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Difficulty: HardCargo Securement: Tie-Down Rules and WLL

A flatbed trailer is loaded with an unblocked structural steel beam that measures 28 feet28\text{ feet} in length and weighs 32000 pounds32{}000\text{ pounds}. The securement straps available have a Working Load Limit (WLL) of 3333 pounds3{}333\text{ pounds} each. What is the minimum number of these tie-downs required to legally secure this cargo under federal safety standards?

  1. A
    4 tie-downs
  2. 5 tie-downsAnswer
  3. C
    3 tie-downs
  4. D
    10 tie-downs

Answer

A minimum of 5 tie-downs is required to satisfy both the length-based and weight-based securement standards.
To legally secure the cargo, the securement must satisfy both length and weight requirements. For unblocked cargo, regulations require at least 2 tie-downs for the first 10 feet, plus 1 additional tie-down for each additional 10 feet or fraction thereof, totaling 4 tie-downs for a 28-foot load. Furthermore, the aggregate Working Load Limit (WLL) must equal at least 50% of the cargo weight (0.50 x 32,000 lbs = 16,000 lbs). Because 4 tie-downs provide only 13,332 lbs of aggregate WLL (4 x 3,333 lbs), a 5th tie-down is required to reach 16,665 lbs, thereby satisfying both criteria.

Step-by-Step Solution

1
Calculate the minimum number of tie-downs required by cargo length for unblocked cargo.
A 28-foot unblocked beam requires 4 tie-downs (2 tie-downs for the first 10 feet + 1 tie-down for 10-20 feet + 1 tie-down for 20-28 feet).
Federal regulations mandate at least 2 tie-downs for the first 10 feet of unblocked cargo and 1 additional tie-down for every 10 feet or fraction thereof thereafter.
2
Calculate the required aggregate Working Load Limit (WLL) based on cargo weight.
Required aggregate WLL = 0.50 x 32,000 lbs = 16,000 lbs.
Federal regulations require the aggregate WLL of all securement devices to equal at least 50% of the total cargo weight.
3
Determine the number of 3,333 lb straps needed to meet the aggregate WLL requirement.
16,000 lbs / 3,333 lbs per strap = 4.80 straps, which rounds up to 5 straps (5 x 3,333 lbs = 16,665 lbs).
Securing with only 4 straps provides 13,332 lbs of WLL, which fails the 16,000 lb requirement.
4
Compare the length requirement and weight requirement to identify the governing minimum.
5 tie-downs are required.
The final securement plan must satisfy the higher of the length-based requirement (4 tie-downs) and the WLL-based requirement (5 tie-downs).

Key Concept

Cargo securement requires satisfying both length-based tie-down minimums (2 for the first 10 feet of unblocked cargo plus 1 per additional 10 feet or fraction thereof) and weight-based aggregate Working Load Limit mandates (at least 50% of total cargo weight).
Estimated Time:2m 0s
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Topics

Cargo Securement: Tie-Down Rules and WLL

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