By Neal Buccino, Media Relations Staff
For 85 years, the George Washington Bridge has stood majestically above the Hudson River’s swirling waters.
But ironically, the most insidious enemy facing the iconic span is water in another form — specifically, the gradual damage moisture can inflict by corroding more than 100,000 steel wires within its yard-thick main cables.
The bridge can’t escape the elements completely, given its river proximity. As part of a major Port Authority rehabilitation program called “Restoring the George,” however, it is soon to become only the third suspension bridge in America to receive the equivalent of a supercharged, water-fighting immune system.
The system to dehumidify the bridge’s main cables will employ a computer-controlled array of fans and tubes for a fairly simple purpose: to drive moisture out and keep it out by continuously pumping dry air through the entire length of the cables.
“This project is historic,” said Paul Crist, Assistant Director of the Port Authority’s Department of Tunnels, Bridges & Terminals. “The rehabilitation and upgrading of the main cables, and complete replacement of the suspender ropes, is a once-in-a-lifetime project – not just for the bridge itself, but for the engineers at the Port Authority.”
The bridge’s four main cables are each composed of 26,474 tightly bound, pencil-thick wires that stretch 5,235 feet between the New York and New Jersey anchorages. The dehumidification system will force dry air through the tiny spaces between those wires to absorb any trapped moisture before exiting through exhaust ports. An elastic polymer wrap will encase the cables to maintain a properly pressurized, dry atmosphere. Once in place, it will take approximately two years for air inside the cables to reach the target of 40 percent humidity – a level at which corrosion is greatly reduced.
“The George has served for 85 years as an important link for the regional economy,” Crist said. “This and other projects will keep it operating for future generations.”
Such dehumidification systems for the main cables of suspension bridges were introduced about 20 years ago in Japan after corrosion was found at several bridges that were less than a decade old. They have since been used across Europe and Asia, and have become a standard feature in new suspension bridges.
The practice of retrofitting these systems into older suspension bridges, however, is still new to the U.S. The 64-year-old Chesapeake Bay Bridge was the first to use a dehumidification a system, in 2014. The Delaware Memorial Bridge, at the age of 61, is the second, with a project currently underway.
The George Washington Bridge remains structurally sound, thanks to aggressive maintenance and extremely high standards used in its original design and construction. It opened in 1931 with just one roadway, although it was designed to add a lower level with four electric rail lines. The lower level, added in 1962, is much lighter than the planned rail bed and leaves much of the crossing’s strength in reserve.
Today, less than 1 percent of the main cables wires have any level of corrosion. But the new dehumidification system is an important investment in the future. It will coincide with the replacement, beginning next year, of all 592 steel suspender ropes that hang from the main cables to support the two road levels.
The bridge, the world’s busiest, is truly one of America’s great engineering marvels and a source of inspiration not only to architects, engineers and travelers, but writers and artists. Emily Dickinson was inspired by the invention of the suspension bridge. She compared their giant steel cables to a parent’s protective arms, and their strength to that of religious faith. Not needing intermediate supports, they are “pierless” as well as peerless, she wrote in 1855:
Faith – is the Pierless Bridge …
It bears the Soul as bold
As it were rocked in Steel
With Arms of Steel at either side …
For modern-day poets – and drivers — the new dehumidification process and other restorative measures envisioned by “Restoring the George” should ensure that sense of safety and security endures well into the next century.