Classification by Table B4.1 + Chapter H

[xxpecoxx]

I began working with AISC Specification (ANSI/AISC360-05) and would like to ask you for advice. I have problem with slednerness checking and understanding Chapter H.

Example: Rolled W profile bending about major axis combined with tensile force.

Process of design:

There is a "Chapter H - Design of members for combined forces..." where we need to compute: - "Allowable tensile strength - " P_c"
- "Allowable flexural strength - " M_c".

To compute "P_c" : Chapter D must be used.

To compute "M_c": Chapter F must be used. At first, we have to check slenderness of flange/web and than compute "M_c" according to F1,F2,F3... and others.

question 1)
Is this procedure correct??

If yes :

There are cases for slenderness check in the Table B4.1:
Case 9 - Flexure in web
Case 1 - Flexure in flange

Now I am going to check width/thickness limit for compute "M_c" value. As I said there is a moment only about MAJOR axis.

questions )
How to use Table B4.1 for combined forces?
Should I used Case9 and Case1 both together for slenderness checking? Or it depends on stress character in flanges e.g. both compressed; both tensile; one tensile + one compressed?

Thank you for your help and sorry for my english grammar.

P.

 

[agostage]

You need to check both case 1 and case 9 and follow the appropriate section in Chapter F. If your member goes into compression then you need to check case 3 and case 10 as well and apply to Chapter E. The rest of your understanding seems to be sound.

 

[xxpecoxx]

But how to do it in cases:

1, If combination "Tension + Flexure" produce fully tensile profile. Is it necessary to use Case1 and Case 9 if resultant is only tension?

2, If combination "Tension + Flexure" produce compression in one of flanges?


Please apologize me for probably simple questions but Im novice in AISC Code.

 

[agostage]

I believe I see, you are trying to justify using compact section design in your moment capacity equations given that the section elements may not go into compression. The way the code is setup one has to select the section of design based solely on the element section properties without considering the load at all. As far as I know there isn't an exception for low bending high tension members yielding a fully tensile profile. One could make their own judgment call based on their own situation and justify it in their calcs verbally, but personally I would never assume my bending elements never go into compression.

 

[frv]

BTW.. almost ALL rolled W shapes produced today are compact for flexure. Read the commentary on p.16.1-47.

 

[xxpecoxx]

Please find attached file.
Soo, is there any difference between Example 1 and Example 2 how to classified them in case of Chapter H ?
Thank you
P.

http://files.engineering.com/getfil...e7b-8d4940c7daf9&file=Tension_and_Flexure.pdf

 

[xxpecoxx]

Anyone who can help me with previous question?
Thank you in advance