Modelling Moment-Rotation for a member

Dear all,

If I want to model collapse of a building by using moment-rotation relationship for each member, do I must set the hinge length equal to zero? or any other requirement for this type of member's modelling? I am a bit confuse since the manual explained that the ductility of member that considered in member input data is based on moment-curvature relationship.

I thank you in advance.

Best regards,
adekajeng

I've forgot to mention that I am using one component Giberson and concrete beam-column members.

If the hinge length is 0.0, the program takes it as 1.o then the plastic rotation is identical to the plastic curvature. However, the elastic curvature is not equal to the elastic rotation so ductility will be difficult to comprehend. The plastic hinge length is usually taken as of the order of half the beam depth up to the beam depth. I suggest talking to someone who designs RC beams or who understands the behaviour of RC beams taken beyond the elastic limit.

I am really grateful and appreciated. Thank you Prof. Carr.

It is meant that if i want to address the moment-rotation in hinge, I must use the zero-length element (SPRING). Am I correct?
if yes, do you have any example of the use of SPRING element for a member with moment-rotation definition in its hinge properties?
SPRING element is able to model strength and stiffness degradation as Giberson's member right?

FYI, we deal with generic (theoretical) models that reflecting RC structure strictly based on its moment-rotation hysteresis parameters. the hinge refer to moment-rotation relationship only (excluding the moment-axial interaction). We already defined the hysteresis parameters based on the recent RC evaluation method (we called it as Berkeley-Stanford method). Unfortunately, we are not sure how to model it with RUAUMOKO. I wish you could help us.

Thank you in advance.

The Spring member is one way of achieving what you want as it uses moment-rotation as the governing behaviour. The SPRING members model things in a way similar to the Giberson member except that it does not have a hinge length to convert rotation into curvature. The hysteresis rules and strength degradation work in the same way as for the Giberson beam. I have examples somewhere but will take time to find them and I am going away for 3 weeks. Make the hinge member a short length as then it can define the orientation of the member though this is not such a problem in 2D in 3D the program choice of axes in 3D for zero-length members has caught-out a few users.

Thank you very much Prof. Carr. Just want to make sure: you meant use short length for hinge member instead of zero-length to avoid any error, right ? my model is 3D.

If you dont mind, I would like to request the following case examples after you back:
- spring element for hinge member governing by moment-rotation
- spring elements as a model of beam-column joint. This one will be very useful for modelling an experimental testing of beam-column sub-assemblage.

Again, thanks a lot for your answers. it is really..really..helpful.

The program uses moment-curvature as then ductility is easy to compute, the elastic yiled curvature is the yield moment divided by EI, the maximum curvature found during the analysis gives the ductility. If the plastic hinge length is 1.0 (also obtained by specifying 0.0) then the curvature in the hinge is the same as the pl;astic rotation in the hinge. The ductility is now a bit more difficult as the rotation at a member end is also a function of the moment at the other end of the member as well. It depends on what you are trying to model but the behaviour of the hinge at an end of the member is a function of the moment at that end of the member. The program (pre 1980) worked with moment-rotation but with the difficulties of understanding ductility and moment-curvature we switched to using moment-curvature as that is what the cross-section understands.

Hi Adek,

because the conversation moved away from moment-rotation modeling, but it changed into some fortran output error, I split this topic and moved the part about the output error in the "output error" section.. This should help other people to find the correct reference on the same problem in the future.

All your latest posts on this can be found here: ruaumoko. forumattivo. com/output-errors-f9/visual-fortran-error-spring-element-t77-15.htm, from which you can continue your discussion.