It could be said that no one fixing or anchor application when considering the design could be the same.
However, the forces acting on the fixing either short term or long term must be carefully considered and determined in accordance to current engineering practice, In general terms, these forces will either act in pure tension, shear or a combination of both.
At the same time, the fixing may also be subjected to not only static loading but also dynamic and shock loading. Therefore, to understand the fixing performance requirements fully, the possible modes of failure must also be looked at, then the selection of the anchor can be successfully carried out.
It should also be said that although more than sufficient information is available for the performance of fixing into concrete (unreinforced), there are a considerable amount of installations carried out into other materials such as masonry. In this case and where no previous test reports or approvals are available, then the only option is to conduct either on-site-tests or in particular manufacturers factories.
When subjected to a tensile force (static) an anchor will fail in concrete either by the concrete itself failing or the fixing steel yielding and subsequent failure. In the case of concrete failure, the tensile strength of the fixing is greater than that of the concretes tensile strength and will therefore fail.
The size of the concrete failure cone will in most cases be three times the anchor’s effective embedment depth hef in diameter and therefore also has an influence on not only the spacing between any adjacent fixing but also the edge distance ac. In the case of steel failure, the engineer needs to consider the respective fixings steel properties and cross-sectional area of the steel As and then calculate the strength of the steel to determine if the fixing is suitable or not.
Having determined the mode of failure that could possibly occur for the fixing, then you can refer to the data for each Nexus fixing to establish a suitable anchor for your application.
As with tension the shear value related to the fixing steel capacity and the fixings distance to the edge of the substrate. Where the anchor is of sufficient distance from the edge, so that no failure of the concrete will occur, then, in this case, the fixings steel capacity must be calculated in the same way as for tension.
Depending on the application there are times when both tension and shear are acting at the same time on the fixing. In this case, both tension and shear must be calculated and whichever the greater will determine the fixing capacities requirements.
