Beam Support

[cesarone82]

Hi all, i've got an apparently simple problem, you can see in the image attached.

I have a beam B constrained with a pivot (don't know if this is correct, i'm italian) to a column.
To model this i had to input two pieces for the column and two pieces for the beam, this only to have a joint in the middle.
In this case i can't model the pivot with end releases because if i use an end release either on the column or on the beam i can only force the moment to be zero in the end of the beam/column, and this is not right because the beam and the column are connected in the joint, but they are not connected to each other!
is there a way to tell Sap that the two pieces of beam column are connected but they don't share moment?!

= a

 

[agostage]

If I understand correctly...

This is a common issue in direct stiffness method analysis. What you're trying to do is not possible with a single joint(node). Drawing the column and beams to a single node is creating an equation where there is some stiffness relation between the members, when in your case there really isn't. You will need to create another node at some nominal distance away (outside of the auto-merge tolerance). Either create a rigid link between the two nodes then with one end condition (pivot). Or put a pivot at each node. Which way to go depends on whether you want shear to transfer between your column and beams.

 

[agostage]

To clarify a bit more...

In 2D for simplicity, one node can capture 2 translations and 1 rotation. What you're trying to capture is 2 translations and 2 rotations with one node since your column and beam can rotate to different values. This isn't mathematically possible for a single node.

 

[osquro]

Hi, cesarone

I will assume that your frame is 2D (X-Z Plane) and that you still have the column and beam divided in two pieces.
What if you move the column 0,1 m in Y direction.
Define a joint constraint EQUAL. Constrined DOF's will be Translation X, Y, and Z. Select beam and column joints that will simulate the pivot and are actually separated 0,1 m.
Assign the constraint to this nodes.

See the image, it seems to work...

 

[vch]

Use Options:
1.Edit/Points/Disconnect - to disconnect all connected at a selected joint elements;
2.Select elements (beams) and their jonts and with Edit/Points/Connect connect them; Do so with column elements
3. Select joints (after steps 2 should be 2) and assign them joint constraints - Assign/Joint/Constraints/ Equal ...- with cheks at translational displacement only