Overturning Moments on Shear Walls

RE: Overturning Moments on Shear Walls

Kurt Villella — Tue, 25 Oct 2016 20:53:49 GMT

Karl,

I have all the levels included and have not entered any lateral loads manually so by your explanation Ram should capture the global overturning.

Some of the wood walls at the upper levels (which were modeled as "other" walls) do intersect and probably are creating the vertical components of force you are suggesting. However, if I use the blue frame story shear arrow in the frame module and isolate the shears applied at only the concrete levels for any particular wall/frame (not accounting for any of the wood loads above) the overturning from the reports is still less than these shears multiplied by their heights. Can you explain this? Seems to me it would be at a minimum equal to the shears at the concrete levels times the heights, and that is with no additional overturning from the wood levels above.

RE: Overturning Moments on Shear Walls

Seth Guthrie — Tue, 25 Oct 2016 20:48:46 GMT

Oops - Karl beat me to it...

If the upper levels are all in the model and there is a lateral system (wood shear walls), then additional overturning should be accounted for. You can use Process - Results - Applied Story Forces to visually confirm.

To check equilibrium of total overturning moments, you will also need to consider any wall axial forces that may be coupled. See RAM SS Walls FAQ for more on that.

Additionally, if the diaphragm out-of-plane stiffness is considered some of the overturning could be in the columns.

For more on podium slabs in general, see Modeling Podium Slabs

RE: Overturning Moments on Shear Walls

Karl G — Tue, 25 Oct 2016 20:44:06 GMT

If all 7 levels are included in the model and the lateral loads are applied at each story, then the overall overturning effect would be included. If the model included the concrete levels only and the lateral load from the wood levels was applied as a lateral load on the transfer level, then that overturning effect would not be included.

You may find the following web page on podium levels helpful:

http://communities.bentley.com/products/structural/structural_analysis___design/w/structural_analysis_and_design__wiki/modeling-podium-slabs

If you have wall groups with intersecting walls forming flanges, a portion of the overturning moment may take the form of axial force couples in the intersecting wall segments. The section "3-Dimensional Effects of Wall Groups" on the web page below has more discussion on this point:

http://communities.bentley.com/products/structural/structural_analysis___design/w/structural_analysis_and_design__wiki/7578.ram-ss-walls-faq