LIEBIG ULTRAPLUS® Concrete Undercut Anchors
There are various types of post-installed mechanical anchors but undercut anchors are by far the strongest and able to resist much higher loads compared to mechanical expansion anchors. This is why they are often used in structures such as the nuclear power plants, where human safety is of utmost importance and failure often has catastrophic consequences.
In general, the suitability of the concrete to resist the transfer of the action load from the application is usually decisive. “Concrete capacity” A fixing can only be as good as the base material it is fixing in to. However, how the mechanical anchor transfers the action load has a significant impact on the concretes capacity to resist the load or action.
How Undercut Anchors Work
Mechanical expansion anchors work, as their name suggests, by expanding in to a pre-drilled hole in to the concrete. The friction created by that expansion is what provides the resistance to the tensile action. In general terms, the greater the tensile action, the greater the horizontal expansion forces that are required. High expansion forces create high compression/stress zones in the concrete which detrimentally effects how the concrete is able to resist the action loads.
An undercut anchor works differently. It works by creating a positive key in to a pre-cut or self-cut void inside the concrete. They either open out in to a pre-cut void as in the case of the Liebig Ultraplus, or they create their own void and key in to that, as in the case of the Liebig Ultraplus BLS anchor. They do not rely on expansion and friction and thus they do not create such high compressive or stress zones in the concrete. As a result, undercut anchors are able to make much better use of the concretes capacity and thus are able to resist much higher tensile loads. In addition to normal tensile action loads, the positive mechanical interlock and the reduction of compressive stress zones in the concrete make undercut anchors more able to manage the action loads which are created in dynamic, seismic, shock and other such high impact application conditions.