The Undercut is Why it Works
The development of the Drillco Maxi-Bolt represents a new design and performance concept for concrete anchors. The Maxi-Bolt's consistent performance approaches the characteristics of an embedded bolt; however, the Maxi-Bolt is installed in hardened concrete.
What is the Reason for the Maxi-Bolt's superior Performance and Consistency?
In the wedge anchor graphic above and the sleeve anchor graphic below, we see typical expansion anchors which depend on the lateral expansion of the anchor's sleeve or wedge against a concrete surface parallel to the direction of the bolt tension load.
The load capacity of such mechanisms is obviously dependent upon the amount of friction developed by this process and may vary with hole size, aggregate type, and the presence of discontinuities in the concrete surface.
In the graphic of the Maxi-Bolt above, note that the bottom of the hole has been conically undercut with a Maxi-Bolt Undercutting Tool. This unique anchorage system develops the tensile capacity of the bolt without slip or concrete failure. The anchorage is developed by expanding the anchor sleeve into the conical undercut. This feature forces the applied bolt load to be taken in bearing between the conical nut and expansion sleeve and between the sleeve and the conical undercut in the concrete. The surface area of this undercut in the concrete is controlled and predictable and is designed to take maximum advantage of the bearing capacity of confined concrete. This anchorage system is so effective that it will consistently develop 100% of the minimum specified 125,000 psi tensile strength of the Maxi-Bolt's ASTM A193 Grade B7 bolting material.