Contact US

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!

*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

steel cross frames in skewed bridges?

steel cross frames in skewed bridges?

steel cross frames in skewed bridges?

I need some intelligent advice for a bridge rehabilitation project.
The exisitng bridge has an skew of about 30 degrees.
It need to be raised up to get required vertical clearnace.
hence we r raising the existing beams up/providing a new deck above.

My question is.....will there be any stresses in cross frames if I raise the beams up by different amount at different supports?

If so ....how can I take care of that!

RE: steel cross frames in skewed bridges?

Of course you will have moments in the cross frames (diaphragms?).
As you will be replacing the deck at the same time try to do the rehab in stages  and cut both deck and relase diaphragms at the same time.After lifing, when these are at the same, or almost same relative level, bolt it back together. This will work for typical steel stringer/RC deck bridge.
If the bridge is RC on RC/PC, situation is more complicated, but the method is the same. Longitudinal cut and jacking in sections are the only solution.

RE: steel cross frames in skewed bridges?

What exactly do you mean by " bolitng it back together"?
The beam and cross frames will be acting as one single unit.
I am going to raise the beam (yes steel beam) and cross
frames togehter.

RE: steel cross frames in skewed bridges?


If you must raise ALL of the beams and cross frames together (and fully connected) but by differing amounts, then you are almost certain to generate considerable stresses in the cross frames.

The only condition that I can see that would give you no such stresses would be if you were to impose a genuinely mathematical 'rigid body' movement to the bridge.

To clarify what I mean, consider your move in three stages
(taking z coordinate as vertical) :
1. Lift every point by the same distance : dz=constant=A
2. Rotate the entire structure about one side : dz=B*y
3. Rotate the entire structure about one end  : dz=C*x

Any combination of these three movements would give zero Xframe stresses.  In other words, if the final movements that you are aiming for fit the equation dz = A + B*x + C*y at every beam/Xframe intersection (and at every stage of movement), then you need not worry about cross frame stresses.

If not, then you need to do what Wiktor says - 'loosen' every crossframe/beam connection before you start, and 're-connect' again after you have finished the move.

Hopefully, 'loosen' means simply slacken off sufficient connecting bolts (eg all bottom chord bolts).  If your structure is fully welded, then you have a much more difficult task, and will have two choices - cut out sufficient welds to make 'hinges' at every beam/Xframe connection (probably cut out all bottom chord welds), or do a detailed structural analysis to see if the imposed stresses can be accepted.

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! Already a Member? Login


Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close