Contact US

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.

Students Click Here

Period of Wood Structure Calculated to Justify Lower Earthquake Loads

Period of Wood Structure Calculated to Justify Lower Earthquake Loads

Period of Wood Structure Calculated to Justify Lower Earthquake Loads

Has anyone ever calculated the period of a 4 or 5 story wood structure by hand? I calculated a higher period by the Rayleigh method than by the approximate method (ASCE 7-10, and was able to reduce my loads by a factor of 1.7. Still double checking my numbers but is this typical in your experience?

RE: Period of Wood Structure Calculated to Justify Lower Earthquake Loads

Isn't there a restriction on how much of a period difference you can use when using the rayleigh method?

Yeah.... Table 12.8-1 of ASCE-7. You can use a period of between 1.4 and 1.7 times the "approximate period" to get your base shear, depending on the Sd1 of your site. I am skeptical how this could be properly applied and get a 1.7 force reduction in the type of structure you describe. That just seems like higher of a force reduction than I'd expect.

Also, I question how much of these provisions have really been "tested" with the taller wood structures that we're seeing today. Heck, I question the deflections that we calculate for wood shear wall buildings too.

I'm not saying that you're wrong. Just that something sounds a little off and that this is something that might require some caution.

RE: Period of Wood Structure Calculated to Justify Lower Earthquake Loads

Thanks for your thoughts Josh. I talked to a few more of the top engineers in our office and they said they haven't ever taken advantage of the code's permission to use the calculated period for a 4 story wood structure, but they wouldn't be against the idea of dividing the loads by 1.7. I checked the numbers, read thru the literature again, and I think this route makes sense. In my opinion the approximate period calculation ( is extremely conservative for wood structures. It assumes a concrete shear wall structure is just as stiff as a wood framed shear wall structure. Both fall into the "all other structural systems" category of table 12.8-2

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! Already a Member? Login


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
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’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:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close