RISA and RAMSS Light Framed Load Take Down / Podium Buildings

[RFreund]

I'm trying to compare the work flow between RISA and RAMSS for modeling light framed buildings with particular interest in podium buildings. There are two important qualities tah I'm focused on which is the one-way distribution of gravity loads on the floor system (trib width method) and the same for the wall framing (i.e. gravity loads continue straight down through walls). I'm most familiar with RAMSS. It does a great job of distributing floor loads to the walls using trib/one-way distribution. However, the walls are meshed which means you need to add columns at point loads (which is fine, I need these loads anyway) and you need to unlink the wall corners (otherwise load gets transferred around the corner to the "non-loadbearing wall"). The annoying part is unlinking the walls. Typically we will pull the wall back from the corner and a short "dummy beam". I'm curious, since RISA has wood walls, are these walls "unlinked" at the corner? Or if you apply load to a N/S wall will you see load in the perpendicular E/W wall?
Thanks!

 

[bones206]

RISA has a toggle setting “ Transfer Forces Between Intersecting Wood Walls”. They also just introduced a feature recently that allows you to decouple an embedded column from the wall mesh, so the point load is taken entirely by the column.

 

[SethGuthrie]

For RAM Structural System, if the walls are gravity walls, then the load tracking is straight down. It's only when the walls are lateral and analyzed in RAM Frame that they are meshed into shells for the finite element analysis. One recent feature was added to allow gaps at the ends of walls without physically separating them (it's within the tilt-up wall types).

 

[CURVEB]

Seth - correct me if I am wrong but my understanding is that Ram SS treats each wall as a rigid body and applies the forces as a uniform load. Any point loads or non-uniform loads that occur on the wall are assumed to be distributed over the full length of the wall. If the point load is not coincident with the wall centerline, it also applies a moment, resulting in a non-uniform distribution.

In other words, the loads don't get passed "straight through" the wall so you don't necessarily see the effect of a concentrated load like you might expect.

To eliminate the issue of a concentrated load distributing over a large area is it good practice to split the wall into smaller segments, with (for example) a single 1-ft long segment centered at the concentrated load?