topic one way slab with offset beams in Robot Structural Analysis Forum

one way slab with offset beams

Anonymous — Fri, 20 Mar 2015 12:06:20 GMT

Hi ,

I am trying to create a one way slab sitting on simply supported beams.

The problem when I offset the beams I get very good results for the slab (momentum and shear) . However, the beams results are wrong. (not AS I EXPECTED)

I tried to release the beams supports (pinned-pinned), but even so I still have momentum much smaller than expected in the mid span.

I read many post about that. (certaintly due to induce forces on the beam because of the offset).

my question is 1- how can I solve this problem in order to design all my structure in one go and not design the slab first with offset than removing the offset and design the beam??

2- how to show this offset in 3D (for presentation), because I mange once to do it, then it disapear (I need to put the mouse on the beam to show the offset)

Thanks in advance

Re: one way slab with offset beams

Rafal.Gaweda — Fri, 20 Mar 2015 12:12:01 GMT

http://forums.autodesk.com/t5/robot-structural-analysis/beam-offsets/m-p/3332921/highlight/true#M2762

http://forums.autodesk.com/t5/robot-structural-analysis/design-of-t-beams/m-p/4749299/highlight/true#M19838

http://forums.autodesk.com/t5/robot-structural-analysis/api-macro-creation-of-quasi-t-amp-l-beams/m-p/5485265/highlight/true#M29748

http://forums.autodesk.com/t5/forums/searchpage/tab/message?filter=labels%2Clocation&location=forum-board%3A351&q=t+beam

Re: one way slab with offset beams

Anonymous — Fri, 20 Mar 2015 12:31:28 GMT

Thank you Rafal for this quick answer, but I already read those posts which didn't answer my question.

is there any way to offset the beam without imposing any extra loadding on it (Keep the momentum same as before the offset)?

Thanks

Re: one way slab with offset beams

AhmedZA — Fri, 20 Mar 2015 13:58:33 GMT

@Anonymous wrote:

1- how can I solve this problem in order to design all my structure in one go and not design the slab first with offset than removing the offset and design the beam??

try use Rigid link instead and also in case of unidirectional behavior you can use an orthotropic slab to make the slab truly one way spanning that just for suggestions but i'm not sure it gives you more accurate results

2- how to show this offset in 3D (for presentation), because I mange once to do it, then it disapear (I need to put the mouse on the beam to

Re: one way slab with offset beams

Rafacascudo — Fri, 20 Mar 2015 14:15:03 GMT

So , you only need the offset to be purely graphical , and the whole structure (slab and beams) having the same results you get without any offsets??

Re: one way slab with offset beams

Anonymous — Fri, 20 Mar 2015 15:50:50 GMT

Thank you ahmedeffect for your answer,

I will try to implemented and see if the rigid link will do.

Re: one way slab with offset beams

Anonymous — Fri, 20 Mar 2015 15:52:16 GMT

No exactly, I want the beam and the slab to work as a whole structure, but with offset the moment on the beams are much smaller than expected.

Re: one way slab with offset beams

teixeiranh — Sat, 21 Mar 2015 21:43:19 GMT

Nice answer!

How can one access those courses on Autodesk University?

Re: one way slab with offset beams

AhmedZA — Sun, 22 Mar 2015 12:58:27 GMT

@teixeiranh wrote:
Nice answer!

How can one access those courses on Autodesk University?

here>>> Autodesk Robot Structural Analysis: Steel and RC Design

Re: one way slab with offset beams

teixeiranh — Sun, 22 Mar 2015 13:34:31 GMT

Thank you!

Re: one way slab with offset beams

Μηχανικος — Sun, 22 Mar 2015 22:11:23 GMT

Hi,

From what i can see from the diagrams it seems that when the insertion point of the beam is in the middle then the beam behaves as a simply supported beam and the supports do not resist any moments.

However when the insertion point is moved at the bottom of the beam then the beam behaves more like a fixed beam and the supports can resist moments, therefore decreasing the bending moment in the middle since part of the bending moment is resisted by the supports.

Can someone explain why does this actually happens? is this the purpose of the beam offset?

Re: one way slab with offset beams

Romanich — Mon, 23 Mar 2015 04:57:15 GMT

Hi Μηχανικος,

For my opinion beam with offsets starts working as a frame with very rigid small columns (rigid links) with h=offset.

Re: one way slab with offset beams

Anonymous — Mon, 23 Mar 2015 10:09:41 GMT

Hi Romanich

Just for a clarification, How can I add the rigid link? does it need to be between columns and beams or between beams and slab? in either way I wasn't able to abbed any help will be appriciated.

based on my understanding it should be replacing the offset , so it should be between slab and beams.

Thanks

Re: one way slab with offset beams

Artur.Kosakowski — Mon, 23 Mar 2015 10:19:25 GMT

Going back to your original questions:

The problem when I offset the beams I get very good results for the slab (momentum and shear) . However, the beams results are wrong. (not AS I EXPECTED)
I tried to release the beams supports (pinned-pinned), but even so I still have momentum much smaller than expected in the mid span.

my question is 1- how can I solve this problem in order to design all my structure in one go and not design the slab first with offset than removing the offset and design the beam??

Model the beams in the way explained in these topics:

http://forums.autodesk.com/t5/Robot-Structural-Analysis/T-slab/m-p/3185418
http://forums.autodesk.com/t5/Robot-Structural-Analysis/Beam-offsets/m-p/3332921

2- how to show this offset in 3D (for presentation), because I mange once to do it, then it disapear (I need to put the mouse on the beam to show the offset)

When you have offsets (e.g. if you decide on the approach from the pointy above that would be in the 2nd model intended for the presentation only) they are displayed when you open the offset dialog and not shown any longer when you close it. If you want to keep them being visible switch their display on in the Display dialog.

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.

Re: one way slab with offset beams

Romanich — Mon, 23 Mar 2015 10:26:26 GMT

rolad77, in addition to Artur's answer - you can use my macro which implements Artur's proposal.

http://forums.autodesk.com/t5/robot-structural-analysis/api-macro-creation-of-quasi-t-amp-l-beams/td-p/5485265

Re: one way slab with offset beams

Anonymous — Mon, 23 Mar 2015 10:39:45 GMT

Thanks Artur and Romanich

Just a final question, what is the x in your macro Romanich?

Thanks again

Re: one way slab with offset beams

Romanich — Mon, 23 Mar 2015 10:54:16 GMT

x is a multiplier for h

Re: one way slab with offset beams

Anonymous — Mon, 23 Mar 2015 11:03:44 GMT

Ok thanks . so get Befff (the effective flangth width) then find x based on it.

great.

Do u have any example of using a rigid connection? (video)

thanks