WHAT IS CRACKED CONCRETE?
Flexural crack widths in concrete caused by tensile stresses
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. Crack widths are
assumed to be less than approximately 0.012” (0.3 mm). Under seismic loading, flexural crack widths
corresponding to the onset of reinforcing yield are assumed to be approximately 0.02” (0.5 mm).
The existence of cracks in the anchor vicinity can result in reduced anchor capacity at ultimate load, and
increased anchor displacement at ultimate load, compared to the anchor capacity and displacement
relative to uncracked concrete conditions. Cracked concrete conditions can therefore have a negative
effect on the performance of an anchor, inclusive of both cast-in-place and post-installed anchors.
Both ACI 318 and the International Building Code (in Canada, CSA A23.3 and the NBC-C) assume
cracked concrete as the baseline condition for the design of cast-in-place and post-installed anchors.
Design for uncracked concrete conditions is permitted only where it can be shown that cracking of the
concrete at service load levels will not occur over the anchor service life. Post-installed anchors must be
qualified for use in cracked concrete when designing for seismic load conditions.
Our Engineering Technical Services team is available to answer any questions you may have regarding
this topic. They can be reached by phone or email at the numbers and addresses listed below:
Hilti Engineering Technical Services – United States
(877) 749-6337 toll free
[email protected]
Hilti Engineering Technical Services – Canada
(800) 363-4458 toll free
[email protected]