RAM Frame Ground Level at Upper Floor - Reaction

RE: RAM Frame Ground Level at Upper Floor - Reaction

Seth Guthrie — Thu, 30 Mar 2023 15:04:59 GMT

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.

RE: RAM Frame Ground Level at Upper Floor - Reaction

RFreund — Thu, 30 Mar 2023 12:51:26 GMT

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.

RE: RAM Frame Ground Level at Upper Floor - Reaction

Seth Guthrie — Thu, 30 Mar 2023 02:03:36 GMT

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.

RE: RAM Frame Ground Level at Upper Floor - Reaction

RFreund — Thu, 30 Mar 2023 01:09:30 GMT

"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:

When I use the graphical results -> Frame Story Shears, I don't see any values for the lowest level. Why is that?
If I want to see the "global" reactions, can use the difference in the building Story Shears?
In general, these seem low based on just solving an overhang beam calculation (i.e. summing the moments and solving for the reaction), can you help offer some thoughts on why these don't add up? If there is a rigid support at the new ground level and at the base, I would think it would be close to the overhang beam solution. I suppose the wall group is acting as a tube that is fixed at the base. So this stiffness is the difference?

RE: RAM Frame Ground Level at Upper Floor - Reaction

Seth Guthrie — Wed, 29 Mar 2023 23:05:24 GMT

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.

RE: RAM Frame Ground Level at Upper Floor - Reaction

RFreund — Wed, 29 Mar 2023 21:19:03 GMT

Regarding my idea to eliminate the "overhang cantilever" affect -

One work around might be to:

Assign the analysis ground level to base
Assign the wind ground level to the upper level
Assign 0 mass to the "first" floor or any floors at/below your new ground floor.

Problems with this:

You still need to design the first floor diaphragm to transfer the loads imposed on the first floor to a lateral resisting element
You might be getting to far away from reality even if you have a load path.