topic Re: building in Rc walls seismic analyses in Robot Structural Analysis Forum

building in Rc walls seismic analyses

Anonymous — Wed, 20 Sep 2017 10:24:46 GMT

Hi.

I have just done a seismic analysis for a building made only of RC shear walls and now I am looking to the results.

Base shear makes sense, since it is also close to the one calculated by hand.

Now I want to design the reinforcements for the walls, but strangely I got very small reactions in particular in terms of moments.

Moreover it is also seems that the worst reactions on the panels are not from the seismic combinations but from the simple case.

Please can anyone help me to understand why my model is not working?

I am attaching the model. Any help is more than welcome.

thanks and regards.

Viviana

Re: building in Rc walls seismic analyses

Artur.Kosakowski — Wed, 20 Sep 2017 10:31:32 GMT

Hi @Anonymous

It seems that you missed the model. Could you also attach screen captures which illustrate your description so that it is easier to understand the situation correctly?

Re: building in Rc walls seismic analyses

Anonymous — Wed, 20 Sep 2017 10:44:38 GMT

I am not able to attach the model. it is too big.

anyway..

I attached a word file with an image of the model from robot and the calculation nots

and then the results

obtained from plate and shell results

thank for your help

Re: building in Rc walls seismic analyses

Refaat — Wed, 20 Sep 2017 11:37:13 GMT

Hi @viviana.novelli

Please try to save the .rtd file with different name and without results then compress it and attached it by using of the websites mentioned in this link.

https://forums.autodesk.com/t5/robot-structural-analysis-forum/sending-bigger-files/td-p/3795062

Refaat

Re: building in Rc walls seismic analyses

Anonymous — Wed, 20 Sep 2017 11:47:52 GMT

https://fil.email/t0m1DFji

Re: building in Rc walls seismic analyses

mustafahesenow — Wed, 20 Sep 2017 12:24:02 GMT

Hi @Anonymous

Could you mention to the wall number you fell it wrong please.

Re: building in Rc walls seismic analyses

Anonymous — Wed, 20 Sep 2017 12:35:43 GMT

I got for all panels,

for all seismic combinations a moment almost equal to zero (?? this is very strange) and

the max moment is for load cases (non combination) 1: only self weight 2: only dead load on the roof; 3: only live load on the roof; 4: only dead load on ground level.

I am not sure why I am getting this results..

Re: building in Rc walls seismic analyses

mustafahesenow — Wed, 20 Sep 2017 13:14:14 GMT

Hi @Anonymous

You have so many walls and some of them block walls you consider them as concrete walls so the moment for sure is going to be very small .

The maximum moment came from vertical load because of the difference between the span . I see that logic.

My recommendation to you is to remove the block walls and just ass linear load to consider their weight .

Please be noted that this seismic forces came only form self weight of structure .

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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: building in Rc walls seismic analyses

Artur.Kosakowski — Wed, 20 Sep 2017 14:54:09 GMT

Hi @mustafahesenow

Thank you for sharing your expert seismic design knowledge with all us on this forum.

Re: building in Rc walls seismic analyses

Anonymous — Wed, 20 Sep 2017 15:45:49 GMT

Thank you so much.

In order to see the effect of the internal walls I had deleted all internal walls and unfortunately my results do not change.

I still have very small moments.

😞

and then why Robot computes the seismic forces by only taking into account the self weight.

EC8 says that imposed load should also be considered (EN 1998 - 4 2004 clause 3.2.4)

thanks

Re: building in Rc walls seismic analyses

mustafahesenow — Wed, 20 Sep 2017 15:56:46 GMT

Hi @Anonymous

Its preferable to do the seismic as dynamic not static you have irregular building.

Attach the model please after doing this adjustment.

Re: building in Rc walls seismic analyses

Artur.Kosakowski — Wed, 20 Sep 2017 16:14:23 GMT

Hi @Anonymous

Looking at the csv you attached my understanding is that you are looking at the results for each of the surface elements separately rather than walls as the whole. I'd suggest looking at the reduced results for panels table instead.

For seismic analysis self weight is included by default but you may also include other masses (e.g. from dead loads) using load to mass conversion tool.

You may find the recording of the Introduction to seismic and spectral analysis webinar helpful.

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: building in Rc walls seismic analyses

Anonymous — Thu, 21 Sep 2017 12:26:56 GMT

Hi,

i made few changes in my model

I defined new material for the internal wall. These are in Brick.

Then I had set a static analyses and a modal analyses.

I have few questions:

1) why the displacements for the combination related to the seismic analyses are always 0.

2) I am not sure how I should check the reactions of the walls? I would check them in plate and shell results. Please advice me.

3) @Artur.Kosakowski why should I check the reactions in reduced results for panels? I read in the manual about this, but it is not clear to me what the difference is between the reactions from reduced "results for panels" and "plate and shell results". Why the reactions are so different between them?

4) why when I check the reactions related to the model analyses, I cannot see the reactions?

this is link where you can find my model.

https://fil.email/38SFH5Ld

Thank you in advance for you help

Re: building in Rc walls seismic analyses

Artur.Kosakowski — Thu, 21 Sep 2017 14:15:22 GMT

Hi @Anonymous

3) @Artur.Kosakowski

why should I check the reactions in reduced results for panels? I read in the manual about this, but it is not clear to me what the difference is between the reactions from reduced "results for panels" and "plate and shell results". Why the reactions are so different between them?

They are internal forces rater than reactions but...

Imagine that you have horizontal force applied to a wall meshed in such a way that you have 10 surface elements at its bottom. The horizontal force will cause vertical tension at the edge it is applied, zero force in the center of the supported edge, and vertical compression at the other edge bit there will be no in plane bending in none of these elements - this is what you can see in the results for the panels table.

Then 'reduce' these vertical forces from all 10 elements to the center of the bottom edge - you will have 0 vertical force plus in plane bending moment for the whole wall. This is what you can see in the panel reduced results table.

4) why when I check the reactions related to the model analyses, I cannot see the reactions?

Because you don't apply any forces. This analysis is intended to find eigenfrequencies of the structure instead.

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: building in Rc walls seismic analyses

mustafahesenow — Sun, 24 Sep 2017 15:31:30 GMT

Hi @Anonymous

In seismic design when you have Rc building with (frame or shear wall system ) you shouldn't consider the block walls as a structural elements contribute some of the seismic force you should consider them only as structural loads