Bearing Wall System vs Building Frame System (Masonry)

[mrpid]

I am studying for the SE II eaxam and came across a question within the NCEES Sample Questions regarding a masonry shear wall. As I approached the problem I consider it a "Bearing Wall System" in order to determine applicable factors. Then when I reviewed the answer in the book NCEES considered it a "Building Frame System". I have came across other errors in this book, so it could be a mistake, but the question I have: when is a masonry wall considered a frame system and not a load bearing system (outside of the obvious)i.e. is there a min. trib load to meet a specific standard. For reference, I am using the IBC 2006.

Thanks in advance for any input,

 

[JAE]

I believe the overall building system is based upon what the majority of the load is supported by. So if you have a steel framed building with lots of interior space supported by columns and beams, with only the exterior supported by load bearing masonry walls, then you still have a frame system despite the load bearing walls.

 

[mrpid]

Thanks JAE. That seems reasonable. In this particular problem, the building system is near 50/50 between load bearing walls and wood columns supporting a wood frame roof. I do not have the book with me or I could actually calculate the LF of shear wall versus LF of wall utilzing columns. I noticed when I was surfing the web that another code defined a load bearing wall as having something like 200 plf. Unfortunately, I cannot remember which code it was referring to, but this still would not define the "system" only that particular wall. You would think the IBC would set limitations/qulifications to define a sytem. Again thanks for response.

Stu

 

[haynewp]

I also thought the load bearing definition was based on supporting vertical load > 200 plf plus wall self weight. This is from the definitions section of the IBC.

 

[mrpid]

Thanks Heynewp,

This seems to be a gray area with this particular situation as most of the one story structure is supported with columns and wood framing, therefore the building system is a dual system;however, the lateral system is 100% masonry shear walls. Since the table in question is titled "Design Coeff and factors for Seismic-Force Resisting Systems", I am inclined to consider this a bearing wall system. I guess the next step is to contact NCEES and see what they have to say, as they wrote the book I am questioning.

 

[haynewp]

There is another definition in ASCE under the seismic definitions part, more like what JAE had said. It is "bearing wall system" and not "bearing wall" being defined.

WALL SYSTEM, BEARING: A structural system with bearing
walls providing support for all or major portions of the vertical loads. Shear walls or braced frames provide seismic force resistance.

It looks like slightly less than 50% of the dead load on that problem is being supported by the masonry, so I would say that is a major portion of the dead load. But I guess they don't think so, seems a little hokey to me.