Bilinear steel beahviour

[Ana Santos]

Hi everyone,

I am modelling the material of my steel frame with the bilinear steel bahviour. However, in the beams elements I want a elastic behaviour of the material... my question is, how can I change the parameters to have only the elastic range of the material ? is by changing the strain hardening parameter ?

Ana Santos

[fakharifar_mostafa]

For elastic material properties, you can simply define an elastic material (el_mat) in the Materials tab, and then assign it to your beam sections under Sections Tab. For elastic member response, you can also define your beam elements as "elfrm: Elastic frame element" type under the element Classes tab. Hope this helps.

[Ana Santos]

thank you

Do you know how I can define the fracture/ buckling strain for a steel HE section ?

[z.gronti]

Dear Ana,

Please refer to the following topic for information about the buckling in steel models:
http://www.seismosoft.com/forum/viewtop ... tion#p4506

What do you mean with the fracture/buckling strain for a steel section?

[Ana Santos]

Hi

thank you for the reply ! I asked that because in the help of the software, where there is describe the parameters to define the bilinear steel model, in the fracture/buckling strain it's writing:
"This is the strain at which fracture or buckling occurs. The default value is 0.1 (this may be a reasonable value for steel rebars in reinforced concrete sections, but rather inappropriate for steel profiles - users should thus set it with care (even using an infinitely large value when no fracture/buckling modelling is desired))."

[fakharifar_mostafa]

For defining the fracture/buckling strain, you can simply adjust this parameter for your steel cross section from the Materials tab. And yes, the help system is absolutely right. This parameter should be adjusted with some caution (in the context of performance based design where performance criteria is being used, all the specified limit states are important and INFLUENCE THE RESULTS!). The default value (0.1) may not be even generalized for RC sections, as this parameter depends on reinforcement detailing as well. Thus, it should be adjusted with some caution. You can even use this parameter to capture the post-peak strength degradation of substandard structures. 0.06 to 0.1 is a good ballpark for this parameter to start. One may implement series of analyses to better calibrate this model for his/her model.

If you are carrying buckling analysis, it is common practice to introduce an imperfection (1/1000 of column height is commonly used) at the member's mid-height. Good luck on your modeling.