model of a seesaw

Hello,

I want to modelling ur torsional stiffness test bench for formula student frame. I´ve a problem with modelling the lower structure. This part should work like a seesaw from a playground. The basic support of the frame is at the back suspension (not pointed in the drafting).

The principal model is drafted in the picture 01 and 02. The lower beam is centrically supported. The intersection points of A & C are simply supported (just like intersection point of B & D). The line of C & D is in every situation stiff.

I need help with the modelling of the pin joints.

Thanks in advance!

Anton