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I have noticed that the properties assigned to steel fiber elements in the examples are all the same. For steel material, Hardening Material with post elastic ratio of 1/30 has been used.
I wonder if it is based on previous research or just an assumption?
Thanks

I have modeled a steel frame with fiber elements.
I need to find the plastic hinges length. I think the only way is to get the stress at both ends of the fiber and do some math calculations based on the distribution function. I appreciate if someone could help me with the theory, introducing references.
Is there any way to do it directly as an output or something?
Thanks in advance

fmk wrote:
> there is the undocumented -dT deltaT option you could try .. it records at the first
> time step t = t1, the next time the domain time t2 is >= t1+deltaT, and so on.

It doesn't work for all recorders. I couldn't use it myself resulted in huge size output files. It doesn't matter if you run analyses couple of times. But when you have to analyze a large 3-D frame say 1000 times, then it will get annoying.
I appreciate if you could do something for all recorders.

IsmBaha wrote:
> Integration point weight wIP defines the integration length of each integration
> point, as LIP = wIP*Lcol
> where LIP integration point length, Lcol is the height of the column element.
>
> For example, as I remember for NIP=5 with gauss-lobatto, 1st integration point weight
> was -> wIP1~= 0.05.
> So with that, LIP1=0.05*Lcol. This LIP1 value recommended to be close to Lp value you
> have in your column. If not close you can change the NIP=3,4,5,6,7... etc to check
> which one is closer to Lp.
>
> If your column section is hardening I'd just use Nip=5 as recommended by others.


Thanks so much for the advice.
Where can I find the weights of integration points? The value 0.05 seems very small compared to plastic hinge length in reality.
I appreciate you give me some reference on that.

silvia wrote:
> the number of integration points goes along with the integration scheme.
> if you use too few integration points you don't have a realistic
> distribution of deformations. typically 4-5 integrations points give good
> results.
> if you have a strengthening system. if your system is softening, you should
> use the beamwithhinges element.

Does the number of integration points imply the plastic hinge length? I was told that the post elastic stiffness factor we use for material properties depends on the hinge length. But we don't define any plastic hinge length in fiber modelling. How does it work?
Thanks,

fmk wrote:
> there is only rayleigh damping or explicit damping through viscous
> materials.
>
> the rayleigh coefficients are typically chosen
> for 2 specific modes and desired damping ratio. typically user selects
> damping ratio at start of analysis. however, as mode shapes change in
> nonlinear system there is nothing stopping user from changing damping
> coeeficients during analysis.


Could you please explain what you mean by "as mode shapes change in
> nonlinear system there is nothing stopping user from changing damping
> coeeficients during analysis."
Thanks so much in advance.

Hi,

I ran time history analyses with the newest version of Opensees. The output file has a problem. I wanted the forces of one of the columns in the structure. Some of the output lines are splitted into two lines; even a force value could be put in two different lines. The problems of this nature I am facing.
I need to mention that the analyses run to the end without any warning. I didn't face this problem when I was using the older versions of Opensees.

Thanks,

Hello,

In SAP2000, softening of the frames modeled with fiber hinges occurs due to calculation of the fiber-hinge response curve, "which proceeds directly from the axial response of individual section fibers. During linear response, fiber elasticity is added to element elasticity, causing softening". Are the same formulations used here in OpenSees? If not, how did you eliminate that additional softening?
Thanks in advance ...

Hello buddhasarah,

Did you solve the problem? I was wondering if you would please send me the files? If it is not OK yet we can work on them together to find the solution. I am PhD student and need the models for my research.
Thank you so much in advance.

Hi jwieser

Could you please send me your files? I need the SAC building models for my further analyses...
Thank you so much.