Is cracked concrete = plain concrete? 1

[McSEpllc]

Hi All,

Do load capacities of anchors in cracked concrete per anchor manufacturers charts apply to plain/unreinforced concrete?

Thanks!

 

[phamENG]

Generally I'd say yes, but make sure you're reading the manufacturer's literature. It will typically tell you whether or not the influence of reinforcing has been taken into account.

That being said, don't assume that because the anchor works the concrete will work (especially if it's a tension load).

 

[McSEpllc]

Thanks Pham

 

[KootK]

Do load capacities of anchors in cracked concrete per anchor manufacturers charts apply to plain/unreinforced concrete?

In general, I would say no. For anchorage purposes, a plain concrete member may be either cracked or uncracked based on the particular situation just like reinforced concrete. In practice, an unreinfroced member may actually be less likely to be cracked in service because it's proportions will often be such that internal stresses are lower.

Certainly, it would be conservative to assume that cracked capacities apply to plain concrete members. But, then, that is also true of cracked members.

I try to not use uncracked values whenever possible given:

1) The difficult to predict realities of temperature and shrinkage cracking as a result of incidental restraint and;

2) The observed fact that anchor installation itself tends to produce cracking in the vicinity of the anchor.

 

[KootK]

I'm not entirely sure that I understand the question here, however, so I'll add this:

Anchorage design methodology (old ACI appendix D) applies to plain concrete just as it applies to reinforced concrete. In fact, the research and testing was largely done on unreinforced concrete. Obviously, supplemental reinforcing provisions do not apply in the absence of that supplementary reinforcing but, then, that's a different animal.

 

[McSEpllc]

Thanks Kootk for the feedback - I see you and certain other names routinely in the responses, I put a lot of weight on those.

What has happened is a contractor missed placing specified reinforcing bars in a 12" x 3ft x 3ft footing, designed to resist wind uplift and downward load at the and of a shear panel. Grabbing whatever dead loads to resist wind uplift loads results in a netwind uplift of only 340 lbs, while the expansion bolts have a capacity of 2,400 lbs for cracked concrete.

 

[Celt83]

McSEpllc:
To echo phamENG's last sentence, now that we know the full picture has the foundation itself been checked as a plain concrete member, you may find yourself in a similar situation as another post in the structural engineering discussion section where the best course of action may be demo and replacement of the footing.

Open Source Structural Applications:

https://github.com/buddyd16/Structural-Engineering

 

[KootK]

What has happened is a contractor missed placing specified reinforcing bars in a 12" x 3ft x 3ft footing, designed to resist wind uplift and downward load at the and of a shear panel. Grabbing whatever dead loads to resist wind uplift loads results in a netwind uplift of only 340 lbs, while the expansion bolts have a capacity of 2,400 lbs for cracked concrete.

You should be good to go. A footing of those proportions is unlikely to need reinforcing, particularly for an uplift of 340 lbs. You could make a pretty good argument for using uncracked anchors here since, if you develop a flexural crack, the jig's up anyhow as you'll have lost your flexural resistance. That said, I'm sure that you can get your 340 lbs using cracked anchor capacity so you might as well just run with that and sleep easy.