×
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 vs Rigid buildings - ASCE 7

Flexible vs Rigid buildings - ASCE 7

Flexible vs Rigid buildings - ASCE 7

(OP)
Greetings,
Per Chapter 6 of ASCE 7 "slender buildings or other structures are flexible if their natural frequency is less than 1 Hz".

In the commentary, it says when buildings have height greater than 4 times least horizontal dimension, then natural frequency should be investigated. It also says that Gust energy is smaller at frequencies aobove 1 Hz, and hence dynamic response may not be significant if frequency is greater than 1 Hz.

Suppose I have a building that is 100' tall and 50' x 50' in plan (h < 4 * horiz. dim). Assuming the calculated natural frequency is less than 1 Hz, does this mean that the building will have to be analyzed as a flexible building with modified Gust factors (6.5.8.2) and eccentricities per 6.5.12.3?

When you design buildings, how do you classify them as slender? using H < 4 * horiz. dim. or using the natural frequency.

I must tell you that 6.5.12.3 is a b*tch. Hope you can shed some light.

~Anantha

RE: Flexible vs Rigid buildings - ASCE 7

The commentary provides general guidance.  The requirement is per the natural frequency.  

A structure with H < 4 * horizontal dimension can still have a natural frequency less than 1 Hz depending on the LFRS.

RE: Flexible vs Rigid buildings - ASCE 7

(OP)
I agree, but I was having an discussion at work and my colleague seemed to disagree with me.

If fundamental frequency is less than 1 Hz, i.e, period greater than 1 second, do you calculate your eccentricities for a flexible building and apply them instead of 0.15 as in figure 6-9?

RE: Flexible vs Rigid buildings - ASCE 7

Yes, I believe so.  See 6.5.12.3.

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