ENSURE YOUR DESIGN SPECIFICATIONS ARE IMPLEMENTED ON SITE

Over-torqueing results in the cone being pulled too far into expansion sleeve. This generates high forces during setting which may be powerful enough to cause spalling at the slab edge (when concrete splits or breaks away in chips), reducing the load carrying capacity of the base material.

The biggest problem with spalling is that it is not always visible to the naked eye. But even when visible and promptly remediable, the reparation can prove labor-intensive to fix, as new fastening points should be found and the steel must be adjusted accordingly. Much worse is when the spalling cannot be seen. This occurs often when it is hidden under a steel plate, for example, and therefore the flaw remains undetected and unrepaired.

With AT-ready tools and the HST2 or HST3 anchors, you can significantly reduce the risk of structural defects caused by improper torque.

Over-torqueing an anchor always results in the cone being pulled too far into expansion sleeve, generating high splitting forces. However, when the anchor sits far from the slab edge, the splitting forces can be absorbed by the surrounding concrete without any damage.

If the anchor is significantly over-torqued, then the steel bolt can be damaged – or even broken apart – by this torsional moment. The result is a clear drop of the steel failure load under tension, shear, or combined tension and shear forces, up to the point of breakage. As with spalling, the biggest problem with anchor damage is that it can easily go undetected. As a visual inspection of a set anchor is impossible, pre-damage can generally only be detected by a polish-cut image of a cross section. Applying torque in order to gauge the condition of the anchor could worsen any existing damage.

Specifying the adaptive torque system from Hilti is your best method of protecting compatible anchors from unseen damage.

An under-torqued anchor can be just as problematic as an over-torqued one. Under-torqueing results in the cone being in the incorrect position i.e. it is not drawn far enough into the expansion sleeve to achieve the specified holding values.

Only once the external load is applied does the anchor shift and the cone get pulled in the right direction. In other words, the anchor was loose and relied on external loading to set it rigidly into place. The maximum load or resistance values can be achieved, but only once the anchor has been pulled slightly from the intended position. The result is an installation with unforeseen displacement, as illustrated.

Loose anchors are extremely easy to avoid when using an AT-ready impact wrench.