When drilled anchors are used in concrete, isn't there a chance that a crack could form and pass through the anchor location, especially if the anchor is in a tension zone? What effect would a crack have on the anchor capacity?
There is a chance that a crack could occur at the anchor location. And depending on crack width, anchor capacity could be significantly reduced. German researchers (Ref. 1) studied the problem by forming cracks of differing widths through anchorage locations and then pulling the anchorage out. They compared capacities of undercut and expansion anchors in cracked and uncracked specimens. For a crack width of 0.016 inch, failure load was reduced by 25% to 50%. Even at a crack width of 0.004 inch, a 20% to 25% reduction was measured. At crack widths beyond 0.016 inch, there was little further reduction in capacity over a wide range of crack widths. British researcher A. W. Beeby (Ref. 2) believes, however, that cracks caused by loading of properly designed structures aren't likely to exceed 0.012 inch. He concludes that the factor of safety of 3 used in the United Kingdom for anchors includes allowances for possible strength reductions due to cracking. He also notes that there is no indication in the United Kingdom of unsatisfactory behavior of anchors as a result of cracking. References 1. R. Eligehausen and R. Tewes, "Rationale for the UEAtc Draft Directives on Anchor Bolts Used in the Tensile Zone of Reinforced Concrete Members," University of Stuttgart, Report No. 1/29-88/4, December 1987. 2. A. W. Beeby, "Fixings in Cracked Concrete," Construction Industry Research and Information Association, Technical Note 136, 1990.