When Tappan Zee Constructors (TZC) completed the Mario Cuomo Bridge project, they anticipated the bridge would have a lifespan of 100 years.
Instead, the $4 billion bridge that replaced the Tappan Zee Bridge in 2017 is allegedly experiencing structural issues related to its stay cables and anchor pipes. According to the New York State Thruway Authority (NYTSA), 61 of the bridge’s 192 stay cables and anchor pipes need retrofitting with steel sleeves to make them durable enough to withstand the load of the 50 million vehicles that traverse it annually.
It is important to note that there is “no immediate danger to users” of the bridge. However, for the cable-stayed bridge to meet its 100-year lifespan, according to NYSTA, the cables and anchor pipes need to be strengthened. On August 22, 2024, the NYSTA filed a $6 million lawsuit to require TZC to pay for the required retrofitting, claiming that TZC is in breach of contract for refusing to complete the retrofit after the initial anchoring & cable work was deemed unsuitable following an independent safety review of the bridge. The NYSTA has already begun preparations for the retrofitting process, which is expected to take three years.
What is a Cable-Stayed Bridge?
In a cable-stayed bridge, the weight of the deck is supported by diagonal cables, in tension, attached to vertical towers (one or more). The towers allow the force of the cables’ tension to travel through the tower foundations into the river, lake, or seabed below using vertical compression, while the cables’ tensile force hold the deck via horizontal compression.
Cable-stayed bridges have gained popularity in recent years due to their affordability and speed of construction. They require “much less steel cable and use more precast concrete sections, which accelerates construction,” according to municipal bridge sources like the Port of Long Beach, home of the Gerald Desmond Bridge.
“Cable-stayed bridges are far less costly for road-deck lengths of 500 to 3,000 feet and they can be built in far less time.” – The Port of Long Beach
What is the Difference Between a Cable-Stayed and Suspension Bridge?
The main differences between cable-stayed and suspension bridges are how the cables and towers work to transfer tension to bear/transmit loads and the deck span range they can support.
In a suspension bridge, like the Golden Gate Bridge, for instance, transmission starts at the deck and travels to the suspender cables, which transfer the load to the main cable. The main sends it to the tower(s), and then through the foundation. The suspension structure can support bridge spans up to 6,651 feet (2,000m) with a deck span to deck length ration of 1:40 to 1:200.
In a cable-stayed bridge, like the Mario Cuomo Bridge, the transmission path is different: the load starts at the deck, then onto the suspension cables, to the tower(s), and the foundation. The cable-stayed structure can support bridge spans up to 3,280 ft. (1,000m) with a deck span to deck length ratio of 1:100 to 1:200.
Anchoring Bridge Cables Safely
In both cases, if a cable or anchor needs to be replaced or repaired, a concrete scan of the bridge deck and tower must be completed before cutting and coring concrete, or affixing new anchors, to be sure that any cuts will not impact structural reinforcements like conduit or rebar. The tension on a single cable in a cable-stayed bridge can vary from hundreds to several thousand tons, depending on the specific bridge geometry and engineering. Cables are usually designed to bear far more weight than the everyday conditions they will experience, in case of failure.
Mitigating the risk of accident or injury while working with cables of this size is vital to the success of a project. GPRS offers 99.8% accurate concrete scanning and is home of the industry’s only Green Box Guarantee. That means if we mark an area on your slab “clear” inside a green box and you hit a reinforcement inside that area, we will pay the material costs to repair the damage. Period.
GPRS Intelligently Visualizes The Built World® for customers nationwide. What can we help you visualize?
GPRS sponsors Concrete Sawing & Drilling Safety Week each January. To learn best practices about concrete cutting, coring, and drilling – on bridges, in high-rises, or in post-tensioned slabs – register your team for a free CSDSW talk today.
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