When can uncracked concrete conditions be assumed?

Hey Customer,

well this is a good question. Concrete cracks when tensile stresses in the concrete imposed by loads or restraint conditions exceed its tensile strength. Concrete is typically assumed to crack under normal service load conditions. Crack width and distribution are generally controlled through the use of reinforcement. With consideration for the protection of the reinforcing steel, crack widths are assumed to be less than approximately 0.012 in  (0.3 mm). Under seismic loading, flexural crack widths corresponding to the onset of reinforcing yield are assumed to be approximately 1-1/2 x static crack width = 0.02” (0.5 mm). Both ACI 318 and the International Building Code assume cracked concrete as the baseline condition for the design of cast- in-place and post-installed anchors since the existence of cracks in the anchor vicinity can result in a reduced ultimate load capacity and increased displacement at ultimate load compared to uncracked concrete conditions.

Design for uncracked concrete conditions is permitted only for cases where it can be shown that cracking of the concrete at service load levels will not occur over the anchor service life. For cases involving design for seismic actions, post-installed anchors must be prequalified for use in cracked concrete as well as for seismic loading.

PROFIS Anchor contains a tool tip that summarizes the above text. Go to the Base material tab and
hover your pointer over the drop down for cracked/uncracked concrete to view the tool tip.
Please feel free to reach out any time, if you need additional information.

Cheers
Lisa

Lisa,

ACI318-14 17.2.3.1 states that sections 17.2.3.2 through 17.2.3.7 need only be satisfied for structures in SDC C, D, E or F. Since the provision for use on cracked concrete is under 17.2.3.4.4 one can understand that for SDC B unckracked concrete may be assumed.

Thanks,
Teo