Separating New York from New Jersey, the great Hudson River has long been an obstacle to transport. The opening of the great George Washington Suspension Bridge in 1932 completed an important new link in the highway systems of the two States
THE HUDSON RIVER is spanned by the George Washington Bridge between Fort Washington Park, Manhattan, and Fort Lee, on the New Jersey shore. The bridge is carried on two towers whose centres are 3,500 feet apart. The anchor span on the Manhattan side is 650 feet long, and that on the other side is 610 feet long. Thus the total length is 4,760 feet. The complicated series of ramps and approach roads connecting Riverside Drive and neighbouring streets with the bridge can be seen on the Manhattan bank.
FOR several generations the city of New York and its environs have enjoyed a reputation for giant bridges. The great structures spanning the East River are described in the chapter “New York’s Giant Bridges”. The George Washington Bridge spans the Hudson River between Port Washington and Fort Lee and is one of New York’s newest bridges. It provides a fresh and vital link between the highway systems of New York State and of New Jersey across the river.
The Hudson is a grand river. The reach that sweeps down into New York City, between majestic, partly wooded heights, is in keeping with its noble upper reaches. A fine piece of engineering, above all a giant bridge, seldom spoils the appearance of its surroundings, but rather serves to enhance them. The new George Washington Bridge across the Hudson is an example of this. It sets off the grandeur of the great river.
To those who planned America’s highways and railways in the past the broad waters of the Hudson formed a serious obstacle. It is not surprising, therefore, that various schemes for bridging it have been proposed.
As long ago as 1868, when the Roeblings’ celebrated Brooklyn suspension bridge was first being planned, similar proposals were being made for spanning the Hudson, for in that year the State of New Jersey passed an Act for the building of such a bridge. The Act allowed for a structure with a clear span of not less than 1,000 feet, with not more than two piers founded in the bed of the river itself, and a clear height of at least 130 feet over the fairway in the centre. Though nothing was done at the time, in spite of the formation of a company for building the bridge, this and other early proposals are of considerable interest. Over twenty years later, the scheme was revived and a new Act was passed, this time by the State of New York. This second Act did not allow the founding of any piers in the river, which was, whatever the type of bridge to be adopted, to be cleared in a single gigantic span from shore to shore.
The bridge company now encountered the law entrenched, for it did not at the time want to build a suspension bridge, which seemed to be the only type possible under the ruling of the New York State Act. The primary purpose of the bridge — it was long before motor transport had any significance — was to link two railway systems. In the opinion of the company a suspension structure was unsuited to the great shifting weights of heavy steam locomotives which were expected to pass to and fro over the structure.
Again, the engineers called into consultation did not think that they could build a suspension bridge on such a scale as that demanded by the Hudson. The original plans had been for a cantilever bridge from 70th Street, Manhattan, carrying six railway tracks and having a clear span of 2,000 feet, the distance between the centres of the piers being 2,300 feet. The New York pier was to be on shore, and the New Jersey pier was to be situated 900 feet out.
LINKING NEW YORK AND NEW JERSEY, the George Washington Bridge across the Hudson River was opened for traffic in 1932. Each of the two towers is 559 ft 6 in high from the top of its pier to the summit of the steelwork. The two great piers have their centres 3,500 feet apart. The anchor span on the Manhattan side is 650 feet long, that on the New Jersey side is 610 feet long. The total length of the bridge, with its approach ramps, is 8,716 feet. The headway in the middle is 213 feet above the river. The two towers contain 41,000 tons of steel.
The engineers had their way with the Government, and an Act was passed in 1894 authorizing a cantilever bridge across the river from a point between 59th and 60th Streets, New York City. But the bridge was not built. The uncertain conditions after the outbreak of war in 1914, followed by America’s entry into it in 1917, caused schemes for bridging the Hudson at New York to be indefinitely shelved during the second decade of the present century. In the nineteen-twenties, however, came more proposals. G. Lindenthal, who had submitted earlier plans in 1888, and O. H. Ammann, destined to be responsible for the bridge, came forward in 1920 and 1923 with plans for suspension bridges at 57th and 179th Streets respectively.
Embedded in Volcanic Rock
Fifty-seventh Street is well down Manhattan Island, and 179th Street is opposite Fort Lee, where the built-up area on the Jersey City bank of the Hudson begins to open out to a certain extent, the river being flanked by high rocky bluffs and half-wooded cliffs.
It was at 179th Street that the site of the Hudson bridge was finally fixed, in surroundings where the boldness of man’s engineering resource was set off by the grandeur of the cliff-flanked river. On the site of the New York pier lies a deep stratum of hard crystalline schist, resting in its turn on strata of limestone and gneiss. The underlying rock on the New Jersey side consists of sandstone and shale, with the Manhattan schist a long way below it, a big fault being situated beneath the river bed towards the New Jersey side.
The bed of the Hudson River consists of silt, with boulders filling up the ancient gorge, and the New Jersey pier had to be sunk through this silt until it reached the underlying shale. The schist on the Manhattan side, however, rises right to the surface below the heights of Fort Washington Park, which face Fort Lee across the river. Above the stratum of shale on the New Jersey side lies one of ancient volcanic rock, and in this the western anchorage of the bridge cables were embedded.
The strata on the New Jersey side lie at an inclination varying from 10 to 15 degrees downwards from the edge of the riverside heights. This natural accident is a favourable one, as it precludes the possibility of the rock sliding riverwards at some future date and carrying the foundations, anchorages and approaches with it. The New Jersey shore, known at this point as Palisades Cliffs, rises to a height of about 300 feet above the level of the river.
Dr. Charles Berkey was the expert chosen to explore the nature and strength of the rocks, and he was afterwards retained as Consulting Geologist. Berkey’s examinations showed that the rock foundation on the New Jersey side varied in strength so as to withstand a pressure ranging from 3,000 lb. to 24,000 lb. per sq. in. The average strength he estimated at about 15,000 lb. per sq. in., more than thirty times the pressure to be imposed upon it by the base of the New Jersey Tower.
THE ROADWAYS of the bridge converge at either end into a great marshalling space or “plaza.” There are three roadways across the bridge itself. The central roadway, 30 feet wide, is flanked on either side by a road 28 ft. 9 in. wide.
O. H. Ammann, who produced the preliminary design of 1923, was appointed Bridge Engineer, and he chose his colleagues and staff well and carefully. His bridge gives a clear headway of 213 feet above the river in the middle. The two great piers have their centres 3,500 feet apart. The anchor span on the New Jersey side is 610 feet long and that at the Manhattan end has a length of 650 feet. Thus the bridge has a total length, between anchorages, of 4,760 feet. The total length of the bridge and its approach ramps is, however, nearly double this, for it amounts to 8,716 feet, or over a mile and a half. The headway just inside the Manhattan pier is 195 feet, and at a similar point on the New Jersey side it is as much as 210 feet clear, for the New Jersey shore is higher at its summit than that of Manhattan.
At either end of the bridge is a broad circulating area or “plaza” for the marshalling of traffic, which converges on the bridge from all directions. The plaza on the New York side lies between 178th and 179th Streets, whose western ends it has swallowed up. In addition to the main ramps leading to these plazas, there are tunnels for road traffic and for rail connexions, though the lower deck of the bridge, designed to carry the rails, was not made part of the first building programme. The design of the bridge allows for a central 30-feet roadway, flanked on either side by two 28 ft. 9 in. roads and by two 10ft. 9in. Sidewalks, forming promenades along the outermost edges of the top deck. Provision is made on the lower deck for four electric railway tracks in connexion with the New York Rapid Transit system.
591 Feet Above Water Level
When the bridge was opened for traffic in 1932, the central carriageway on the upper deck, and the lower deck, with its four electric lines, remained to be built. The aim of the engineer was not to complete the structure before opening it, but to relieve existing motor traffic congestion as rapidly as possible.
Having provided a through way over the river for the most urgent traffic requirements, he intended to complete the less badly needed features at a more leisurely rate. There is nothing new in this policy. It was observed, for instance, in the building of the Simplon Tunnel under the Alps between Brig (Switzerland) and Domodossola (Italy), a single-track tunnel having been opened some time before its companion was built.
The cables of the George Washington Bridge are made up of stranded steel wire, over which squeezers were passed after they were in position. Each cable is a yard in diameter. They are arranged in two pairs, one pair on either side of the carriageways. The centre of each pair of cables, that is, the point midway between the two, is 106 feet from the centre of the neighbouring pair. The centres of the cables in each pair are 9 feet apart. Thus the centres of the outside cables on either side of the bridge are 115 feet apart. These cables, are supported on saddles mounted in the tops of the steel towers at a height of 591 feet above mean water level, and are 15 feet above roadway level in the middle of the span. Unlike those of the veteran Brooklyn Suspension Bridge across the East River, the deck is supported from the cables by vertical suspenders alone.
The anchor chains, to which the huge cables are secured at the ends of the bridge, are embedded in concrete for a distance of 112 feet at the New York end and for 150 feet at the New Jersey end; they are connected with anchor girders running at right angles at their lowermost ends. The two anchorages differ from each other considerably. That situated on Manhattan Island consists, in essentials, of an enormous block of concrete in which the anchor chains are embedded. On the New Jersey side, the chains and girders of the anchorage are secured in concrete-filled tunnels bored down into the natural rock formation, which here rises considerably above the level of the bridge decks.
THE ANCHORAGE of the George Washington Bridge on the Manhattan side is formed by a mass of concrete, with a volume of 110,000 cubic yards. This great concrete anchorage was completed in five and a half months, as many as 1,200 cubic yards being handled in one day of sixteen working hours.
As first inaugurated, the bridge thus took the form of a simple suspension structure, designed on a tremendous scale. The building of the lower deck, with its four railway tracks, involved the addition of two stiffening members set 106 feet apart and having a depth of 29 feet. The two towers are of steel, with arch members below the bridge deck level and below the suspension cable saddles set in the tops. It was originally intended, for aesthetic reasons, that these towers should be encased in masonry. The great masonry towers of the Roeblings’ East River bridge have been much admired, and it was a form of traditionalism which at
first demanded the placing of stonework round the piers of the George Washington Bridge.
Popular taste, however, seems sensibly to have approved the undoubted beauty and majesty of the open steelwork. Purpose, after all, is the great keynote in architectural and engineering beauty, and there is no denying the manifestation of purpose in those mighty towers above the Hudson. This aspect has been realized in the best work right down the ages. In great buildings, embodying the best traditions of Gothic, we see it everywhere. The loveliness of Westminster Abbey, for instance, is due to the fact that the salient features of its design do not merely serve their definite purposes, but also emphasize them. Though there is not much resemblance between Early English Gothic and modern American, as exemplified in the George Washington Bridge, they have this much in common, emphasis of purpose.
To have covered the steel towers with stone facing would have made them appear colossal shams, just as if someone had lined Westminster Abbey with pitchpine matchboarding. As they stand, these two magnificent towers contain 23,600 tons of silicon steel and 17,500 tons of carbon steel, giving them a total content of 41,100 tons of steel. Exhaustive experiments were carried out beforehand with celluloid models of the towers and with steel girder members, which were tested to breaking point, the results being carefully recorded.
Huge Open Cofferdams
In the building of the- bridge, the engineers responsible found, from Berkey’s trial borings, that they could place the foundations of the great New Jersey tower on a bed of solid rock (shale and sandstone), whose surface was nowhere deeper than 100 feet. After a number of tentative proposals, they decided that the foundations should consist of a huge block of concrete situated under each of the two leg members of the superimposed steel tower. The vertical load exerted by the tower upon the foundation caused a maximum edge pressure of about 400 lb. per sq. in. The trial borings showed that even on the river side, the top of the rock bed would be struck well within the limit of 100 feet. It was met with at an average depth of less than 50 feet and the maximum depth came to only 75 feet.
It was therefore decided that the use of open cofferdams was perfectly feasible, even though it involved the use of cofferdams which, taking into consideration their depth and their area, were to be on a scale never before attempted. Had the builders of the George Washington Bridge decided to use separate caissons for the foundation blocks, they might well have experienced considerable difficulty in maintaining, through connexions, an even degree of pressure distributed within the adjoining caissons, and thereby a single action beneath the pier as a whole.
The open cofferdam allowed for easy and careful preparation of the rocky bed on which the foundations of the pier were to stand. The sites of the foundations had to be dredged out before the sheet piling, forming the walls of the cofferdams, was sunk. These walls were placed in position, 5 feet outwards from the site of the walls of the future piers on all sides. Timber bracing had first, however, to be sunk inside the cofferdam area, the sheet piling following outside this preliminary work.
Dredging was started in the beginning of May 1927, and within twenty days the dredgers had removed more than 75,000 cubic yards of silt from above the underlying rock-bed. The silt contained boulders, and several large, rocky obstructions were encountered in the course of excavating this otherwise harmless material. Divers were sent down to drill them for blasting. In this manner, the last traces of the major obstructions had been removed within a space of ten days. Some smaller boulders, however, still remained, and were encountered during the sinking of the sheet piles.
BUILDING THE ROAD DECK. Work proceeded simultaneously from either tower and the floor was completed on the central span in less than four months. This photograph was taken from the tower on the New Jersey side of the bridge.
The site was ready for this process within two months of the start on dredging operations. For the building of the two cofferdams, one for each pier supporting a leg member of the tower, 1,558 tons of steel sheet piling were required. The cofferdams had double walls, and the pockets in these were filled with concrete along the sides facing across the river. Elsewhere the side pockets were filled with ordinary silt from the river bed. One serious accident took place during the sinking of the cofferdams. This was caused by a blow-in at the upstream, shoreward corner of the northern cofferdam. It happened on December 23, 1927, luckily early in the morning when most of the men were out of the workings. Even so, three who were in the cofferdam lost their lives. No great difficulty, however, was encountered in repairing the material damage.
Concreting followed, the concrete piers being faced with stone to a depth of 7 feet below low-water level. The two piers were ready for the erection of the steel tower bearings by April 1928, nearly a year after the preliminary dredging had begun. Each of these piers consisted of an 89 feet by 98 feet concret foundation block, on which a similar block 84 ft. 6 in. by 76 feet was superimposed, the upper block being faced stone. These piers rose to a height of 14 ft. 11 in. above mean sea level at Sandy Hook, at the mouth of New York Harbour.
On the Manhattan side, as the strong stratum of schist rose well above high-water mark, there was no need for cofferdams, and it was possible for the 80 feet by 88 ft. 6 in. Foundation blocks to be built up on the cleared space without difficulty. The upper part of each pier was reduced in size to 76 feet by 84 ft. 6 in. to take the ornamental granite facing. This last, being a purely decorative feature, was not added until the autumn of 1932, the pier blocks having been ready for the superimposition of the towers since the spring of 1928, as on the New Jersey side.
Building the New Jersey anchorage, much of which was underground, was a stupendous task. The miners employed on the excavation of the anchorage had to dig out 17,300 cubic yards of rock for the anchor chain tunnels alone. Between the surface of the ground and the lower extremity of the tunnel system they sank a vertical shaft, with the usual type of pit headgear at the top, for the removal of rock spoil. The bottom level was reached during June and July 1928. A cross gallery, containing tubs running on rails, was driven between the bottom of the shaft and the bottom of the tunnels, which were connected to it by spoil chutes. The shaft was 250 feet feet deep and 7 feet by 9 feet in section.
The big cutting through the rock surface above, which was to take the approach road to the bridge from the environs of Jersey City, involved the removal of 197,500 cubic yards of spoil over a length of 830 feet and a width of 146 feet. The anchorage pits above the tunnels accounted for a further 6,500 cubic yards of rock. The anchor blocks are 69 feet long, 26 feet high and 27 feet wide; they contain anchors for the stiffening trusses. Work in the two anchorage tunnels proceeded alternately, the men working in one tunnel while the other was being cleared of fumes from blasting operations. The two tunnels thus progressed simultaneously and the same men worked in both.
The building of the New York anchorage, as of the New York piers, was a simpler operation than that simultaneously in progress across the water, though it involved heavy enough work. It contains no less than 110,000 cubic yards of concrete, and this was produced sometimes as rapidly as 1,200 cubic yards in one sixteen-hours’ day. The entire mass was completed in a space of five and a half months, or over two months ahead of schedule.
MANHATTAN TOWER of the George Washington Bridge rises 559 ft. 6 in. above the top of the pier on which it rests. Each of the cable saddles at the top of the tower consists of four huge castings, of which the heaviest weighs about 55 tons.
Erection of the two great towers began as soon as the foundation bearings were ready to receive them. Each tower is 559 ft. 6 in. high from the top of the pier to the summit of the steelwork, though the roadway passes through the New York tower at a level 16 ft. 6 in. lower than at the New Jersey tower. The building of these towers took place simultaneously, though the men at work on the New Jersey tower had a start of six weeks because of the earlier completion of the New Jersey piers. Each tower rests on sixteen steel pedestals set on the tops of the piers. The first pedestal of the New Jersey tower was placed in position by derrick on June 23, 1928. These pedestals were complete when they arrived for erection on the piers. Each pedestal consists of a steel member 14 feet square and 6 ft. 6 in. high, secured to the top of the pier by six 2½-in. anchor bolts over which it was lowered.
From these sixteen pedestals, eight to a pier, the tower superstructure was built up progressively, the derricks being situated between the two legs of the tower, and on the legs themselves for the erection of the cross-arches. Much the same procedure was observed on both towers, but in the New York tower each pedestal, instead of arriving whole, came in two pieces and had to be assembled on the spot.
Erection and riveting of the tower superstructures were discontinued during the winter of 1928-29. The riveting of both towers, however, was completed by August 1929. On an average, nine or ten gangs, each gang consisting of four men, were engaged in the riveting of each tower, though sometimes thirteen gangs would be on the job at once. Each of the cable saddles on the towers consists of four huge castings, the heaviest weighing about 55 tons.
Spinning and stringing of the cables and slinging of the footbridges to be used during that process followed the completion of the towers. The footbridges were laid from aerial ropeway carriages passing from tower to tower and between the towers and anchorages. The spinning of the cables was completed on August 7, 1930. On March 19 of that year 87 tons of wire were spun in twelve hours. This was a record.
Special precautions were taken against fire throughout the building of the bridge. At first thought this may sound rather strange, considering that the structure is composed entirely of steel, concrete and masonry. Wood, however, is used extensively during the building process.
Floor erection began on September 12, 1930, and was completed between the two towers by December 29. Floor erection in the side spans made rather slower progress. The work was completed on the New Jersey side on January 1, 1931, and on the New York side on January 21 of that year. The approaches to this giant bridge provide a distinct study in themselves. First there are the two great plazas for the marshalling of traffic at either end of the bridge. In these are situated toll booths through which all vehicles entering the bridge have to pass, and where their drivers pay the appropriate duty for using the bridge. Big floodlighting towers have been set up in the plazas to make their negotiation as easy by night as by day.
On the New York side, the layout of the approaches appears complicated in plan, though it works most smoothly. Most notable among the approaches is the great series of ramps, with up and down carriageways connecting the bridge with the world-famous Riverside Drive, with their strange loops and magnificent concrete arches. Then there are tunnels, carrying 22-feet roadways, beneath 178th Street. In these tunnels elaborate precautions have been taken against contamination of the air by carbon monoxide gas given forth by the passing vehicles. Along the side of the tunnel run two great ducts, together as high as the tunnel itself, one carrying a constant flow of fresh air to the tunnel and the other carrying off the vitiated air.
ON THE MANHATTAN SIDE the approaches to the George Washington Bridge are arranged in such a way as to expedite the circulation of traffic and to give access from many neighbouring streets. This photograph shows the bridge before the central carriageway was completed. The aim of the engineer was to relieve existing traffic congestion as rapidly as possible.