Picture taken by: Ahsan Iqbal, 09.03.2009
Image taken from: http://en.wikipedia.org/wiki/File:Parts_of_an_Umbrella.svgUmbrellas are something that I have always taken for granted and never bothered to explore the science behind the curtains. This has been an eye opening investigation on my behalf and hopefully you feel the same.
The umbrella operates on a very simple idea; it is an instrument designed to protect from rain or sunlight. The structure of an umbrella consists of a hollow tube that has a spring running through it, a runner is a part that moves up and down on the tube facilitating the opening and closing of the structure. The upper part of the protective structure consists of ribs that are connected to the top of the umbrella; the stretcher is joined to the runner and acts as the connection between the ribs and the runner.
An umbrella is opened by applying upward force on the runner; this results in pushing the ribs outwards to form a canopy. This action produces tension in the stretcher as well as in the joints at the end of the stretcher. The main issue in constructing an umbrella structure is its apt operation below the elastic limit of the materials used in the construction; so the material returns to its original shape once the runner is released (pushed downwards). Another key matter in the design of an umbrella is the precise rib distribution (hexagonal, octagonal, and so on depending on the size of the structure) about the tube at the center; to balance the weight once the umbrella is opened.
The only external force applied to the structure is that produced by wind; this applies bending moment about the tube and tension in the joints of the stretcher and the ribs alike.
I found this blog about the umbrella interesting and rather unusual example of how tensile and compressive forces are used make the umbrella open and close on the uses demand. Are there any other type of load or forces acting when it is being used in bad weather as the structure of the canopy often breaks or gets out of shape a,d this is a common problem with umbrellas.
ReplyDeleteAbdul Awal
well explained.how do u describe it when it get out of shape?
ReplyDeleteImran Zubair
There is no standardisation for umbrellas; the materials used in the construction vary in accordance to the price it is to be sold at, often compromising the structural integrity.
ReplyDeleteI was in London a few weeks earlier and Tesco had this deal: 'buy a newspaper and get an umbrella free', clearly a product that cheap will most likely shatter in bad weather.
The only other force that I can think of is the impact force of the raindrops on the roof of the umbrella, but that is negligible as rain drops merely hit and slide down. One can test an umbrella by chucking a bucket full of water on it just to see if it is strong enough.
Ahsan Iqbal, Structural Bandicoot