The first project manager we visited in this series was General Leslie Richard Groves, the project manager responsible for the successful completion of the Manhattan project. For our next remarkable project manager we're going to go back a little further in time to the period just after the American Civil War when the Brooklyn Bridge was built, directly connecting Brooklyn with Manhattan. In those days, Brooklyn was the suburbs and Manhattan was the business district so most people had to cross the East River to get to work. Up until the bridges completion in 1883, people crossed the East River in ferries; fine in the summertime but more problematic in wintertime when ice could stop the ferries. By 1867 New Yorkers had had enough inconvenience and called on the New York Bridge Company to put together plans for a bridge. The New York Bridge Company assigned a senior engineer to the project, John A. Roebling, and made him responsible for the plans and the project.
The Brooklyn Bridge took 16 years to build (from project initiation to completion) and our story spans two generations of Roeblings - John and Washington, father and son. John Roebling died as a result of an injury he suffered while supervising the project work in 1869. His foot was crushed by a ferry as he was fixing the location of the first tower and he died 16 days later of lockjaw. His son, Washington Roebling, took over the project and completed it. At the time the bridge was built, it was customary for the engineer who designed a structure to take responsibility of managing the project which built it. The Roeblings were not only remarkable and forward thinking engineers (the design and many technical innovations were the father's ideas), they were remarkable, persevering, and effective project managers. This article focuses on the project management aspect of this project, but because Roebling senior was actually responsible for the plan, we give credit to both.
The construction of a bridge over such a long span (remember this was 1867) was the first technical challenge that had to be overcome. The bridge has a total span of 6,016 feet and a main span length of 1,595.5 feet. To put this challenge into perspective, it was not until 1890 that a bridge with a longer main span was built over the Firth of Forth in Scotland. The technical challenges are the most interesting aspect for the technical crowd, but the Roeblings also faced political challenges and safety challenges. The political challenges were mainly caused by the fact that the bridge started in one municipality and finished in another so the Roeblings were faced with satisfying two key stakeholders with sometimes competing interests. Further challenges were provided by increasing jealousy from competing engineering firms. The project started with a budget of $7,000,000 (excluding land) which was a huge sum in those days. As the project moved forward the budget gradually increased to $12,000,000. Safety at construction sites doesn't become a major issue until a completely new and untried approach to building is used for the first time. Inventing the technical solution is one challenge. Now find a solution that produces the deliverable that can be performed safely!
Another problem faced by Roebling was the financing of the bridge. The financing came from a rather complex set of subscriptions from both municipal governments and private industry. Financing was not always received according to the project plan which not only made completion of the project to any sort of schedule difficult, it also increased the cost of the project.
John Roebling was assigned the project in May of 1867 and submitted his plans, surveys, and estimates for the bridge in September of that year. The plans were turned over to a team of consulting engineers provided by the army. The consulting engineers were engaged to ensure the plans were properly done and that the project was feasible. The consulting engineers approved Roebling's plans with one minor modification, that the height be increased by 5 feet to a height of 135 feet, to ensure that marine traffic would not be interfered with. Work commenced on the bridge on January 3, 1870. Unfortunately John was not around to see work start on his project as he died the previous year but the work was passed off to his son, another engineer, who had been involved in one capacity or another from the outset.
Washington Roebling received the first change request for the project before work had actually started. In the world of bridge construction your customers can easily understand the impact of asking for a doubling in the bridges size after 80% of the work is completed. The change request was to increase the carrying capacity of the bridge to anticipate future demand. This change was estimated by Roebling to cost an additional 8% over the original budget. The additional cost was accepted, the change accepted and Roebling changed the bridge plans accordingly. The next change originated with the project: it was determined that the original plan to use pilings as foundations for the twin towers of the bridge was not feasible, the foundations would need to rest on bedrock which was 78 feet below grade on the one side and 45 feet on the other.
The first project phase involved creating the two towers that form the structural base of the bridge. As mentioned, these towers are not only below the water (approx. 80 feet) but between 45 and 80 feet below the river bed because they have to be set on solid bedrock rather than on pilings because of the tremendous weight they bear. The problem to be solved was how to dig an 80 foot hole 80 feet underwater? The solution Roebling chose was caissons. Caissons are water tight structures that carry workers who do the excavating. The caissons are lowered into the water until they rest on the river bottom. Compressed air is then pumped into the caisson to create a breathable atmosphere. The inspiration for this solution came from the diving bell which was the submersible of its day. The diving bell worked on the same principal: a diver was locked in the bell; compressed air pumped in then the diver was lowered into the water.
The caissons used for the Brooklyn bridge tower were constructed of wood calked with pitch and lined with steel and fit the footprint of the bottom of the tower, 102 feet by 172 feet, plus 11 feet on each side. This massive structure was lowered into the water until it rested on the bottom, and then the construction workers began excavation of the river bottom. When they had reached the bedrock 80 feet (or 45 feet depending on which tower was being worked on) they began the construction of the actual tower which then rested on the caisson. Manual excavation would have taken forever and there were no machines which they could lower with the caisson which could do the job so Roebling decided to use dynamite to speed the process.
Imagine the combination he was dealing with here. The interior of the caisson had to be lit so the workers could see what they were doing and the only light available at the time was gas light. The atmosphere in the caisson was charged with compressed air and, to top it all off, the caisson was constructed from wood! Not what I would call a safe working environment and, in fact, explosions and fires did happen. That's why Roebling had the caissons lined with steel to protect the wood and pitch from open flame.
Once the caissons reached bedrock, cement was hydraulically inserted beneath its floor to provide a solid, level platform for the tower and then the platform was built in place using the caissons as its foundation. The process that Roebling devised to build the tower in place and sink it onto the caisson base is too technically complex for me to explain here. Just bear in mind that this was all unexplored territory for bridge building, Roebling and his team had to improvise these solutions on the fly, without having an opportunity to prove his methods with pilots. If you're interested in the technique that Roebling used to sink his towers, there is a great article in the Catskill Archives on the subject. Just visit their website at: http://www.catskillarchive.com/rrextra/bbstory.Html
The construction of the towers above the water line was a much simpler process and the first tower was completed in May of 1875 and the second was finished in July of 1876. The next challenge was the cables that transfer the weight of a suspension bridge to its towers.
Washington Roebling fell ill at this time to health issues stemming from what divers call "the bends". The bends are caused by nitrogen bubbles in the blood that don't dissolve as a diver returns to the surface of the water too quickly. Compressed air was used to keep the water from flowing into the caissons as the digging proceeded to the river bottom. The use of the compressed air duplicated the problems that divers have when making deeper dives. We know now that a limit to the time a diver spends at depth and a slow ascent are the two key strategies to defend against the bends, but this knowledge wasn't prevalent at the time Roebling was building the bridge. Although Washington Roebling was incapacitated, he enlisted the help of his wife to act as lieutenant. Mrs. Roebling studied mathematics and engineering until she was able to carry Roebling's instructions to the work site and oversee their implementation through project engineers. He never completely recovered from his case of the bends, suffering ill effects from it for the rest of his life. Roebling was lucky; fires, explosions, and the bends would take the lives of 20 workers before the caissons were completed.
Roebling made use of another significant innovation in constructing the bridge: steel for the 4 massive cables that support the bridge. These 4 cables run from both sides of the river and over the two towers. Up to that time no-one had ever used steel to create cables for suspension bridges, they used iron. Roebling was constructing a longer, heavier bridge than had been constructed to that point and knew (or suspected) that iron would not be strong enough to suit the purpose. He bucked conventional wisdom, and the project budget, and chose to construct the cables from steel. As to whether iron cables would have been sufficient, we'll never know but we do know that Roebling's steel cables were.
The bridge was initially designed for foot traffic, horse drawn traffic, and trains. The trains would run on two elevated tracks, the horse drawn traffic on four lanes below, and the foot paths were on an elevated promenade above the train tracks. The two train tracks meant the bridge had to be constructed to carry heavy loads so each cable was constructed to carry a maximum of 11,200 tons. Each cable was 15" in diameter and consisted of 19 strands containing a total of 5,434 individual wires! Roebling used vertical cables suspended from the 4 main cables to suspend the bridge and then added stiffening trusses to make the bridge wind proof.
Construction of the bridge proper began in 1879 after completion of the two towers and rigging of the 4 main cables. By 1883 the bridge was completed and ready for its grand opening. Though Washington Roebling was unable to attend, his wife represented the Roebling interests and officially opened the bridge. The project was to have one last brush with tragedy that day. A lady pedestrian ascending the stairs to the walkway tripped and fell, screaming as she did. Her screams set off a panic amongst the rest of the pedestrians on the bridge who thought her screams were an indication the bridge was in trouble. In the ensuing panic, 12 people were killed and 35 seriously injured.
The Roeblings, father and son, not only exhibited a remarkable degree of engineering skill in designing and engineering the longest suspension bridge to have been built to that date, they also exhibited a remarkable degree of project management skill in seeing the project through to the end. Let's take a look at a few of their project management accomplishments:
Planning the project The Roeblings planned the successful completion of, what to that point was the longest suspension bridge. The plan was solid as proven by its successful execution.
Customer management Don't forget that the Roebling's had two individual municipal governments to satisfy. These governments did not necessarily share a common set of interests, and when they did share a common interest, such as limiting the money spent on the bridge, these interests were not always in the best interests of the project. The Roeblings persevered through the times when money was tight and succeeded in securing sufficient budget to build the bridge the way they knew it should be built.
Managing Change There were several sources of change during construction of the bridge. Some came from the stakeholders of the project, such as the increase in scope of the bridge to handle an anticipated increase in traffic, or the increase in the minimum required height, and others came from the project such as the change from iron cables to steel. The Roeblings handled the changes well, rejecting changes that did not add value to the project and implementing the ones which did with a minimum of disruption to deliverables and schedules. The Roeblings were particularly adept at dealing with the upsets that the bridge financing threw their way. The bridge was 90% funded by Brooklyn and Manhattan (New York) and 10% funded by private capital. The Roeblings survived a stock manipulation scandal, numerous budget increases, and the threat of a discontinuation of funding altogether and still delivered the project.
Lessons Learned/Corrective Action/Changing the Plan Washington Roebling learned from mistakes on the Brooklyn Bridge project, and other projects, took corrective action when needed and did not hesitate to make changes to the plan when it was clear to him that they were warranted. A good example of his ability to learn quickly and avoid unnecessary mistakes on the project was his use of compressed air to enable work at the bottom of the deep caissons. The technology was fairly new but was in use at the time in diving bells. Washington Roebling adapted the technology to his purpose to enable the men to work in the caissons. Keep in mind that as the men excavated the silt at the bottom of the caissons the water would want to rush in the opening this created. The compressed air served to keep that water out.
Managing the Risks The first risk to be managed during the construction of the bridge were the risks to the workers' safety. Although the record shows that 20 workers died while working on the bridge, the fatalities all occurred around the building of the caissons, a new venture. Mitigation strategies were implemented in an attempt to avoid accidents, such as the lining of the wooden caissons with iron but the combination of compressed air, open flame and explosives were clearly more than this strategy could deal with. Other project risks, which could be better predicted, based on other bridge projects and other municipal projects were well mitigated. An example of those risks and mitigation strategies is the risk of a stress fracture in any of the steel trusses or girders used to build the bridge. The mitigation strategy used was the testing of samples of all the components using a hydraulic press.
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