×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Critical Stress for Structural Members

Critical Stress for Structural Members

Critical Stress for Structural Members

(OP)
I am trying to learn how to calculate basic structural members with the help of "Limit States Design in Structural Steel" textbook.  

For lateraly unbraced beams, Mr is smaller than or equal to Phi x S x Fcr,
where  Mr is moment resistance
       Phi is resistance factor
       S is elastic section modulus
       Fcr is CRITICAL STRESS

How do I find Fcr???  Equations or tables.  The textbook does not say how nor gives any examples.

Thank you in advance.

RE: Critical Stress for Structural Members

Mr = phi x S x Fy
Where Fy = specified minimum yield stress (which is usually 300MPa or 350 MPa depending on the type of steel being used)

RE: Critical Stress for Structural Members

(OP)
Thank you civeng!

MeckMan

RE: Critical Stress for Structural Members

I presume you are starting to learn LRFD.
As you will see after, depending on the type of sections and their availability to develope plastic hinges, the elastic modulus, will turn into the plastic modulus. This is the real meaning of a limit state behaviour.
For the plastic modulus you will find them easily in section data tables.
Please enjoy the Limit State Design, because that is the way.
Regards,
CV

CV
carlosvalinhas@netcabo.pt

RE: Critical Stress for Structural Members

It looks like you are studuying in the uk ?
if so, take a look at the BS5950 in the first pages, you have steel grades, and corresponding stresses for each steel grade depending on the thickness of the steel member.

Usually py = 275, and you should use something around 255 to 245 N/mm2

hope it helps...


Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources