Ski Builders Forum

Hello, Thanks for all the great information. I am building a press using 4 W 8x31# X 40' I beams. 96 inches long. Mounted on w 12 X 35# x 40' 16 inches. Will these be strong enough? will post pics if they are. If not, they will become a very expensive rail road ties used in landscaping. Thanks in advance.

I'm terrible with my US units, so this may not be accurate...

As we preach to everyone though, do the math, if you can't then post the relevant info here (Area moment of Inertia, I, Ixx) and the distance between supports and we can generally help. This is generally available from tables on the net for sizes of beams. A site for reference is here http://www.engineersedge.com/standard_m ... erties.htm

To work out simple bending supported at each end with uniform loading (i.e. pressure), look here http://www.engineersedge.com/beam_bendi ... tion_1.htm

For you, assuming
a) that calculator above is correct,
b) i know how to use it with imperial units, and
c) 50psi evenly distributed across 96 x 8",
you're looking at around 0.134" deflection, or 3.4mm, which is a fair bit, but unlikely to result in destruction of the beams. This seems reasonable, considering my I beams are a similar weight to yours (31lb/ft = 46.1kg/m, mine are 46.7kg/m) however mine are higher and therefore have a higher moment of inertia. I see about 1mm deflection of the upper beam in mine at ~50psi.

You can reduce the deflection of the bottom beam (where your mould will be affected) by supporting the bottom beam in the centre as well as both ends, i.e. by putting vertical frame supports at this point, or wheels in the centre as well as each end. The deflection of the upper beam shouldn't be as much of a problem, as the air bladder will form the shape.

Your 12x35 vertical supports are pretty much the same as mine, maybe a tad heavier, and should be fine.

Make sure you built it strongly. Thick bolts or arc welded.

My thinking was a bit off. Minus 6.5" for either side makes it a 83" gap. Use a higher design pressure, so 100psi, makes the deflection around 0.15" which is 3.8mm.

I did a quick calc for you. the clear span is 96"-6.5"=89.5"
I use 50 PSI over 6" becuase if you have a 8" wide hose when flat, when it inflates it is not putting 8" of pressure on your beam, i assume 6". I am assuming 36 ksi steel for the W8X31.

Bending.......... 300 kip-in<655 k-in (allowable strength)............ (Beams OK)
Shear........... 13.4kips<29.5 kips (allowable strength)............ (Beams OK)

Deflection =.0786" @ center span

These beams are fine in terms of strength. It is your preference how much deflection you can live with. That is a pretty stiff beam in my opinion.

Gentlemen, Thank you for the feedback. I will add a center support. If it is worth building... it is worth over building. highest regards.

Thought you were doing a double wide?

Doublewide? I am the two beams side by side. Is that a doublewide?

2 skis pressed side by side.