By Chandrahas M. Halai
Modi! Modi! Modi!
This is how a 19,000 strong crowd of Indian Americans greeted their favourite Prime Minister Shri Narendra Modi at Madison Square Garden in New York on 28th September, 2014.
Madison Square Garden is a huge structure to accommodate a large crowd. Also, it has no internal supports; hence the audience was able to get a clear view of their leader talking to them.
Madison square Garden was constructed in 1968. This structure is cylindrical in shape having an outer diameter of 425 feet. This cylinder supports a roof which is a light-weight tensile structure called the hanging dish.
For pictures of the structure you can visit the website
https://www.severud.com/icons/madison-square-garden/
In a structure, a member under a tensile load can be lighter and thinner than a member under compressive loads, even if the internal forces experienced by both the members are equal in magnitude. This is because the compressive members buckle whereas members under tensile loads do not.
The roof structure of Madison square garden consists of 2 concentric steel rings. The outer ring is supported by the columns of the cylindrical structure. The inner ring is suspended on a series of 48 radial cables running between the rings. This is covered by precast concrete panels supported on the cables. Here, the cables are in tension. They pull the central ring outward hence the central ring is in tension. The cables pull the outer ring inwards hence it will be in compression. Hence the outer ring is called the compression ring. The roof system doesn’t exert any outward thrust or inward pull on the columns that support it. Only the downward weight of the roof is transmitted to the structural system below.
Engineering like art is also inspired by nature. This is also called bio mimicry. The light weight tensile structures like that of Madison square Garden are inspired by spider’s web. Just a look at the picture below will convince you about this.
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