Out of plane forces in wall panels

[rn14]

Risa always assumes vertically spanning walls in the design it seems. Even the regions above and below the openings span vertically. I realize this is possible to some extent due to the boundary conditions but what about the fact that in a masonry or concrete wall many times you cant actually develop the bars in this direction? Is this why the 'transfer loads' checkbox exists? How do you folks like to design wall panels with Risa?

 

[JoshPlumSE]

Regions above openings are usually designed as Lintels for gravity loads. Look at the detail report for the wall opening and you will see all the lintel design information / analysis results.

The "transfer loads" check box exists to pull the shear and moment from the regions that won't be designed or detailed to resist the forces they get from analysis. The region above an opening (for shear wall type forces) is a good example. In the end, the shear force will likely get into the adjacent regions anyway, but the shear diagram would look more discontinuous without that that transfer loads box checked.

 

[rn14]

For gravity loads that is fine. I am referring to out-of-plane loads, say c&c loading. Typically when done by hand you would design the region above the opening to span horizontally to the adjacent piers and then design the piers to span vertically. Risa tries to design the region above the opening to span vertically.

 

[JoshPlumSE]

I see what you mean now. RISA wall panels are really viewed (for code check purposes) as one of two things. Either a load bearing wall or shear wall (with our without openings) that is loaded entirely in plane. Or, as a cantilevered wall wall loaded out of plane. This is why we have two detail reports, one for in-plane results, and one for out-of-plane results.

You've got a wall with openings loaded out of plane. That works fine for analysis. However, it will not work for the horizontal reinforcement design for the regions you mention as they don't obey the assumptions RISA uses in it's rebar calculations. For these cases, you will have to review the "analysis results" (Mx, My, Mxy) and such to determine how much horizontal reinforcement is needed to resist the forces by spanning horizontally. The program will not do this for you at all.

 

[TehMightyEngineer]

There was a similar topic about this a little while ago: [URL unfurl="true"]http://www.eng-tips.com/viewthread.cfm?qid=375671[/url]

Professional and Structural Engineer (ME, NH)
American Concrete Industries

http://www.americanconcrete.com