hinge unloading

[sww]

Dear all,
I perform a time history (Nonlinear Direct Integration ). I am puzzled with hinge unloading.
SAP200 help contains these statements "Hinge unloading occurs whenever the stress-strain
(force-deformation or moment-rotation) curve shows a drop in capacity, such as is often assumed
from point C to point D, or from point E to point F (complete rupture)."
But if the moment drop from the value of point c to the value of point b,
will the path follow the curve ?
The particular statement is Written in accessory.
Thanks in advance.
Regards.
sun weiwei

 

[peppiniello]

Are you sure you can use a Hinge during a NL TH analysis?

A Hinge is something you use for Pushover analysis, which implies monothonically increasing effects

If you want to keep using a TH analysis you must define a hinge as a Nonlinear Link Moment-Curvature element

check it on the manual, anyway

hope this helps

 

[masomenos]

Yes, you can use hinges (frame assignment) for NL TH, but you must use the nonlinear direct integration method when defining your analysis cases. This option to analyze plastic hinges in NL TH only appeared in version 9. You can use default hinges or define your own hinges under the Define menu before you assign them

peppiniello is correct to point out that the SAP2000 manual says hinges can only be used for static loading. CSI says they are updating their manuals to better explain this but the capability is already in the program

 

[arigato]

Im using version 8.2.3 and the manual i have for it clearly states that I can use hinges for non-linear time history analysis. Do they not work well if your not using version 9.0?

I am having a problem with a small and simple one storey 3d structure (with offset mass to create torsion) with no gravity loads and applying an earthquake in one direction to it. At the end of the record, and even 20 seconds after the record, the hinges seem to have a significant residual moment in them. That is, if i set the Mp of the hinge (perfectly rigid plastic ) equal to 2.3 meter-tons I get a moment of about 0.12 meter tons, which doesnt make sense because i cant have any residual forces in the structure if there is no externally applied forces on the structure. I set the time incriment to something obscenely small and yet I still get a force of 0.12 in the hinge 20 sec after the record. I get residual deformations but that seems ok. Is this because my version of sap isnt 9.0 or better?

 

[peppiniello]

arigato,

i think that
if Fext=0 , it must be Fint=0
wich means that internal forces are self-equilibrated, and not identically zero

in your case there must be some "trapped" balanced internal force, which is normal if you have residual displacements. I think of a mass connected to a spring and a friction damper: at the end of the external excitation there's a residual displacement and Q=KUres (commonly a base isolated building after an earthquake)

the same may applies to your hinges and elastic members at the residual state determination

hope this helps

 

[arigato]

Hmm. Im not convinced that the internal forces are equal to zero but my advisor last week said its not possible to have residual forces if there are no applied loads such as gravity involved. Ill present the damper case to him and and see what he says.

Thanks