SPEAR building

[TUC]

I am working on a 3D RC frame that is already modeled in Seismostruct. It is about the model ch4-RC-03.spf (SPEAR building) that its results are compared with those obtained from experimental tests (and they do match very well, as it is shown in the program¢s Verification Report).

My question has to do with the consistency of modeling sections with fibers (either for DBE or FBE elements) together with modeling diaphragmatic action in floors.
It is known that when using fiber sections with nonlinear elements then the neutral axis "shifts" due to cracking of concrete and if the axial deformation isn¢t free to be developed then additional -unwanted- axial forces are occurring at element¢s centerline (and also additional bending moments). This restriction of element¢s axial deformation is resulting from the constraining condition through the definition of diaphragm.

However, the results seem to be very realistic (compared with the experimental results). Is there any kind of assumption while modeling the above structure concerning this issue that I didn¢t noticed? I also noticed that beams have large values of axial forces that makes it suspicious..

Thank you.

[seismosoft]

Dear TUC,

Your considerations (on the axial restraining effect that the introduction of rigid diaphragm constraints induces) are fully correct, and we do warn users about this in the Help System/User Manual of SeismoStruct.

However, it is equally true that slabs do exist in reality, hence the aforementioned axial restraining effect is not necessarily spurious (i.e. numerically induced), but may indeed be representative of an actual behaviour of the structure.

In the case of the SPEAR building, in particular, the floor slab was very stiff (so that the loads/deformations imposed by the actuators would be accurately transmitted to the structural members), hence it is not necessarily surprising to see the numerical model with rigid diaphragm constraints reproducing so well the experimental results.

Seismosoft Support

[TUC]

Thank you for your reply.

I suppose that this matching between experimental and out of modeling results, concern mostly the characteristics of global responce of the structure rather than local. For instance, the observed large values of axial forces in beams aren't realistic (about this issue, i also noticed that the additional distributed mass due to gravity loads along beams are defined through the option included in element classes and not through sections module so the stress recovery can't take place and that pulls away even further the retrieval of correct internal forces, isn't it ?).

Is it possible to have the full comparison results (whichever are made) between the model made up in Seismostruct and the experiment? (that will be helpfull for my project...)

Thank you.

[Romain]

Hi TUC,

Let me just add some comments based on my past experience in this model/topic:

- Different solutions to model the slab properties may result in significant differences at both global and local response parameters. This is particularly true for irregular structures like this one.

- If you want to be more precise, you can model the in-plan stiffness of the actual slab by defining truss elements for each slab area such that the axial stiffness of the truss elements match the slab one. For this particular structure, however, the differences between this approach and a fully restrained one are reduced (in agreement with the last post from Seismosoft Support).

- You should keep in mind that the axial stiffness of common elements is much higher than the flexural counterpart. Thus, small axial deformations will automatically turn out in large axial forces.

- A "full comparison" would certainly help to clarify some of your questions, but as far as I know such experimental (local) data don't exist or is not available.

Hope this clarify some of your questions,
Romain

[TUC]

Thank you Romain for your useful comments.

The suggested way of modeling "manualy" the diaphragmatic action of floors through truss members i had also in my mind indeed. I was just wondering which is the influence of the modeling combination: fiber sections/elements + full restraining of nodes through the definition of rigid diaphragm.
I can see what you are saying about how easy is to obtain large axial forces (resulting from relatively small axial deformations) but keep in mind that because of these axial forces and due to shifting of the neutral axis, there are also aditional moments generated...

It will be useful if i could examine some of the results of the comparison between modeling and experiment, even some of them.. (for instance some of the diagrams of time history responce like the one it is shown in the attached picture that is in the Verifivation Report that concerns the variation of a displacement, maybe of a node belonging to the roof?).

TUC

[TUC]

Dear support,

Is it possible to have the comparison results between modelling with Seismostruct and experiment for the SPEAR building (the full scale or half scale with infills structure, whathever)? Are they available?

Thank you.

[seismosoft]

Dear TUC,

We have sent you the experimental results in our possession, and point you also to this website: http://www.ikpir.com/projects/spear/

Seismosoft Support

[TUC]

Dear support,

Many thanks for the attached file and the website.

Regards,
TUC

[fakharifar.mostafa]

quote:Originally posted by seismosoft

Dear TUC,

We have sent you the experimental results in our possession, and point you also to this website: http://www.ikpir.com/projects/spear/

Seismosoft Support


Dear SeismoSoft, Is there such a similar weblink providing more related information about the "Ch4-bridge-01.spf" file ("EXAMPLE 1–Multi-span continuous deck bridge" providing the experimental data?
I've been specifically studying this model for a while and want to learn more about it. (I have the related papers, looking for experimental data). Do appreciate your help.

[seismosoft]

No, we have never come across anything of that sort for that particular experiment.

Seismosoft Support