Belle of Liberty

Letting Freedom Ring

Monday, October 24, 2011

Happy 80th, George Washington Bridge

I like to think of the George Washington Bridge as “my” bridge.  I remember crossing it countless times when my mother would bring us into New York to visit friends, the museums, and the dentist in Queens (!).  I remember crossing it on a classtrip in the 7th or 8th grade to visit the World Trade Center.

I’ve used it as a backdrop countless times for photos of our sales representatives for our company’s regional magazine.  But we became best friends when we noticed some unusual activity while taking one set of photos.  Nothing ever came of it, thank God.  But the GW knows I’ve got its back.

The governors of New York and New Jersey proposed, as early as 1906, a bridge over the Hudson River between 179th Street in Manhattan and Fort Lee.  The governors appointed an Interstate Bridge Commission for the purpose of constructing one or more trans-Hudson bridges.

The Commission reported that the 179th Street crossing was the most economical, being the narrowest part of the river, with comparatively little land damage on either side.  The approaches overland are short.  The foundations, boring into the rock of the Palisades, was considered to be sound.  Furthermore, the channel span need not, in the engineer's opinion, be over 1,400 feet, allowing enough passage for all river traffic, the north limit anchorage for large vessels being below this crossing. From the geological condition, the engineer estimated the projected the cost would be about $10 million dollars, one-third the cost of a bridge lower down the river.

One of the great bridge builders of the early 20th century, Gustav Lindenthal, dreamt of constructing a Hudson River bridge from midtown Manhattan to New Jersey. Lindenthal's Hudson River Bridge was designed to connect rail lines in New Jersey with those in New York City and New England.  Part of this rail link was completed in 1916, when his Hell Gate Bridge opened over the East River.

A protege to Lindenthal, Othmar Ammann, who would become synonymous with mid-20th century bridge design, opposed his superior's idea. Ammann argued that the Lindenthal plan would require expensive approaches in already congested midtown Manhattan, which would be politically controversial.

Instead, Ammann pushed for a Hudson River Bridge between 179th Street in upper Manhattan and Fort Lee, which would accommodate both motor vehicles and light rail.  The bridge’s location would be at high points in Manhattan and New Jersey, allowing enough clearance for tall ships without extensive approaches.  Furthermore, the location was at a relatively narrow point on the Hudson River, simplifying construction.  Ammann believed that the crossing would be an easier political sell, since it would require neither the approval of influential business leaders in midtown Manhattan nor the necessity of persuading railroads to use the bridge.

Facing internal opposition, Ammann struck out on his own, joining forces with newly-elected Governor George Silzer of New Jersey. The new bi-state Port Authority had given lukewarm reception to motor vehicle projects, but thanks to the persuasion of Ammann and Silzer, there was enough support on both sides of the Hudson to construct the proposed bridge.  In 1925, the Port Authority agreed to take responsibility for constructing the bridge, and employed Ammann as master bridge designer and chief engineer.  Cass Gilbert, the designer of the landmark Woolworth Building, provided architectural assistance to Ammann at the new agency.

Soon after the Port Authority announced the Hudson River bridge project in 1925, Ammann commissioned consultants for various designs.  Initial plans devised by the Port Authority and the Regional Plan Association (RPA) called for a suspension bridge with a 2,700-foot-long main span, with piers approximately 400 feet beyond the pierhead lines.

The final design of the proposed bridge posed an engineering challenge for Ammann. Its 3,500-foot-long main span would be twice that found on any existing suspension bridge.  However, considering the length of the main span, the side spans between the anchorages and towers are relatively short. The side spans were of differing length: 650 feet on the New York shore and 610 feet on the New Jersey shore.

In a revolutionary shift from prevailing suspension bridge design convention, Ammann proposed eliminating the stiffening trusses that had been essential for suspension bridges in an earlier age, when they were designed for heavy rail traffic. Instead of using trusses, Ammann theorized that as the weight per linear foot of long-span bridges increased, the deadweight of the bridge deck and the four cables would be sufficient to resist heavy wind, thereby eliminating the need for trusses. Each of the 106-foot-long floor beams weighed 66 tons. Even with a single deck only 10 feet deep, and a depth-to-span ratio of 1:120, neither heavy traffic nor high winds caused the bridge to sway. However, the bridge was designed to accommodate a second, truss-stiffened deck that could be added later.

Two suspension systems were considered for the span. One suspension system, known as an eyebar network, employed hundreds of thin metal bars that are connected at the cables and deck by eyelets. (This suspension system is employed at the Manhattan Bridge.) Another suspension system, known as the spun-cable system, employed tens (and even hundreds) of thousands of spun wires spun from anchorage to anchorage over the towers.  Because Ammann viewed both systems as equally effective, he contracted out the suspension system for competitive bid.  It was John A. Roebling and Sons, the firm founded by the designer of the Brooklyn Bridge, which won the contract for its cable-spun suspension design.  Each of the four cables was made with 61 large strands, and each strand was spun from 434 wires wound together across the river. Four 180-ton saddles atop each of the towers hold the main suspension cables in place.

A number of tower designs that borrowed from Gothic, Baroque and Art Deco conventions were submitted.  One design featured monumental granite-clad, Gothic-style towers, similar to those found on the Brooklyn Bridge, which would house restaurants and observation decks. Economic pressures and public opinion, however, prompted Ammann to use exposed latticework on the 604-foot-high, 20,000-ton steel towers. Indeed, given the advances in steel construction at that time, it was determined that the steel frame alone would be sufficiently strong to carry both the towers' dead and live loads, while the frame's flexibility reduced the weight - and cost (the Port Authority saved approximately $1 million on the new design) - of the steelwork.

The New Jersey tower was located 76 feet into the Hudson River, while the New York tower was built on land to avoid the steep drop from the Manhattan shoreline.  Both towers were comprised of twelve 50-foot-long sections; each tower section was floated one-by-one to the piers.  Each leg of the towers houses an elevator.

The 110,000-cubic-yard concrete masonry forming the anchorage for the cables on the New York side weighs 350,000 tons. On the New York side of the bridge, the tower foundation and anchorage were both constructed in Fort Washington Park. On the New Jersey side of the bridge, the anchorage lies in the solid rock of the Palisades. For the tower foundation, the largest cofferdam ever constructed was sunk into the Hudson River.

For the first time in New York, an entirely professional bridge crew was employed to build a major bridge. Like the engineers who designed the structure, the professional bridge workers had a great competitive spirit. They were divided into separate teams, one for each of the towers, one for spinning the cables and one for installing the roadway. A friendly rivalry even ensued between the New York and New Jersey tower teams, with each side racing to finish their tower first. The cables were spun in 209 working days with a work force of 300 men.

The "Hudson River Bridge," as the George Washington Bridge was called in the early days, was twice the length of any existing span, and it required an intricate system of access roads to handle large volumes of traffic.  The bridge's two steel towers, embedded deep in rock and concrete, soar 604 feet into the sky, each as tall as some of Manhattan's great skyscrapers. They contain more than 43,000 tons of steel.  Rope cables were strung from anchorages on each shore and draped in an arc between towers, like a giant silver braid. When 36 of them had been placed, catwalks were erected to provide walking platforms.

Cable spinning required two spinning wheels on each side of the river that traveled back and forth to create strands about the diameter of a pencil. The strands were spun into four great cables, each a yard in diameter. Steel suspender ropes were then hung from the cables, each containing some 107,000 miles of wire.  Within this silver web, steel sections were put in place to form the roadway, which progressed from each shore until the last section joined the other in the middle. Finally, the concrete was poured, the lanes were laid down, and the bridge was painted.

The Port Authority did its part to publicize the unprecedented project. In addition to print, the agency employed filmmakers and still photographers to chronicle construction highlights.  My mother and my uncle were some of the first pedestrians to cross the bridge on opening day.  Mom said it was pretty windy up there above the Hudson.  While the GW was, in its earliest days, the longest suspension bridge in the world, it has not been surpassed in busy-ness.  More traffic passes over this span than any other bridge in the world.  There may be other bridges that are longer or more famous, like its older brother, the Brooklyn Bridge.  But there is no link that’s more vital, particularly to New York City and the areas it links – Long Island, New England, and New Jersey.  When something happens on the bridge, or its approaches, the metro New York area turns itself into traffic knots.

The bridge almost didn’t make it to its 62nd birthday, and eight years later, might not have celebrated its 70th.    However, the bridge is still here to celebrate its 80th birthday, outlasting its brother to the north, the Tappan Zee. 

Many happy returns, old friend.  Not only are you a symbol of real progress, but of economy in bad times (1931), coming in under budget, strength, beauty, and endurance. 


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