AISC vs CISC: design of composite HSS sections

[HanStrulo]

Hi Everyone.

I have a question regarding the composite filled HSS sections in bending+compression. This is for anyone familiar with both AISC and CISC.

As I understand, in AISC, tables 6-4 and 6-5 give the cross section strength of these sections considering an interaction diagram.
in CISC, they are giving the axial resistance equations alone and bending resistance alone and a combined resistance (section 18-2-4).

The AISC seems similar to how we usually design concrete columns and the CISC seems similar to how we design steel columns. is there any reason for the difference?

The reason i am asking this question is because i have a couple sections that were designed using AISC but seem to have less capacity using the CISC. I don't know how to compare them directly.

Thanks alot.

 

[WillisV]

AISC provides multiple ways to design CFTs (concrete filled tubes) in Chapter I. The plastic interaction diagrams you are referring to provide additional strength, but the basic P/M interaction equations just like CISC are a valid and permitted method. My guess is CISC just hasn't taken the time or effort to codify the more rigorous interaction method.

 

[HanStrulo]

Thanks for the response.

Another question that i have is why CISC is requiring interaction between axial and bending AND bending alone to be less than 1 while AISC is only requiring interaction between axial and bending to be less than 1?

 

[jayrod12]

Due to the beta and omega factors, theoretically on a lightly axial loaded beam-column you could have the first check pass, but the moment unity check fail. Therefore it needs to pass as a beam, and a beam-column.