Reading a Book about Air Sustained Structures...

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Summary:

I would like to have a question answered
As in constructions that consist of a membrane of some textile and are sustained by pressurized air bombs. A paragraph mentions that in the face of strong winds or snowfall the internal pressure rises... but i don´t understand exactly why is that. I´m just curious and would like to know.

pd. English is not my first language so if you see a mistake feel free to correct me :)
 

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  • #2
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sustained by pressurized air bombs
I think you mean "air-filled cells".

If wind or snow or whatever exert a force on the structure, the cells get smaller, resulting in higher pressure. I think that's what is meant in what you're reading.
 
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Kinda, yes. The book has two separate sections, one dealing with "air-sustained structures" and a different one for "air-cell structures". I would get why in a closed cell, with to membranes enclosing the air, it would increase pressure but the one i actually meant is the type of structure that presents only a single membrane stuck to the ground by poles or cables.

This kind of structure, well, it says that it needs a sort of "colander" to let excess air go so the pressure doesn't "suddenly decrease". I don´t understand how the pressure works in those cases. Why would filling a single membrane with air "suddenly decrease" the pressure inside it if it isn´t let out? Unless it's perfectly sealed to the ground the air would escape from under wouldn'´t it??

Also the winds and snowfalls would increase pressure on the membrane but if there is a "colander" wouldn'´t it mean that the pressure inside and outside would remain the same (as the structure is being virtually constant in being filled with air)

Edit. Sorry, i had a lot of spelling mistakes. That´s what I get for not using spellcheck, i guess.
 
  • #4
sophiecentaur
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I am trying to read 'between the lines' here anti would help if you were a bit more specific about the application. However, I am assuming that the structure you refer to could be a dome or a wing.
If you continually pump air into the structure and you have a built-in leak then the short term behaviour will be much the same as for a closed cell structure; changes in external forces could be too fast for any damping due to the holes to work. Slow changes of applied force would allow more deformation.
Analogies can be tiresome but the basics for an electrical analogue are not unlike the effect of a varying load on a Capacitor, charged through a source resistance. The source resistance Rs and load resistance Rl will affect the steady state (mean) and 'ripple' voltages on a reservoir Capacitor. The lower the source resistance (aka pump power), the less effect will Rl have on the mean volts and the greater the C, the less ripple / instantaneous change on the volts.
the structure is being virtually constant in being filled with air)
How "Virtually constant" will depend on the 'C and Rs' or pump power and volume capacity.
 

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