Through Bolts

Through bolts are a type of torque-controlled anchor used in concrete, once fixed they expand.  They rely on friction and therefore must be installed using a torque wrench.  Overall, they are a high-performance anchor that is relatively inexpensive.

These types of bolts are suited to through-fix installations because they fix straight through the fixture into the substrate.  This method is prone to putting a lot of stress on the substrate.  It is essential that you use a torque wrench when installing a through bolt, it is simply not possible to install without one.  The torque applied sets the anchor and it also creates a clamping force.

It is common for installers to overtighten through bolts using a long lever, you may think that tighter is better, however, all that this will achieve is over-stressing in the anchor.  If you under torque you run the risk of the fixture moving after load relaxation, therefore it is very important to use a torque wrench to install correctly.

Make sure that the correct sized hole is drilled when installing, the diameter is generally within the manufacturers’ instructions.

Expansion anchors must not be fixed too close together, as when the anchor expands it can lead to an increased stress load onto the substrate and potentially cause the substrate (concrete) to fail.

The problem with all expansion anchors is that they suffer from load relaxation, when you have torqued it up correctly they will relax. The stress in the bolt will be dissipated into the substrate over a given period of time.