Foundation for 12 kips Pull-Out Force 4

[shp6]

Hi all:

I am designing a small steel assembly for a mechine, which has four "legs". The legs of this assembly will be bolted to an industrial floor on grade. Due to the overturning moment, the pullout force for legs is approximiately 20 kips per leg. The self weight of the assembly can provide about 2 kips (500 lb per leg). The floor slab is a conventional 5" reinforced concrete slab which will not be able to resist this force. Therefore, I need to make concrete blocks underneath these legs.

Can anyone please tell me how to determine the size of the concrete block (20 kips will need a monster block by self weight alone)? How to take the friction between soil and concrete block into accout or not? Do you have any other method besides concrete blocks? Please do not ask me to use "rock anchors" or "tie back" since it is supposed to be a small project. Please let me know your thought and experience. I will really appreciate. Thank you.

 

[JAE]

shp6

If the legs are not too spread out, a mat foundation under the entire structure would work well. The overturning check would then engage the whole mat and not just a single block under each leg.

Alternatively, you could use a drilled pier of some sorts and drill deep enough to provide the necessary holddown weight. I'm always reluctant to utilize soil friction for holddown/overturning conditions as soil parameters are sometimes hard to pin down without a large variability in safety factor.

You can also dig down and construct a large footing with a pedestal for the columns. The footing, if wide enough, can engage the soil above and your calculations would then include the weight of the footing, the pedestal, and the soil on top of the footing. Some engineers use the soil directly over the footing while others (myself included) use a splayed area of soil (30 degrees from the vertical) that add to the downward counteracting force.

A spreadsheet can be quickly written to let you try different ranges of footing size, thickness, depth, etc. to get an optimum design.

 

[whymrg]

Can you use one foundation for all legs? In this case you will have weight of equipment plus weight of concrete foundation and moment.
If you can make eccentricity (e= M/P) less than half of foundation length (e<L/2) you may use equation for bearing pressure:

q= 2P/[3B(0.5L-e)]

This may be better than 4 monster blocks.

 

[shp6]

Hi: Thank Jay and whymrg. The reason I posted this question is because we do not want to open a big hole inside our mechine shop. The &quot;legs&quot; I have so far is about 1 foot by 1 foot and bolted down with two 1&quot; diameter A490 bolt or threaded rods. My idea is to build some kind of underground block to anchor these bolts. We only want to open a hole say 2 feet by 2 feet the most to place each leg. The depth may vary depends on the method we choose. I heard that there is some kind of drilling deep anchors which may be able to help. If anyone has other ideas, please let me know. Thanks.

 

[Ingenuity]

Hi shp6,

Re the &quot;deep drilling anchors&quot; maybe you are referring to ATLAS or MANTA-RAY, basically galv steel screw anchors. But this does seem to be getting close to a &quot;soil anchor&quot; which you said you wished to avoid.

BUT if you are indeed considering vertical anchors...you could consider a passive (or active) vertical soil nail/bolt - drill a 6&quot; or 8&quot; hole using your TEI Rig (this is the one that fits thru a standard door way and is electric powewered, 6 foot high mast), drill it about 10 feet deep (depending on your site conditions this will take less than 1 hour per hole is no casing is required), install 3.5&quot; dia HDPE corrugated duct for corrosion protection, install 150 ksi threaded bar, grout inner and outer annulus, cure, proof test to 20 kips (you have all the stuff to do this), use the 150 ksi bar, plate and nut as anchor attachments for machine.

Is the loading from the machine static or dynamic? For a &quot;small machine&quot; it sure has a good sized overturning moment/uplift.

I know i may be way off track, but since i know you and the &quot;gear&quot; that your shop, has you may wish to revisit this option.


HTH

 

[dlew]

shp6,
If you want to hold each 20 kips uplift on each legs just by weight of concrete, you would need a block weighing 30 kips (safety factor = 1.5), that is ONLY 7.5 cubic yard of concrete (6' by 6' by 6' block)
Other solutions would be the mat footing under the entire equipment or the anchors described by JAE, whymrg and Ingenuity

AEF

 

[LPPE]

I'm just curious - What kind of machine that weighs about 3 kips produces a possible uplift on each leg of 20 kips?

 

[shp6]

Hi:
Thanks to Jay, whymrg, Ingenuity, dlew, and pylko. Just for you curiosity for this mechine, let me try to describe this setup for you. As Ingenuity knew, I am working in a company has a lot of stressing rams. These rams can take as much as 1700 tons of force. These rams includes two part: outer shell and inner piston. These two parts are screwed together internally. From time to time, we need to disamble them to clean inside and calibrate the ram. Believe or not, to unscrew these rams it takes about 60,000 ft-lb of torque based on our previous experience. The largest ram has a size of 2 feet in diameter and 3 feet height. It weights 6000 lbs (sorry, not 3000 lbs as I mentioned previously). In order to produce this 60,000 ft-lb at a distance of 2 feet, I need to use a hydrolic piston to produce 30 kips force. In order to make this entire setup smaller, I have two floor beams length 5 feet each and the reaction force from the legs is approximately 20 kips in tension or compression. I hope this will give you some sense about this setup.
Ingenuity, I think I may go for the method you mentioned. I need to get more info about this method. Thank you for your help. I hope you are doing everything well there.

 

[JAE]

Try

http://www.abchance.com

for the kind of anchors that ingenuity was talking about.

 

[Ingenuity]

hi shp6,

You remind me of fond but frustrating memories!

The first time I did 0.5&quot; x 31 strand stressing we blew the gland seal on the jack!! It was in a remote area of the world and although a 31 strand jack weighs only 900 lb, returning the jack back to origin for repair was not an option.

To remove and replace the gland nut took an almighty human effort. We had VERY limited tools available to us, so we chain blocked the jack base to three 40' containers (120 degree angles), bolted long steel sections to the top face of the gland nut, and with 4x250lb men (i did not fit this category, so i guess i supplied about 1/10th the required force) proceeded to tighten/loosen the nut. Only done it once by hand, hopefully never again!

For a 6000 lb jack that can stress 91 strands if i am not mistaken - that is an absolute monsters!

I take it that the 30 kip hyd piston is in a horizontal position. So take care of the horizontal force at the foundation too!

I know you want a compact, self-contained base, but maybe it is worth splitting up the jack base from the piston base. Seperate them by say 10 feet horizontally and use the mechanical advantage - less hyd force required, hence less foundation reactions. You can attach a steel lever section to the top of the gland nut using the tapped holes on the nut circumference. On the infrequent times that you have to do this setup i am thinking that the bases could be demountable so reduce congestion in your shop - just flush recesses for bolting the removable base with temporary covers for forklifts. Just a thought.

Also, soil anchors can also work in compression - mini/micro/pin piles - and have tremendious capacity in the right soil conditions.

I have designed and constructed several soil anchors/mini piles in the past, but local geotech knowledge is worth a lot (everything!), so speak with your geostructural guys for specific details.

Good luck. You get some interesting projects!!!

HTH

 

[shp6]

Hi: Ingenuity, Thanks for your advise. After talking to our shop manager, we may want to do a mat foundation instead of mini pile as you mentioned. The reason for that is we do not have the right equipment to drill a 10 feet deep hole here and the soil condition is unknown, either. Based on my quick calculation about the mat foundation, we need a 7'x7'x2' concrete base with steel to form this foundation. We figure that will be faster and less questions. We do not make the decision yet. I am actually doing both calculations to see which one is faster and cheaper.
The story you mentioned is very interested. I did not know these pistons are so difficult to seperate. These 1700 ton rams are like monsters. I am actually designing a crane to be integrated into this system and a pipe column will be used. This crane needs to take at least 8000 lb force and the arm is about 7 feet long. This crane is another monster for us but I think I am getting closer to get this monster. In addition, as you mentioned, I designed this system to be able to be disassembled and moved. As you know, we are looking for an new office and prepare to move soon. I have to make sure this system can be easily moved to our new home. I designed everything bolted instead of welded. You know bolting sometimes causes some problems but we will make it to work.
It is an interested project. I wish you were here to see us building this system. I will send you a picture to you when we completed it. You can probably build the same system in your shop.

Thanks again and good luck.

 

[Ron]

shp6...one other consideration, assuming you have some reinforcement (even wire mesh) in your slab is to &quot;key&quot; your footing or pier under the slab. That way you get the benefit of the slab weight as well as the footing weight, and you minimize the amount of cut into your existing slab. You can use this idea in conjunction with soil anchors, a relatively small pier, and the keying action of the slab.

To do this, cut a hole in the slab about 20-30 percent smaller than the diameter of your pier (will need a hole in the slab at least 15 x 15 inches, just to get shovel in and excavate for small pier). Excavate for small pier by hand, digging as best you can larger than the hole cut in the concrete slab.

Install soil anchor in bottom of hole, leaving anchor hook to extend about half way up into the pier.

Install minimal reinforcement/anchor bolts. Place new concrete and finish to level of existing slab.

Your resistance is then the addition of soil anchor + dead weight of pier + dead weight of concrete slab over influence area of at least 10'x10' (you can prove this by computing edge effects of rigid pavement under load!)

 

[shp6]

Thanks Ron. As I mentioned before, my system has four legs spreaded at four corners of a square shape. When the load is applied, the two legs in the diagonal direction will be in tension/compression at the same time while other two legs have the opposite reation. In this case, my mat foundation will be bent upward diagonally due to pull-out force while other two tips are in compression to the ground. In other word, my system will be self-equilibriumed. That is one of the reasons I want to use mat foundation. I do appreciate your comments which will give my system a lot of extra resistant force. I will consider it if my mat foundation can't work out with this force or this way can reduce the thickness of my foundation. I will take a look at this method. Thanks.

 

[Ingenuity]

shp6,

If you can get a small mat to work, i would agree that it will be better than having to &quot;play&quot; with soil anchors, most especially if you do not know your soil props.

Just for your info...you have a small drill rig in you geostructural section. It is made by TEI in Colorado. We also have one. It fits thru a 2.5 wide x 8 feet high door and it is electrical powered for the hydraulic system. Drills with 6 feet long bits. It is NOT hand operated, and has hyd feed, travel, tilt etc. Pretty nifty machine for limited access drilling. The manufacturer will tell you it can drill max 4&quot; holes, but we have drilled 6&quot;+ dia to 80+ feet depth, simultaneous with steel casing, below sea water level. Interesting job that i would not wish upon anybody.

I would like to see the photos when the &quot;project&quot; is finished.

Good luck.

 

[Ron]

shp6...if you have the room and the option, I would agree that mat is a better way to go.

 

[austim]

Hi, shp6.

Please forgive me if I have misunderstood your setup, but something about your basic concept puzzles me somewhat. I suspect that you may be making your project unnecessarily complex.

As I understand your postings, your foundation problems arise from the need to react a 30,000 lb. (horizontal) piston force which is applying a 60,000 ft.lb. dismantling torque to the inner component of a large ram. What I don't understand is why you have to take that force down to the foundation.

From your comment that your vertical forces are self-equilibrating I take it that your 'structure' accommodates both the stressing ram and the dismantling piston. It sounds as if one side of your structure resists the overturning moment on the ram, and the other takes the equal and opposite moment on the piston. I haven't seen any mention of your proposal for resisting the 60,000 ft lb torque on the ram itself.

In principle, with no external loads on the whole setup of ram plus dismantler, you should be able to design an entirely self-contained structure which would impose no loads on the foundation other than self weights. Making it truck transportable ought to be an option.

It sounds to me as if your calculation for the vertical forces looks something like this:

30 kips * 3ft high / 5ft length of ground beam = +/- 20 kips approx.

That is, each ground beam is subjected to a moment of something like 90 kip ft. If you were to have a 'torsion tube' (capable of resisting 100 kip ft for round numbers) connecting the two ground beams, it would provide all the resistance that you are seeking from your foundation.

Developing this a little further: if you take a 12 inch square box section made of 0.5 inch plate and subject it to a torque of 100 kip ft. you develop a shear stress of little more than 9000 psi. That is, we are not really dealing with large forces(which I suggest from the perspective of a bridge/wharf etc designer).

Now I put my head on the block for others to dissect -

My proposed 'foundation' would be a small grillage of 4 12*12 inch wide flange sections * about 3 or 4 feet long, with all flanges butt welded toe to toe, 0.5 inch plate at each end and with suitable local stiffening for attachment of your various ram options and the dismantler piston assembly. (WF webs parallel to your 30 kip piston force). Total weight of grillage - about 1 ton or so. Fully truck transportable, and no need to disturb your workshop floor slab at all.

 

[Ingenuity]

austim,

true...true...if the action and reaction are on the same &quot;platform&quot; then it is self equilibrating. Basically, like undoing a rusty bolt-and-nut assembly, with two spanners/wrenches.

I thought the piston was to be seperated from the jack assembly, but re-reading the threads it appears that all will be housed together, so no external actions are present.

You got me thinking now...if the piston was mounted directly on the outside of the outer shell of the jack casing and pushed against a steel lever that projected from the inner gland nut then you do not need any framework at all - other than the steel brackets for the piston and the lever attached to the inner gland.

The piston reacts againt the inner nut and out shell, pushing the outer shell clockwise, say, and the inner nut counter-clockwise until the two are seperated.

Good to see your &quot;down-under&quot; engineering at work!

Well Done!

 

[austim]

Ingenuity,

You are too gracious. I am still waiting to see if shp6 has something more to tell us that would invalid my entire line of logic.

It is a long way from a pair of wrenches to your 3 containers, chain blocks and half a ton of humanity

 

[shp6]

Hi: all, I hope everyone had a great weekend because I did.
In this weekend, I summaried the ideas from all of you and came out with a great system which doesn't need any frame or heavy foundation. The idea is as following:
We are going to unscrew the inner piston from the outer shell of a ram. I can simply make two thicker circular plates, bolt one of them to the inner piston at the top and bolt the other plate to the outer shell at bottom. A &quot;handle&quot; can be attached to the edge of each plate. A vertical bar will then attach to these two handles. The 30 kips hydrolic jake will be mounted horizontally between these two bars at the mid-height of the ram and apply the force to open this ram. In order to make the entire system to rotate, a &quot;pin&quot; will be placed at the center of the bottom plate to allow the rotation to take place.
In this system, there is no excessive overturning moment or force need to be taken care. Please let me know what do you think. I am here to thank all of you. YOU ARE THE ONE TO MAKE THIS SYSTEM HAPPEN. YOU INVENT THIS SYSTEM.

 

[Ingenuity]

shp6,

i am still having a great weekend....long weekend for me!

seems like you have a plan...make sure that the setup of the handles and bar works for both loosening and tightening....the tightening process is okay until you get to the last 3 or so threads, then it becomes real tough. If it not fully tightened it shall not hold full force and will leak hydraulic fluid.

Also, the &quot;handles&quot; and &quot;vertical bar&quot; will have to be pretty stiff for the load and eccentricity.

There should be existing tapped holes in both the top of the inner piston and the bottom of the outer shell to enable you to bolt on the circular plates. Check the thread size - metric vs US. Since this is monster jack it is probably custom made, and possibly made in Switzerland, so hence metric thread, and you do NOT want to strip these threads!

i assume the &quot;rotation&quot; you are talking about is only to enable the system to rotate to reset the handles/bar/horiz jack ready for the next &quot;push&quot;. Obviously, during the actual &quot;pushing&quot; of the horiz jack the bottom plate will need to be fixed to the outer shell.

What stroke horiz jack are you planning...it will have to be somewhat limited as you are pushing in a linear direction but the rotation/loosening is happening in a circumferential direction.

May i also suggest that you go to &quot;austim&quot;'s post and click on the bottom of it where it says &quot;click here to mark this post as helpful...&quot;...austim does deserve some &quot;rewards&quot; for his insight.

keep us updated on how it all works out.