Failure modes of anchors
The weakest point in an anchor fastening determines the cause of failure. In the following picture are shown the common modes of failure:
The failure types 1-3 are typical failures of properly set anchors. They occur mostly when single anchors that are a suitable distance from an edge or the next anchor, are subjected to a pure tensile load. These causes of failure govern the maximum loading capacity of anchors.
The 3a setting failures occur usually when:
- Steel rupture typically in over-torqued anchors
- Slip in not cleaned bore holes
The failure number 4 occurs when anchor is set too close to an edge. The ultimate loads are then smaller than those of the previously mentioned modes of failure. The tensile strength of the fastening base material is exceeded in the cases of break-out, edge breaking and splitting.
Edge distances (distance from the anchor to the edge of the concrete), spacing between anchors, concrete strength and condition all influence how anchors will perform. If using multiple anchors to handle larger loads, it should be determined how the load is distributed between the anchors to prevent overloading. Using multiple anchors in the same core rig baseplate slot requires special consideration, because the spacing between anchors, as well as unequal load distribution, can decrease anchor performance.
