Cantilever Column R Determination
Cantilever Column R Determination
(OP)
I would like to determine the R value for a steel cantilever column that supports wood beams and framing. ASCE 7-05 references special, intermediate and ordinary moment frame systems under the cantilever column section in table 12.2-1. It referances 14.1 for detailing requirements for each type which then sends me to AISC 341 which discusses moment frames with R = 3 and higher. Most of the requirements are in regards to the beam to column connection. What is special for different methods when it comes to cantilevered columns?
akastud
akastud






RE: Cantilever Column R Determination
Don't forget about the requirement listed in table 12.3-3 either.
Mike McCann
MMC Engineering
RE: Cantilever Column R Determination
akastud
RE: Cantilever Column R Determination
Mike McCann
MMC Engineering
RE: Cantilever Column R Determination
It is my understanding that the R, Omega & Cd values are defined in ASCE 7. But, to determine what an OME,SMF, etc actually is, one must go to the ACI or AISC to figure out what kind of detailing is required to meet that specific Seismic Force-Resisting system.
Is that what you meant in your second sentence, above?
RE: Cantilever Column R Determination
akastud
RE: Cantilever Column R Determination
Yes... exactly.
akastud:
I suppose that you could look at it that way, but I think you making the problem harder than it is. If you simply chose an OMF, the design forces may be higher, but there may not be the need for a special inspection, depending on the jurisdiction, due to the FS in the higher loading. Additionally, for cantilever columns what usually controls the size of the member is the allowable or tolerable lateral deflection at the applied lateral load, not the shear or bending stresses. The OMF is more conservative and simpler to detail. For high and mid rise buildings, use the SMF as it is more economical with material, but keep it simple in Residential and low rise with the OMF.
Mike McCann
MMC Engineering
RE: Cantilever Column R Determination
Les lateral deflection does control, but if I use a SMF (R = 2.5)the load producing that deflection is half the load in an OMF (R=1.25) and Cd is the same so the half load produces half the required I which results in a significantly smaller column and footing even if I use the SMF requirements.
akastud
RE: Cantilever Column R Determination
Mike McCann
MMC Engineering