossover steps between the two sets of tracks, developed by NYCT, provide safe crossover from one track to the other for NYCT maintenance personnel.

Despite the extremely tight existing clearances on the main bridge, access ladders and platforms for signal maintenance were designed to conform to OSHA and ANSI requirements. The previous signal ladders were not OSHA compliant and provided no platform for signal maintenance.

Write 5003 on ROADFAX card for more information