Uniformly Loaded Containers

Container Lifting Supplement

Central point load Rg
Vertical corner forces 25%Rg

Uniform loading is the simplest case where the position of C of G acts through the geometric centre of freight unit, consequently all four slings will be equally loaded and sustain the maximum possible loading of Quarter of Rg. The sling force is determined by its angle and given by equation (3) below.

The sling lifting force F must not exceed WLL of lug this, in turn, will limit the Gross Weight (GW) capacity for any given sling arrangement. Equation (4)

Corner Fitting Forces for Uniform Loading

Uniform Loading
Tilt angle θ is zero Corner fitting forces

The applied force on the sling, that shown acting downwards, results from a quarter of the container weight Rg. It follows that the vertical reaction force V, acting on the corner fitting, must equal the applied vertical downward force and from equation (1) the sling force F is given by sling angle  α and the container weight Rg by the following equation.

F =
 Rg
4 sinα
The limiting GW capacity is when lugs are loaded at their Working Load Limit WLL and from equation (3) above is.
GW = 4 WLL sinα
Gross weight capacity for sling forces over working angle range
Gross Weight distribution in Tons from Equation ( 4 ) over sling angle range for Uniform Loading.

A simple graphical illustration for the above GW equation is shown here over sling angle range 30° to 90° for uniform loading where Load Factor is 0.25 and all slings carry the same load over that portion parallel to the side of container.

The limiting load envelope is bounded by the semi-circular arc that encompases O and P having a radius of Twice WLL centered midpoint between them, the lifting force envelope for 12Ton WLL is the red area, whilst the purple area is for 8.5Ton WLL.

The GW values are given by the length of the radial lines eminating from lug centre O and intersecting the semi-circular boundary. When the sling angle is vertical sin α= 1 and GW is at its greatest whilst at 30°, sin α= 0.5 its lowest. The more acute the angle the lower the GW, the sling tension never exceeding WLL of lug.

Limiting Gross Weights for Uniformly Loaded Freight Units

These graphs give the GW range for sling angles from 30° to 90° together with Maximum Gross Weights for WLL of 8.5 Ton and 12 Ton displayed via MGW links below graphs

Working Load Limit 12 Ton

Working Load Limit 8.5 Ton

All Gross Weights given here are for the lifting lugs and ancilliary gear attached to the lugs ie chain, shackles, chain connectors etc, that when loaded, appart from the lug do not make contact with the freight unit sides.

When spreaders are used the force in the sling portion above the spreader is greater than that below and depends on lifting gear arrangement attached to top lifting point.