RAMPS on etabs 1

[jenofstructures]

I modeled a house with a sloped roof then i also put a 20psf live load, but when i run the analysis, the dead weight and live load in the roof didn't transfer to the beam connected to the slab. How can i do it right? I already meshed it since a etabs considered a slope slab as ramps. Do i need to define this as shell and not as membrane?

please help me
thank you very much

 

[ishvaaag]

Hmmm... not thinking in ETABS terms, but yes; membranes are good only for in-plane forces, and a roof has out of plane forces as well (and mainly, usually).

 

[WillisV]

ishvaag - true in general; however, if you put out of plane loads in ETABS on a membrane element then ETABS distributes the force to the edge members internally using tributary width algorithms.

 

[ishvaaag]

OK, WillisV, thanks.

 

[jenofstructures]

but the problem is, the load in ramp doesn't distribute to the side member right. When i get the stress diagram, the beam just carry its own load.

 

[kabitchovitch]

hello jenofstrucure
you have two choice
1- you can model your structure with sap2000 , sap2000 has an option to transfer the loads to the frames elements a coording to the shell's locals axis ( assign area load/ uniform to frame (shell) ), then run analyis and check the forces in the frames.
2- you can export your model as an s2k file then import it with sap2000 , then re load your shell elements with this option ( assign area load/ uniform to frame (shell) ).
sorry for my english.

 

[slickdeals]

The load is not distributing to the beam because your mesh points are probably at the ends of the beam and as a result the loads are being transferred only to those nodes and not along the beam's length.

Post your model.

 

[WillisV]

Use a shell element. The gravity load transfer algorithms of ETABS only work correctly for membranes if they are not inclined (i.e. not ramps).

 

[jenofstructures]

slickdeals, how can i make it non distributable automatically?
i mean, i want to see the loading at the beam first but if it distributed automatically, how can i check if it?

thank you very much!!!!

 

[ge0san]

jenofstructures,
Try using shells and manualy meshing the ramps to have nodes compatible with beams elements in more locations than start/end of the beams.
This should work for you.

 

[jenofstructures]

thank you geosan ill try it

i still cant get the right forces on the beam

 

[jenofstructures]

Hello everyone

below is the link to my sample model on ETABS ramp model

please tell me my mistakes because i still get the right uniform load that i need in the beam. I still get a lesser value than the manual computation i made.

Thank you

Poems are made by fools like me, but only God can make a tree. engineers creates wonderful buildings, but only God can creates wonderful minds

 

[kaisun]

I have run your attached file.
What I see in your model are:

one beam has both end released and the other is fixed.
also the ramps were not meshed.

I suggest you select both the ramps then go to the assign menu ->shell/area -> area oblect mesh options.
under ramp and wall meah options, select subdivide object into 4x4. then run the analysis. that should work.

 

[jenofstructures]

i believe the ramp is already meshed, but anyways ill be attaching the model again. What i'm asking is my model is not transferring the load rightly from membrane (or slab) to the beam. I think the beam that is fixed on the other and released on the other had nothing to do with it. I used different kind of support so that i can seethe difference on the moment

Poems are made by fools like me, but only God can make a tree. engineers creates wonderful buildings, but only God can creates wonderful minds

 

[kaisun]

Sorry, it's my mistake. The model were meshed but it's too rough. when you mesh the model, the load will be transfer to the beams. you may try to increase the number of the mesh to see the differences. and about the end fixed beam, I see your point. Though, it has nothing to do with the issue.

 

[jenofstructures]

What do you mean about being rough?
That's my point, i want to transfer the load to the beam

Poems are made by fools like me, but only God can make a tree. engineers creates wonderful buildings, but only God can creates wonderful minds

 

[ge0san]

jenofstructures,
I uploaded the file named "slope3.edb":

http://files.engineering.com/getfil...f-f169-4826-836f-5bc57e036601&file=slope3.EDB

I hope it is visible and that you are able to download it.
In the file I modified the following:
- I manually meshed the ramp elements: they are now physically/geometrically composed of several (e.g. three) elements. Supplementary, I have assigned internal mesh at some given step.
- I also defined the "SLAB1" section as shell.
The model seems to have an acceptable behavior now.

 

[jenofstructures]

thank you very much


Poems are made by fools like me, but only God can make a tree. engineers creates wonderful buildings, but only God can creates wonderful minds

 

[ge0san]

You're welcome!

 

[jenofstructures]

hello ge0san, i can't open the files, it seems to be in more advance ETABS version

I only have 9.2 version here in the office

Please saved it in earlier version?

thank you

Poems are made by fools like me, but only God can make a tree. engineers creates wonderful buildings, but only God can creates wonderful minds