Cantilever Column Systems - R Value / Detailing

[anthonyc007]

I have a question regarding the “R” value for cantilever column systems in ASCE7-05 (well, several, actually). Section G of the table gives values for seven different types of systems.

The way it is phrased is this: “Cantilevered column systems detailed to conform to the requirements for:” Then lists:
1. Special steel moment frames
2. Intermediate steel moment frames
Etc.

How does a cantilever column conform to details for a special moment frame? By definition, it does not take moment at the top; therefore, the FEMA 350 / AISC requirements are not applicable. Do you just check the column size restrictions? If so, what about tube steel / HSS type columns?

What is the difference in detailing requirements between SMF and OMF with respect to steel cantilever columns?

What is a “timber frame” and how do I ensure detailing conformance?

Since the base plate is the only connection to take moment, perhaps that is what should be detailing according to moment frame requirements. What is the difference between, say, a SMF base plate and an OMF base plate?

Basically, if a plan checker asked me why I chose a particular r value, how can I justify that decision?


-AC

 

[jdshiv]

I have the same question, myself.

Does it perhaps relate to the requirements of what shapes are allowable to use for the columns? For example, you could use HSS shapes for Ordinary, but might be limited to compact flange WF for Special?

I am eager to hear what others have to say about this.

(p.s. my project is under California CBC 2007, DSA; there may be different local requirements, for example in Los Angeles.)

 

[sandman21]

DSA is most likely going to make you design it OMF it does depend on the checker but more are going towards that. I have asked this question several times, yet to receive an answer.

Personally, I just put the dog-bone in the column and call it a SMF.

 

[anthonyc007]

Personally, I just put the dog-bone in the column and call it a SMF.

I think this is an irresponsible attitude. If anything, if you are going to throw a dart, you should pick the lowest possible R value (1.25, in this case).

I am surprised no one has any experience with this issue. No one has designed a cantilever column in the 4 years since ASCE 7-05 was published? Really?

-AC

 

[PARTAN]

for W shapes, you can consider special steel moment frame and for HSS or Pipe, you can consider an ordinary SMF

 

[anthonyc007]

for W shapes, you can consider special steel moment frame and for HSS or Pipe, you can consider an ordinary SMF

Great! What publication states this premise?

-AC

 

[sandman21]

I think this is an irresponsible attitude. If anything, if you are going to throw a dart, you should pick the lowest possible R value (1.25, in this case).

I think it is irresponsible that you do not know why and where a dog-bone is required and cannot see why my statement is a complete joke.

 

[JKStruct]

I believe that you have to meet the shape requirements described in AISC 341 (compactness, etc.), for whichever system you choose to design.

On a side note, your attitude, tone, and sarcasm dripping in your responses is irreverent and is not making you any friends. If I were you, I'd be more polite if you want more responses.

Obviously you wouldn't put a dogbone in a cantilevered column. Sandman was joking.