ISO1496-3:2019 Testing Bottom Corner Fittings.
Test No3 Lifting from 4 bottom corner fittings.
Bottom Corner Lifting Test.
This test simulates the Static plus Live Loads
as covered in "Lifting Cycle" above by doubling the MGW . A uniformly distributed internal payload P
having the value of ( 2R - T)
is applied over the floor of container to give twice the rating of 2R
and is lifted by slings attached to a central beam at the limiting angles shown in Table below
and simply suspending it to induce a force of 2Rg
.This lifting mode also tests the frame strength induced by the resolved horizontal compressive forces that result from the accutely angled slings. The unit remains suspended for 5 minutes and when lowered any permanent deformations of the frame are recorded .
Limiting Lifting Angle α From ISO 3874
Test No 4 External Constraints Restraint Simulation Test
When mounted on a transport unit, and in motion, twistlocks transfer forces to the unit when accelerating and braking via the corner fittings, these forces in turn, are reacted by the bottom side rails of the container frame via direct horizontal forces. These horizontal forces forces are influenced by the rigidity of the platform on which the unit is mounted. (Another set of vertical forces are also induced by the inertia force acting at the C of G at a point above the corner fittings resulting with the familiar effect of the forward end tipping down when braking and rearing up during acceleration
This inertia or body force is product of mass x acceleration acting at the C of G of freight unit hence the need to keep C of G always as low as possible.)
In reality it would be prohibitive to conduct live tests on CTU's to ascertain integrity of these products subject to the above actual loading cases so an alternative mandatory simulation test described here is used. This test subjects the container to horizontal corner forces only and neglects the stiffness of the support platform and inertia effects.
Restraint Simulation Test
In this test the CTU is supported by the corner fittings alone, one pair being fixed, whilst the opposite pair are on sliding supports. Horizontal forces are applied to these corner fittings, usually by hydraulic cylinders, to simulate dynamic forces induced by acceleration and braking. These forces simulate ± 2g acceleration and are evaluated from the product of MGW x 2g only or Rx2g.
The loading is again uniformly distributed having a total value of R - T.
These simulated dynamic forces are replicated by applying half the total horizontal force simultaneously to each corner fitting attached to sliding supports, first pulling and then pushing, inducing tension and compression respectively in the bottom side rail that, in addition is under bending whilst supporting the distributed internal loading. Perhaps the most significant aspect of this test is that it subjects the corner fittings to horizontal direct tensile forces (applied in opposite direction to that shown here) that are more critical than the compressive forces induced by pushing, as shown here in Restraint Simulation Test.