VERY LOW THCKNESS BASE PLATE IN IDEA STATICA

[OnePowers]

Engineers. Salutes to all of you out there!

I have a question. I am modeling a circular base plate for an HSS round in the IDEA STATICA program. It's an 8 floors structure. The results show that a thickness of 5mm or 0.2in is enough. Only the anchors fail, but they are close to OK (as you can see in attached image). Before, I used RAM CONNECTION to design the base plates, but now I am giving to opportunity to this new program. However, This is the first base plate that I got with a so low thickness. ¡¡5mm or 0.2in!! Loads 1 and 2 are similar

What could be happening? I must to check something before calculating? I appreciate your comments.

Thanks.

 

[XR250]

Why are you using such a thin plate? Why is it circular? Why so many bolts?

 

[dik]

Can you use an octagonal plate with 8 bolts? What is the magnitude of your load? 597kN, about 135K which is not much approx. 8x8 (200x200) ish? Mz is torsion? I generally don't use a BP less than about 1/2" or 5/8" (12mm and 15mm) and often much thicker... also only for small plates, I occasionally use 3/8 (10mm) but just for simple light loaded conditions. How large a diameter is your tube?

I can barely read your numbers... is that a 200 bolt circle? and maybe a 100 dia tube? That tube's a little much for 135K...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Brad805]

I would check your deflected shape, restraints, and how your loads are applied to the connection. I suspect one or more of those aspects need fine tuning. You can send in a request to tech services as well. If in NA, the help is quite good.

 

[rather_be_riding]

Hard to read your loads, but do you have a reasonably large compressive load and therefore might have very little uplift on the plate even at the worst location? That might explain the very thin plate recommendation?

@XR250 - why the dislike for round base plates? I'm not looking for an argument - genuinely curious if you have a practical reason for this.

 

[phamENG]

IdeaStatica is a Component Based FEM program. It uses FEM to analyze the assembly, and then compares the calculated stresses in each element to code requirements. It's a fantastic program - if you know how to use it.

The plate check is for plastic strain. So it's saying that your plate never enters the plastic reason of the stress-strain curve. Given the relatively low moments for the size of the tube and connection, that's believable.

But remember that these programs are not a replacement for engineering judgement. There are plenty of other things that you should consider beyond the strength - serviceability, fatigue, heat input and weld-ability, etc.

 

[JLNJ]

If it's a vertical load, the base plate doesn't need to be thick. The force can be driven right down through the bearing of the column perimeter.

If you have significant moment, maybe you have analyzed it incorrectly.

 

[nivoo_boss]

I'd say as well that the reason for thin plate recommendation is low moment in the joint.

 

[XR250]

....why all the bolts?

 

[Aesur]

I haven't used the program before, but suspect that the vertical loading being negative implies downward loading and is of such magnitude that it cancels out much of the moment and therefore little to no bending in the plate. As others have said the load is then transferred in bearing directly to the pedestal at the column so the plate is more of a filler. I am curious what is failing with the bolts, I would be surprised if it's the steel with those loads; if it's concrete (breakout I suspect) then can you get away with less bolts?

In response to @rather_be_riding in regards to the round base plate, I cannot answer for XR250, however I tend to avoid round baseplates because they are more labor to produce and setting anchors could be more difficult resulting in higher costs.

 

[Tommy385]

Hi,

IDEA is pretty good tool if the user knows how to use the program.
In given example there is almost no tension in bolts because of high compressive force (ca. 600 kN)
The bolts are probably failing in "concrete" (check forces in bolts/anchors and capacity of your anchors, capacity is probably very small) and there is probably no bending in plate because all of the compression force goes directly in concrete (check stresses in concrete)
(go to tab "check" and there you can see deformed shape, stresses, stresses in concrete etc. all graphically)

 

[rather_be_riding]

Aesur - very slow reply sorry. I've been flat out.

In a world where almost every plate I design is cut by a machine, round no longer seems to matter in terms of labour to my thinking. Likewise, post-cast anchors don't care too much. Cast-in maybe - I reckon you have to be careful either way and I simply require the use of templates to ensure they're on the money.

15 years ago, I would totally be on board with your reasons. How things change.

 

[Aesur]

@rather_be_riding, Hopefully things have slowed down enough for you to get a breather - it's crazy seeing how busy everyone is this year, especially with such high cost of materials.

In my area the smaller fabricators still use breaks and manual cutting whereas I'm sure the larger fabricators use laser and plasma cutters for plates. Maybe this is different in your area. An additional issue with round plates is it generates much more waste material which is typically factored into the cost. While this definitely depends on the use of the plate, ie light poles, power poles, etc.. typically use round plates to get enough bolts, for the common types of structures we design square are the most efficient and they don't affect the aesthetics of the structure being buried in concrete.

 

[rather_be_riding]

Aesur

Obviously rather different here (Melbourne, Australia). Everyone seems to bother me for DXF 1:1 files for cutting. A good lesson in never assuming that everyone does things the same way. Great point regarding waste material. Because I'm structural/mechanical and most people get stuff cut by a laser/profile cutting specialist, it kind of comes out in the wash as other, completely unrelated projects get nested into the gaps in the sheet. I often create baseplates with round holes in the middle in fact - that hole becomes other parts whether on my project or someone else's.

I don't think we're getting hit with the high costs you're seeing (presumably in America). It's been a strange year. Multiple months of zero incomes, several where I can't find a way to breathe. Ain't consultancy fun!