Dunnage and load securing are the systems used to keep cargo stable during transport, storage, and handling. In a truck trailer or shipping container, pallets, boxes, straps, airbags, edge protectors, and blocking all work together to stop unwanted motion. This matters because even a small shift in cargo can damage products, injure workers, or make a vehicle unsafe to drive.
Good load securement is a practical application of forces, friction, pressure, and center of mass.
Key Facts
- Friction force limit: Ff,max = μN, where μ is the coefficient of friction and N is the normal force.
- Cargo acceleration creates an inertial force: F = ma, so heavier loads need stronger restraints.
- Load shift risk increases when the center of mass is high, off center, or not supported from below.
- Straps apply tension that increases normal force and helps resist sliding, tipping, and separation.
- Dunnage fills gaps, spreads pressure, protects surfaces, and transfers forces to stronger parts of the load or container.
- Working load limit is the maximum force a strap, chain, or device is rated to hold during normal service.
Vocabulary
- Dunnage
- Dunnage is material placed around or between cargo to support, cushion, separate, or immobilize it during transport.
- Blocking and bracing
- Blocking and bracing are rigid supports that prevent cargo from sliding, rolling, or tipping by transferring force to the floor, walls, or other strong structures.
- Load securement
- Load securement is the planned use of restraints and supports to keep cargo from moving under normal transport forces.
- Center of mass
- The center of mass is the average location of an object's mass and is the point that determines how the object balances and tends to tip.
- Working load limit
- The working load limit is the maximum load a tie-down, strap, chain, or fitting is designed to safely carry in regular use.
Common Mistakes to Avoid
- Leaving gaps between pallets or walls, which allows cargo to gain speed before impact and increases damage during braking or turning.
- Using straps without edge protectors, which can cut or weaken the strap at sharp corners and reduce the actual holding capacity.
- Relying only on cargo weight, which is wrong because heavy cargo can still slide if friction is low or acceleration forces are large.
- Stacking heavy items on top of light items, which raises the center of mass, crushes lower cargo, and increases tipping risk.
Practice Questions
- 1 A 500 kg pallet is on a trailer floor with a coefficient of friction of 0.30. What is the maximum friction force resisting sliding? Use g = 9.8 m/s².
- 2 A truck brakes and a 1200 kg load experiences a forward acceleration of 0.6g. What forward inertial force must the securing system resist? Use g = 9.8 m/s².
- 3 A container has tall boxes stacked near one side, small gaps between pallets, and no airbags or blocking. Explain which load movement risks are present and what securing methods should be added.