The anchorage in the concrete is produced by the foot of the spread anchor creating a wrenching cone.

The anchorage resistance depends on:
– The concrete strength (fck)
– The length of the spread anchor (L)
– Distances to the edge of the concrete (TN)
– Distances between each anchor (TN)

The larger the wrenching cone, the more resistant the anchorage. It is at its maximum when the distance between the 2 anchors is greater than 3.5 times the anchoring length (L) and the distance to the edge of the concrete greater than 1.75 times L.