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Tips for this structure I am designing

Tips for this structure I am designing

Tips for this structure I am designing

(OP)
Hello all,

I need to design an structure which is able to support a cylinder loaded with 10 tons of weight distributed around its external face

The current model is the one you can see in the pictures. A FEM analysis has been carried out using "Simscale" and this is the result.

I would appreciate any advice or comment in order to improve this structure (made of steel, initially).

On the other hand, you can see a picture of a 2D model, in which a vertical load plus a moment is applied (exactly the ones caused for the cylinder plus external weight), and you can see the reactions in red. In green, I have written the reactions that the FEM simulation is calculating. I wonder which could be the discrepancy in the left support, in which 2D and 3D simulation are differing in the force direction

PICTURES:
https://imgur.com/a/yxEs0

Thank you in advance
Regards,

Javier

RE: Tips for this structure I am designing

JM_10,

If you are not confident about what you are doing, maybe it is time to contract this out to a structural engineer. However informative the FEA is, there is soil mechanics, all sorts of QA issues, especially if this thing is welded, plus building codes, and occupational health and safety. We don't want to lose control of ten ton (tonnes) of stuff.

--
JHG

RE: Tips for this structure I am designing

the biggest difference in your reactions is FEA is predicting a redundant self-reacting pair of loads (66), which you couldn't calculate by hand. You can relieve with a roller. Odd that element 1 is reacting almost as much normal (bending) load as element 5, but 1 is braced and 5 has to carry this in bending; but maybe you have to (possibly to access one side of the structure). Have you considered load cases that'd out the cable stays in compression ?

agree with the previous comment ... be very careful with a load of 10 tons. I'd suggest having some "learned" input.

another day in paradise, or is paradise one day closer ?

RE: Tips for this structure I am designing

(OP)
@drawoh @rb1957

Thank you for your answers

About contracting this out, initially the company is not considering it. However, we have time to learn some inputs and develop this carefully

So,

Yes, 1 is braced and 5 not, but not for particular reason, we just thought it would not be needed, as putting two cables in the upper side is more effective

Cables in compression have not been considered. But the structure will not turn to the cables side, center of mass is so far on the other side, even further than the first pinned support

So then, using a roller should be considered? Actually, even with this setup, both FEM and analytical calculations show conservative values

Thank you


RE: Tips for this structure I am designing

JM_10,

I have done some safety calculations. I made very limited use of FEA. I went through the structure joint by joint looking for weakness. Most of your failure points are bolts, flanges and welds. Let's just pick one element in your structure.

You have two cables. I can work out the loads on your cables using statics. I may have to make some assumptions about the rigidity of your base. Your cable has a load rating which must not be exceeded. You have cable fittings at each end with load ratings that must not be exceeded. You have some sort of brackets fixing your cable fittings to the floor and to your structure, that must be strong enough. You have bolts and/or studs holding the brackets to your floor and structure whose load ratings must not be exceeded.

It is very easy to make FEA show structural strain under load. Working out the stresses of a complex structure is an order of magnitude more complicated, and it requires a thorough understanding of the loads and how your reactions work.

Since I am not a civil engineer, I do not understand studs in concrete floors. How flat is your floor? How flat will your welded base be? I wonder if your mounting system is imposing strain on the structure holding your ten ton weight.

--
JHG

RE: Tips for this structure I am designing

Without knowing all the story and constraints, it's difficult to propose improvements. Perhaps though a single cable would be simpler? And taking them down onto the base member so there are only two base connections to design rather than the current three connections?

Maybe just a problem with my reading of the numbers but the free body diagram reports vertical equilibrium whereas I read 54+51-53-57=-5. I really don't like results that aren't in static equilibrium so would check this.

rb1957, consider the vertical (axial) force in the post member. It is applied near midspan of the base member and equilibrium requires essentially equal reactions at either end of the base regardless of the brace to one side.

RE: Tips for this structure I am designing

(OP)
Thank you very much for your help. Here you can see some auxiliary pictures to follow my response:
https://imgur.com/a/Q03F2

@drawoh

The floor is already prepared for such a weight. It consists in a Hall prepared for particle physics experiments, and there are already about 90 tons weight of other structures. However, the fixation of the cables to the floor has not been discussed yet, but some technical code will be followed

The design load of the stainless cables is around 450 KN, while the analytical analysis returns 65 KN in the one cable configuration, so it should be strong enough

For the critical points such as bolts and welds: That is my mayor concern. I have been designing the bolted joint between the cylinder and the frame, you can see the picture with the drawing of where these bolts will be placed (link above). Followed "Eurocode_Design of joints_en.1993.1.8.2005-1", and it should be working with that setup (using M20 bolts grade 8.8).

The rest of the beams will be welded. Here I have not started having inputs in welding yet, but I plan to keep using Eurocode.

I do not get what you mean by "working out the stresses of a complex structure". You mean FEA is not reliable for stresses? I am working on the analytical calculations too. I am trying to isolate each beam and try to set up constraints and external loads, then follow "Ultimate limit states norms" from different codes like Eurocode Steel design. However, not sure If I am doing it correctly, so I would appreciate any advice or recommended lectures


@steveh49

About the cables, the reason of using two (actually four, due to symmetry) is the deflection of the cylinder. We aim to get the lowest deflection of the cylinder, so an additional cable helps in that way

The free body diagram: I am sorry for the confusion. Green numbers in the reactions are values from the FEM analysis, the ones in red are the analytical values.

Also, for the vertical reactions note that self weight of the beams are also be taken into account



Again, thank you very much for your time

RE: Tips for this structure I am designing

Quote (DrawOH)

Since I am not a civil engineer, I do not understand studs in concrete floors.

If you can picture a calculation pad or quadrule pad and flex it... see how the pages 'slide' as it bends. Headed studs prevent or restrain this 'sliding' and make it stiffer and stronger. If you glued all the pages together... same effect.

Dik

RE: Tips for this structure I am designing

dik,

I think you are talking about reinforcement, something I know even less about. I was remarking on the tensile reaction force of his cables on the floor. This relies on threaded studs extending out of the concrete floor.

--
JHG

RE: Tips for this structure I am designing

JM_10,

Your initial FE model shows a gradual transition of stresses from your big tube into the WF beam frame. If this is bolted, the stresses do not look like that at all, especially if the joint is in tension. The stresses will be concentrated around where the bolts are. Even if you weld the thing, all of the tensile force goes through the weld bead. I suspect your FEA is assuming that the whole face is under stress. This only works if you braze it (successfully) or glue it (successfully).

--
JHG

RE: Tips for this structure I am designing

(OP)
@drawoh

Ok, that is something I had planned. I have to change the model to include the bolts

But since now I am dealing with the other matters, do you have some advice about what I am doing and how I am doing it(using Eurocode). Maybe it is not the way to follow or maybe I should have other readings. I have never worked in a project like this...sorry for the questions

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