Steel Foundation 1

[fkd]

Dear Experts,

I'm developing some standart steel structures for industrial buildings, warehouses and farm facilities for serial production aiming to find the fastest way to provide the client with the building ready to use. At this point the steel structures issues are done but occured to me a way to save some extra 10 days in the hole process and that's the point were I do need advices.

I'm thinking about doing the footings also in steel something like a large adequated stiffined base plate to resist the soil pressure with a short collum of adequated lenght and top connections, such assembly will be installed over the botton of excavation with a layer of fast curing Grout over the compacted soil.
We will achieve a plus concerning to the precision of the footings location too.
All the steel will be Corten (ASTM A242 or A588) protected with bi-component epoxy shop primer.

Does anyone of you have ever heard about something alike this "crazy idea" (point of view from some of my local Brazilian collegues)?

Thanks in advance

Fred

 

[Ron]

Fred...your idea can work, but will likely be expensive. One major point that your idea doesn't seem to address is stability under wind. You need a lot of mass in the foundation to resist overturning in wind loads.

One thing you might consider is a shallow driven pile to create a foundation pier. Could be done in wood or steel, then connect your building to it. I don't know your availability of piling contractors, so that might be an issue.

 

[ishvaaag]

I think cost and durability are the key points.Stability against wind could be gained through box action, provided general stability of the box against uplift and horizontal wind is enough, where the first comments counts totally. The steel being corten is warrant of durability against ordinary at most humid atmosphera, but the soil can have other aggressive agents against which corrosion it won't be possible in general to warrant. But in any case steel piles are made to be embedded in soils, and propve to be longlasting enough. All points your application be more critical than steel piles since closer to the surface, where both water presence and air must vary more and enhance corrosion. I wouldn't rely on thin grouts over steel plates as means of protection against corrosion. So albeit possible, a thorough investigation of durabilities under different conditios would be necessary (maybe is done somewhere) and of course sooner a investigation of the costs, just to see if your client is ready to undertake the move (can remain competitive?), what may avoid further considerations.

 

[fkd]

Ron, the model I've used is based on a "rigid" frame with simple suported collums thus the structure don't transfer moments to the foundation (ideal condition) only axial loads, the major problem in my concern is the pulling efecct that can(?) be resisted by the self weight of the compacted soil over the foundation, in adittion our local wind codes generated something near 0.65 kN/m² sucction over the roof sheating so the reactions are not large too. Regarding to the shallow driven pile it's a common solution here but I'm intenting to avoid the need of equipment alocation to reduce costs and also speed up the process.

Ishvaaag the corrosion problem I guess that can be aproached as you suggested and here for steel piles the codes impose a thickness reduction to be aplied at the plates embbebed in soil so I guess that this kind of approach would accetable, what do you think? Concernig to costs, my initial calculations based on a finite element model with the stiffiners (ASTM A242) modeled as shell elements and the botton plate as a membrane (ASTM A588) under uniform pressure leeds me to a resonable steel weight.

Thank you all for the fast reply, and have a nice end of weekend.


Fred

 

[ishvaaag]

Then all remains a thing of examinign durability. I suggest you start a search for such thing in the internet, the durability of steel or steel protected by grouts underground. If the building has short life for explotation it may be worth to try, because in any case some protection you will gain from some embedment etc. Then it would be to find an owner wanting to try the benefits of your approach, pereferably small scale, just to see. In any case some minimal depth would be necessary -settlement, heave, etc- and one way or another put through concreting to the protection of your steel, so you would be mostly gaining manpowers' time in the field (total maybe not if accounting fabrication and erection, who knows).

 

[LPPE]

One other thing - don't let anyone tell you your idea is "crazy". Some of the greatest engineering inovations have come from ideas that were initially thought of as "crazy". Always think outside the box.

 

[phuduhudu]

How about a composite version of what you suggest. Put in the blinding on the compacted soil and then put your steel column with base plate on this but keep the base plate very small just to support the column temporarily. Then just pour your footing concrete around the plate and steel column. So you end up with a steel column embedded in the footing. That way you can get your frame up before pouring the footing. You just need to be careful of the temporary condition. The bases could be pinned down with rebar into the soil as a temporary measure. And then you should make sure the footings are poured before sheeting. Carl Bauer

http://www.bauerconsultbotswana.com

 

[fkd]

Pylko - Thanks for the encoraging words


Calbauer- your idea is very good it will save some steel I'll think about this, and try the analyse the composite structure, maybe with adding some kind of shear stud, over the botton plate, or pieces C sections welded to it due to small thichness of the bottom plate we can achieve an effective composite action. I will also evaluate the magnitude of initial (erection) possible reactions, I guess that your idea will improve the hole model.



Thank you all


fred

 

[phuduhudu]

I wasn't thinking of composite structural action as such. All you need is for the steel column to be able to transfer it's load into the concrete and for this to be able to distribute it's load to the ground as usual. If you are concerned about shear transfer into the concrete you could weld some studs to the bottom of the column or just drill through the flanges and stick the studs through. Carl Bauer

http://www.bauerconsultbotswana.com

 

[Gourile]

I think the most important problem with your idea would be its cost. As the soil bears a certain stress, you will have to provide a definite bearing surface to transfere column loads to the ground, no matter you use concrete or steel for your foundation. In concrete, a high thickness provides enough moment of inertia for the footig to bear the bending moment on the root of the column. For steel, as someone else refered, you either have to use thick stiffened plate or a double skin (box shape) to provide such a moment resistance. Durability is another factor, which offcourse can be satisfied in your casse. But in your approach, you will loose some extra safety gained from passive resistance of the soil and solidness of the footing ehich is not taken into account in normal calculations. You will also have wrapping problem when welding high thikness plates, so you may have to be using special material amd welding procesure to avoid this deformation and wrappings and it will cost you even more.

 

[srm]

I assume that your building will have a normal concrete floor slab.

Why not bolt the column baseplate directly to this floor slab using standard concrete anchors? Then there is no problem with misplaced holding down bolts or possible corrosion of the embedded steelwork.

Mesh reinforcement may be adequate to transfer the column reaction over a large enough area of slab to achieve the allowable bearing pressure.

 

[fkd]

--> Gourile the plates thickness aren't big enough and the sizes of the welds are relatively small and they will be MIG welded, so I'm sure that I won't have warping problems.
The bottom plate work as a menbrane so I dont need heavy plates they are about 3.00mm thick and that why stud bolts become a problem.

---> SRM Your idea is good, but there are some issues to consider concerning to the soil's top layer adequation and further, here is a common practice to cast the floor slabs after the copletion of the roof assembly, including sheating due to weather matters.

Anyway thank you all for the advices.

 

[LPPE]

If you're relying on these column footings to resist the lateral shear load (ie columns not integrated into floor slab system), you may wish to consider your coefficient of sliding friction for steel on soil, instead of concrete on soil. I would imagine the value is a little less than that of conc. on soil.

 

[ishvaaag]

If you are quite standardized maybe a more rational way is:

1) place preparatory layer of concrete
2) place there precast rectangular footings with baseplate placed
3) weld column
4) place slab on the ground.

the advantage is you get prefabricated, no contact ground with steel remains, and you gain neccessary depth, thickness and weight in the foundations.

For the precast part even lightweight concrete should be considered for portability.

 

[fkd]

Pylko ---> this is an issue that must be studied and for sure cant be forget, my oppinion is that as we have a layer of grout under the footing the sliding coefficente between soil and grout is similar to concrete and soil but we will have to ad some shear bars welded at the outer side of the botton plate to face this problem.

Ishvaaag ---> I will take your advice and start this way, but as I'm a steel structures fabricator I want to sell my product, but before selling this I will, as adviced, make some real models and try to test them in house, maybe using them in a warehouse that we acctualy need to build for ourselves.


Once more thank you very much,


Fred

Fred