×
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

floor frequency

floor frequency

floor frequency

(OP)
Hi,
I am analyzing a industrial building with many vibratory equipment on elevated floor.
I isolated a portion of a floor from col. to col. and performed a dynamic analysis to calculate fundamental mode of floor.

My results are so scattered in x,y and z direction and mass participation is very low in earlier modes.

I have two questions (see attached excel file)

1- How much mass participation is required to consider a mode as fundamental mode for that direction.
2- what happen if natural frequency of floor matches with natural frequency of machine. As per my analysis at resonance vibrations will be under acceptable limits.
Please help me to understand results. Thanks in advance.

RE: floor frequency

1) This is an engineering judgment call. There isn't any rule of thumb. If a beam has a natural frequency then the mass participation of the overall model may be very low... even though this one beam's behavior is almost totally controlled by this one mode.

That being said, if adjacent members / beams/ bays do not have the same kind of natural frequency, then they will tend to dissipate the energy from that one beams vibration. I tend to think of this as just an increase in the damping of that one mode. Though that may not be a precise theoretical description.

This also depends on the amount of damping you expect for your structure. Do you have architectural elements (full height floor partitions, floor material, cladding and such) that will tend to increase damping?

2) If you've done an analysis of the vibration response at near resonance, then you already know what will happen. You get dynamic amplification of the response. There are hand calc methods you can use to calculate this amplification. Also, it's not just about whether the structure is going to fall down. It's also about whether the equipment operation can tolerate the vibrations and whether an operator can work on the floor without experience significant discomfort.

RE: floor frequency

(OP)
Hi,
Thanks for your feedback. I will perform analysis more in depth.

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