8 foot steel stand, few questions for the engineers.

[atraperegrinus]

I have an 8 foot sump, and my DT will be 72"

DT - 72x32x24
Sump - 96x24x20

DT is acrylic no frame obviously, with eurobrace.

so im planning to have the stand fully encompass the sump so i can keep it 1 solid steel base instead of free standing legs.

Ive been considering 2x2 or 3x3 1/4" thick wall steel for the stand construction.

I was wondering if i have 4 vertical supports in each corner for the 72" DT above the stand. using 2x2 or 3x3 1/4" thickness square tube would i need to have( centered over the 72" span ) a vertical center brace? i'd love to go with no vertical support so i can freely work in the sump under the tank, or id even consider one or two removable ones.

if that will not work, what form factor would i need to make this possible?

I have no problem what so ever fully supporting the backside of the stand with plenty of vertical supports aswell, i only need the front side open.

open to suggestions and ideas. if someone needs me to make a 3d model in sketchup quick i can, i'm just feeling a bit lazy today.

thanks!

edit, if i can get away with a less subtiantal steel size and thicknesss please let me know. i have a source for cheaper steel and would rather overbuild but not to the point of absurdity lol.

I considered just doing wood too, but i wanted to avoid having a huge 2x6 or 2x8 joist taking up a ton of space under the tank aswell.

 

[asdfghp]

So, if I read this right:
What size (box) beam (mild steel) is required for a 96" span with an evenly distributed load?

 

[atraperegrinus]

So, if I read this right:
What size (box) beam (mild steel) is required for a 96" span with an evenly distributed load?

not even 96, just 72. the whole stand will be 96, but i'll put verticals under the 72" length part which is where the end of the display tank will sit.

there will be 24" of extra stand, this is an in wall so it will not ever be seen.

i'll work on a 3d model tomorrow to throw up a quick visual.

edit: screw it i did it now

obviously i would add in corner supports n whatnot this is just a rough idea.

this would let me drop the full length sump in underneath without having to put down plywood, i have water channeling in the floor to prevent water accumulation so i dont need to worry about that.

 

[Gorgok]

If i am to believe the calculator a 2 x 2" 1/4" wall horizontal would deflect ~1/4", a 3 x 3" .070". A doubled up 2 x 2" (2 x 4") 11 gauge horizontal would be under .100" (calculator doesn't account for the extra flats, welds etc)... With 3/16" wall you drop under .060". All with 2000 lbs on just that beam.

You could also consider rectangle tube, like 1.5 x 2.5" which is the same weight (price) as 2 x 2" though a better shape to support horizontal loads. Same for 1 x 3".

I wouldn't go to 1/4" wall on a stand myself, its not an efficient way to gain strength. Usually 11 gauge is plenty, though 3/16" may also be okay for some pieces.

 

[atraperegrinus]

If i am to believe the calculator a 2 x 2" 1/4" wall horizontal would deflect ~1/4", a 3 x 3" .070". A doubled up 2 x 2" (2 x 4") 11 gauge horizontal would be under .100" (calculator doesn't account for the extra flats, welds etc)... With 3/16" wall you drop under .060". All with 2000 lbs on just that beam.

You could also consider rectangle tube, like 1.5 x 2.5" which is the same weight (price) as 2 x 2" though a better shape to support horizontal loads. Same for 1 x 3".

I wouldn't go to 1/4" wall on a stand myself, its not an efficient way to gain strength. Usually 11 gauge is plenty, though 3/16" may also be okay for some pieces.

Okay, that's good to know. I'll look into that. Thank you very much. If anyone else wants to add ideas and opinions I'm all ears I have time to decide yet

Edit: was that deflection with the 72" unsupported span? Just making sure

 

[Gorgok]

Yes, so it will be less when the ends can't rotate up as easily being welded to the verticals, cross members, etc. Verticals on the back will also help it a bunch.

 

[atraperegrinus]

Yes, so it will be less when the ends can't rotate up as easily being welded to the verticals, cross members, etc. Verticals on the back will also help it a bunch.

Perfect, thank you!

 

[Fuel Doodle]

Looks like you had enough engineers answer and don't need me this time


Sent from my iPhone using Tapatalk

 

[jccaclimber]

If i am to believe the calculator a 2 x 2" 1/4" wall horizontal would deflect ~1/4", a 3 x 3" .070". A doubled up 2 x 2" (2 x 4") 11 gauge horizontal would be under .100" (calculator doesn't account for the extra flats, welds etc)... With 3/16" wall you drop under .060". All with 2000 lbs on just that beam.

You could also consider rectangle tube, like 1.5 x 2.5" which is the same weight (price) as 2 x 2" though a better shape to support horizontal loads. Same for 1 x 3".

I wouldn't go to 1/4" wall on a stand myself, its not an efficient way to gain strength. Usually 11 gauge is plenty, though 3/16" may also be okay for some pieces.

I'm getting different numbers, which makes me think my calculator may be off. Just to double check your assumptions:
2000 lbf uniformly distributed across 72 inches (on a single simply supported beam, so ~2:1 sf). E = 29e6 PSI. Neglecting the support from the section beyond the tank, ie simple supports at both ends.
Case 1 - 2"x2", 0.250" wall
Case 2 - 3"x3", 0.070" wall
Case 3 - 2"wx4"t, 0.120" wall

 

[atraperegrinus]

I asked for a quote for 1.5"x3" 3/16" wall tube for the top and the bottom and verticals all 1.5"×1.5". Shouldn't be too bad, last time for my 7 foot stand was a grand total of $23 so if i stay under a hundo for All of it I'll be quite happy. I get scrap price through family who works in a steel mill.

 

[Gorgok]

Case 1 - 2"x2", 0.250" wall
Case 2 - 3"x3", 0.070" wall
Case 3 - 2"wx4"t, 0.120" wall

The 2nd case was also 1/4" wall (as per OP options), deflection was .070" though that was rather unclear.

The calculator is using E of 30e6 by the looks of it. But that shouldn't change much. And i assume it was more off than that little would do it...

This is what i used (no idea if they have ads and such, i see none...):
https://www.easycalculation.com/engineering/mechanical/deflection-hollow-rectangular-beams.php

It was nice in that you could make custom sizes, but it seems suspect on further examination.

And this was a good sanity check, though not uniform loads:
http://metalgeek.com/static/deflection.php

It does agree with much of the above, these values are always higher (as they should be with point loads) and the I is the same (though you are limited to squares).

But it does seem strange that the one i used doesn't mesh with this and doing it manually:
http://www.engineersedge.com/beam_bending/beam_bending1.htm

Where they say a calculation of 5/384 * (W * l^3 / E * I) is the max deflection. The calculator doesn't use 5/384. They seem to use the mm to inch conversion factor (10/254 or ~.0393701). Wonder if thats the cause.

This agrees with the previous, though you have to take the weight to line pressure (weight/length) in the calculator...
http://www.efunda.com/formulae/soli...dy_display.cfm?case=simple_uniformload#target

Not that it was that big of a deal to just enter it all in google and doing it 'manually' :sad2: after this gogglefu.

(5/384) * (weight * length^3 / E * I)
Where I = ((width * height^3) - (inside width * inside height^3)) / 12

So the 2 x 2" 1/4" example is:
(5/384)*((2000*72^3/(30000000*((2*2^3)-(1.5*1.5^3))/12))))
0.35547428571"

In short, the one i used is undershooting the values some, which may not be a big deal with as much overshooting as i used for load on the beam. But the last calculator seems accurate, you just have to manually do the I...

 

[Gorgok]

I asked for a quote for 1.5"x3" 3/16" wall tube for the top and the bottom and verticals all 1.5"×1.5". Shouldn't be too bad, last time for my 7 foot stand was a grand total of $23 so if i stay under a hundo for All of it I'll be quite happy. I get scrap price through family who works in a steel mill.

I would probably even omit the rectangle on the bottom unless you have it on levelers, the floor will support it just fine. Though at scrap prices (as in ~$35 for a ton) it really doesn't matter...

 

[atraperegrinus]

I would probably even omit the rectangle on the bottom unless you have it on levelers, the floor will support it just fine. Though at scrap prices (as in ~$35 for a ton) it really doesn't matter...

Yeah sorry it was unclear, the bottom would be 1.5x1.5 aswell. Thanks a bunch guys for your help! Kinda nice to see the math all laid out.

 

[jccaclimber]

<snip>

In short, the one i used is undershooting the values some, which may not be a big deal with as much overshooting as i used for load on the beam. But the last calculator seems accurate, you just have to manually do the I...

Your hand calc. matches mine. I'm getting:
Case 1: 0.355", @2000, lbf. Still 0.196"@ 1100 lbf which is more than I would want in a stand.
Case 2: 0.093" @2000, 0.051"@1100, guessing this to be acceptable
Case 3 (4x2x0.120"): 0.113"@2000, 0.062@1100, also guessing this to be acceptable.

In trying to determine acceptable for a stand I've been looking at the RocketEngineer design and estimated the 6' 125 gallon case at 0.055" (E=1.5e6).

In any case good leveling and having flush corners with welds that don't stand up seems to be as much of an issue as anything else.

 

[Gorgok]

I figure under 100 thou on the overestimated load is probably going to end up pretty good in real application. These are still free end calculations, not welded in to the verticals/ends. Add to that a center vertical in the back tied to the front with a cross member. Being acrylic it will need full support so it will have more cross members than that, and at least one layer of ply too. Pretty soon not much of that flex is left.

The doubled up 2 x 2"s would actually fare better than the 2 x 4" calculation, as technically the inside height is less four times the wall thickness, not just two. Bringing it down to a deflection of .076" @ 2000 lbs. Which is a better solution in practice i think than the massive 3 x 3" that it beats in stats, even though the wall thickness is under half. Rectangle tube is still my choice just because its quicker to weld up as you wont have a long series of short beads to run to tie the doubled up beams together.

I = ((2*4^3)-((2-.24)*(4-.48)^3))/12)

 

[atraperegrinus]

I was going to do 6 cross supports across the top and add 2 additional verticals on the back side, as well as the plywood as mentioned, and likely a layer of foam, pretty sure thats usually recommended under acrylic. All with 1.5x3 and 1.5x1.5 3/16. Going off what you guys have said i should be pretty set. Thats 2 verticals in the 72" span, so 5 total verticals on the backside 3 total up front leaving the 72" open