Calculation of anchors with stand-off
An anchor with stand-off is designed as a bar element loaded by compressive or tensile force, shear force, and bending moment. The calculation of the bending moment has been improved to respect better the real behavior of stand-off anchors.
The value of the bending moment depends on the ratio between base plate stiffness and anchor stiffness. For a very weak plate and stiff anchors, the bending moment in the anchor will be as follows:
For stiff plate and weak anchors, the bending moment will look like this:
In previous versions, the bending moment in stand-off anchoring was always calculated as in the first case, assuming a weak plate and stiff anchors. The lever arm for moment calculation was the distance between the mid-plane of the plate and the concrete plus one-half of the anchor diameter. This was quite an over-conservative approach.
Since release 22.1.5, the calculation of the bending moment has been updated. The value is determined directly by the finite element model. The anchor is modelled as a beam element and moments in it respect the actual stiffness of the system. The anchor is fixed on both sides, one side is 0.5×d below the concrete level, and the other side is in the mid-plane of the plate. The extreme of the calculated moment is taken into account in the code check then.
Available in both Expert and Enhanced editions of IDEA StatiCa Steel.