×
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

First Harmonic in Bridge calculations

First Harmonic in Bridge calculations

First Harmonic in Bridge calculations

(OP)
I am designing a steel truss pedestrian bridge and I have run across a problem.

My company uses the AASHTO first harmonic criteria of 3.0 hertz or an alternate weight criteria of W>180e(-0.35f).  The customer wants me to explain why the alternate weight criteria can be used, but I do not know where it came from.  I have found several mentions of it in varying DOT standards but no document expalaining it.

Does anyone know whre I could find an explanation of the alternate weight spec for harmonic frequency in bridges?  

Any help would be greatly appreciated.

RE: First Harmonic in Bridge calculations

The dynamic problem can be simplified into two components that will characterize the dynamics of the bridge: mass and stiffness.  The fundamental frequency is a function of mass and stiffness.  Therefore if additional mass(can be related to weight by acceleration due to gravity) is used then the frequency will be lower and less likely to be excited by pedestrian or vehicle traffic.

Regards,
Qshake
pipe
Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

RE: First Harmonic in Bridge calculations

I believe the second formula in AASHTO is based on the work of Professor Thomas Murray of Virginia Tech.  I have also read, but I cannot recall where, that Professor Murray did not intend for his work to justify pedestrian bridges with natural frequencies less than 3 hz.   

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