Lifting Pad Eye & Cast-in Hook Calculator

What it checks

A lifting lug or pad eye is the attachment point a shackle connects to when a fabricated item is lifted. This calculator covers two families: a steel pad eye to EN 1993-1-8, and a cast-in lifting hook in concrete to EN 1992-1-1.

For the pad eye it verifies the plate in tension across the net section at the hole, shear-out, bending, block tearing and bearing against the pin, the pin itself in shear, bending and combined action, the weld to the parent item, and the Type A hole geometry requirements that the plate must satisfy before any of the strength checks are meaningful.

The design load is not the item weight

The load on one lifting point is built up from the item weight through several multipliers, and every one of them matters: the weight is divided between the lifting points, then increased by a dynamic amplification factor for the lift, then by a factor of safety appropriate to a lifting operation, and then adjusted for the sling angle - because a sling at an angle applies more force than a vertical one for the same vertical load.

Sling angle is the term most often underestimated. A pair of slings at 60 degrees from horizontal carries about 15 per cent more force each than a vertical lift; at 30 degrees the increase is 100 per cent. The tool takes the angle explicitly rather than assuming vertical, and the geometry checks change with it too, because an angled load pulls the pin against the side of the hole rather than straight into it.

Hole geometry comes before strength

The Type A requirements set a minimum for the material each side of the hole and above it, expressed as a function of the hole diameter and plate thickness. On the tool defaults these come out as roughly 34 mm required against 50 mm provided beside the hole, and 17 mm required against 50 mm above it - both satisfied with margin.

These are not arbitrary detailing rules. A pad eye with too little material beside the hole tears out rather than yielding, which is a brittle failure with no warning, and the strength formulae assume it does not happen. If the geometry check fails, no amount of extra plate thickness elsewhere makes the strength numbers valid.

Formula reference

Net-section tension at the hole

$N_{u,Rd} = \dfrac{0.9\,A_{net}\,f_u}{\gamma_{M2}}$

Gross-section yielding

$N_{pl,Rd} = \dfrac{A\,f_y}{\gamma_{M0}}$

Shear-out at the hole

$V_{Rd} = A_v\,\dfrac{f_y}{\sqrt3\,\gamma_{M0}}$

Bearing on the pin

$F_{b,Rd} = \dfrac{1.5\,t\,d\,f_y}{\gamma_{M0}}$

Pin shear

$F_{v,Rd} = \dfrac{0.6\,A\,f_{up}}{\gamma_{M2}}$

Pin bending

$M_{Rd} = \dfrac{1.5\,W_{el}\,f_{yp}}{\gamma_{M0}}$

Sling force from angle

$F = \dfrac{W}{n\,\sin\alpha}$

Design load on a point

$F_{Ed} = \dfrac{W}{n}\cdot\dfrac{\text{DAF}\cdot\text{FoS}}{\sin\alpha}$

Assumptions and limits

The dynamic amplification factor and factor of safety are inputs, not defaults the tool can choose for you. They depend on the lifting operation, the crane, the environment and the applicable lifting standard or client specification - an offshore lift and a workshop lift use very different values, and the difference is large enough to change the design.

The pad eye is checked; the item it is welded to is not. Local reinforcement of the parent plate, the load path into the structure and the stability of the item while suspended are separate assessments. The tool also assumes the pin or shackle pin is a good fit in the hole - an oversized hole changes both the bearing area and the pin bending span.

Static analysis of a controlled lift. Snatch loading, impact, wind on the suspended load and repeated lifting (fatigue) are outside the scope, and a lifting point that will be reused many times may need a fatigue assessment this tool does not provide.

FAQ