Anchor Knowledge Center WHAT IS CRACKED CONCRETE?

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 HNATechnicalServices@hilti.com Hilti Engineering Technical Services – Canada (800) 363-4458 toll free CATechnicalServices@hilti.com