Response Modification Coefficient “R”

[LannyBudd]

When designing a special reinforced concrete shear wall, when would you use R=5 in ASCE7-10 Table 12.2-1 and when would you use R=6? Special reinforced concrete shear walls are listed twice in Table 12.2-1; once in Section A “Bearing Wall Systems,” and again in Section B “Building Frame Systems.”

What is the difference between Bearing Wall Systems and Building Frame Systems? I don’t understand how you can classify SRMF into 2 different Seismic Force Resisting Systems.

 

[wannabeSE]

If the majority of the building's gravity loads are supported frames (columns), it is a building frame system. If the majority is supported by bearing walls, then it is a bearing wall system. This answer is in Chapter 11 definitions: Frame>Structural System > Building Frame System and Wall System, Bearing. Sometimes, deciding one or the other may be challenging.

 

[KootK]

If you've got no columns and a bunch of walls providing gravity support to your floors, you've got a bearing wall system. If you've got columns all over and walls only in discrete locations (shafts), it's a frame system. Somewhere in ASCE, there's an axial load value that defines when you cross over into being a bearing wall. It doesn't take that much.

In general, more axial tends to delay flexural yielding and decrease ductility. I've always found the terminology confusing. "Frames " makes me think of moment frames.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[KootK]

I may have been lying about the axial load threshold. I was thinking of another clause. This link is helpful: Link

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.