×
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

Flexible Structures Damping Ratios

Flexible Structures Damping Ratios

Flexible Structures Damping Ratios

(OP)
There seems to be a gross lack of good data that provides guidance for what damping ratio to use for tall, flexible structures.  I'm talking about 100-150 ft monopoles with natural frequencies in the range of 0.3 to 0.9.

Some sources mention using values of 0.01 for steel poles and 0.02 for concrete without any real reference as to why. What I do know is that the gust response factors required in ASCE 7 can vary all over the map, depending on which value is used.

For example, a tall slender steel stand-alone monopole (meaning no long span wires attached to it to help the damping effect) of a given mass and a Fn =0.4 can produce a gust response of 1.43 using a damping ratio of 0.01.  Merely changing that ratio to 0.02 will reduce the G factor to 1.20. Since this directly affects the resultant wind pressure to be used, it seems like ASCE 7 has provided a lot of sophisticated tools with which to fine tune a wind load analysis, but then leaves you totally in the dark as to how to apply some of them.

Anybody out there got a better feel for the logic behind these ratios, or is the solution to just possibly be stuck with overdesign structures by 20%?

http://www.spiraleng.com

RE: Flexible Structures Damping Ratios

No, the solution is to go and belt a similar structure with a hammer and measure the decay rate.

It does vary a great deal, depending on the terminations and joint types.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

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