Cracked Concrete Definition

[snoren]

Does anyone know what defines cracked concrete? How wide and deep can the crack be? I want to specify a mechanical anchor at a joint or crack in the concrete but I'm not sure how wide of a crack is too wide for it to qualify. Any suggestions? Thanks.

 

[Lion06]

In my mind, any crack of any width qualifies as cracked concrete. Additionally, if you can't see a crack, but analysis shows that the tensile stress is greater than 7.5*(f'c^0.5), I would also assume it's cracked.

 

[BlastResistant]

Just spec an anchor that's ICC approved for use in cracked concrete. That way you don't have to think about.

 

[TXStructural]

Unless it is protected from cracking, as with PT, or a member is significantly oversized, it will probably be cracked. If the placement is outside of a flexure or shear area, you may not have (many) cracks. As a reference, 318 App D D.5.2.6 applies where analysis indicates that there will be no cracking at service load levels. In compression zones, cracks may or may not form such that they could interfere with anchors.

For one-way members, ACI-318 Eqn 9-9:
Mcr = fr * Ig / yt
Mcr: cracking moment
fr: modulus of rupture = 7.5 * sqrt(f'c)
Ig: mom. of inertia of concrete section
yt: distance from the centroid to the extreme fiber

ACI 318 Appendix D requires anchors approved for cracked concrete in all seismic applications. These anchors must be approved for the specific seismic category.

 

[Teguci]

Oversimplification -
Top of a beam - uncracked
Bottom of beam - cracked
Even for PT (and precast) I'd still assume a cracked bottom surface since ultimate loading often sends PT concrete into tension.

 

[steellion]

Agreed with BlastResistant, I always assume cracked concrete in anchor design.

 

[snoren]

So would you consider a contol joint be in the parameters of cracked concrete? Is there a limit to how deep or wide the control joint can be? I just want to make sure that even if I specify a mechanical anchor for cracked concrete that my conditions qualify at a control joint. Thanks.

 

[Teguci]

I would keep your anchor 1.5 x Heff away from the contraction joint or calc the anchorage assuming it is against an edge. In my mind, the contraction joint does not help confine the concrete across the joint.

 

[vandede427]

to me, having provisions for "uncracked" concrete is complete sillyness. if it's concrete, it's cracked.

 

[BlastResistant]

I would not consider a control joint to be a crack. I would consider it to be an edge, and would calculate appropriate edge distance or follow anchor manufacturer's edge distance recommendations to ensure proper anchorage. Other than that, I always consider concrete cracked, even in new design and even in compression zones.