×
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

Crane Monorail Unbraced Length

Crane Monorail Unbraced Length

Crane Monorail Unbraced Length

(OP)
Does anyone know of research or code allowances to support increasing the Lc for a hanger supported monorail crane loaded from the bottom flange?  The idea is that since supports are on top and load is on bottom, the beam would not really be in pure bending, moving the neutral axis up and reducing the compression felt. Unless, of course, this doesn't happen and the "roller" support model allows the top flange to go into compression just as though it were supported from below on a pin and roller.

Otherwise, can I reasonably say the unbraced length is from the point of application of the load to the nearest support?  

Help is much appreciated.
 

RE: Crane Monorail Unbraced Length

I don't think so.  There is some research that shows that bottom flange loading tends to stabilise the top flange because the top flange has to follow the path taken by the load, but I don't know of a definitive reduction you can apply.  Certainly, you can't take the unbraced length as the distance from load to support.

RE: Crane Monorail Unbraced Length

There will be a lateral component that will tend to destabilise the beam - take the full length.

RE: Crane Monorail Unbraced Length

(OP)
Thank you, I'll be taking the full length without reduction.

RE: Crane Monorail Unbraced Length

I agree with the others.

Loading on the bottom flange tends to right the beam if the compression flange wants to buckle to the side. Whereas, loading on the top flange does just the opposite. There are some coefficients that someone has developed to take into account the position of load (ref. Salmon & Johnson) but they are not used in normal design practice. I also use the full length for unbraced length. Incidently, the neutral axis does not move.

An additional question might be how to handle lateral forces applied to the bottom flange. I have seen some engineers go thru a complicated torsional analysis for this but what happens when you get to the hanger?

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