Ductility is Critical

Undercut anchors are the ultimate post-installed anchor category as their load transfer mechanism is bearing, similar to that of headed studs cast into concrete. Tensile loads are transferred into the concrete employing an expansion sleeve driven over a cone into a cavity formed at the back of the drill hole. This mechanical interlock prevents the anchor from pulling out and results in high load capacities and small displacements. Undercut anchors typically show low sensitivity to extreme conditions like large crack widths. If they are made of steel with sufficient material ductility, undercut anchors show a high resistance against cyclic loading. When designed properly and with sufficient embedment depth, undercut anchors have high strength, stiffness, and ductility levels. The design of undercut anchors can also qualify them for ductile connections in seismic design. Their general robustness makes undercut anchors the preferred choice for critical connections where high load demands are to be transferred into the concrete safely (Figure 1).