×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

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

Wood joists smaller than actual standards

Wood joists smaller than actual standards

Wood joists smaller than actual standards

(OP)
Hi everyone,

I encountered wood joists which their actual size is 1.5 by 9 inch (exactly). They are SPF No.2.
Why does it measure this way and how would these joists be checked using the building code tables? Would these be considered deficient 2x10? Or buffed 2x8?

RE: Wood joists smaller than actual standards

I would recalculate the section modulus for the reduced-depth section and then find the reduction factor (ie. S_true / S_standard) then apply that to the moment capacity. Other concern would be: if these are existing, does the current SPF values for bending strength still apply? For a 2x10 floor joist, I probably wouldn't lose sleep over it unless there are some other deficiencies noted.

RE: Wood joists smaller than actual standards

That is almost precisely a 2x10. It was probably milled at 1/5x9.25 but with a bit of shrinkage from drying you end up with 9".

RE: Wood joists smaller than actual standards

What jayrod said. I've encountered this a lot where crawl space companies convince people they need 17 dehumidifiers cranked to the max under their house. Measured a 2x10 at 8.5" deep once. I've seen continuous girders under continuous floor joists lift off of their foundation piers because the joists (which were nailed to the girders) shrank so much they lifted the girder (which was not nailed to the CMU...). The best part was the other engineer who insisted it was the 300# pier sinking...

RE: Wood joists smaller than actual standards

Alan -

You do understand that the actual size of a 2x10 is 1.5 x9.25, right? Just take a look at the NDS supplement Table 1A.

If it's 1.5" by 9.0" then it is a little bit small. That might mean it shrank more than expected. Regardless of why it's this size, you can still use the NDS exactly as you would before. You just use a slightly different area, moment of inertia and such. But, anywhere the code refers to nominal size (like the basic design values) this would still be considered a 2x10.

RE: Wood joists smaller than actual standards

Part of the shrinkage consideration is dependent upon where within the log the 2x_ was cut from. See the image below, gives a relatively idea of the expected shrinkage depending on grain orientation. Wood tends to shrink twice as much in the tangential direction when compared to shrinkage in the radial direction.

RE: Wood joists smaller than actual standards

One thing to add, make sure these joists weren't field ripped. If the product has been ripped down from larger stock, that will affect the visual grade, and may affect the allowable design properties for this particular material.

RE: Wood joists smaller than actual standards

thanks for the insight phamENG, never seen anything like that before

why would field ripping affect the allowable design properties ChorasDen?

RE: Wood joists smaller than actual standards

Mike Mike - visually graded lumber is graded based on rules like grain size, grain angle, knot size, and knot location.

If a a 2x10 is no2 with a 4 inch knit along the centerline and a 2x6 can only have a half inch knot at its edge, ripping it down will lead to a 2x6 or so with a massive edge knot that drops it to less than no2.

(I made up sizes for the example)

RE: Wood joists smaller than actual standards

Pham has it covered, but basically, the grading rules allow for certain defects, at certain locations, and are limited to a certain size within the structural member. If you rip down a visually graded member, it will need to be regraded to ensure it conforms the to the allowances/requirements of the grading standard for the new product 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! Already a Member? Login


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
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