×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Are you an
Engineering professional?
Join Eng-Tips Forums!
• Talk With Other Members
• Be Notified Of Responses
• Keyword Search
Favorite Forums
• Automated Signatures
• 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.

# Impulsive Natural Period, Ti

## Impulsive Natural Period, Ti

(OP)
The formula(s) for the impulsive period of the tank E.4.5.1-1 (a & b).
There is a note stating: "Substituting the USC units specified above: Ti = 0.128 sec"
However, I do not see any tank dimensions provided above to put into this formula. Putting in values for tanks I am considering, i get a Ti in the ball park of this, but I am a bit thrown off by them providing a certain value as it depends on specific tank dimensions.
Is this an error in the code?

Also, I notice that the value for Ci is truncated at 1.5 H/D. It is approximately linear from 1.0 to 1.5 H/D, is it unfounded to extrapolate linearly to 2.0?

Thanks

### RE: Impulsive Natural Period, Ti

In the latest revision, that "Substituting" note has been deleted. I think it was just extraneous stuff that found its way in there.
See this paper for background: https://pdfs.semanticscholar.org/9351/cd259d0ae432...
Not sure about the H/D limit. One thing is that most "large" tanks where seismic design is most critical will fall well below this limit.
Note that in the standard procedure, period is taken as zero/rigid for the impulsive mode, so trying to calculate an impulsive period is an option, but not a requirement.
I believe that paper is based on the Veletsos method which is not limited on the H/D ratio. But when I have worked through the Veletsos method in the past, there are some questions as to how certain terms in that paper are defined, which leaves the answers less definite than is desired.

### RE: Impulsive Natural Period, Ti

#### Quote (CaliEng (Structural))

There is a note stating: "Substituting the USC units specified above: Ti = 0.128 sec"
However, I do not see any tank dimensions provided above to put into this formula. Putting in values for tanks I am considering, i get a Ti in the ball park of this, but I am a bit thrown off by them providing a certain value as it depends on specific tank dimensions.
Is this an error in the code?

Although design methods in API 650 do not use the value of impulsive period of the tank, I think this empirical formula given for information only..
Regarding the value Ti=0.128 sec. can not be valid for all H/D ratios but should vary between 0 to 0.3 sec...

The shell thickness vary with height and for higher H/D ratios, flexural deformation of shell dominates and in this case you may use Housner formula..

In order to understand better the behavior of storage tanks during seismic event , I will suggest you to look New Zealand code, Seismic Design of Storage Tanks: 2009 and Eurocode 8 Part 4: Silos, tanks and pipelines.

#### 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.

#### Resources

Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a partâ€™s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

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:

• Talk To Other Members
• Notification Of Responses To Questions
• Favorite Forums One Click Access
• Keyword Search Of All Posts, And More...

Register now while it's still free!