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 being 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 would then lift it and put it 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.
Read more about this topic: Hangzhou Bay Bridge
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