Tappan Zee Bridge – East Anchor Span

THE ISSUE

Although CDI had successfully felled dozens of bridges and other structures in New York City and State over the last 60 years, the New York State Thruway Authority chose the conventional dismantling methods proposed by Tappan Zee Constructors (TZC), a Joint Venture between American Bridge, Fluor, Granite and Traylor Brothers, to remove the Tappan Zee Bridge for reasons related specifically to this project.

During the dismantling of the cantilever truss main span over the Hudson River channel, both lower chords of the East Anchor Span separated from their pin connection to the kingpost and dropped, causing the emergency evacuation of iron workers from the span itself and creation of an Exclusion Zone around the unstable structure that reached halfway across the Hudson River channel.

Following a drone inspection of the structure and conversations with their bridge engineer of record on the project TZC determined their management personnel and Union workers would not be permitted to either approach or access the span for both safety and legal reasons under New York labor law.

PROJECT PLANNING

Given American Bridge’s and the other Joint Venture members’ prior experience with CDI on other bridge demolition projects, and CDI’s perfect demolition track record with the State and City of New York, and specifically, the New York Fire Department’s Explosives Unit, CDI was asked to provide an informed opinion on how the structure could safely be lowered into the Hudson River for removal. CDI’s opinion was to include interface with Governor Cuomo’s office, which CDI had worked with on several previous bridge demolition projects. The State of New York and the Governor were particularly interested given the proximity of the new Governor Mario M. Cuomo Bridge just 50’ to the north of the structurally failed, yet standing, Tappan Zee East Anchor Span.

In parallel to discussions with CDI, TZC worked with Resolve Marine Group, Inc. (Resolve), an international, blue water salvage company to develop a span retrieval program. Using methods they had perfected raising sunken ships, worldwide, a plan was developed by Resolve to lay anchor chains on the bottom of the Hudson, perpendicular to the longitudinal axis of the anchor pan. If CDI could fell the anchor span onto those chains, in an upright position, Resolve would be able to use its proprietary salvage equipment to lift the span and relocate it for salvage or disposal.

Under its subcontract with Resolve, CDI and its third-party consultants moved quickly to perform a finite element analysis of the failed, yet standing, East Anchor Span and a real-time structural monitoring program to ensure safety of personnel during preparation operations. CDI developed an explosives plan that would safely remove the four (4) massive steel support towers under the east/west piers to bring the span down vertically, onto the chain retrieval system.

“After a good inspection, the felled truss is in a great condition for follow-on salvage – mostly intact, upright, and resting nicely on the chains, between the piers.

It has been a pleasure working with CDI to achieve a successful conclusion to the felling operation on a very dangerous anchor span. I look forward to the next opportunity to do so!”

Todd Schauer, Director of Operations – Resolve Marine Group

CDI’s crews first performed pre-shimming of the lower chords to the top of the steel-bent piers to reduce the damaged span’s response to wind and temperature changes. CDI then performed preparatory burning, placement of explosives and positioning of at-source protection to prevent fly of material that might damage the new Governor Mario M. Cuomo Bridge. CDI personnel drained fuel from equipment stranded on the anchor span deck and pre-removed items of safety or environmental concern from the deck so they would not release contaminates into the already environmentally challenged Hudson River.

DETONATION

The structure was shot on January 15, 2019, as soon as boat traffic in the adjacent Hudson River channel had been halted and traffic had been cleared from the new Governor Mario M. Cuomo Bridge to permit placement of seismographs to document peak air overpressure and vibration impact of the demolition on the new structure.
The felling of the span went exactly as planned with the span landing upright on Resolve’s chain retrieval system. There was no damage to the adjacent Governor Mario M. Cuomo Bridge. The Hudson River channel was opened to traffic and Resolve was able to lift the fallen span, per plan, clearing the way for TZC to continue with conventional demolition operations on the balance of the bridge, as planned.

Click HERE to watch the Tappan Zee Bridge-East Anchor Span implosion.