| Applies To | |||
| Product(s): | RAM Structural System; Ram Frame | ||
| Version(s): | Any | ||
| Area: | Modeling; Analysis | ||
What do Wall Groups do?
Assigning Wall Groups is done in RAM Frame using Assign - Wall groups. This is an optional assignment that has no effect on the analytical behavior of the model. Walls that intersect still act monlithically even if no wall groups are assigned. The RAM SS Walls FAQ discusses how this works for 4 walls making a box
If no wall groups are assigned, then all walls and columns default to being in Wall Group 0.
By assigning wall groups to a collection of walls and columns, you can report Wall Group Forces which represent the resultant total forces, axial shear and moment, acting about the centroid of the wall design group.
This is most useful for determining the entire overturning moment on a collection of walls.
Total Moments on a Wall Group
How does the orientation of the Wall Group Affect reported forces?
When you are assigning wall groups to members in the model, the last selected element determines the orientation of the Wall Group. This element is painted an darker orange color to highlight it.
This "orienting element" sets the major axis for shear forces similar to the way columns are treated (see RAM Steel Columns FAQ). Shear forces parallel to this wall are reported as major axis shear forces. Forces acting +90 degrees to this axis are reported as minor axis shear forces. Moments about this 90 degree axis are Major axis Moments.
In the figure below the long wall on Grid A runs North-South parallel to the global Y axis, so forces from south to north yield positive major axis shears and moments.
Major Axis Shear
Minor Axis Shear
If there is a case where the Major and minor axis forces are opposite hand from your expectations, check the wall group orientation. When assigning Wall Groups, the last assigned, orange element determines the orientation of the Wall Group. The yellow elements are the others in the group.
Assigning Wall Groups Sets the Orientation
Confusion can occur when you start with a wall group like the one above, but then last "orienting element" for the wall group is changed to be in another group instead (walls can only be in one wall group). This leaves the original wall group without any user defined orientation, at which point the program reverts to default 0 degree (+X) orientation. This is apparent when wall group forces are reported or shown on screen as seen in the image below.
A Wall Group with no orientation reverts to the default positive global +X direction
To fix this, just re-assign one wall parallel to the desired orientation to be in the wall group again. You will need to rerun the analysis after assigning wall groups.
Can Wall Groups include Columns?
Yes, columns can be included in Wall groups, which is advisable for columns and walls that touch and therefore act monlithically. For more see RAM SS Walls FAQ #pilaster
How are Wall Groups different than Frame Numbers?
Ram Frame reports Frame Story Shear for elements that have the same Frame Number, but this is a simple sum and always reported in reference to the global axis. As noted above, wall group forces include not only shear, but net axial loads and moments about the wall group centroid as well, and wall group force are in reference to the wall group local axis. In many cases it is advisable to assign the same frame numbers and wall groups for consistency in reports.
How are Wall Groups in RAM Frame different from Wall Design Groups in Ram Concrete?
Wall Design Groups in Ram Concrete are used to isolate cross sections that the program will design and apply reinforcing to. Wall groups in both programs report net cross section forces. In both programs, wall groups can be assigned to walls that form 3 dimensional groups, or even to discontinuous walls, but cross sections of walls within Ram Concrete never jump across gaps. Here are a few other distinctions.
- Wall Groups in Ram Frame are limited to lateral walls.
- Wall groups in Ram Concrete cannot yet include columns.
As with Frame numbers, the general advise is to use the same group numbers across the modules for consistency.