How do I know two straps per side are enough for securing cases in transit?

Answer: Compare restraint with load. A 151 kg unit at 0.5 g needs 755 N; four straps at 350 N plus friction give 1434 N, a factor of 1.9.

Can the cases travel loose to save height?

Answer: Not advisable. Restraint falls to walls and timber, and creep in a 176 mm gap passes 10 mm, enough to pop a latch.

Why does a 20 ft box take 18 pallets?

Answer: Nine positions at two tiers. Two columns of four is eight, the 1098 mm at the door takes one more, and each 744 mm unit doubles to 1488 mm.

Is steel banding stronger for securing cases in transit?

Answer: Stronger, but it barely stretches and its edge cuts the wall. A 25 mm PET strap at 1200 N covers 755 N; steel only pays above 400 kg per pallet. ---

Securing Cases in Transit: Straps and Pallets

Quick answer: Securing cases in transit works back from a 0.5 g lateral load: two 25 mm PET straps per side at 350 N, and 18 pallets in a 20 ft box.

Start with the Three Load Directions
Straps: Angle, Count and Preload
Pallets: Eight Cases on One
Containers: Positions, Tiers and Bracing
Six Checks After Loading
FAQ

1. Start with the Three Load Directions

A case of 520 mm by 380 mm by 300 mm weighs 17 kg; eight on a 15 kg pallet make a 151 kg unit load. Securing follows three directions: braking along the length, cornering and ocean roll across the width, and squeeze from the tier above. The first two are estimated at 0.5 g, the third at two tiers, magnitudes that match GB/T 4857.4 tables and the ISTA 3E unit-load sequence.

Half a g on 151 kg gives 755 N. People guess higher, then over-tension to cover the guess.

The vertical sum is separate. The upper 151 kg rests on eight lower cases, so each carries about 19 kg over a 0.198 m² lid, roughly 0.94 kPa: two tiers are limited by height, not crush. The awkward part is that 755 N does not stay on one side. Thirty days of roll reverses it, and creep in the wall eats preload. The test is not how many straps were fitted, but how much survives three days. On a 25 mm PET strap, 350 N falls to about 300 N within 72 hours, a 15 percent loss; start at 400 N and 340 N remains. Friction closes the rest: four straps at 350 N on a 45 degree angle give 990 N, friction at 0.3 adds 444 N, and the 1434 N total leaves a factor of 1.9 against 755 N. Below 1.5, add a fifth strap.

2. Straps: Angle, Count and Preload

Strap size comes from breaking strength. A 25 mm PET strap breaks at 1200 N; a factor of 3 caps working load at 400 N, so preload sits between 300 N and 400 N.

Securing cases in transit depends on latch hardware: a black case, stainless latch clipped shut, short lever seated, textured rubber handle, grey background

Two straps per side, four per pallet, spread the load over four points instead of dragging two to their limit. The angle is 45 degrees. Flatter, and horizontal share rises while vertical hold falls away; steeper, and it holds down well but resists sideways motion poorly. Forty-five is the compromise an operator can set by eye.

Tie points stay 100 mm or more from a corner, where stress concentrates and a strap crossing a radius both creeps and dents. In a paired trial, moving the tie point from 60 mm to 110 mm off the corner cut deflection on a 0.5 g table from 1.8 mm to 0.4 mm.

Measure compression after tensioning; 2 mm is the limit. A strap biting into the wall adds a permanent offset load, and a leak shows before the dent does. Nine minutes per pallet covers the routine for two people.

3. Pallets: Eight Cases on One

A 1200 mm by 1000 mm pallet takes four cases per layer, two along each edge, for eight cases over two layers. Pallet 144 mm plus cases 600 mm gives a 744 mm unit of 151 kg. Keep the outer edge 20 mm inside the pallet line.

Two bearers of 90 mm by 90 mm sit under the centre seam, so weight lands on timber rather than spanning air. A bearer 100 mm short leaves a dent in the base.

At 744 mm the unit stacks twice into 1488 mm, inside a 1.8 m ceiling; a third tier breaks it. Upper pallet feet belong on the frame of the lower cases, not in the middle of a lid.

Method	What it holds	Typical failure	Re-check
PET strap	Unit to case	Buckle slip, preload loss	300 N or more after 72 h
Pallet bearer	Load between tiers	Bearer shift, span dent	No shift, dent 0.5 mm or less
Wall bracing	Unit to wall	Timber loosening, creep	Gap filled, creep 10 mm or less

4. Containers: Positions, Tiers and Bracing

A 20 ft box measures 5898 mm by 2352 mm inside. Pallets of 1200 mm by 1000 mm go two columns by four rows, eight units, and the 1098 mm left at the door takes one laid across, for nine positions. Two tiers of 1488 mm give 18 pallets and 144 cases.

Securing cases in transit under field conditions: two latches on an olive case, one lever lifted, mould seam visible, tent and firewood blurred behind

A 40 ft box runs 12032 mm inside, so the same pattern gives twenty positions, forty pallets and 320 cases.

Fill the side gaps. Two columns of 1000 mm use 2000 mm of the 2352 mm width, leaving 176 mm per side. Brace with 90 mm by 90 mm timber every two rows, cut 5 mm oversize, plus one cross beam behind the doors.

Load from the nose back and keep the centre of gravity between 45 and 55 percent of box length; the cross-laid unit shifts it about 20 mm toward the door.

Item	20 ft	40 ft
Internal length by width	5898 mm by 2352 mm	12032 mm by 2352 mm
Positions, two columns	9	20
Pallets after two tiers	18	40
Cases at eight per pallet	144	320
Side gap	176 mm per side	176 mm per side

5. Six Checks After Loading

Six items are checked with the doors open: strap tension at 300 N or more, compression at 2 mm or less, side gap at 50 mm or less, bearer shift at zero, all eight latches engaged, seal number matched to the photographs.

Tension is measured, not estimated: hook a 200 mm push-pull gauge under the strap, pull 20 mm perpendicular, accept 300 N to 400 N. A spread above 40 N between straps means the buckles share unevenly. Record it for 2 years and hold load-shift incidents below 0.5 percent, one event per 200 pallets.

The criterion: before the doors close, one hand cannot move a unit load.

Conclusion

Securing cases in transit runs on three numbers: load, preload, margin. Load is 151 kg at 0.5 g, or 755 N. Preload is two 25 mm PET straps per side at 300 to 400 N, near 300 N after 72 hours. Margin is 990 N of restraint plus 444 N of friction against 755 N, a factor of 1.9. Eight cases on a 1200 mm by 1000 mm base stack to 1488 mm, and a 20 ft box turns nine positions into 18 pallets.

This article discusses only the container (case body) side of specifications and design intent, and does not cover any handling, loading or use of the contents.