What is this structural system's R factor?
What is this structural system's R factor?
(OP)
I am designing a residential structure in SDC D. It is 2 stories. The 1st story is an open carport. 2 story steel HSS columns are used from the foundations to the roof. Wood shear walls are used at the 2nd story. There are NO moment connections at the 2nd story or roof. The base of the columns need to be fixed to reduce story drift.
The structure derives its lateral force resistance from the shear walls (at the 2nd story level) and through bending in the steel HSS columns. A R factor of 6.5 (per ASCE 7-10) has been used based on light frame shear walls. This would control over an R factor of 8 with special steel moment frames. Does fixing the base of the columns at the foundations require an R-factor based on cantilever columns (R=2.5)? I think it would not because the wood shear walls provide some restraint at the 2nd floor and roof diaphragms. What R factor would you consider this to be?
The structure derives its lateral force resistance from the shear walls (at the 2nd story level) and through bending in the steel HSS columns. A R factor of 6.5 (per ASCE 7-10) has been used based on light frame shear walls. This would control over an R factor of 8 with special steel moment frames. Does fixing the base of the columns at the foundations require an R-factor based on cantilever columns (R=2.5)? I think it would not because the wood shear walls provide some restraint at the 2nd floor and roof diaphragms. What R factor would you consider this to be?






RE: What is this structural system's R factor?
The highlighted section is from ASCE 7-10 12.2.3.1.1.
RE: What is this structural system's R factor?
Story 1: Inverted pendulum. Your columns act as cantilevers with a large seismic mass near the top.
Story 2: Hybrid steel moment frames where your light frame shear walls are essentially the beams of those moment frames.
Inverted pendulum would be the most conservative route, obviously.
I could get behind the lesser of the value for light frame shear walls and ordinary steel moment frames.
I wouldn't tell the moment frame story at all in a special or intermediate moment frame. In those systems, dissipation is meant to happen in the beams. With your beams being wood shear walls, that would be a pretty tough sell.
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.
RE: What is this structural system's R factor?
RE: What is this structural system's R factor?
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.
RE: What is this structural system's R factor?