When I change the ground level as detailed here: LINK How can I find the reactions of the imposed global lateral restraints?
Additionally, let's say that I want to eliminate the "overhang cantilever" affect that these global lateral restraints would have on a shearwall. Therefore, I want to disengage my shearwall from the diaphragm at the new ground level so that any forces from above are transmitted to the foundation. Is this possible? In my case I'm using a semi-rigid diaphragm.
Also inherit in this technique is the assumption that any forces on the new ground level would be resisted by the global lateral restraints. Therefore, I would still need to find these forces and verify that the diaphragm at that level can distribute them somewhere (i.e. exterior basement walls).
Thanks
You can disconnect the nodes in Ram Frame if the diaphragm is rigid. If it's meshed (semi-rigid and/or 2-way) then you would actually have to make an opening.
Answer Verified By: RFreund
Thanks for the response. I suppose one final question...
Is it possible for me to disconnect the shearwall nodes at the 1st floor from the diaphragm nodes? As if I had an opening around thee entire perimeter of the shearwalls on the first floor.
Yes, the change in shear is what I would check the diaphragm for. I'm not sure why you are not seeing it on screen. Perhaps it's misplaced because of something with the frame numbering or just occluded by the solid deck or walls in this view. Or maybe it's not plotted because of the ground level setting. Regardless the reported values can be used.
Since your lateral system is comprised of boxes I suggest that you define them as wall design groups and then report the total moment in the groups . Summing the moments from the various walls about a common work point is tricky otherwise. For more on Wall Groups see RAM Frame Wall Groups FAQ.
"For a backstay effects from an elevated ground level, which cause shear reversal in a wall for example, there are no reactions to report per se. There is just a force transfer from the wall above to the diaphragm, and eventually out. You can't use reactions there, but you can use member forces or frame story shear output. "
I see the "Change X" and "Change Y" in the Frame Story Shears output report which is negative at the first floor. This would be the force to design the diaphragm to shearwall connection. A few questions:
You can report reactions for any of the supported nodes, even if they are at an upper level.
For a backstay effects from an elevated ground level, which cause shear reversal in a wall for example, there are no reactions to report per se. There is just a force transfer from the wall above to the diaphragm, and eventually out. You can't use reactions there, but you can use member forces or frame story shear output.
We enhanced the ground level setting a couple of versions ago such that you can have the lateral loads based on an elevated base level without actually adding the diaphragm lateral restraint, that might be what you want. If not, maybe send me a section sketch of the desired behavior.