I was modeling a monumental stair and was playing with different support assumptions for some of the landing framing, which leads me to ask a clarifying question. I started out with pinned ends as I normally would and got a typical simple span moment diagram for the supported member. I changed it to fixed ends and still had an essentially simple span moment diagram with negligible end moments. But it uses plate stringers which would be very flexible, so that's not so surprising. Then I tried applying a spring to model a semi-rigid connection since I have some other software that can generate M-theta curves and rotational stiffness constants. I had expected the spring to result in an end-moment somewhere between zero for the pinned condition and the small moment for the "rigid" connection to a flexible support. Instead, I got a moment diagram with end moments that were 52% of the theoretical fixed end moment with infinitely rigid supports. Am I correct in thinking this is because the spring is tied to the node and not the member? I was thinking it would be like RSS Frame where you assign the spring to the beam end, but I'm guessing since it's a nodal property in Elements, the spring stiffness overrides the support rigidity. Is that correct? What would be the recommended way to model semi-rigid framing connections in Elements? The manual only talks about springs at footings.
Thanks,
Jason
Correct, in Ram Elements we can apply nodal spring supports, but we have nothing like a beam end spring, or partially fixed end condition. Beams ends can only be hinged or fixed. The only way to have such a model in Elements is to change the section inertia for the last part of the beam, i.e. segment it into parts and change the section for the end part to be smaller. STAAD.Pro is more versatile for this.
Answer Verified By: Jason McCool