×
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

beam bending

beam bending

beam bending

(OP)
I am trying to compare FEM analysis to hand calculations for I-beam bending.  I am using "Roark's Formulas for Stress and Strain", seventh edition, for hand calculation formulas. And Patran 03 (nastran 01) for the FEM.  

The cross sections are height=4.5 in, flange width = 3 in, flange thickness = .25 in, and web thickness = .125 in.  The only value I have varied is length.

 Looking at the mid point of the beam and using span/depth ratios greater than 15 I have found a difference in deflection of at most 20% (span/depth~30) and only about a 1% difference in extreme fiber stress.  The difference in deflection decreases as the span/depth ratio increases.  Down to < 5% when span/depth ~ 55.  And the extreme fiber stress stays within 2% no matter the span/depth.

I assumed that the difference is due Roark's formula neglects shear deflection so I then added shear deflection using Roark's equation 8.10-1. The added shear deflection only marginally changed the deflections and hence the percent differences.  

Now for the questions.  Can anyone explain why FEM and roark deflections do not match? Also how do the extreme fiber stresses match when the deflections do not?

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