Brittle failure - not suitable for SDC C or above.

[CCFCE]

I am trying out Quick Anchor to design anchor bolts for a steel building per ACI Appendix D. In the output i am getting a value for tension and shear x and shear y, but each has the "Brittle failure - not suitable for SDC C or above." note. I can not see in appendix D what this is. Has anyone else seen this?

 

[frv]

Look ad D.3.3.4.

 

[CCFCE]

do you have any thoughts about what is the controlling factor that would make it ductile? I have been trying different s spacings and supplemental reinforcing conditions as well as f'c but doesn't seem to make much difference.

 

[frv]

Sure-

It means that the bolt fails- not the concrete.

 

[CCFCE]

thanks. it finally occurred to me after i posted this. i was so caught up in the numbers and formulas that i wasn't paying attention.

 

[CCFCE]

so no matter how excessive the load is for concrete, it has to exceed the bolt? seems excessive, when you consider the 0.75 factor already included

 

[CCFCE]

am i correct in assuming that if the capacity of the concrete (50k) exceeds the actual load (46k), i still have to design the concrete up to the steel capacity (80k)? i want to be sure because i am having to increase the ftg sizes to make this happen, and i see no way to make @ 3' diameter caisson work at all

 

[WillisV]

That is one option. The other option is to design the baseplate to yield before the concrete breaks. Note that the IBC and now ACI 318-08 have provisions that allow you to wave the "ductile" requirement if the concrete breakout strength is 2.5 times the demand.

 

[CCFCE]

the base plate is designed by the metal building supplier so i have no control over that. do you know what section of the IBC allows waive ductile if breakout is 2.5 times demand? is this in ACI 08 and not 05? i think 2007 CBC uses 2006 IBC which uses ACI 05 and not 08 thanks for your input

 

[WillisV]

It is located in IBC 2006 1908.1.16 (see italicized portion of reference to D.3.3.5)

It was not in ACI 318-05. It has been placed in ACI 318-08
in Section D.3.3.6 (the 0.4 factor is just reciprical of 2.5)

 

[frv]

Please note the 318-05 doesn't give you much guidance on using shear friction to boost your capacity. 318-08 does. It may be worth getting just for that.

 

[CCFCE]

thanks for the section. i had it right in front of me but didn't see it.
is shear friction added to appendix d in 08? i don't think CBC 07 which uses IBC 06 uses 318-08, so i don't know if that would be allowed.

 

[frv]

The IBC doesn't specify a year for 318. See IBC 1901.2.