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


Buckling Analysis Results

Buckling Analysis Results

Buckling Analysis Results

I'm new to Staad and am running my first buckling analysis. The structure is a walkway consisting of two parallel aluminium trusses at about 2m centres with a floor between them. The floor is at the level of the truss bottom chords. Overall span is 25m and the truss bays are 1.4m long.

I've applied the dead loads, live loads, and handrail loads with ultimate limit state factors using Repeat Loads to combine the primary load cases. The maximum compression force in the top chord is around 500kN (from P-Delta analysis) and the analysis reports that the buckling factor is 4.0 (buckling analysis).

To determine the effective length of the top chord, do I simply solve the equation below?
(4.0 * 500E3 N)= pi^2 * E * I / Le^2

This gives me a bit over 3m as the effective length for elastic buckling which is a bit shorter than I expected so I wanted to check whether Staad reports results the same way as I'm used to from other software. It seems to have its own way of doing things in some other areas...

RE: Buckling Analysis Results

Truss bays are 1.4m long. The top chords are tied together in some way at the 1.4 m mark, right?

Going back to a simplified method and assuming fixity and sway, the k value would be 2.1. So, KL = 2.1 * 1.4 = 2.9 meters. So, 3 meters seems relatively reasonable to me.

Now, I don't really know how the tops chords are braced / connected to each other. So, this is really just a wild guess. But, as far as wild guesses go, it sounds like you're in about the right ballpark.

RE: Buckling Analysis Results

Thanks, Josh.

The top chords are braced by U-frame action. No direct connection between the two top chords as that is the walking path.

You're probably right about the order of magnitude of the effective length. I was thinking of the case of a single truss where the reduced eff length is due to the varying compression force in proportion to the 'bending moment'. In this case, I have that plus the U-frame action. So it's telling me the U'frames are about 45% of a standard brace working in tension (ie fully effective).

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!


3D Scanning in the Automotive Industry
With over 100 years of production history, the automotive industry has been at the forefront of manufacturing technology since its inception. Whether the transformative technology of the day was the assembly line, the integration of robotics into the manufacturing process, or the switch from steel to aluminum frame chasses, the automotive industry has consistently implemented advanced technology into its manufacturing and production workflow to improve manufacturing and product performance. Today, the same is true. Download Now
Green light on lidar: Developing low cost systems for autonomous vehicles
Lidar has been around for quite some time, but to date, it’s been custom—and expensive. Right now, there isn’t a clear-cut solution that’s suitable for all applications, such as lidar in autonomous vehicles. As they explore options, optical and mechanical engineers are forced to make choices and tradeoffs during the design process. 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