×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

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

Transmission Towers- Staggered bracings

Transmission Towers- Staggered bracings

Transmission Towers- Staggered bracings

(OP)

Hi,

I have a quick question about a transmission tower I am currently modelling in PLS Tower. I dont have the drawing with me at the moment but I need a quick answer. I have attached a sketch to show staggered bracing in tower legs. Can someone please help me to understand what the L/r ratio for the leg is? If I am right it would be 2.4 in x, y and z axis (according to AS3995)? I think because buckling length for member L is twice length in both directions and there is a 1.2 factor in the standard as well (or any standard for the matter I want to know the principle).

If that is true, then whats the point of having a staggered bracing because buckling length is big, wny not have normal symmetrical bracing?

Many Thanks

RE: Transmission Towers- Staggered bracings

In case someone doesn't normally look at this room, I'd also post in the Structural engineering and other subjects room. It's a basic structural question, not just for towers.

RE: Transmission Towers- Staggered bracings

For Tranmission Towers, and any 3D space frame, you have to look at the KL/r ratios in three dimensions, not just two.

Remember that.

Mike McCann, PE, SE (WA)


RE: Transmission Towers- Staggered bracings

I can only speculate, but they may have decided the connection simplicity of the staggered braces was valuable enough to deal with the mid-length bracing forces that would develop.

----
The name is a long story -- just call me Lo.

RE: Transmission Towers- Staggered bracings

Because when your structure was originally designed the 1.2 staggered bracing factor wasn't there, and because the controlling buckling direction for single angles is in the "z" (weak principal axis) direction. With staggered bracing vs. standard bracing the "z" unbraced length was halved while the "x" and "y" stayed the same. So an increase in strength (rx or ry controlled vs rz) for the same amount of bracing.

But full-scale testing proved that staggered bracing wasn't as strong as theorized, so the codes added the 1.2 factor to compensate.

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


Resources

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