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File: Load Restraint Transafe Forum Esperence.pdf
Paul Dore Logistics Engineer Phone 0437 988148 [email protected]
Tie Down Restraint Fundamentals
Paul Dore
Logistics Engineer WA
Load restraint is serious… ~5 Australians die each year
6th Dec 2014
Note it’s over dimension load with a couple of extra items “thrown on top”
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Load Restraint
1. Introduction – Overview of the Law and the Performance standard
2. In Transit Force Directions and Key Risks
3. Tie Down Restraint Fundamentals
Today’s Content
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1. Introduction
Benefits of learning about load restraint? l SAFETY
– An unsafe load can be devastating – Even basic knowledge helps
people to avoid the pitfalls l PROTECTION OF PROPERTY
– Understanding load restraint will help protect the millions of $ in property – product, trucks, trailers
l EFFICIENCY – Load restraint knowledge can be
used to find better cost-effective solutions
l COMPLY WITH THE LAW 7 –tonne Aircraft Engine (Restrained for 900kg)
The law is worded:
Loads must be restrained to prevent unacceptable movement during all expected conditions of operation. The load restraint system must, therefore, satisfy the following requirements:
i. The load should not become dislodged from the vehicle.
ii. Any load movement should be limited, such that in all cases where movement occurs, the vehicle’s stability and weight distribution cannot be adversely affected and the load cannot become dislodged from the vehicle.
Loads that are permitted to move relative to the vehicle include loads that are effectively contained within the sides or enclosure of the vehicle body such as: a) Loads which are restrained from moving horizontally (limited vertical
movement is permissible); b) Very lightweight objects or loose bulk loads (limited horizontal and vertical
movement is permissible); c) Bulk liquids (limited liquid movement is permissible);
1. Legal Compliance Performance Standards
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1. Legal Compliance Performance Standards
To achieve the movement limits from the previous page: l The law is based on G-Forces l Loads must be restrained against forces equal to:
0.8g 80% of the
weight forwards
0.5g 50% of the
weight rearwards
0.5g 50% of the weight
to either side
0.2g
20% of the weight upwards
Don’t forget….. And so that the vehicle's stability is not adversely affected
Looks simple....... But BEWARE!
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1. Restraint Methods
Tie Down Direct Restraint
Containment
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2. Force Directions - Forwards Forces (0.8g)
Many figures in this presentation are extracted courtesy of The Load Restraint Guide, NTC
- Forwards Forces are the Highest Risk. - Friction, Pre-Tension and Lashing Angle are key for Tie-Down Restraint - Often loads can slide from under the restraints before the tensile capacity of the lashings are reached (i.e. 2.5t strap can’t necessarily restrain 2.5t load)
Painted Steel is Low Friction
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2. Force Directions - Rearwards Forces (0.5g)
Many figures in this presentation are extracted courtesy of The Load Restraint Guide, NTC
l Legislation requires 0.5g rear restraint capacity
l Do things really fall off the back of a truck?
l Often seen as a myth
Likely Suspects are:
l Acceleration
l Steep hills & driveways
l Impact to rear
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2. Force Directions - Rearward Forces – Frank and Betty Video
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2. Preventing Spearing Product Belly Chaining Method
• Stops “spearing” with low height or multi-bundle loads
Belly chain holds top layer, Bottom layer held by clamping from top
Toll West
No Down Force Middle Pipes
✗ ✗ ✗ ✗ ✗
✗ How much friction does a wheel have?
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2. Force Directions - Sideways Forces (0.5g)
l Sideways – Corners, bends, swerving – Camber Especially roundabouts
Many figures in this presentation are extracted courtesy of The Load Restraint Guide, NTC
Driver thought that chains (no down-force) plus side pins was sufficient blocking for sideways
✗ ✗
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2. Force Directions - Vertical Forces
l Bumps and vibration – Bouncing will often disturb
or settle loads – Light loads are especially
vulnerable
X Load settling – especially where there are gaps in the load, can result in lashings losing tension.
Inwards forces and load settling results in slack lashings (gaps = high risk)
XX
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2. Force Directions - Toppling l Toppling in all directions
– Less stable loads will topple – For all the reasons described previously
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2. Wind Loads
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2. Dunnage – Dos and Don'ts
l Rounded Corners – REJECT
l Double stacking - Dangerous
– Grillage if necessary – Only OK as product protection,
not as load restraint – Use pallets?
l Do not use Rectangular dunnage on thin edge,
– VERY Dangerous
X
X
X
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2. Rolling Dunnage = Real Danger
Brisbane Gateway Arterial Rectangular dunnage between bundles of plate, turns minor rear end shunt into serious incident. Driver survived but truck a write-off. Root Cause = poor loading practices with rectangular dunnage
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2. Don’t leave loose dunnage on the deck
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3. Tie-down Restraint – Friction is Critical
l Friction is critical for the tie-down method l But Not understood well l Friction is the force that resists motion (grips) between two
surfaces
Ff Forward Force
The Straps pull DOWN! and Friction Holds the Load BACK!
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3. Clamping Relies on Pre-tension
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Pre-Tensions 3500 - 4000N or 350-400 kgf Standard Ratchet
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Dow
n-force
3. Tie-Down – Lashing Angles
Dow
n-force
Lashing tension D
own-force
Lashing tension
Dow
n-force
The restraint from a lashing also varies depending on the lashing angle
l Vertical lashings put all their tension into the clamping force
l As the lashing angle decreases, less clamping force is exerted
l The steeper the lashing angle, the more down-force
Aim to keep angle 30o or greater.
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3. Tie-Down Restraint – Pre-tension vs full tension
Restraint is not 2500 kg.f Standard Ratchet 300 kg.f Clamping with 0.4 friction
Restraint approximately 2500 kg.f Direct attachment – Slides to Full Tension
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3. When There Are Not Enough Lashings
Restraint is not 2500 kg.f Standard Ratchet 300 kg.f Clamping with 0.4 friction = 510kg.f of Restraint
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How Far Could the Load Really Slide?
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2.4t Load Fails – 2.5t strap?
Pre-tension is critical...using a 5t strap does not solve this problem
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Forwards, Blocked with Cross-over Straps and Higher Tensioning ratchets
28 www.engistics.com.au
3. Restraint Options
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3.Tie-Down – Webbing Strap Restraint
Table F5, from the NTC Load Restraint Guide
Putting all the information together…
We can determine the number of lashings required.
Note:
1. Unblocked loads need a lot of lashings. Even with reasonable friction, because 0.8g is much higher than 0.5g with friction as 0.4
2. Improved friction helps a lot.
3. Blocking forward is great if you can do it.
4. Caution if lashing angles are low it gets impractical to lash only
1 2 3
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Friction µ = 0.40
1 lashing @ 60
degrees
2
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Tie-down Restraint – Case Study
Emergency Braking
Forward Force
Restraint Forces Timber Pallet
60 degrees
Typical 50 mm webbing at 60 degrees
800 kg.f
600 kg.f
500 kg.f
820 kg.f
610 kg.f
400 kg.f
Friction is more important than the number of lashings!
Friction µ = 0.60
Restraint Forces
Anti-slip Matting
600 kg.f
910 kg.f
1
1,000kg
Restraint Forces Steel
Stillage
Friction µ = 0.25
2
1 250 kg.f
380 kg.f
510 kg.f
Forward Sliding Forces - 1000 kg load
