Max load for a frame..

[ports394]

I've got a 1000 gallon tank sitting in a stand. The stand has a ring supporting the tank bottle (its plastic), and the 4 legs are held together by flat steel to make a boxed bottom. The tank will be filled with water and some solids. I estimate it'll be 10,000 lbs.

We need to raise the tank 1 foot higher than it is. The easiest option is to build a wooden frame to put the tank stand onto.

One of the guys in our office says to just put 4x4" post thats 12" long vertically under each leg and then use 2x4" wood to box the bottom. 2 of the flat steel plates have bolt holes in them, so he would then put in some 2x4 under the steel, bolt to it, then bolt sideways from the 4x4 into the 2x4. That way the legs should stick to the frame decently well.

How do I find the compression load capacity for the 4x4 pressure treated wood?

I'm thinking that we should get some 2x6, flat it flat, and stack the peices, under 3 of the sides (the 4th needs to be open to have a discharge pipe), and frame it that way. It's overkill, I know. It'd end up being a a large U with a cross brace.

 

[Ron]

If this tank is outside, you'll have wind loads on it...therefore a lateral load on the joint at your "leg extenders"...not good.

If the tank sloshes, you'll get lateral load...not good.

Why not just build a cross-braced steel frame that matches the leg pattern of your stand, lift it and set the whole thing on it, then bolt it all down.

To answer your question, you're looking for compressive stress parallel to the grain. Now that you know what you're looking for, do something else.

 

[MikeHalloran]

Is anyone in the office a structural or mechanical engineer?


Mike Halloran
Pembroke Pines, FL, USA

 

[ports394]

The tank is indoors. Hopefully there shouldn't be any major sloshing in the tank, it's a simple waste tank, pump into the top, drain out of the bottom. There will be a waste recirculation within the pump, and to the top of the tank.

I'm the office ME. I remembered an old statics textbook that had some basic wood tables in it, but I couldn't remember the name of them.

I'm avoiding welding the frame because with wood, I can build it myself in a day. The plant I'm borrowing resources from currently is in a 1-week shutdown period and all of their maintenance/welders are in use.

To me, using the bolts to distribute force at a 45deg angle, or even laterally to the 4x4" posts is a bad idea. I agree that it wouldn't distribute evenly, and could cause rotation.

I think a 2x6" U-frame with a cross brace would be sufficient when bolted to the the original steel frame. The 2x6" should be able to take the 2500 lbs on each side compression without any issues.


ports

 

[rb1957]

you're going to stack with the 6" side flat (ie 8 pieces tall) for 12" ? and each side will be reacting more than 1/4, since you're leaving 1 side open ... i'd guess that two sides are going to react 4,000 lbs each, not that that sounds like a problem either.

 

[ports394]

This is the first photo.

 

[ports394]

Sorry, I'm new to this forum module, didn't see how to include multiple photos in the post.

Basically the ring supports the 1000 gallon bottle, and the ring+cross braces distribute the force to the 4 2" pipe legs. The 2" flat steel between them, as you see in the second photo bends upward. It's not taking the load, I think it's mainly to keep the legs from spreading.

All 4 legs would be under the 2x6" frame, and should distribute the force downward evenly. the open side would be braced across the bottom, and I just need to leave the upper part open to get the 3" pipe through. But the way it looks now, the steel wouldn't be touching the 2x6" even if it was there.

I am raising the center of gravity on the tank, and that's why I was looking at the 6" wide wood, instead of the 4x4" to give it a wider base.

ports

 

[desertfox]

Hi ports394

Not an elegant solution but why not just sit the four legs and the flat strip between them onto a channel section, you can obtain channel section a foot deep.

http://www.roymech.co.uk/Useful_Tables/Sections/chanA_dimprop.html

desertfox

 

[ports394]

I like your idea desertfox. But once the whole thing is in the channel, I'd still need to lift it approximately 12" inches. Would the lift legs be welded on?

That's the part that slows us down. The plant is on Day 3 of their 3-5 day shutdown. And I would still need to purchase the steel, and then schedule time for someone to weld it together. I've learned to weld, but I wouldn't trust my structural welds.

 

[BAretired]

I like the idea of the 2 x 6 laid flat. Let the boards cross at the corners, i.e. alternate boards, four each side. This leaves 1.5" for the discharge pipe on every face.

The bottom two boards will be on opposite sides and should be fastened to the floor to prevent accidental rollover.

BA

 

[rb1957]

you have to weld things together, you can bolt them ...

channels 12" tall would be subject to rolling, though maybe not at the loads we're talking here.

there's no need to support the entire length of the sides ... all the load is coming down the corners, surely (that was always a warning word when my bss used it) a nice big hunk o'wood (2x6s, 4x4s, whatever) with a bearing plate on top, to hold them together maybe just some glue (it'll be under compression) maybe sometime around the feet to stop them from walking away from where they should be ...

 

[desertfox]

Hi ports394

I meant place the frame you want to lift up onto the channel, the channel being vertical in the 12" direction, which gives you the height increase your looking for and then just weld the frame to the channel flange.


desertfox

 

[JAE]

Are you in a seismic area? Some parts of the country (such as southern Illinois, have very high seismic requirements and an interior, heavy, tank would require attachment to the floor or some foundation to resist overturning (depending on the mass and height of the tank relative to the base width).

 

[ports394]

This is what we went with.

 

[ports394]

At a max load, between the frame, tank, and full liquid weight it could be 10, 000 lbs. The 4x4 post compression loads are well above that. The tank sits level, and the force should be split evenly between the 4 legs, and the bracing inbetween will keep the legs vertical and square.

I've loaded the tank up to the 1000 gallon capacity, and also to 700 gallons and recirculated it with the pump sitting behind it. The tank didn't shake, or slosh.

Because it is a pilot plant, and many of these modifications are temporary, we can get by with quick fixes like this, and using PVC.

ports