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

GRK analyzed as lag screw vs. wood screw

GRK analyzed as lag screw vs. wood screw

GRK analyzed as lag screw vs. wood screw

In CSA O86, there is a distinction between Wood Screws and Lag Screws. The yield modes are more or less the same, however the safety factor is 0.6 for lag screws vs. wood screws. More importantly, Wood Screw provisions account for a higher embedment strength in the point side member (rope effect), while the Lag Screw provisions make a distinction based on the direction of the load vs. grain.

Wood screws larger than #12 are to be analyzed as lag screws because of the shank/thread dimension limits. When reviewing the literature for GRK screws, it seems that they give capacities that are all over the map.

1. The comparison table (PG. G26) shows a value of 366lbs or 466lbs for all diameters
2. The tables on PG G28-G30 show various values for different embedment, but note that Wood Screw provisions have been used
3. Tables on PG G48 seem to suggest an NDS approach, and offer different capacities for parallel and perpendicular loading.
4. When reviewing a similar type of self-drilling screw (ASSY), their documentation makes it clear that Lag Screw provisions are used. And this is reflected in their tables. However, from the naked eye the ASSY screw is quite similar to the GRK screw. Both of which appear to be more refined than a lag screw or wood screw alternative.

How are other designers handling these types of fasteners? Is it sufficient to go off the manufacturer's data, even though the provisions may not be as specified by code? Is it sufficient to use ESR reports and apply a judgement/FOS to the results to get capacities within the threshold between NDS, CSA Wood Screws, and CSA Lag Screws (or sim)? What is the capacity of a GRK?

RE: GRK analyzed as lag screw vs. wood screw

I personally use the wood screw provisions, as outlined in their catalog. I went through your exact process of humming and hawing how to handle them, and ended up defaulting to the manufacturer's guidance. My justification is that these do not fall squarely into either category (wood screw or lag), and are therefore similar to other proprietary fasteners (such as hangers, truss plates, etc). While they do not have a CCMC report (wish they did), they reference their catalog values on testing to an ESR Report, which seems like the next best thing.[/sup]

RE: GRK analyzed as lag screw vs. wood screw

As a follow-up, I emailed ITW to acquire lag screw values and to get their feedback. Here is the synopsis of their response:
1. The unique design of the GRK-RSS with the T-star drive is not covered by ASME B18
2. It is interpreted that the IA Cross Recessed Oval Countersunk Head wood screw in the standard is the closest representation of the RSS.
3. Certain features of the screw are not considered as they are not comparable.
4. GRK has been tested, approved, and published ICC-ES report
5. ASME B18 shows only values on shank diameter, not on the strength of unique design of screws

The rep provided another report sheet that has the lag screw values. Probably a good resource. I agree that using the catalogue table values is adequate as it looks like they have been aligned with some test data.

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