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Hi everybody,

I was trying to use the save/restore command to perform manshock-aftershock analysis for wall structures with post-tensioning. However, I found that the save/restore command works pretty well with conventional system while it was not working well with systems including post-tensioning (i.e., prestressing). In the post-tensioned system, I used Steel02 material with initial stress/strain (or using initialStress/initialStrain materials) for modeling prestressing. Right the model just couldn't save and restore as expected for the conventional system. So, is this situation appeared in anybody else's case? How can I solve this problem, thanks a lot!

HW

Hi, I have been confused with the acceleration results using force based (FBE) beam column elements. I used a simple 2D one story one bay frame model for validation. Both the column and beam elements are elastic. For the beam element I used the following options: 1. elatsic beam column element, 2. FBE with elatsic section, 3. FBE with fiber section assgining each fiber with elastic material, 4. DBE with elatsic section and 5. DBE with fiber section assgining each fiber with elastic material.

For the acceleration results, the resuls of DBE and elatsic element are identical. However the results from FBE are different than the others. It seems to me that the axial stiffness of FBE is different than the others. Anybody knows what's the problem behind this? thanks a lot.

giovannimilan wrote:
> wuhaoshrek wrote:
> > giovannimilan wrote:
> > > wuhaoshrek wrote:
> > > > fmk wrote:
> > > > > transformation handler cnnot handle one node constrained to
> another
> > > > > constrained to another. you should have been seeing warning
> messages.
> > try
> > > > > Penalty method, but you may have numerical problems due to
> > conditioning as
> > > > > some of the penalty factors are going to add up if your values
> are
> > poorly
> > > > > chosen.
> > > >
> > > > I see rigidDiaphragm command can only be used for 3D problem. What if
> I
> > want to
> > > model
> > > > the rigidDiaphragm effect in a 2D problem? Other than using elastic
> element
> > with
> > > > large stiffness, if there any options? thanks.
> > >
> > > Maybe with the rigidLink beam.
> > that's incorrect cause rigid link will constraint translationnal DOFs.
>
> I am quoting the wiki page
>
> $type beam both the translational and rotational degrees of freedom are constrained.
>
> source: http://opensees.berkeley.edu/wiki/index ... nk_command

YES, I know. But RigidLink beam will constrain all the DOF while RigidLink bar will constraain all the translational DOFs (vertical and horizontal) in a 2D problem, which is not right for modeling a rigid diagphram. Rightnow I believe in a 2D problem, if you wanna model rigid diagphram, just use EqualDOF command and make all the rotational DOFs of the nodes in that plane to be the same, that's it. The horizontal DOFs should not be constraint, rather depending on the axial stiffness of beams. That's what I thought.

giovannimilan wrote:
> wuhaoshrek wrote:
> > fmk wrote:
> > > transformation handler cnnot handle one node constrained to another
> > > constrained to another. you should have been seeing warning messages. try
> > > Penalty method, but you may have numerical problems due to conditioning as
> > > some of the penalty factors are going to add up if your values are poorly
> > > chosen.
> >
> > I see rigidDiaphragm command can only be used for 3D problem. What if I want to
> model
> > the rigidDiaphragm effect in a 2D problem? Other than using elastic element with
> > large stiffness, if there any options? thanks.
>
> Maybe with the rigidLink beam.
that's incorrect cause rigid link will constraint translationnal DOFs.

fmk wrote:
> transformation handler cnnot handle one node constrained to another
> constrained to another. you should have been seeing warning messages. try
> Penalty method, but you may have numerical problems due to conditioning as
> some of the penalty factors are going to add up if your values are poorly
> chosen.

I see rigidDiaphragm command can only be used for 3D problem. What if I want to model the rigidDiaphragm effect in a 2D problem? Other than using elastic element with large stiffness, if there any options? thanks.

Hi Dr fmk and lin guan, I have similar concerns about modeling a real (or close to real) high-rise building using force-based beam column element. For modeling shear walls or core walls in a high-rise building, is appropriate to modeling the walls using a equivalent frame model? I mean using FBE for the wall at center, and using rigid element to connect the wall node to the adjacent coupling beams. thanks.

hi,
Is it the truth that when a node is the retained node (master node) in a equalDOF command, it can not be served as a constrained node (slave node) in a later line that includes equalDOF command? Yet if a node is the constrained node (slave node) in a equalDOF command, it can be used as a restrained node (smaster node) in a later line. Is it correct? thanks.

Hi, Frank,
I have created a new material with DLL file. But when I copy the file to my laptop (both win7 64bit), it doesn't work. I remember the same problem happened when i start to use my current office computer, I did rebuild the new material, but when I try to rebuild this time, it failed. I even could't rebuild it again in my office computer (failed with the example ElasticPPCPP as well, following the demo). Do you have any sense what happened then? much thanks.

Hi, Dr frank,
Yes, I was actually hoping it happen. I noted the collapse initiated at a certain node, above which that portion of the model would collapse vertically. When I checked out the sectional response (M-phi, N-eps) of the element connecting that certain node, I couldn't find a reason that cause the collapse of that part. This is the part that confuses me. So I was wondering if the program is giving a unreasonable result due to numerical issue around that period, or is there any other explanations that you may provide? Thank you.

Hi, all,

I have been using fiber beam-column elements to represent a RC shear wall structure. The analyze is dynamic with incremental intensities of ground motion. A lean-on column was connected to wall elements to consider gravity loads and further the P-delta effects. In the wall sectional modeling, besides cyclic degradation considered in the concrete material model, I accounted for the fracture of reinforcing steel by incorporating "MinMax" material model to the regular steel02 model in OpenSees.

For some ground motion, I could observe wall collapse vertically through the animation (some nodes literally displaced significantly in the vertical direction). Is is a possible phenomenon? Thx.

fmk wrote:
> it shouldn't .. are there recorded steps between the .01 and .014?
>
> look at the source code for MinMax (it is really quite simple (what you
> care about are setTrialStrain() method):
>
> http://opensees.berkeley.edu/WebSVN/fil ... terial.cpp

Hi Frank,

Because I set a initial strain for the original material(roughly 0.004), so when I use the uniaxial material test to test the minmax material, it started with 0 strain corresponding to a initial stress value, and the material get fracture at a strain value 0.01. However in the dynamic analysis, the material started with initial strain (not 0 strain) and correspond to a same initial stress. So when the maximum strain value(0.01) in the minmax command actually developed a fracture value equal to 0.004+0.010=0.014. I think the problem is with initial strain, the bound value in the minmax command refers to the strain value excluding the initial strain. That's why it happened like this. Right?

fmk wrote:
> yes it's as if the material fractured (though the other material itself
> does not know it).
>
> no. if you provide a min and max then if the material hits any strain
> outside these values it is considered gone, fractured, or whatever you
> want to call it.

Hi Frank,
I just come across a problem. I used Steel02 material for truss element to model post-tensing bar, and I set wrap the material with a MInMax material with maximum strain to be 0.01(PT fracture at 1% strain). I used "uniaxialTest" command to firstly test the stress-strain of the material, and it works just fine. However, when I run the dynamic model, and check the stress-strain again, then I found the material fracture until the strain goes to 0.014, rather than 0.01. I used fiber section (with only 1 fiber) for corotTrussSection element to model PT, and use "recorder Element -file $dataDir/PT_Story1.out -time -ele 11 21 31 41 section fiber 0. 0. $IDPT stressStrain" to recorder the stress-strain of the material. It seems very strange the material got fractured until it hits a higher strain value than that I specified in MinMax. Since I can only record the strain of the material in this way, I can't double check using recorder -element force command. I can't explain why it is like this. Do you have any idea why? Thank you.

linguan118 wrote:
> fmk wrote:
> > remove the sectionTag from the element recorder.
> Dear fmk,
> Thank you for your reply, but it still doesn't work for me!

recorder Element -file $dataDir/C22_stressStrain_Ele100_3450_RSD7_N.out -time -ele 100 section fiber -34.500 0. $IDBondSteelD7 stressStrain;


like this it's working. btw I used zero length fiber section element.

linguan118 wrote:
> Why not use ReinforcingSteel model?

Can you give an example on the parameters for ReinforcingSteel material, like for normal ASTM A706 reinforcing bar? thanks. or do you have analytical model
parameters calibrated for certain commonly used reinforcement?

mghaffarinia wrote:
> Hi dear sir/madame,
> I just only wanna create a rigid element between two points which do not
> deform at all. I tried to create a normal elasticbeamcolumn element type
> and assign a very big value for the modulus of elasticity. However, it
> doesn't work (or at least It comes to me so) and I receive very strange
> results (such as 7e+6 for rotations!!!!)
> Then I tried to create this rigid element by using GeolTrans function by
> assigning joint offsets at the ends such that all element length is
> covered. however this gives me the same odd results.
> Is there any other standard way to define a rigid member or maybe the ways
> that I used which is trust-able?
>
> My problem can take place due to other parts of my model. However I am not
> sure about this rigid link. If I will be sure about this element then I
> will go and search other parts of my model code.

Hi, I used rigdLink. I think the thing you want it for rigid can be interpreted as the distance between the two nodes
would not change at all during the analysis. I used rigidLink, and checked the distance for that. I found the distance
is pretty good, although it may not as accurate, in terms of the digit number. This could give you almost the same
outcome as using a very stiff elastic element. Have you got any updated solution so far?