Urban Growth: Understanding the Need For A Bridge and Establishing the Design Requirements
The main objective of this unit is to encompass these three basic issues of industrialization through lessons that focus on the East River bridges. The first step is for students to understand why the bridges came to be seen as necessary in the first place. 19th Century maps of New York, copies of which can be made from the Yale map collection in Sterling library, are very useful in showing the growth patterns in both Manhattan and Brooklyn. These should be transferred to an overhead so that they can be viewed by the class as a whole. Combined with population data and data on the growing numbers of commuters using the ferries the maps create a compelling picture of urban growth. After listing the basic criteria for a successful port, students should use a 19th Century nautical chart to see how well New York meets each of them. Maps should also be used to calculate commute times based on various forms of available transportation to illustrate the original reason for growth in Brooklyn. Students should use the data and contemporary news accounts of related events such as the freezing of the East River in the winter of 1866-67 to write editorials making the case for a bridge in 1867 and outlining the benefits it would bring to the communities on both sides.
The next step is to assign students the task of establishing the design criteria an East River bridge will have to meet. Using contemporary illustrations (probably best projected on an overhead) students will note the heavy river traffic with numerous vessels that require significant vertical clearance. The maps and illustrations will indicate the distance to be spanned and the significant population density on both shores. These visuals will also reveal that the local topography offers little (especially on the Manhattan side) to provide natural support to a bridge. Students should also consider the volume and type of traffic that a bridge in this location will have to carry. After viewing the illustrations and engaging in a discussion on the various considerations, students will write a request for a design proposal, listing all the requirements an East River bridge will have to meet.
Individual Bridge Profiles
The Brooklyn Bridge - 1883
The story of the Brooklyn Bridge is the stuff of legend and it would certainly by easy to focus the entire unit, if not a good portion of a semester teaching it in all its glorious details. For the purposes of this unit, however, it is only necessary to focus on certain significant elements that illustrate the basic historical trends of industrialization. The design John Roebling proposed that would satisfy the necessary criteria for crossing the East River was a suspension bridge of such size that it would remain the largest of its type in the world for 20 years after its completion. Its essential feature is a single uninterrupted span 1595 feet in length held 133 feet above the water at its highest point with no obstructions to navigation below it. The building of the bridge entailed two great technical challenges which should for the basis for the lessons on this bridge. The first was the building of the colossal stone towers that bear the entire weight of the bridge high enough for the necessary clearance beneath. The second was the construction of the four enormous cables with the strength to support the central span and anchorages strong enough to hold them in place. These two elements of the bridge, one working in tension and the other in compression, needed to be in balance for the bridge to stand.
At 268 feet, the towers were certainly the "most conspicuous features" of the bridge, but the most compelling part of the story of their construction took place out of sight in the pneumatic caissons where the digging of the foundations took place. It is absolutely imperative that illustrations be used when teaching about caissons because they are so fantastic that they literally defy description. The best are contemporary sketches that appeared Harpers Weekly and Scientific American which show both cutaway drawings and illustrations of the type of work carried out by the men inside. One particularly dramatic photograph shows the immense size of the Brooklyn caisson prior to launching with the scale provided by the comparatively small men standing on top. Washington Roebling described the caisson as a huge diving bell built of wood and iron, shaped like a gigantic box with a heavy roof, strong sides and no bottom. Filled with compressed air, it would be sent to the bottom of the river by building up layers of stone on its roof. The compressed air would keep out the water and make it possible for men to go down inside and dig out the riverbed while the tower continued to be built on top. Eventually the caisson would reach bedrock at which point it would be filled with concrete and become the foundation of the tower. Using the drawings as a guide, the students should list all the technological advances that were necessary for the caissons to work. This should include steam power, air compressors, air pressure gauges, air locks and inventions specific to this task such as the ingenious method of removing the dredged material from the caisson without losing pressure or using time consuming air locks.
The actual work in the caisson however tells a different part of the story. Like most industrial workers of that era, the men in the caissons worked long hours six days a week under horrendous conditions for only two dollars a day. Only when the Brooklyn caisson reached a depth of twenty-eight feet did management decide that the work was so hazardous that the pay should be raised to $2.25 a day. That men would be willing to risk their lives in such obviously dangerous circumstances while putting their trust in a new and largely untested technology is astonishing. Although Washington Roebling was in fact very concerned for the safety of his workers and took all the same risks himself, his attitude was an anomaly for this era and may well have resulted in part from the continual public scrutiny his project was under. Students should understand that benefits for workers did not exist in this era so when laborers in the caissons did begin to suffer from the dreaded "caissons disease" (better known today as the bends) they received little more than short term treatment by the company doctor and then were simply sent home. If a worker's injuries were bad enough to make it impossible for him to work he was out of a job. Aside from the physical risks, working in the caissons was extremely unpleasant. The air was heavy and dank while the temperature never dropped below 80 degrees and was frequently higher. There was a constant stench from the black East River mud which covered every interior surface. Roebling's master mechanic, E.F. Farrington, describing the scene in the caissons said that "one might, if of a poetic temperament, get a realizing sense of Dante's inferno."
Under such conditions it is no surprise that the men in the caissons quit in droves. Over 2500 different individuals worked in the Brooklyn caisson from start to finish. That comes to about one man in three deciding to walk off the job or about 100 a week. What is surprising is that so many were willing to take their places. For every man who quit there were at least a dozen willing to take his place. Most of them were Irish, German or Italian immigrants so poor and desperate for work that they were willing to take any risk for almost any wage. Many were described as thinly clothed and undernourished which made their chances of enduring the conditions in the caissons less than likely. Students should consider all the circumstances that might lead a recent immigrant to take a such a job and write a first person fictional account of why the decision was made and what the work was like.
Only when the cases of the bends began to occur with increasing frequency in the Manhattan caisson did the workers attempt to improve their circumstances by going out on strike. Although it was the only time there was such a job action during the entire time of construction, the case is illustrative of what workers were up against when they tried to fight for their rights. The entire work force of caisson men refused to go to work on May 8, 1872. They stood out on the street nearby and demanded three dollars for a four hour day because the work had become so dangerous. The bridge company offered $2.75 a day but that was rejected the strikers and a worker who tried to break through their lines was badly beaten. After three days of negotiations, the director of the bridge company simply announced that any man who did not go back to work immediately would be fired. With that the strike ended as the men decided that it was better to take the risks at $2.25 a day rather than have no job at all. The best way to teach this lesson is with a role play. Students should be divided into four groups: one representing the bridge company directors, one representing the caisson workers, one representing unemployed immigrants looking for work and a final one representing "the public." After hearing a report on the recent cases of caissons disease, the workers group will take a vote to strike and explain their demands. The bridge directors should marshal their arguments and limit any offer to no more than $2.75 per day. The unemployed should make it clear that they are willing to work if the others refuse and should be able to explain their desperate reasons. The public meanwhile may be divided along class lines, but certain attitudes of the time should certainly be present. The basic philosophy of the time on these issues was Social Darwinism which taught that those who would compete for jobs such as those in the caissons are the least fit whose eventual demise would only be a benefit to society as a whole.
The story of the construction of the cables is useful to illustrate the fact that the bridge was being constructed at the very cusp of the age of steel. Students should note that the Brooklyn Bridge is the only East River crossing in which the primary supporting towers are made of stone. In the later bridges steel as a building material had matured to the point that it was the only reasonable choice. The cables, however, were to be made of steel and because it was such a new material the choice of which type of steel became a source of controversy.
Washington Roebling's initial specifications for the cable wire set forth certain strength and performance requirements without specifying how the steel was to be made. The lowest bid came in from his own family's wire company, John A. Roebling and Sons for wire made from steel manufactured with the new Bessemer process (Roebling had sold all his interest in the company to avoid a conflict of interest). Confidence in and knowledge of the Bessemer process was weak enough however that a certain individual with a financial interest in one of the other bidders was able to sow doubt about whether that type of steel was the best for the job. The older more expensive type of steel, crucible steel, was considered the finest grade and was used principally for tools. The contract for the cable wire was awarded therefore to the lowest bidder for crucible steel, but the reality was that no wire manufacturer could produce enough wire produced by the old method in enough quantity at the price quoted. The result was a fraud in which wire that had failed inspection, much of which was in fact made of Bessemer steel, was being switched with good wire and sent to the job site. Fortunately the Chief Engineer discovered the fraud before too much defective wire was spun into the cables, but Bessemer steel (now properly inspected) was the steel used after all.
Student work on this issue could take the form of letters to the editor supporting one or the other types of steel. Those writing in support of the crucible steel should focus on the time tested nature of the method, the high quality of the steel produced and the question of whether the strength of the entire bridge should be dependent on a relatively new cheap mass produced steel. As one editorial writer observed, should the bridge be built with "the cheapest wire, or the best wire at the cheapest rate?" Those writing in support of Bessemer steel should point out that the method had been around for over 20 years, that it had been used extensively in building railroads, that it was the most economical and efficient method of steel production.
The method developed by John A. Roebling for "spinning" the cables in place is another excellent example of the technical ingenuity of this era. Construction of the cables had to be done in place to avoid obstructing river traffic and because once constructed they would be too heavy to pull to the tops of the towers. Pulled by a traveler rope strung over the tops to the towers, a loop of wire was pulled across and over the towers by a big iron wheel which thus laid two wires at a time. As a continuous loop, the traveler rope could carry two of these carrier wheels, one going each direction, at the same time. Like the caissons the system is difficult to describe without illustrations but I have not found any really good ones. The PBS video by David McCauley,
Building Big: Bridges
, has some excellent film footage, however, of this system being used on the construction of the Golden Gate Bridge. The basic method is so good that it is essentially the one still in use for the construction of suspension bridges today.
The Williamsburg Bridge - 1903
Because so many of the great technological leaps were accomplished in the design and construction of the Brooklyn Bridge, examination of the other East River bridges can be - and probably will have to be - shorter. Thus consideration of the Williamsburg Bridge can be limited to two basic themes: the questions of aesthetics which arose as a result of the design of the bridge and the continuing changes brought on by immigration and urban growth. The impact of new technology is significant primarily in the use of the bridge as a link in the newly electrified mass transit system rather than in its construction.
Even before the opening of the Brooklyn Bridge leading citizens of the Williamsburg section of Brooklyn began to push for a bridge that would connect their community to Manhattan. 19th Century maps of New York show clearly how growth in Williamsburg was separate from the early center of Brooklyn due to Wallabout Bay and its surrounding marshland which lie between them. By the late 19th Century the community was made up mostly of upwardly mobile German and Irish immigrants and first generation native born who had been able to escape the tenement slums of Manhattan. Despite being annexed by Brooklyn in 1855, Williamsburg continued to see itself as a separate community with interests more allied to New York. Because of geography, the citizens of Williamsburg realized that the benefits of the Brooklyn Bridge would not easily flow to their community.
In 1897, after more than a decade of delays caused by political and financial problems, a design for a suspension bridge was completed by Leffert L. Buck and construction began. By that time traffic on the Brooklyn Bridge had exceeded all expectations and ferry traffic hadn't diminished at all. To handle this burgeoning growth, the design specifications called for a bridge built with two levels to handle six lanes for trolleys, two lanes for carriages and a pedestrian walkway all of which would require a deck half again as wide as the Brooklyn Bridge. The needs of a growing city and developments in transportation technology were placing greater demands on bridges in New York.
Buck's design was one in which the design specifications were well met, but aesthetic considerations seem to be secondary. For the first time in a bridge of this size steel would be used for the entire bridge, including the towers which would rise 350 feet - 80 feet taller than the towers on the Brooklyn Bridge. As this was one of the first times steel was used in this way, the design of the towers is conservative, relating more to earlier designs such as the Eiffel Tower which was built of wrought iron. The result is a vertical truss with an ungainly profile which compares unfavorably to the monumental gothic towers of the Brooklyn Bridge or the elegant steel frames used in later bridges. Adding to the bridge's aesthetic shortcomings, Buck felt the increased load specifications required a massive stiffening truss which runs 40 feet high the length of the bridge. Finally, the side spans of the bridge is supported in a straight line by steel viaducts rather than suspended from the cables. The result is a span which does not have the continuous graceful curve that is usually associated with suspension bridges. The design for the Williamsburg bridge therefore can be seen as one in which the use of material in a new way and the tremendous load requirements of a growing city led to a bridge which is simply functional - nothing more. Writing in
shortly before the completion of the bridge, one critic stated that one can look over the entire bridge "without finding a single detail which suggests a controlling motive, either in its design or fashioning other than bald utility."
Student work on the Williamsburg bridge should focus in part on this conflict between aesthetics and "bald utility." Photographs of all the East River bridges appear in Sharon Reier's excellent
The Bridges of New York
, but students can probably best judge the comparative beauty of the various bridges when they go to see them. One of the assignments due after the trip should be for students to choose which bridge they think is the most beautiful and which they think is the most ugly and explain why. Discussions prior to the trip as to what factors add to or detract from the beauty of a bridge will serve to provide students with a vocabulary to explain their position. Students should be consider the influence new and relatively untried materials can have on a designer's confidence in his ability to create forms that are graceful as well as functional.
One unquestionably positive effect of technological advances on the construction of the Williamsburg Bridge was the decreased time of construction: only seven years - less than half the time required for the Brooklyn Bridge. Upon completion it played a significant role in the evolution of the immigrant communities in New York. Viewed initially by the German and Irish residents of Williamsburg as bringing the economic benefits of easy access to Manhattan, the bridge was ultimately more important as an outlet for the Eastern European Jewish immigrant community in the overcrowded slums of the Lower East Side. Within the next few decades Williamsburg and adjacent Brownsville became thriving Jewish enclaves while the Germans moved on to Richmond Hill and Jamaica, Queens. Thus, a bridge built in response to urban growth ended up influencing the social and ethnic patterns of that growth.
The Queensboro Bridge and the Manhattan Bridge - 1909
The next two bridges to cross the East River - the Queensboro Bridge and the Manhattan Bridge - were built almost simultaneously between 1901 and 1909. The Queensboro was completed first in July of 1909 and represents the only cantilever type among the major East River crossings. This type of bridge, used most famously in Scotland's Firth of Forth Bridge completed in 1890, is another good example of the innovation in design and use of new materials so common in the Second Industrial Revolution. Students need understand the basic concept of the cantilever design in order to understand why such a design was chosen for that specific location and to understand the controversy surrounding the bridge during its construction. In the cantilever design the overwater span is supported by piers which are kept in balance by the counterweight of the land span. Rigidity is provided by the triangulated members of a truss. The result is a structure that cannot support as long a central span as the suspension type, but has greater rigidity and is usually more economical to built. The design works at the 59th Street location because it makes use of Blackwell Island (today called Roosevelt Island) for central supporting piers. The bridge was also another step forward in the use of new materials as this was the first use of nickel steel which is stronger and lighter than carbon steel. Another innovation was the use of eyebars to connect the primary members with enormous pins weighing 7000 pounds each.
Because the Queensboro does not have a center suspended span, as many cantilever bridges do, the resulting structure is one that has the basic profile of a suspension bridge and one that functions a bit like one as well. The upper chord of the truss is in tension and follows the basic line of a suspension cable as it travels from the top of the towers down to the center of the span and back up again. The towers need to be tall enough to provide the necessary support for the upper chord and are kept in balance by the opposing forces just as towers in suspension bridges. The major difference is in the compression members of the bottom chord which provide support and rigidity that is not present in a suspension bridge.
The choice of a cantilever design for the bridge resulted in controversy as the bridge was nearing completion mostly as a result of a tragic coincidence. In 1907 the Quebec Bridge which was being constructed over the St. Lawrence River in Canada collapsed killing 75 workmen. It was to have been the longest cantilever bridge in the Western Hemisphere and its collapse called into question the use of that type for long spans. Despite the fact that the Queensboro Bridge was shorter by a third, public outcry led to an investigation of its stability and carrying capacity. The investigation did raise some concerns and resulted in the reduction of the number of elevated tracks to two and the removal of some structural material seen as adding too much dead weight to the structure. After the Quebec disaster, cantilever bridges lost favor as a choice for spanning long distances while the suspension type became the standard.
The Manhattan Bridge was completed only three months after the Queensboro, but it makes use of what had become a fairly traditional suspension bridge design. The main structural innovation results from the increasing confidence in this bridge type and in steel. For the first time the towers were built in a two dimensional plane rather than the rigid three dimensional structure used in the Williamsburg Bridge. The result is a tower with far more grace and elegance, yet able to stay erect because of the balance of forces on it. For students it provides a good comparison with the Williamsburg bridge which was completed only a few years earlier and is the only other all steel suspension bridge in the group.
Hell Gate Bridge - 1917
The last of the East River Bridges to be considered in this unit provides an excellent point of comparison with the others not only because of its design, but because it is the only one to be built exclusively for rail traffic. Designed by Gustav Lindenthal - the designer of the Queensboro Bridge - the Hell Gate Bridge was the longest steel arch in the world when it was completed. As a railroad bridge it was to provide a vital link in what was after all the dominant transportation system of the industrial age. Prior to its completion there was no direct rail link between New England and points south through New York City. Passengers traveling what is now called the "northeast corridor" through New York had to switch from Grand Central Station to Penn Station to continue their journey. Ironically, the bridge was completed just as the automobile began its steady rise to become the nation's dominant form of transportation. Within twenty years of the completion of the Hell Gate Bridge the most important bridge links in the nation's transportation network would carry cars, not trains.
Consideration of the Hell Gate Bridge must include a clear understanding of the arch as a basic design form and how it is used in this particular example. In theory, the arch is the strongest and most stable of all the basic bridge types. The curving form of the load bearing structure acts in compression transmitting force to its ends which must be opposed by an equal or greater resistance to keep them from spreading apart. In many cases this resistance is provided by massive abutments or by topographical features such as the sides of a gorge or hills, but it can also be provided within the structure of the bridge by members acting in tension which tie the ends of the arch together. In the Hell Gate Bridge, this service is provided by the bridge deck which is not only supported by the arch above it but also helps it to stand up. This type of arch is sometimes referred to as a tied or bowstring arch. The structure of the arch itself is created by a series of truss panels which provide strength and rigidity without undue weight. This construction utilizing steel members in triangular forms is essentially the same as Lindenthal used in the Queensboro Bridge to provide strength for the cantilever. An important technological advance was the use of carbon steel which provided greater strength for its weight. Thus steel again provided a designer the opportunity to utilize a traditional bridge form on a much larger scale with a far larger load capacity.
Having decided upon the basic form he was to use, Lindenthal wanted to address two issues: how to make the bridge appear strong to the ordinary citizens who would be using it and how to make it aesthetically pleasing. For Lindenthal, who had strongly criticized the lack of aesthetics in the Williamsburg Bridge, the two issues were interconnected. Those features which were to make the Hell Gate Bridge appear strong would also make it attractive. The elements that were added for this purpose, however, are not structurally necessary and do not add to the strength of the bridge. To make the arch look stronger, he increased the distance between the upper and lower chords of the truss at each end. The resulting combination of a flatter curve on top which reverses slightly at the ends and a deeper curve on the bottom creates an image which is strong but also graceful and engaging. Another non structural element added by Lindenthal to his bridge were two massive masonry towers situated at each end of the arch. To the lay person, the towers appear to provide the buttressing that such a massive arch would require. They also give the bridge a striking monumental appearance which provides a counterpoint to the graceful curves of the arch. It recalls a similar combination which is evident in the Brooklyn Bridge.
As a product of the late industrial revolution, the Hell Gate Bridge provides students with a number of issues relevant to this era. One is the question of aesthetics which has already been explored to a certain extent with the Williamsburg Bridge. Industrialization had created the need for new and improved bridges, it had provided new materials and innovations in design to accomplish the task, but the designers and builders of the age often wrestled with the question of whether a bridge needed to do more than provide "bald utility." Students should be able to explain whether Lindenthal's non-structural alterations to the basic bowstring arch form add or detract from the Bridge's essential value. Another issue students need to consider is the role changing technology can play in redefining the importance of a bridge. The invention and mass production of the automobile, both key developments of the late Industrial Revolution, resulted in an entirely new transportation network. While the other East River Bridges have been modified for the automobile, the Hell Gate Bridge cannot be. Students might compare the role of the Hell Gate Bridge to the adjacent Triboro Bridge which was built in the 1930s as a critical link in the region's auto road network. Which bridge is more important in the lives of those who live in and around New York? Is it possible that the importance of the bridges could change if the economics of transportation were to change? There are many who believe, for example, that rail travel may indeed be the answer to many of the nations transportation problems.