PSI required to minimize air mattress displacement

[thewolf5589]

Hello--can anyone please help me estimate the PSI required in an air mattress to minimize or even prevent displacement if a person, say 220 lbs, walked across it?

Mattress material and wall thickness variable. Surface area variable.

Also, if scenarios where the person is standing still, walking (gently and or stomping), and jumping are considered, I would appreciate it.

Thanks!

 

[russ_watters]

Welcome to PF!

You can't prevent displacement. To minimize: higher = better.

 

[thewolf5589]

Hey Russ, thanks. I'm building a prototype for a pet project. I imagine it should be similar to an air mattress conceptually (inflates with air, similar construction) but it'll be different, so let's call it an airbag going forward.

Bear with me...Force exerted by a 250 lb man standing still is ~1110N. Assuming ~sz 12 shoes are worn, the pressure exerted is ~2.4 PSI when standing with both feet (and ~4.7 PSI when standing with one foot). Assuming the force is doubled from jumping, pressure exerted is ~4.7PSI with two feet and ~9.5PSI with one. So if airbag PSI > 9.5, displacement should be minimal from a 250 lb man?

Someone suggested water would be better to achieve my objective--so long as the airbag was constructed with firm material. Thoughts?

 

[Nidum]

I don't entirely understand the question - if you really want minimum displacement then use a rigid block ? Some clarification of your basic problem would be helpful .

Calculation of pressure rise in an air bag under localised loading is not straightforward . Fitting a pressure gauge to some sample bag designs would be easier than attempting the calculations .

Stiffness of an air bag depends on it's geometry and construction . An inflatable mattress will behave in a different way to a balloon .

Stiffness of bag also depends on spread of the load . An air bag fitted with a rigid walkway is stiffer than a bare bag .

There might be alternative solutions using materials like foam rubber or using a mechanical construction .

 

[thewolf5589]

Hey Nidum, Thanks. I'm hoping to build a carpet that exists in two forms: flat and contoured. The airbag will rest beneath the carpet. For flat, the airbag will be deflated, and for contoured, it will be inflated. When inflated, the airbag will stretch the carpet away from the floor forming a gradual sloping bump, so based on this, I believe air to be the best medium but am surely open to suggestions. Also, can you think of a better word than contoured..?

While the airbag is inflated, I'm trying to determine how it'll be possible to walk on the carpet without transforming the airbag's shape and disturbing other areas of the carpet through air displacement.

To your point about geometry and construction, adding ribs acting as support to the airbag's interior will help, although when deflated, the airbag and ribs will need to be truly flat. Also, to your point about a rigid walkway, I suppose by placing the carpet on top, there's some additional support through load distribution.

 

[russ_watters]

The difficulty with air is that it is compressible, and if you use it to inflate something that has to be flexible, it's going to move around and compress. If you filled it with something that is not compressible, like water, then you'd only have to worry about it moving around, which may be easier to constrain.