Sap2000 beam axial force under lateral load 1

[david.h]

Hi, I am trying to analyze a braced frame in 3D with EQ loads applied to the center of the diaphragm. diaphragm constrains applied to all joints.
Interestingly I did not get the axial load in beams in the braced bay.
Is it because SAP applied the loads through the diaphragm to the joint with the braces directly?
How can I fix it to get axial force in beams?
Thanks a lot.

 

[Celt83]

Assuming you have used a rigid diaphragm:

diaphragm constrains applied to all joints.

the math behind a rigid diaphragm element does not permit differential movement between nodes, so if every node is connected to the diaphragm they all move the same amount. Since the nodes all move the same there is no axial strain, review the definition of strain, in the elements connected at each end to the diaphragm nodes.

This can be handled in a handful of ways with the most typical being:
- release nodes along the frame from the diaphragm to allow for axial strain development
- change the diaphragm to a semi-rigid model (this can substantially increase computation time as the floor will be analyzed as a finite element mesh.)

 

[david.h]

Appreciated