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!

*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.

Jobs

damping ratio (beta) for use in calculating gust effect factor (G)

damping ratio (beta) for use in calculating gust effect factor (G)

(OP)
I am referring to ASCE 7-02, Section 6.5.8.2, Gust Effect Factor for Flexible or Dynamically Sensitive Structures.

The equation for the gust effect factor (G) includes the variable R, or resonant response factor.

The equation for R includes the variable beta which is a damping ratio.

As far as I can tell, there is nowhere in the code where it gives any equation or values for this damping ratio, beta.

Does anyone know how this value is calculated?  Thanks for your assistance.

RE: damping ratio (beta) for use in calculating gust effect factor (G)

Look in the commentary in the back of ASCE 7-02.  Under the section C6.5.8 there is a section titled Structural Damping.  This gives you some ideas of possible betas to use as well as references.  Looks like ratios of 1% and 2% are typical for the US for buildings.

Interesting to note is this states ratios of 0.15% to 0.5% for signs are typical but the guide to the use of ASCE 7-02 sample problem for a sign uses 1%.

With that said I may have missed something

RE: damping ratio (beta) for use in calculating gust effect factor (G)

(OP)
I might be crazy, but I don't have a section about Structural Damping in my ASCE 7-02.  I do have the example you referred to that uses a damping ratio of 0.1.  But there is no section in my text that gives any suggestion where that number might have come from.

RE: damping ratio (beta) for use in calculating gust effect factor (G)

Oops... my mistake.  The wind guide I have is for 7-02 but the commentary I was reading is 7-05.  These minor details always getting in the way.

You know 7-02... 7-05... whatever it takes

RE: damping ratio (beta) for use in calculating gust effect factor (G)

mpdst11, What type of structure are you analyzing?  Are you sure it classifies as a flexible structure (NF < 1 Hz)?  

RE: damping ratio (beta) for use in calculating gust effect factor (G)

(OP)
Thanks CFS, I will have to take a look at the 7-05.

Meca, the structure I am analyzing is a 7 story concrete office building.  I have it modeled in RAM and it has a natural frequency of 0.7 Hz.

I am trying to calculate the wind pressure on the penthouse and screen walls on top of the structure.

RE: damping ratio (beta) for use in calculating gust effect factor (G)

On this subject...

 I calculated the gust effect factor for rigid buildings across a range of heights for each exposure (B,C,D) and I am getting a factor that is above 0.85 mostly for heights under 400 ft. Is this true? Because if it is then the 0.85 default value isn't conservative. I've double checked my math and it looks ok but it doesn't make sense when ASCE-7 05 says that 0.85 is a conservative value.

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


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