User:Martin Scheuring/CritiqueonTappanZeeBridge

The Tappan Zee Bridge has done more than what is was designed for, and has also done it with a more cost efficient design. It is a cantilever truss bridge that spans the Hudson River at one of its widest points connecting Tarrytown, New York and Nyack, New York. The bridge was built by the Madigan-Hyland engineering firm in 1955 and cost 80,800,00 dollars to build2, the equivalent of 682,932,494.32 dollars today. It has a total length of 16,017 feet and is 90 feet wide1. The main cantilever span is its longest span and is 1,212 feet in length and also provides a maximum clearance 138 feet above the water. The bridge is built out of steel and concrete1. The Tappan Zee Bridge was built to only last fifty years and carries a load that is twice of what it was designed for on a daily basis. The Tappan Zee Bridge has done more than what is was designed for, and has also done it with a more cost efficient design. The Tappan Zee Bridge was built as an expansion of the New York State Thruway to connect the rest of the state of New York to New York City. It serves as a more northern crossing of the Hudson River to New York City and to New England states rather than using the George Washington Bridge. The original design of the bridge was include a steel tied- arch for the span of the main channel of the Hudson River1. The design was changed to a cantilever bridge because steel fabricators would not bid on the main span because their estimates exceeded those of the chief engineer. The reason the estimates were so high was because of material shortages due to the Korean War. The bridge’s caisson design also saved millions of dollars in concrete. Eight under water caissons support seventy percent of the bridge’s dead weight using a “buoyant” design that stores compressed air in small compartments and water is periodically pumped out to achieve desired buoyancy. The caissons are supported by steel piles driven into rock. The caissons are an efficient way of carrying the dead weight of the bridge and it also saved money. This cassion design is smilar to that design used for the Burdekin Bridge in Australia3. The main span is made of steel and has two cantilever spans and one suspension span. The loads from the spans are transmitted to the two main towers which then carry the load to the caissons below and is then pushed to the rock below. The bridge was designed to carry near 100,000 cars on a peak day during the year, but currently carries 125,000 cars on a daily basis1. This creates more stress on the bridge then what was originally planned for. This design is a scientifically efficient way to keep the bridge stiff while it is also an economical way to build the bridge. The Tappan Zee Bridge represents a gateway to Connecticut and other New England states for people from New Jersey and Southern New York State. It is impressive how the bridge was only designed to stand for fifty years, but has lasted the test of time while carrying a traffic load that is double of what it is supposed to. The design used is out of steel and concrete which fits in with most of the buildings in the area as it is part of a large city with industry. It also does not standout when looking at it from the Tarrytown side at the less industrious Nyack side. The Bridge is named after the Tappan Indian tribe that lived in the area and Zee comes from the Dutch word meaning “wide expanse of water” which is what they called the Hudson River. These two names represent the people who first inhabited those two areas that the bridge connects. The bridge is known for its long span and its cantilever design that is not very common in the area. The Tappan Zee Bridge is considered to be a work horse bridge in doing more than what it was designed to do. It is also efficient in the fact that it was built during a time of a shortage of materials that were needed to build it. Engineers were also able to adapt a design that would cut costs in concrete and in steel. It has efficiently done its job with the least amount of materials necessary. This structure is efficient, economically efficient, and elegant. I think that it would be an efficient design of bridge to build today in an area where there was not as much traffic. b