User:Johnj7733/hangzhou bay bridge

The Hangzhou Bay Bridge is one the worlds longest trans-oceanic bridges at a length of about 22 miles, but it does not have the largest main span. The Hangzhou Bay Bridge is an example of incredible architecture as well of a structural art.

Introduction

Hangzhou Bay Bridge

The Hangzhou Bay Bridge was designed by Ty Lin International and the main contractor was the China Railway Bridge Bureau Group Co. Ltd. The Hangzhou Bay Bridge is located in the Zhejiang Province in China and bridges the Hangzhou Bay in the East China Sea. Being a six lane traffic bridge with three lanes in each direction it creates an important connection for two of the nations most important cities Ningbo and Shanghai. The preparatory work for the bridge began as early as 1994 and the construction was started in 2003. The construction was concluded in 2007 but the bridge was not officially opened until a year later due to a number of tests that were still being conducted on the bridge. The Hangzhou Bay Bridge was constructed as a part of the national highway system in China.

Structural Description

The Hangzhou Bay Bridge is of the cable stayed bridge form. This form was chosen for this project because of the strength of the cable stayed bridge in adverse conditions. The bridge is constructed in the delta of the Yangtze River Delta which experiences some of the highest tidal forces on the planet. The location of the bridge is also prone to earthquakes as well as extremely high winds during typhoon season. The bridge form was chosen because of its strength against all of these forces. The bridge form as well as the materials that were used to construct the bridge were decided on based on the different forces that the bridge will be facing.

Many bridges use concrete piles to support the deck but the Hangzhou Bay Bridge took a different approach and used steel piles. This choice was made based on the fact that the steel piles would be much stronger against corrosion from the extremely high tidal forces in the bay. Using the steel piles instead of the concrete piles also made the bridge far more constructable especially in the extremely difficult working conditions that they would be facing. It is not strange to see waves in the bay reaching 25 feet tall. In these conditions it would be almost impossible to construct the bridge without the use of some new construction technology and vehicles. During the construction of the bridge two massive cranes were used, one being 2,200 tons and the other being 3,000 tons. These heavy duty cranes were used to transport massive girders from the shore to the part of the bridge where they were needed. The cranes would also be used to lift the massive girders into place. The steel piles used were also transported using these cranes.

The load paths in this structure are somewhat easy to follow. The gravity load on the bridge as well as the rest of the loading on the deck such as cars are the easiest to follow which is further explained in the qualification as structural art section. The loads on the bridge due to the extreme tides are somewhat difficult to read, but they are clearly accounted for. The steel piles are the structural supports that resist the tidal loads. The piles are driven deep into the sea bed to reduce the moment on them. Having a small moment or force causing bending in the piles keeps the bridge upright. The steel is extremely strong against corrosion and are therefore the best material that could have been used in the piles.

When looking at the loading due to wind loads on the bridge the main portion that is important to analyze is the main spans. Because the two main spans are relative short the wind loading is insignificant. The wind loads however would be accounted for due to the outward bend of the towers that support the tension cables. This theory of widening the bottom of towers was first used by Gustav Eiffel when constructing the Eiffel Tower. The bent shape is very good at transferring the wind load to the base supports of the structure.

Qualification as Structural Art

The Hangzhou Bay Bridge has been referred to as one of the greatest masterpieces of modern architecture. The Hangzhou Bay Bridge is definitely an example of great architecture but it is also a form of structural art. Structural art is defined by the three S's : scientific, social and symbolic, as well as the three E's : efficiency, economy and elegance.

When looking at the Hangzhou Bay bridge from with respect to it scientific, social and symbolic meaning it is clear to see where it fits in as a form of structural art. The main cable stayed spans are the true forms of structural art in this structure. For the scientific meaning of this bridge it is clear to follow the forces that are acting on the bridge from the deck all the way to the supports of the bridge. Being of the cable stayed form the forces in the deck are clearly carried through tension in the cables from to the top of the support towers and carried to the sea floor through compression. The Hangzhou Bay Bridge is extremely important in the social aspect for the region. Shanghai is one of the most important commercial regions in China and prior to the construction of the bridge it was over four hours driving to one of the countries most important port cities Ningbo. Now after the construction of the bridge the commute between the two major cities is about two hours. This has created a much easier link between the two previously separated areas, increasing the commercial and industrial background of the two areas. This bridge is symbolic of the growing economy and drive of the Chinese economy to continue its growth.

With respect to the three E's it is also able to be classified as structural art. The bridge is of an extremely elegant form that is able to show the importance of the visual lightness of the structure while still being able to emphasize the path that forces follow in the structure. It is clear that this bridge is extremely light just by looking at it, the slender deck, thin tension cable and support towers. The elegance of this structure also makes it possible to see the efficiency of the structure. Based on the light appearance of the structure one would think that some structural integrity had been sacrificed. However this is not true, the Hangzhou Bay Bridge has a lifespan of over 100 years which is comparable to most bridges.. The bridge is built mostly of steel which allows for it to be extremely slender while still having incredible strength. The deck of the bridge was constructed using an orthotropic steel decking, which means it is a steel plate reinforced by cross braces composed of more steel. A thin layer of asphault and concrete are laid on top of the deck giving it overall lightness as well as strength of the deck. From the economic standpoint this bridge was also a great success. For being one of the longest bridges constructed over water in such difficult building conditions it did it extremely well. First of all the construction time for the bridge was built in a relatively short time, five years, for its size.. When comparing the Hangzhou Bay Bridge to another cable stayed bridge it is possible to see the success in the economy of the bridge. The Sunshine Skyway Bridge in Tampa Bay, Florida is much shorter but when comparing its unit cost per meter it becomes clear just how well the Hangzhou Bay Bridge did based on economy. The Sunshine Skyway bridge is only about 4.1 miles long but its unit cost is about $37,000 per meter. The Hangzhou Bay Bridge on the other hand is 22 miles and costs about $39,000 per meter. It is slightly more but when considering the fact that the bridges were completed in roughly the same amount of time that difference begins to seem insignificant. The construction of the Hangzhou Bay Bridge also required the use of many more construction vehicles due to the extreme working conditions in the bay.

Overall the Hangzhou Bay Bridge can be considered a form of structural art based on the three E's and the three S's.