How does Ram SS calculate torsional shear on a shear wall for rigid diaphragm analysis? I am trying to verify my output with a few hand calcs, and the torsional shear on my shear walls in Ram Frame is less than I expect.
For my hand calc of torsional shear in Excel, I'm using the equation Vi = Mcr (Ridi / ΣRidi^2)
where,
Vi is the torsional shear in shear wall i
Mcr is the applied moment about the center of rigidity, which is story shear * (inherent + accidental eccentricity)
Ri is the relative rigidity of shear wall i
di is the distance to the shear wall from the center of rigidity
I've been comparing member wall forces of +X seismic loading and -X seismic loading, to check the sign of the torsional shear component (i.e., whether it is additive or subtractive to the translational shear). The sign convention of torsional shear makes sense to me.
For a rigid diaphragm analysis in RAM Frame, all nodes connected to the diaphragm are assumed to translate and rotate as a rigid membrane. Diaphragm forces for lateral load cases are applied as a nodal load at one point on the diaphragm. These lateral forces are directed into the frames based on relative stiffness: the stiffer the frame or wall, the larger the force directed into the frame. If the load is not applied through the center of rigidity, then there will be a torsional moment on the diaphragm and that moment will be inherently considered in the structural analysis.
I expect your hand calculations to closely approximate the calculation of the wall shear forces for one-story structures. For multi-story structures, especially those with changes in wall stiffness between levels (wall thickness changes, wall height changes, wall geometry changes, etc), it is possible for forces to be dragged out of any given wall and transferred into stiffer walls, which would complicate the verification that you are attempting.
Also, relative stiffness of the walls in RAM Frame would be based on both shear stiffness and in-plane flexural stiffness. Depending on the wall height/geometry, either one of those be dominant at any given level and could complicate the calculation of the relative wall rigidity.