Link Element Interaction

[huffte]

Can you provide details on the treatment of biaxial interaction behavior when using bi-linear kinematic and plastic link-type elements?

I find no details in the Help file, only basic information about the required input for each type.

I am using both types and they appear to be working properly, but I am not sure that I can get the information I need from the existing post-processor. Specifically, for unsymmetric structures and/or loading in two directions, I can get link hysteretic curves plotted for one axis at a time only whereas the total displacement within rhe link at a given instant is larger than that about any single axis.

Any guidance here will be appreciated.

[seismosoft]

Dear huffte,

We might have misunderstood your query, hence do correct us if needed, but what do you mean exactly with "biaxial interaction"?

As stated in the Help System, currently, SeismoStruct's link elements feature uncoupled DOFs only, hence no true interaction between different DOFs can actually take place.

Do let us know, please.

Seismosoft Support

[huffte]

While the uncoupling of the DOF's is understood, I am still wondering if there is a way I can know the maximum link deformation. Perhaps a more concrete way of saying it will help.

I can plot the D2 hysteretic curve and paste the data into Excel to find the maximum value. Let's say it is 6.00 inches.

Now I can plot the D3 hysteretic curve and paste the data into Excel to find it's maximum value. Let's say it is 8.00 inches.

I may be missing something - pardon me if I am - but my chief interest is in the maximum deformation of the link. I can estimate it by assuming that the maximum D2 deformation occurs simultaneously with the maximum D3 deformation. This isn't necessarily true and my instinct is that it will seldom be true, but I am not sure.

It is a conservative assumption to assume they occur simultaneously. So I could estimate the maximum link deformation in my numerical example to be (6^2+8^2)^(1/2) = 10 inches.

So by "interaction", I meant to ask if there are internal calculations in SeismoStruct which keep track of the vector sum of link deformations in the 2 shear directions (D2 and D3) at each time step.

If the feature is not there, I think it could be very useful. A user could actually study the validity of the "simultaneous assumption" outlined above.

Again, I'm happy to continue using SeismoStruct and using the assumption to estimate my link defromations and I love the programs by SeismoSoft. Please keep up the good work.

[seismosoft]

Huffte,

Thanks for the clarification. We can confirm that the vectorial displacement calculations that you mention are indeed not internally carried out by SeismoStruct.

One question though, can you not calculate the vectorial displacement value at each of the analysis step (by applying SRSS to the component values obtained at each step of the analysis), and in this way estimate the actual maximum displacement of the link (which you may then also compare with the conservative value yielded by the application of SRSS to the maximum component values)?

Regards,

Seismosoft Support

[huffte]

Yes. I see your point. You are clearly correct. In the same manner in which I copy and paste the data into Excel for each individual DOF I could paste the data for both DOF's into Excel, combine vectorially at each time step, and then find the maximum.

And this method is perfectly suited for a project in which a few analyses are being run.

Perhaps this is another one of those places where a great deal of time could be saved for users running dozens of analyses if the combining were somehow done internally and immediately available in the post-processor.

Thanks very much for the timely response.