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.
The Undercut is Why it Works
What is the Reason for the Maxi-Bolt's superior Performance and Consistency?
In the wedge anchor graphic to the left 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
In the graphic of the Maxi-Bolt to the left, 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.
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