hello Dear friends
I am working on nonlinear analysis of plane frame by using TL approach. I wrote a code and study large deflection of a cantilever correctly. when I implement the code for pinned fixed diamond frame tangent stiffness matrix become singular. I check rigid body motion of frame and think it is ok. is there any special procedure for removing rigid body motion. as I told the frame has two fixed and two pinned corner. is it correct that I modify tangent stiffness matrix for pinned corner because moment is zeros in these corners. if there are examples that solve this frame I will be appreciate that aware me.
thanks a lot.