Concrete Breakout Strength of a Single Anchor in Tension

Pursuant to ACI 318-08 Standard, Section D.5.2.2, the answer to your question is that Nb is in Pounds, as follows:

Nb

= basic concrete breakout strength in tension

of a single anchor in cracked concrete, lb,

see D.5.2.2, Appendix D

Be very careful how you apply this formula as there are a multitude of modification factors and "qualifications", including (but not limited to) seismic design, edge distance, anchor groupings, anchor spacing, anchor type, & other conditions, etc. considerations that have to be taken into account and/or applied. You had better re-read the entire anchor section (Code & Commentary) before proceeding....

===Signed,

Captmoosie, BSCE/MSCE/PhD/PE

Civil, Structural & Environmental Engineer

OK, thanks a lot, that is also what I expected.

As for all the modification factors they are very close to 1 in this particular case, I just think it is a lot to expect 89.000 pounds of tension force before concrete breakout ?

But thank you

Hello srosendal:

I see that you're writing the pounds-force value (for allowable tensile force) in European terms (example: 89.000 #). I assume that you're in Europe somewhere? I also assume that you really mean 89000 # (pounds-force)?

Anyhow, getting back to your question. It is quite conceivable to develop 89,000 # for a cast-in-place anchor. Problem is that you haven't provided enough information in your query for me to state that your numbers are correct. For example, I have no idea what type of anchor you have in this instance (L or J-shaped anchor, headed anchor, straight rebar section, etc.). Additionally, is there additional cast-in-place rebar provided that surrounds the anchor which prevents it's pull-out? I also do not know what diameter size and yield strength that you have in this particular case.

You must also adhere to the provisions of ACI 318-08, Chapter 12, in terms of providing minimally acceptable reinforcement development length, all in regards to the type of anchorage provided and relevant conditions occurring, in order to satisfy the applicable covenants of Appendix D5 & D6. Be very very careful how you interpret these provisions, as one false assumption can ruin your day!

You must also check the anchorage for allowable tensile force of the anchor steel itself versus the allowable concrete tensile tear-out (see Appendix Sections D5 & D6). [Note: If you have treaded projected end of the anchor steel with steel nut and washer you must check the allowable tensile load of the steel using the Tensile Area of the anchor.]

I'm just curious if it would not be better to utilize a drop-in anchor where the respective manufacturer's have provided tabulated allowable tensile & shear values for their anchors? These published values are based on certified laboratory testing results that include factors of safety and statistical numeration........

Hilti, etc. manufacture excellent anchors of all types.

Good luck!