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[Ask] Defining DOF in Stiffness Matrix

[Ask] Defining DOF in Stiffness Matrix

[Ask] Defining DOF in Stiffness Matrix

I got problem in hand calculation about defining unknown DOF at beam-column joint. Beam-column joint has to behave as simple connection. As I know for rigid, there are 6 unknown DOF for one member frame. How about simple connection?

Thank you.

RE: [Ask] Defining DOF in Stiffness Matrix

a true pin (simple connection) resists no moments. How many degrees of freedom do you think there are?

RE: [Ask] Defining DOF in Stiffness Matrix

I believe that there are six degree of freedom for each 3D joint rather than for each member, that to be more specific, since the beam-column joint has to behave as simple connection (Not rigid connection) the DOF those related to the ROTAION TRANSLATION will be eliminated and just need to deal with DISPLACEMET TRANSLATION, taking into account the frame either 3D or 2D.

Hope this my be helpful.

RE: [Ask] Defining DOF in Stiffness Matrix

If we're talking about the stiffness matrix you have the following at that one beam to column joint:
1) X translation of the joint (shared between beam and column)
2) Y translation of the joint (also shared)
3) Z translation of the joint (also share)
4) strong axis rotation of the beam at that joint (not shared)
5) weak axis rotation of the beam at that joint (not shared)
6) torsion of the beam (may or may not be shared, I'll assume it's shared)

two rotational degrees of freedom for the column at the joint that are not shared.

Total of 8 degrees of freedom at that one location.

RE: [Ask] Defining DOF in Stiffness Matrix

I think you should to learn how to form a stiffness matrix in local points of structures and of course then exchange it to global coordinates.
To forming local stiffness matrix you should characterize DOF in every local point. for this i will attach you a file that shows you DOF in different types of supports; Then the number of rows and columns in local stiffness matrix equals to DOF in that kind of support.

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