Benjamin_Franklin_Bridge

=Benjamin Franklin Bridge - Pride or Foresight?=



II. Introduction III. Cities of 1920’s a. Camden b. Philadelphia c. Other IV. Ahead of Demand a. Traffic Reality b. Future Traffic of 1920’s V. Design and Construction of the Benjamin Franklin Bridge VI. Current Demand VII.Conclusion VIII.References IX.Bibliography ||
 * < **OUTLINE** ||
 * < I. Abstract

I. ABSTRACT
The Benjamin Franklin Bridge was built in 1920. At the same time many other monumental buildings where being constructed by the United States government. Even though the size of this construction might seem oversized, the construction and design was mainly guided by the traffic demand and growth of the 1920’s. Philadelphia and Camden had engaged in a magnificent project which concluded with a building that would inspire civil pride and have enough strength to withstand the demands 80 years after the inauguration.

II. INTRODUCTION.
Around the 1900’s, although already a world power, the United States became larger and stronger with every year. As the Romans in their time, the US engaged in large building projects known to be remembered “for the ages”. All around the US, coast to coast, projects which required massive amounts of technology advancements and incredible budgets where being built. It was a way of saying to the world “look at us, we are the Americans.” Washington D.C had the Lincoln Memorial (1922), New York City had the Brooklyn Bridge (1880), San Francisco engaged in the Golden Gate by 1930, the New England states started the construction of the highways that would connect them (1922). In Panama the Panama Canal was inaugurated (1920) and Philadelphia built the Benjamin Franklin Bridge (1926). Was the oversized project of building the Benjamin Franklin Bridge a matter of civic pride? or was it a matter of responsibility and vision of the future which lead to the dimensions of the bridge?.

A. CAMDEN
With a total of 116,309 habitants in Camden County by 1920, which had grown from 94,538 habitants in 1910, the city was growing in a steady but alarming rate. A difference of almost 23% every ten years. From the US census of 1920, Camden county was composed of 44,078 families. By giving pessimistic figures that for every family only the head of the household had a job and only 50% of the families had jobs. From that figure, again using a pessimistic value, we suppose that only 5% worked in Pennsylvania. We end up with an astonishing value of 793,000 vehicles being moved, from and back to the city of Camden, every year. Before the construction of the bridge, the only feasible way of crossing the Delaware river was by ferry.

B. PHILADELPHIA
Philadelphia by 1920 was already a big city. It consisted of 1,823,779 habitants. The US Census of 1920 says that it was composed of 402,946 families.Now by giving the same pessimistic value of 50% of employment, again only for the head of household but this time we will give only 1% of them transport themselves to Camden for work. We end up with 1,450,000 vehicles per year moving from and back to Philadelphia. Now by adding Camden vehicle move and Philadelphia’s move, only from both cities we get 2,250,000 vehicles per year.

C. OTHER CITIES.
By the time that Philadelphia began construction, the US had other cities that where overpopulated. The state of New York had 10,385,237 habitants. San Francisco, CA had almost 500,000 habitants. Washington D.C. was composed of 437,571 habitants. Philadelphia was considered one of the biggest cities of the US, but they where not properly connected to the surrounding states.

IV. AHEAD OF DEMAND.
“Convenience must be measured not only in terms of the present traffic but of that of the future”

A. TRAFFIC REALITY.
By 1920’s ferries in the Delaware River, carried over 2,424,846 vehicles and 47,722,264 passengers per year. The types of vehicles consisted in ordinary, commercial, industrial, trucking from NJ farms and touring vehicles from Pennsylvania and other long distance locations. Only ordinary and temporary touring from Philadelphia vehicles conformed 80% of the full traffic carried by the ferries. It was observed that during a common day, at peak hours, the ferries would carry up to 400 vehicles per hour. The traffic of passengers grew from 16 million per year in 1900 to nearly 47 million by the 1920. This was an astonishing rate of growth by the 1920’s. It had tripled in 20 years.

B. FUTURE TRAFFIC OF 1920’s.
“It would be a short-sighted vision indeed that did not take into view the growth that would come about” This was said by the engineers in their 1920’s report. All calculations and statistical analysis where made in 1921. The engineering commission calculated that in 1926, near opening day, vehicles per year would reach 3.8 million. In 1923 the ferries were already carrying 4 million vehicles. By 1925 the traffic through the Delaware River was 5.6 million. At this rate it was calculated that by the tenth year from the opening 15 million vehicles would cross the bridge every year.

V. DESIGN AND CONSTRUCTION OF THE BENJAMIN FRANKLIN.
The location of the bridge was a critical step. It was necessary to find the precise streets where the bridge would start in Camden and end in Philadelphia. A place where the length of the bridge would no make the construction over budgeted and a place where the streets that would connect the bridge, be able to handle the traffic that was to move in and out from the bridge. In addition, the location should be close by transportation speed lines. From the 48 million passengers that moved in the ferries, 70% were commuters from trains.

The final bridge design consisted of 6 vehicle lanes, 4 speed-line lanes and two 10-ft sidewalks. All layered in a single horizontal plane. This allowed the vehicle to pass which was a common problem seen in previously built bridges, see figure. The structure consisted of “a single span 1750 feet long center to center of main piers providing an obstructed opening for navigation between peir-head lines” It is 126 feet wide and raised 137 feet over the water. A colossal engineering project for the 1920’s making it the largest suspension bridge in the world during that time. The bridge was calculated to handle over 6000 vehicles per hour.

The materials needed in the construction of the bridge spawned a new industry. The main suspension cables are 30’’ thick and are made up of 18,666 wires. A size comparable to other bridges around the US, see figure. Because of these unprecedented cables, machines were designed by engineers and hundreds of contractors were needed for the production of the wires. New construction techniques were developed, and others had to be innovated like the underwater construction for the bridge main towers.



The budget for the building was calculated to be $28,871,000 US dollars in 1920, which would be over $321,140,229 dollars today. In the end the construction cost was of $45,200,000 which converts to $502,772,273 today.

VI. CURRENT DEMAND
Since 1920 various bridges have been built to reduce the strain on Benjamin Franklin Bridge. The distribution of lanes has been changed and after the September 11 attacks, the sidewalks were closed. Two train lanes are laid on the outermost sections of the bridge, and the pathway has been divided into 7 vehicle lanes which depending on the time of the day change from 3 to Philadelphia and 4 to Camden or vice versa.

Currently over 83 years old, the bridge is estimated to carry 100,000 vehicles daily. In average, 4200 vehicles cross the bridge per hour. Although many bridges have been constructed in various other sections of the Delaware river, the bridge can still hold for future demand.

VII. CONCLUSION
Although this bridge might be seen as a monumental building, it serves both purposes. The magnitude of the bridge with a colossal founding that generates a sense of civil pride in every user that crosses it. It generates a feeling of what the american society is capable of building. In addition, the engineers carefully planned every aspect of the construction and the biggest question for them was “would it be able to hold for future demands?” Everything in the planning and construction was based on that fundamental question. It is the responsibility of the engineers to come up with a solution that would be able to confront almost every problem. The growth of traffic during 1920 was one of the main one.

VIII.REFERENCES
1 page 635; Census data obtained from __Population 1920 Census__ 2 page 14; __Report to the Delaware River Bridge Joint Commission__. 3 page 849; Census data obtained from __Population 1920 Census__ 4 page 13; Report to the Delaware River Bridge Joint Commission. 5 page 14; __Report to the Delaware River Bridge Joint Commission.__ 6 page 14: Report to the Delaware River Bridge Joint Commission. 7 page 59: __The building of the Delaware River Bridge.__ 8 page 1: Report to the Delaware River Joint Commission. 9 Calculation done using Inflation Calculator. 10 Benjamin Franklin Bridge Image by Jim K. Georges. 11 Vehicular Traffic over Delaware River Image. page 59. The Building of the Delaware River Bridge 12 Bridge Comparison of Cross Sections Image. page 2. The Building of the Delaware River Bridge 13 Comparison of Cable sections of various rivers Image. page 41. The Building of the Delaware River Bridge 14 Cable Compactor before and after Image. page 40. The Building of the Delaware River Bridge

IX. BIBLIOGRAPHY

 * 1) Modjeski, Ralph, et. al; __Report to the Delaware River Bridge Joint Commision of the States of Pennsylvania and New Jersey on the bridg over the Delaware River connecting Philadelphia, PA and Camden, NJ__; Board of Engineers, 1920; pp. 34
 * 2) __Population 1920__; Volume III; Department of Commerce. Washington Government printing office 1922
 * 3) Carswell, Charles; __The building of the Delaware River Bridge__; Enterprise publishing Co. 1926; Burlington, NJ. pp 68.
 * 4) __The inflation calculator__; Dollartimes.com; accessed March 16, 2009. 