Displacement Response

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Displacement Response

Postby tazarv » Sun May 18, 2008 5:47 am

Dear Dr. Silvia
I'm still working on why my fiber model Lateral Displacements under earthquake excitation are so small. I was wondering if you could tell me why even your example ( I mean Ex2c.Canti2D.InelasticFiberSection.EQ.tcl) has small lateral displacement too.
http://opensees.berkeley.edu/OpenSees/m ... nual/HTML/
It is around 0.001 in. I have increased the PGA in above-mentioned example but model was failed.
I would appropriate it if you could explain more about this small displacement.
Mostafa Tazarv
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Postby silvia » Sun May 18, 2008 12:18 pm

look at where your structure sits wrt the response spectrum.
Silvia Mazzoni, PhD
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Degenkolb Engineers
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Postby tazarv » Sun May 18, 2008 11:29 pm

Dear Dr. Silvia
I have asked about your example "Ex2c.Canti2D.InelasticFiberSection.EQ.tcl", not my fiber model.
Generally, for a column with 60"*60" dimension and 10.97m height, 0.001 inch under "BM68elc.acc" is too small. I have increased GMfatt up to 1000 in Ex2c, as you know well it is an imaginary Ground motion (PGA increased to 50g), but maximum Lateral Displacement was 6inch.

I was wondering if could give even an additional reference to study more if you were busy to a answer more comprehensive.
Mostafa Tazarv
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Postby silvia » Mon May 19, 2008 5:12 am

my example was not very realistic in dimensions, it was just for demonstration.
if you are really interested in this specific case, you should plot the response spectrum for this ground motion, and plot where the example structure is -- even just elastically.
Silvia Mazzoni, PhD
Structural Consultant
Degenkolb Engineers
235 Montgomery Street, Suite 500
San Francisco, CA. 94104
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Postby tazarv » Tue May 20, 2008 7:46 am

first of all, I don't like to pick an example and conclude that OpenSees isn't good. I am just finding out why my model, my friend's models and also your models have small lateral displacements under severe ground motion in spite of accurate period . I just want to solve it with your advice and go ahead.
anyway, I have done whatever you told me. I plotted displacement sectrum for "BM68elc.acc" with three damping ratio (0, 2 & 5%).
By opensees calculation, the period of "Ex2c.Canti2D.InelasticFiberSection.EQ.tcl" was 1.17 Sec. The minimum displacement in this period (with these three damping ratio) was 3 Cm that are considerably more than its nonlinear lateral displacements( 0.001 inch).

I would appretiate it if you could put a script of SDOF here which its nonlinear lateral displacement under an earthquake was greataer that 15Cm.
Mostafa Tazarv
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Posts: 44
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Postby silvia » Tue May 20, 2008 10:23 am

please do give me such a SDOF structure and the corresponding ground motion.
you know, if you run the entire ground motion, rather than the 10 seconds in the example, you do get 0.003 inches.
if you look at the acceleration file, the peak acceleration is 0.06 inch/sec^2, that's like 0.00016g.
please do scale the ground motion up to maybe 0.5g, so a factor of 3000 and you do get something like 25 inches, that's like 62 centimeters....

Please do check you response-spectrum analysis.
Silvia Mazzoni, PhD
Structural Consultant
Degenkolb Engineers
235 Montgomery Street, Suite 500
San Francisco, CA. 94104
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Postby tazarv » Tue May 20, 2008 11:20 pm

Dear Dr. Silvia
I really appreciate your time. 8)
I had done this example with GMfatt=1000 around 35 Sec before start bothering you. But there is something in script in GMfatt line ( Ex2c.Canti2D.InelasticFiberSection.EQ.tcl) that shows Input ground motion is in g unit not in in/sec^2 as below:
"set GMfatt 1.0; # data in input file is in g Units -- ACCELERATION TH"
Therefore, the peak acceleration is 0.06g and also by scale factor 3000 as you mentioned the PGA will increase around 180g. :oops:
again I appreciate your time and I will send you another model. :wink:
Mostafa Tazarv
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Posts: 44
Joined: Sun Dec 09, 2007 6:08 am
Location: University of Nevada Reno

Postby silvia » Wed May 21, 2008 5:38 am

oops,
then the scale factor should have been g!
put that in instead of 1.0, then it'll be right.
Silvia Mazzoni, PhD
Structural Consultant
Degenkolb Engineers
235 Montgomery Street, Suite 500
San Francisco, CA. 94104
silvia
 
Posts: 3912
Joined: Tue Jan 11, 2005 7:44 am
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Re: Displacement Response

Postby dichthuat » Thu Sep 28, 2017 7:39 pm

Does it still work? I must try this to see how could it be
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