Tappan Zee Bridge

Tappan Zee(Photo credit: New York State Thruway Authority)

New York’s largest-ever bridge project is on track for a successful completion after years of gestation.

By Jim Harris

For more than 10 years, the replacement of New York’s longest bridge seemed to be little more than a distant dream. That dream is now moving swiftly toward becoming a reality.

The last of the eight main span towers of the New NY Bridge, which will replace the Tappan Zee Bridge, were topped off in mid-December, marking the latest major milestone for the $3.98 billion project. The bridge project is the largest of its kind in the history of New York State and is one of the biggest ongoing bridge projects in the country.Tappan Zee info box

“Replacing the Tappan Zee Bridge with such a magnificent structure sends a powerful message to the world that nothing is too big or too difficult for the Empire State,” New York Governor Andrew M. Cuomo stated, marking the achievement. “The new bridge will be built for the ages and strengthen our region’s infrastructure for generations to come.”

The new 3.1-mile twin bridge is on track to open in 2018. Plans to replace the bridge were initially discussed in 1999, but the project didn’t move forward despite 430 meetings, 150 different discussed concepts and $88 million spent over a more than 10-year period.

Cuomo, with the support of President Barack Obama and the U.S. Department of Transportation, finally moved the project forward in October 2011. At that time, new design/build state legislation was enacted and a fast-tracked federal environmental review and procurement process were completed. Construction began in 2013 following the awarding of contracts. The state says “an unprecedented level of transparency and community involvement” with the project continues to this day.

The project’s design/build team includes several of the world’s leading design and engineering firms. The consortium – known as Tappan Zee Constructors LLC or TZC for short – includes engineering and construction firms Fluor, American Bridge, Granite and Traylor Bros. Design firms working on the project include HDR, Buckland & Taylor, URS and GZA. 

The TZC team is closely collaborating with employees from the New York State Thruway Authority. The Thruway Authority owns the Tappan Zee Bridge and its replacement. More than 6,300 people have worked on the project thus far, including nearly 1,700 subcontractors and suppliers.

‘A Vital Crossing’

The new twin-span crossing will replace the existing Tappan Zee Bridge, which was opened to traffic in 1955. The new bridge will feature eight lanes (four each in the eastbound and westbound direction) for general traffic, as well as four breakdown and emergency lanes, space for bus rapid transit and commuter rail, a bicycle and walking path with six viewing areas, cashless tolling and LED lighting.

Located 25 miles north of midtown Manhattan, the bridge crosses the Hudson River at one of its widest points north of New York City and carries much of the traffic between southern New England and portions of New York west of the river.

The bridge is part of the New York State Thruway mainline and carries traffic travelling on Interstate 87 and Interstate 287 between Rockland and Westchester counties.

“This is a vital crossing to the region,” Project Director Jamey Barbas says. “This is a heavily traveled bridge that is important to state commerce and the community. We need to rebuild because the existing bridge has become functionally obsolete; while safe, it doesn’t meet modern needs the way a new bridge would.”

The existing bridge handles an average of 140,000 vehicles daily, significantly above the 100,000 daily vehicle loads it was designed to handle. In addition, the bridge’s curved design, narrow lanes and lack of emergency shoulders has led to regular congestion as well as accidents, Barbas notes.

Support Systems

Eight 419-foot concrete towers support the new bridge’s two 2,300-foot cable-stayed main spans over the Hudson River. The towers, which stand at a five-degree angle, are more than 100 feet higher than the existing bridge and feature a sleek, chamfered design.

A total of 192 stay cables ranging in length from 190 feet to 623 feet will be installed on the bridge. The cables are anchored into the towers and are tensioned to carry the load of the roadway.

More than 220 million pounds of structural steel will be installed to support both spans. The project is using more than 300,000 cubic yards of concrete, most of which was produced on floating batch plants. More than 1,000 foundation piles were driven into the river to support the bridge, TZC says.

Stay cable installation began in July, and more than 80 cables are now anchored and tensioned. The cables are being installed as the balanced cantilever increases with sections of structural steel on alternating sides of the towers. The cables are comprised of high-strength steel strands packed in a protective sheath.

Roughly 90 percent of the bridge’s support structures have been completed, including the fabrication and placement of 126 steel girder assemblies that support the approach roadways.

More than 3,000 road panels, or roughly 3.4 miles of road deck, have already been installed on the bridge’s approaches. Each panel is 12 feet long, ranges between 22 and 45 feet wide is more than 10 inches thick.

Project Phases

With the towers now capped off, crews are looking toward the project’s next milestone: the completion of the bridge’s westbound main span bridge. Once that’s done, traffic on the existing bridge will be switched to the new bridge, TZC Construction Manager Bob Kick says.

That will allow TZC to demolish the existing bridge and finish the eastbound spans of the new bridge. During this stage, TZC will complete the piers and other portions of the eastbound span that overlap with portions of the existing bridge approaching the Hudson River. The eastbound bridge will open to traffic following this phase.

The final stage of construction includes finalizing the roadways leading to both spans of the bridge and completing the pedestrian/bicycle path.

A Collaborative Team

The TZC team and personnel from the Thruway Authority are located in the same office, making it easier for the teams to interact and share information throughout every phase of the project.

“The way our entities work together is truly the make-or-break proposition of this project,” Barbas says.

TZC and Thruway employees meet weekly to discuss issues facing the project as well as to share the latest project status and 3-D models. Building information modeling (BIM) is being used heavily on the project.

“The key is to have these conversations and good collaboration between all the related parties instead of handling in silos,” Barbas adds.

Collaboration between all of the project stakeholders has helped the team overcome a number of challenges. Perhaps the greatest of these is the project’s scope and timeframe.

“We’re trying to complete a large volume of work in just a short period of time,” Kick says.

TZC used precast concrete extensively during the early stages of the project to accelerate construction. The steel girders used on the project were assembled in a facility near Albany, N.Y., and then taken by barge to the work site. The girder assemblies range between 290 to 410 feet in length and have an average weight of 700 tons, he adds.

Pile Driving

All of the bridge’s steel piles are now installed in the river, including those for piers located beneath the existing bridge’s 30-foot clearance. These piles were driven after two panels of the existing bridge’s road deck were temporarily removed in an overnight operation. This gave crews more overhead space to use cranes and pile hammers, TZC notes.

The placement of the piles involved designing a floating cofferdam frame that acted as a template for the pier’s foundations. This cofferdam also gave the construction team a water-free workspace. The 12-foot-tall cofferdam was moved between two of the existing bridge’s piers and secured using mooring lines in shallow water near the shoreline. The cofferdam’s hollow form was then drained of water and prepared for foundation pile installation.

Pile installation occurred over the the course of one evening in April, during which lanes of traffic were closed to allow the removal of a portion of the existing deck. After the piles were successfully installed, the deck segments were reinstalled and lanes were reopened to traffic.

“The success of the operation was the product of careful coordination with the tri-state region’s state departments of transportation, the New York State Thruway Authority and TZC,” TZC said in a statement posted on the New NY Bridge website after the operation was completed. “Since the start of construction, similar collaborative efforts have resulted in remarkable solutions for the historic twin-bridge crossing, including the transition to cashless tolling and the installation of structural steel high above the Metro-North Railroad tracks near the Westchester shore.”

Monitoring Progress

The new bridge is designed and constructed to last 100 years without needing major structural repairs.

“We’re focused on quality, even on the smaller details of the new bridge,” Barbas says.

The bridge will feature a state-of-the-art structural health monitoring system, which includes a number of sensors and other instruments that help monitor seismic conditions and other movements as well as factors such as wind and temperature. The system is now being installed, and will be used in conjunction with BIM to monitor structural health.

“We can tell, for example, if the cables are not tensioned as they should be, and will be notified when the bridge isn’t functioning properly,” Barbas adds. “This information will help us protect our investment in a way we were unable to in the past.”

TZC and state officials are proud of the progress the project has already made, and are optimistic about its future.

“This bridge will truly be an iconic feature on the river,” Kick says.

Heavy Lifting

Tappan Zee Constructors (TZC) is using one of the largest floating cranes certified for U.S. coastwise operation to build the new twin-span Tappan Zee Bridge.

According to TZC, the Left Coast Lifter – dubbed “I Lift NY” – has a lifting arm of 30 stories and is capable of lifting 1,929 tons, “the equivalent of 12 Statues of Liberty.”

The crane is being used to lift large sections of the bridge that were fabricated off-site, and will also help remove the existing Tappan Zee Bridge. Quick facts:

  • Boom length: 328 feet
  • Boom width: 65.7 feet
  • Barge length: 384 feet
  • Barge width: 99.8 feet
  • Depth: 22 feet

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