an element with a plastic hinge at the bottom

[Ahil_Anand]

I want to model a cantilever column by an element with a plastic hinge at the bottom. The element infrmDBPH is suitable, but as I think this element consider two plastic hinges at the top and the bottom (not one plastic hinge). Could you please help me for my purpose?

[Ahil_Anand]

I also created RC column (restrained at bottom x+y+z+rx+ry+rz, restrained at top y+rx+ry+rz). My model was matched well by experimental results, but after a few loops, there is no strength and stiffness degradation in the remained loops. In fact, these loops had a bigger shear force than the experimental results (against experimental results which were reached to almost zero value).
I use Takeda curve in one model, Ram-Osg curve in another model and also a model without any curves. But the problem was remained. I think that SeismoStruct cannot show the lower loops(low force -high displacement), or there in a bug with the software. I sent one of my models (with Takeda curves at the bottom) to your support email.

[seismosoft]

Hi Ahil_Anand,

Note that the DBPH type is the least accurate among the frame element types of SeismoStruct. Try using the FBPH or the FB element instead.
Note also that what you are describing is the inelastic behaviour in the the highly inelastic range, after several hysteretic cycles of loading. Very few programs
worldwide are able to catch the behaviour even in the first hysteretic cycle, not to mention the response after 8 or 10 cycles.

Regards,
Seismosoft Support

[Ahil_Anand]

Thank you for your help. I need to verify a RC column with shear failure. Could you please suggest to me a report or paper of an experimental RC column to have a good verification by seismostruct?

[seismosoft]

You can have a look at the verification report of SeismoStruct to find plenty of resources.

Seismosoft Support

[Ahil_Anand]

Dear Seismosoft,
I create a RC column with springs at the top and bottom. I also sent it to the email of the seismosoft support team. I have a bad problem with the model. Please see the below figure:


the red lines is the hysteresis for the middle of the column by seismostruct, and the blue line is experimental reports. As shown in the figure, the first loops are well, but after that, I don't know why the loops are very far from the shear force. After, I didvided the frame element of the column into three parts and the results presented as follows:

When I continue this manner and divide the frame, the analysis was not finished. Could you please help me for the problem? How can solve this and how can have better results?

[seismosoft]

What type of frame element are you using?
Have you applied correctly the axial load?
If you have shear failure, have you added the corresponding performance criterion with residual strength?
Regards,
Seismosoft Support

[Ahil_Anand]

I used infrmFB. The axial load is correct.
No, I don't have performance criteria. I only once created several criteria based on the following values, but my analysis did not finished:

For reinforcement:
Yield+ 0.0012
Yield negative -0.0012
Rupture + 0.08
Rupture nagative -0.08

For concrete:
Crush core -0.008
Crush cover -0.0035

For ruptures and crush, I choose "no residual strength".

[Ahil_Anand]

Dear seismisoft,
Thank you for your help. Infact, I should use "residual", not "no residual". My graph is very better now, but, it still has a bad drop in one loop. Could you please suggest to me strain value for concrete core? I use -0.008.
For yeid reinforcement, I use fy/E.

[seismosoft]

It has to be calculated. See the Mander et. all 1988 publication (included in the bibliography of the help system).
But also check the shear failures too.
Seismosoft Support