Local force response and summation stress is different

[AnggaSetiawan]

Dear All

I would like to ask about validation the response of fiber element with force based beam column element.

I make model simple cantilever of RC and steel column structure with fiber model implement regularized integration point of hinge. I give vertical load with load integrator and lateral load with displacement integrator. I checked all stress and strain of the fiber component along section depth, then I summed all stress to get the axial force and bending moment results. Also, the local force recorder is activated. The manual calculation also to be performed which implement fiber section to get moment vs curvature curve.

The result shows that the local and global response in Opensees equal in all response component, the summation the stress-strain distribution and total force from the Opensees result and from manual calculation also almost equal in all component. Even though the local/global response of axial force response from Opensees is equal with the manual calculation/summation stress, the bending moment of both is significantly different.

Would you like to give me suggestion or information?
Thank you very much for the attention.

[fmk]

i am not quite sure I understand the question.

are you saying:
1) that you have compared section response output with a hand calc using the stress responses of the individual fibers and found they are in agreement
2) that when you look at global equi comparing global forces applied with the forces output from the element you found those to be in agreement for axial force but not moment

[AnggaSetiawan]

Dear FMK

Here I share the output data of analysis
https://www.4shared.com/office/ZsqYpRmT ... heck2.html

1. of course I made the comparison from Opensees with hand calculation in Fiber section in tcl program
2. yes, the agreement in case of total fiber stress is axial force but the bending moment is different

Thank you for the attention

based regards,
Angga

[AnggaSetiawan]

Dear Mr.FMK

Here I share the output data of analysis;
https://drive.google.com/open?id=0Bzu3T ... 285d2dINUE
Thank you

[selimgunay]

A more straightforward way to make this check can be:

Change the materials to elastic materials and increase the number of fibers (30x30 for example). Check if the recorded stress at a particular location is equal to the theoretical value from s=My/I. If this equation holds correctly, there may be other reasons for the inconsistency that you are experiencing.