Westchester-bound rush-hour traffic finally had its own span on the Gov. Mario M. Cuomo Bridge Wednesday morning, four days after its ribbon-cutting ceremony Friday. Crews were mobilized to proceed Friday evening until Terry Towle, Tappan Zee Constructors (TZC) President and Project Executive, made a safety decision.
“It looks like one of the members of the old Tappan Zee Bridge structure slipped in one of the joints,” Towle said during a media conference call with Project Director Jamey Barbas, P.E., Saturday afternoon. “(TZC) engineers investigated, and at 6:30 p.m., I thought it would be a problem and canceled the traffic shift at approximately 8 p.m.”
The old bridge was last inspected more than one year ago when plans were made for its disassembly. Dismantling of the old bridge will take through to the end of the year.
Safety zone established
Coast Guard Sector New York, notified around 7:45 p.m. Friday that TZC requested an emergency safety zone, closed the Federal navigation channel. The western (Rockland) side reopened Saturday at 12 noon, the eastern half is closed until further notice. Vessels may cross the area after checking in with the Coast Guard patrol commander enforcing the safety zone.
Boaters must check with the on-scene USCG assist via Channel 13 or Marine Radio – Channel 16 VHF-FM (156.8 MHz) to arrange transit. For information, call VTS New York watch supervisor at 71-354-4088.
Sunday night, Towle said TZC engineers determined the east anchor span “is damaged but currently stable with certain key components highly stressed.” There is a possibility it will fail, and if it does, then “it will fall within a (USCG-established) safety zone (south) that does not affect vessel traffic or the structural integrity of the new eastbound bridge.”
Dismantling a bridge
“The main span was part of a continuous truss. As the contractor demolishes parts of the truss they have to look at the loading conditions that remain to ensure stability,” explains Andrew Herrmann, partner emeritus of consulting engineers, Hardesty & Hanover.
Photo from an EarthCam construction camera of the old bridge.
A truss is a series of triangles made up of load carrying horizontal, vertical, and diagonal steel members held together at their intersections by large steel plates called gussets, says Herrmann. During demolition, when removing members of the bridge, loads in remaining members change and have to be checked to make sure no component is overloaded.
Additionally, some of the deterioration is hidden and not found until members are taken apart, he says. “Engineers try to prepare for all contingencies and generally have a series of demolition stages where they examine and prepare for the different loading conditions at each stage.”
Opened according to schedule
The eastbound span was originally scheduled to open August 15; however, the contract with TZC allows extensions that included delays caused by inclement winters and severe storms that made work conditions unsafe. Barbas told reporters at Saturday’s conference call, “TZC advised me and the governor’s office a while (three weeks, one month) ago that the bridge would be open to traffic on September 8.”
Andrew Cuomo’s Democratic challenger Cynthia Nixon commented last Friday that a “ribbon-cutting ceremony should not have been held if the bridge span was not yet safe. Nixon and Republican gubernatorial candidate Marc Molinaro issued erroneous statements, Molinaro claiming, “The closing of the second span of the new Tappan Zee Bridge due to safety concerns, just hours after its opening, is shocking.”
There was never a safety question about the new bridge’s eastbound span, which was ready to accommodate traffic last Friday night.