topic Re: STRIP FOUNDATION DESIGN... A PROPOSAL! in Robot Structural Analysis Forum

STRIP FOUNDATION DESIGN... A PROPOSAL!

TSOFA — Mon, 17 Oct 2016 16:06:24 GMT

Hi,

I modeled a steel structure with a strip foundation. I would like your opinion for my way of modeling. I used beams, columns, panels and rigid beams. Please find the attached file.

-Do you think that it works ok?

- even though i used the "correct" tab, when I run the model and the program creates FE again it gives me nodes really close to each other ( see the bottom nodes of rigid beams that I use to connect the foundation beams with the foundation panel). How I can correct this?

thank you in advance,

Sofia

https://we.tl/o6LggFW5Jn

Re: STRIP FOUNDATION DESIGN... A PROPOSAL!

TSOFA — Mon, 17 Oct 2016 22:06:44 GMT

@Rafal.Gaweda or any other who can help? Thanks!!

Re: STRIP FOUNDATION DESIGN... A PROPOSAL!

Rafal.Gaweda — Tue, 18 Oct 2016 08:19:21 GMT

1. Turn off kinematic constraints in job preferences

2. Move corner bars 1689 1801 1818 1930 to corners.

So far you have:

HINT : If you are correcting mesh it is always good to make it on frozen panels \ meshes

3. Set Model Generation tolerance =1mm

Corrected model attached.

Re: STRIP FOUNDATION DESIGN... A PROPOSAL!

TSOFA — Tue, 18 Oct 2016 08:48:37 GMT

Thanks Rafal!

do you think that this is a correct approach to foundation design? do you think that the loads from the superstructure are distributed correctly to foundation? If I use RC design for foundation columns, beams and slabs, I will have correct results?

Re: STRIP FOUNDATION DESIGN... A PROPOSAL!

Rafal.Gaweda — Tue, 18 Oct 2016 09:02:15 GMT

For me the model is correct are results should be fine.

Re: STRIP FOUNDATION DESIGN... A PROPOSAL!

TSOFA — Tue, 18 Oct 2016 10:25:02 GMT

Dear Rafal,

i am attaching two models. The one is the same that I sent you before, but I added the self weight of the structure (I forgot the s/w at the model that I posted at my 1st post). The second model is the same structure without foundation but with fixed supports. The problem is that the results are really different. If you check the pdf that I am attaching, when I optimize the main chords of the trusses, the optimized steel section that gives me is huge! I can't believe that this could be correct. Why the results of two models are so different? Would it be safe to design the steel sections from the model with the fixed bases and then to design the foundation from the other model?

https://we.tl/BLtQHyb0x6

Re: STRIP FOUNDATION DESIGN... A PROPOSAL!

Rafal.Gaweda — Tue, 18 Oct 2016 11:21:35 GMT

Dear Sofia

Before you start comparing design results you should compare models and FEM results.
IF you take a look at My diagrams on 190 191 205 206 (gable columns model) and 1to4 in "wind foundation 2017" model for case 1 you will see copletely different diagrams. Why? Because in "wind foundation 2017" model purlins 225to227 232to234 are not connected to upper chords (make big zoom to see it) etc

Re: STRIP FOUNDATION DESIGN... A PROPOSAL!

TSOFA — Tue, 18 Oct 2016 20:59:11 GMT

Hi again,

first of all, I can't understand how this happened because I haven't touch the superstructure. What I did was to erase base supports and create the foundation. What activity you think that caused these changes to my model?

I corrected the model and run it with some more loads. Soil weight at foundation & foundation weight, and two possible positions that truck loads the beam foundations.

I think that something is wrong with my model. The reinforcement of foundation increases at the internal corners. Moreover, the shear force of the slab foundations are very high for wind loading and the internal corners have the highest values of shear force. Even the cases of wind where the roof of the structure is symmetricaly loaded, the way that the slab is loaded is the same.

could you take a look?

https://we.tl/SjQBEHk6ld

Re: STRIP FOUNDATION DESIGN... A PROPOSAL!

TSOFA — Wed, 19 Oct 2016 22:59:24 GMT

Sorry for this, but have you seen the model? thanks a lot

@Rafal.Gaweda

Re: STRIP FOUNDATION DESIGN... A PROPOSAL!

TSOFA — Thu, 20 Oct 2016 00:55:43 GMT

Hi, Rafal or any other out there...

first of all I found a mistake. My thinking was to connect with rigid elements (pipe Φ10cm of rigid material, that I created) the foundation elements (foundation beam with slab foundation, columns foundation with slab and foundation beams). It seems that I forgot to attach the rigid material to my solid pipes Φ10, so the results were wrong. I corrected that and the values of shear force of "raft slab" foundation (the web of the strip foundation) are now lower. The problem is that the shear forces are still high at the inside corners of the strip foundation. The area that the shear force is high, is very small and I don't know why this is happening.

The second thing that I did is to model the foundation strip a little bit different. I attach the model, but it gives me warning of "seperated structure" and I can't find why. Could you?

Thanks!!

https://we.tl/cjlXCWKpYg

Re: STRIP FOUNDATION DESIGN... A PROPOSAL!

Rafal.Gaweda — Thu, 20 Oct 2016 09:14:09 GMT

As I mentioned in post 3 you should move corner bars to corners

But it seems you have not managed to do so.

Re: STRIP FOUNDATION DESIGN... A PROPOSAL!

TSOFA — Thu, 20 Oct 2016 09:43:25 GMT

ok, thanks!!

the problem is that after I correct the model I don't freeze the FE meshing!!