pinned releases in LUSAS

[lvkb]

I am trying to model a pinned release between two thick in LUSAS that is free to rotate in all 3 dimensions. LUSAS only allows releases of beam elements in the y and z directions so I am trying to connect my members by using a joint, but am confused about what translational stiffness to put in to make my model work. At the moment I am getting that my two beams move apart by 8000m which is not right!

 

[johnhors]

The easiest way to incorporate a beam local x axis release is to assign a beam geometric property to the beam where the area is zero.

Your beam axial stiffness is E.A/L (Young's Modulus * Area divided by length) , then use joint stiffnesses of say 1000 times that value. If Lusas generates stiffness matrix ill-conditioning warnings, then reduce your values accordingly.

 

[johnhors]

What I should have said is set the torsion constant in your geometric properties to zero, torsional stiffness = G.J/L where G is modulus of rigidity and J is the torsion constant (= polar moment of inertia for tubular sections).