Post installed anchors capacity_Ultimate load vs allowable load

[Nitesh Sadashiva]

Hello all,

I was checking the knee brace connection where brace was framing to beam bottom flange at top end and to grout filled CMU wall at the bottom end. While connecting brace to CMU wall, we are to use end plate with post installed anchors and brace gusset will be field welded to embed plate. When I check the capacity table of post installed anchors in the product technical sheet, it shows ultimate load and allowable load. Initially my understanding was ultimate load indicates LRFD capacity and allowable load indicates ASD capacity. But the ultimate load in technical sheet table is 5 times larger than the allowable load. In a normal steel connection, the difference between ASD and LRFD is 1.5 times. Now if my loads are in LRFD, can I take the ultimate load capacity from the table? Then if my loads are ASD it is not justifiable to consider allowable loads as it give 5 times less capacity where the load is reduced only by 1.5 times. Please see the attached document for the technical sheet table. As I am new to this post installed anchor connections, please forgive me if I am asking something blunder. Your help will be much appreciated.

[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1648544400/tips/SIMPSON_TITEN-_SREW_ANCHORS_wdfevl.pdf[/url]

 

[phamENG]

No, ultimate load in this case is the failure load and not the LRFD capacity. Allowable is for use with ASD. See this SE Blog Post from Simpson. It's a little old, but the information is still generally valid.

 

[JLNJ]

The large (apparent) safety factor is due to the variability in the strength of the connection for post-installed anchors.

 

[Enable]

JLNJ has it. That's why safety factors are best dubbed factors of ignorance. At least that way the names correlate more appropriately, since the greater the ignorance of the particulars the greater the factor!

 

[Ron]

The safety factor of five accounts for variable bond strength due to concrete strength, variable cleaning of the hole, variable diameter of the hole and temperature curing issues.

 

[Nitesh Sadashiva]

So if my loads are LRFD, is it okay to considered allowable load capacity from the table and multiply by 1.5? Do we really use ultimate load in any case?

 

[dik]

As far as a SF=5, I seem to recall in the notes that this is for a single fastener, too.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?

-Dik

 

[phamENG]

It varies by manufacturer. Most have a technical bulletin or a page in their catalog that discusses the procedure. If you can't find it, contact your regional engineering rep for the manufacturer.

 

[phamENG]

As for using the ultimate load, it let's the designer consider other safety factors if appropriate.