modeling of a RC column

03-Analytical/modelling capabilities
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newman
Posts: 38
Joined: 06 Jan 2017, 18:12

modeling of a RC column

Post by newman »

Hi Seismosoft.
I want to model a RC column. The base is restrained in all degrees of freedom. The considered analysis is pushover at top of the column in X direction. There is also a axial force at top of the column. This column is not a cantilvet type. So, please help for a correct model. Which method is correct?:
1_ The restrains at top are: x+rx+ry+rz and axial permanent load at top.
2_ The restrains at top are: x+z+rx+ry+rz and a lumped mass (the axial load divided to g=9.81) at top of the column instead of axial load.
If you have more guids, please say to me. It was menthion that in the first method which has axial load, the direction of Z should be release in restrains tab.
huffte
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Joined: 22 Jul 2011, 10:19
Location: Cookeville, Tennessee, USA
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Re: modeling of a RC column

Post by huffte »

Hi newman. How can you push the top in the x-direction if you restrain the top in the x-direction? It is unclear what you mean by "correct model". You are the one to determine the correctness of your model depending on the type of behavior you wish to emulate. When you say it is "not a cantilever", I assume you mean that there is rotational restraint - that the column is to bend in double-curvature as you push the top. If that is the case, it seems to me you would restrain y+rx+ry+rz, with a permanent axial load at top. My comments assume that z is the vertical axis. You will likely need either a single inelastic FB element or a subdivided inelastic DB element to represent the column. Best of luck newman.
Tim Huff
newman
Posts: 38
Joined: 06 Jan 2017, 18:12

Re: modeling of a RC column

Post by newman »

Yes, it is double curvature. I had a mistake in my writing. X-direction and Z-direction are released.
My question is that if I don't release the Z-direction and I use a lumped mass instead of axial load (in z-direction), the model is correct or not.
huffte
Posts: 978
Joined: 22 Jul 2011, 10:19
Location: Cookeville, Tennessee, USA
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Re: modeling of a RC column

Post by huffte »

It seems to me that if you place a lumped mass at a supported node, that the support, rather than the column, will carry the entire vertical force for most any analysis type. If I were modeling this situation, I would release Z-translation and apply either a lumped mass (with loads generated from masses) or a permanent load to represent the axial force in the column. Stay with it, newman, you will get there.
Tim Huff
newman
Posts: 38
Joined: 06 Jan 2017, 18:12

Re: modeling of a RC column

Post by newman »

Thank you.
You mean that I should release the z-direction in the both methods (first method with lumped mass and second method with axial load)?
newman
Posts: 38
Joined: 06 Jan 2017, 18:12

Re: modeling of a RC column

Post by newman »

Please note that if I use axial load in z-direction, the model should be release in z-direction at the top of the column to run the model. But, if I use a lumped mass at the top, the model was run even the z-direction is restrained.
huffte
Posts: 978
Joined: 22 Jul 2011, 10:19
Location: Cookeville, Tennessee, USA
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Re: modeling of a RC column

Post by huffte »

It seems to me, once again, that if you restrain the top of the column in the Z-direction and apply a nodal mass there, the axial load never gets into the column. I think you should not restrain z-translation at the top node. It should be easy enough to see if I am correct or mistaken though. Run the model with a lumped mass at the top and the z-translation restrained. Look at the results for axial load in the column after the analysis has finished. If there is no axial force in the top of the column, then the load never got into the column. And the only axial force in the base of the column would be the self weight. I am uncertain as to why you want to restrain the top of the column for z-translation. But perhaps you are trying to match the results of some experiment for which the top of the column was prevented from moving vertically.
Tim Huff
newman
Posts: 38
Joined: 06 Jan 2017, 18:12

Re: modeling of a RC column

Post by newman »

Thank you so much.
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