Modeling of Truss element

Hello to everybody,
I'd like to model a truss element to insert in a c.a. frame a bracing syste. How can I do? Should I use a frame element?
Thank you very much.

model it as a Spring member 'k', you supply a stiffness but if use the Truss option for the spring member then you supply the AE and the propgram evaukates the length L to get the stiffness k = (AE)/L

a brace in an RC frame.. are you doing NLTH analyses to assess the retrofit of an existing structure (FEMA356, ASCE41, etc.)?
Just curiosity.

Cheers,
Dom

Yes, I'm doing an analyses on an existing structure retrofitting by a particular brace system..