Container Handling

Lifting Lugs

Container Handling

Container lifting lugs are the principal means used to handle freight transport units by coupling them with their corner fitting apertures hence their integrity is of prime concern. Not only are they used for lifting but also for draging and upending containers to discharge them, therefore an appreciation as to their ability to withstand forces other than those induced by lifting needs a mention.There are two mandatory strength tests in ISO 1496 Part 4 that apply specifically to bottom corner fittings that must be satisfactorily complied with for them to be issued with a CSC Plate. Together they guarantee integrity of containment of corner fittings, principally by welding, to secure them to the load bearing frames of containers.
The test are: lifting container from bottom 4 corner fittings, Test No 3 and an external constraint test Test No 4 where the unit is constrained by twislocks in the bottom horizontal apertures at one end whilst corner fittings at the opposite end are loaded by horizontal forces.

Container Corner Fittings

The specification for corner fittings are given in ISO 1161/BS 3951 and Lloyds Register Guidance Note A. They are manufactured from both steel and aluminium and are secured within the container's main frame by side rails, end rails and corner pillars by welding. In the case of steel fittings these are made from an appropriate SG cast iron. The exact composition is usually a manufacturers own impact resistant "Special Steel" to withstand shock loading when secured to rail wagons and shunted.
Before the mechanics of brittle fracture were fully undestood, corner fitting impact strength requirements ommitted any reference to this failure mode and many corner castings on containers carried on rail cars failed in colder climes, nowadays corner castings for working at low temperature of -40°C are fitted as standard especially for overland container transportation. Corner fittings guidelines

Bottom Corner Fitting

Side and end apertures have the same profile.

Top Corner Fitting

Lugs used in the side aperture only, NEVER the end.

The top corner fittings are NOT THE SAME as those at the bottom. The bottom fittings have identical lifting apertures in the side and end faces and either can be used for lifting fully loaded containers. The top corner fittings are primarily used for lifting via the top face apertures, the end aperture is profiled to suit a hook and must only be used for lifting empty containers. The side aperture has the same profile as the bottom apertures and can be used for lifting empty units and, in exceptional circumstances used for handling light process units.

Weight Ratings

Up untill 2005 the MGW of Series 1 containers was linked to the types A,B,C,D as defined in ISO 668 1995 and Plated containers up to 2005 will be limited to Certified Test Weight displayed. After 2005 all Series 1 containers, other than Type D (10ft length) were re-rated as "Heavy Tested" to 30,480kg or 30Ton.
Non ISO compliant containers may be rated at higher MGW typically 35,000kg and should be prominantly displayed together with other relevant information.
Specification for 45ft containers were also added and became Type EE, EEE also rated at 30,480kg. Further information can be found at ABS Rules for Certification of Cargo Containers.
The Maximum Gross Weight (MGW) or Rating is the sum of the empty container weight T (Tare) and its payload P. Both should be quantified in units of mass, kg or lbs Ton, however, when lifting we need to overcome inertia forces due principally to gravity and such forces or weights are defined as Rg to differentiate the difference between mass and force.

Limiting Transportation Loads

Multi axle vehicle for overweight non standard transport unit
Since most cargo platforms are transported by road, the factor that governs the MGW of any unit is the limiting vehicle axle loading. This is in the form of a mandatory weight restriction that may vary from the country of origin and any other country through which the load may pass, there may even be weight restrictions on roads that need addressing.
In the UK and EU the axle loading results with a maximum Gross Trailer Weight (GTW) of 48 tonne and is normally shown on a plate or sticker fitted to the vehicle.
Since the minimum weight of transporting vehicle must be 3.5 tonne the maximum possible MGW of payload is 44.5 tonne. In reality the payload will be less since transport vehicle may be well above the minimum quoted here. Above example is that of an 8 axle transporter.

Allowable Lifting Methods

A summary of specified lifting methods is given in the British Standard publication of ISO 3874, this replaces BS 3951:1989 previously used as the main reference when container handling. The current standard refers to the lifting of CTU's as being "Allowed" or "Not Allowed" methods of lifting and provides detailed charts for all specified lifting methods. The main methods of lifting freight units from their corner fittings are shown below.

Top Lift (6.2) Spreader

Four point vertical lift from bottom corners, side or end apertures.

Top Lift Sling (6.3)

For empty or lightly loaded Units. Never when laden.

Bottom Lift Sling (6.4)

Single Point Lift. Main method for lifting fully laden CTU's. See below.

End Lifting      

Not a classified method in ISO 3874 but in widespread use for Side Loaders.

Top Lift Spreader (6.2)

These spreaders are normally used for rapid throughput of standard ISO containers at all modern ports and are substantial telescopic fully automatic devices lifting with ISO twistlocks via top corner box apertures. However, when handling Out of Gauge units, ancilliary gear is often used to couple the spreader to the OOG cargo unit for lifting from the bottom corner fittings with vertical slings. This ancilliary gear often takes the form of a simple basic "Dumb Bell" type adapter, shown here, made from two corner castings connected by tubular section. They can be quickly connected to the spreader twistlocks, the sling assemblies being connected to bottom lifting lugs. OOG cargo should be uniformly distributed resulting with Central of Gravity hence the load is carried equally by all 4 vertical slings.

Top Lift Sling (6.3)

For lifting empty and very light Process Units. This method uses the TOP corner fitting's side apertures only, the top end aperture has a different profile to that of the side. The end aperture was designed to be used with a hook and only for lifting empty containers. Lifting lugs must NEVER be used in the END apertures of top corner fittings. Certain freight units, in particular Flat Racks, have their end apperture blanked off to prevent hooks from being used. The main problem with using the top corner fittings is the necessity to gain access at an elevation of at least 8ft. The example shown here is a lightly loaded process unit that could only be lowered from the top into position to avoid ground level obstructions. This is a prime example where the "Handling by unspecified lifting methods.(5.2)" clause cited below has been implemented.

Bottom Lift Sling (6.4)

This is the most common method for lifting CTU's with Lifting Lugs and applies to both Side and End lifting and are covered separately. The basic method uses a pair of two leg slings attached to lifting lugs at one end and connected at their top to a hook, this configuration is referred to as Single Point Lifting. Depending on both the lifting height and weight of unit being lifted some intermediate gear may be required. The example here shows a container being lifted using slings attached to conventional dockside slewing derrick crane where spreaders are needed, these are usually steel tubes strong enough to react the axial force induced by slings where attached to spreader. The need for spreaders is to prevent slings making contact with container's top side edge rail with the possibility of causing serious damage. When handling empty or light non ISO Standard process units, spreaders are often dispensed with to minimise lifting gear requirements. Other typical sling arrangements used are shown below for various height and weight limitations, Many types of lifting gear assemblies are available off the shelf or for hire.

Typical Bottom Lift Sling arrangements

Two Leg Slings

For empty containers or light process units. Forces at contact points on top side rails.

Top Lifting Beam

For minimum head room and limited lifting height. Substantial heavy beam is required.

Truss & Single Spreader

Beam replaced by truss. Spreader under compression.

Two Spreaders

Most common type, spreader forces half those for single spreader
When Single Point Lifting with any of these arrangements the Centre of Gravity ALWAYS aligns itself with the top lifting point. For eccentrically loaded containers this could result with serious problems arising from the unexpected motion of container during alignment.

Handling by unspecified lifting methods. (5.2).

Over the years there have been many developments in container handling, in particular, the now widespread use of Side Lifting Machines for which there is still no reference to this lifting mode in ISO 3874. Now that BS 3591 is obsolete and has been withdrawn there is greater flexibility to the interpretation of the current ISO standard when container lifting and now includes the following clause:

5.2 Containers may be handled by methods other that those specified in Clause 6 but only after careful evaluation of the equipment by means of which the container is to be handled and of the methods of operation envisaged, with respect to international container standards."

A NOTE has also been added to Section 6 of the current standard that applies to exeptional operating situations where, in the past, it was impossible to work within the strict limits imposed by the "Allowable" methods of BS 3591. This NOTE, applies to all Specified Lifting Method Tables and states what is "Allowed" and "Not allowed" for any Container Transport Unit:

"NOTE There could be exceptions in cases when combinations of container types, size, load, design and operating conditions could not be taken into account in relevant Specified Lifting Method Table. Such situations should be carefully evaluated by those competent to do so in order to decide whether a safe and satisfactory operation can be ensured."