member bi-linear factors

Hello
I'm Francesco.
I'm using Ruaumoko for Puschover analysis.
I want to ask you some questions:

1) What does RA Bi-linear factor (or Ramberg-Osgood r) (Axial) and RB Bi-linear factor (or Ramberg-Osgood r) (Flexure) mean when i write in (insert in ruaumoko) the member bi-linear factors and hinge properties?

2)Does the user have to insert "curvature ultimate" and "moment ultimate" or the program calculate then automaticaly after writing the parameters at the point 1) and yield interaction surface

i'm sorry for my not good english
thanks a lot
Francesco

Ciao Francesco,

1) the r factor is the ratio between the post-yield and the pre-yield stiffness. For example 0.05 means that after yielding the stiffness of the member is only 5% of the initial stiffness.

2) I am not sure what you are asking but you will have to calculate your ultimate curvature with a sectional analysis program, and then check manually at which step ruaumoko reaches it. I do not think there is a way in Ruaumoko to make it stop when a certain curvature value is reached.

Don't worry about the English, as long as people can understand you you are fine!

Repeat you introduction in the welcome section, where everybody can read it!

Ciao.

P.S. I will soon move this post in the member modeling section where it should belong.

These factors represent the post-yield stiffness of the members, see the "r" in the figures in the Appendix B of the manuals. In the very first version of the programs the only data required were the yield actions and the bi-linear factors as the only hysteresis models were bi-linear (elasto-plastic is a sub-set) and Ramberg-Osgood so these data items are separate from the rest of the hysteresis data. I have a policy of full backwards compatibility with the data so 20 year old data sets should still run with no changes and give the same answers (assuming no corrections affect the results) as were obtained 20 or 30 years ago. This means that possible tidying of the data is not so easy. New features have to work but all the old ones have to work as well. RA and RF (frame members) or RF and RT (spring members) are to allow different bi-linear factors for the axial actions and flexural actions or between the spring translation terms and the spring rotation (theta) actions.

Dear professor,
thank you for your kind answer.
I have to model simple cantilever subjected to axial and horizontal loads. I want to introduce a bi-linear sectional model (moment-curvature law).
In the following i wrote the two lines of the program for the hysteric model:

0 -0.000835 0.246 0.246 ! Member Bi-linear factors and Member hinge
-5202 -2160 313 290 235 145 831 0 ! Yield surface

My doubt is if I have to introduce "r" factor in the first position (RA axial) or in the second position (RF flexural). I remind you that my case study is a cantilever subjected to axial and horizontal loads. I'm looking forward to your answer.
Thank you
Best regards
Francesco