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CHAPTER 6

LOAD SHORING

INTRODUCTION

This chapter defines load shoring and assists the load planner in determining when, where, and how much to use. Organizations offering cargo for air shipment must provide shoring. Shoring is lumber, planking, or similar material used to protect the aircraft cargo floor or 463L pallet surfaces. It decreases the approach angle of aircraft ramps, protects airport parking ramps, spreads weight over a larger area, or keeps 463L pallets off the ground. Shoring is very important. It can make the difference between carrying or not carrying a given piece of equipment or load.

Not all AMC aircraft have the same cargo floor pressure limits. Consult your affiliated AMC ALCS for specific loading guidance and remain flexible.

THE NEED FOR SHORING

Although shoring spreads out the weight of a load, the weight of that load is not spread over the entire surface of the shoring. Shoring only increases the area over which a load rests at an angle of 45 degrees from the load contact areas to the surface on which the shoring rests.

Shoring only increases the area of contact by the shoring thickness on all sides of the object resting on it (Figure 6-1). For example, a 2-inch shoring thickness increases the area of contact by 2 inches on all sides of the item resting on it provided the shoring extends at least 2 inches outward around the item being shored. The spreading effect of simple shoring is the same regardless of the shape of the area of contact.

To determine how much shoring to use for a given load, compare the area of contact between the load and the shoring to the area of contact between the shoring and the aircraft cargo floor. To calculate the contact area of rectangular loads, multiply the width of the item by its length.

Assume that a plank is 2 inches thick. A box resting on it is 12 inches long by 6 inches wide. The area of contact between the box and the plank is 6 times 12 inches, or 72 square inches. Extend imaginary planes down and out from the edges of the bottom of the box through the plank at 45-degree angles. Where these imaginary planes meet the cargo floor, the area of contact will be 10 times 16 inches, or 160 square inches (Figure 6-2).

In this case, the area of contact has increased by 122 percent, or more than doubled. When 2-inch-thick shoring is used, the area over which the load is distributed is enlarged by a 2-inch border all around the area of contact of the load and the shoring. This border is as wide as the shoring is thick. If the shoring is 1 inch thick, the load bearing border added is 1 inch wide; if the shoring is 3 inches thick, the load bearing border added is 3 inches wide, and so on. Generally, using shoring thicker than 4 inches is not practical. The relation between the width of the border and the thickness of the shoring applies to all shoring.

TYPES OF SHORING

There are three main types of shoring which are named for the way they are used to protect the aircraft cargo floor. They are rolling shoring, parking shoring, and sleeper shoring. All other nonspecific types of shoring are considered special shoring.

Rolling Shoring

Use rolling shoring to protect airport parking ramps and the loading ramps and cargo floor of the aircraft from damage. This type of shoring is used to protect surfaces from damage when moving a vehicle across it (Figure 6-3).

The majority of vehicles shipped by air, such as those with pneumatic tires, do not exceed weight limitations and do not require rolling shoring. However, vehicles with cleats, studs, or other gripping devices and treads that allow concentrated contact require rolling shoring. Cleated or lugged wheels can easily damage the aircraft floor or soft surfaces such as asphalt because the total weight of the vehicle is transferred to the cleats or lugs. Therefore, the weight is concentrated into a very small area. Vehicles that allow concentrated contact require rolling shoring thick enough to prevent damage. See Chapter 2 for information on combat and construction vehicles.

*In all cases, the minimum thickness is 3/4 inch. For cleated vehicles such as bulldozers, shoring shall be thick enough for the cleat or lugs to sinks into without contacting the cargo floor. Movement personnel should always plan on rolling and parking shoring for tracked vehicles, even those with new rubber pads. That tracked vehicle may deploy with new track pads, but it will probably not redeploy with new ones. Any vehicle or piece of equipment that requires rolling shoring to load aboard the aircraft will also require parking shoring.

Parking Shoring

Use parking shoring to protect the aircraft floor from damage during flight (Figure 6-4). Any vehicle requiring rolling shoring also requires parking shoring. Each aircraft has specific floor weight limitations that apply to wheeled and non-wheeled items of cargo. If the vehicle exceeds these weight limitations, it must have parking shoring before it may be transported by air. There is no need to learn the mathematical process used to calculate shoring requirements. But some general considerations regarding parking shoring should be remembered when planning an airlift movement:

  • The minimum thickness of parking shoring is 3/4 inch.
  • Use parking shoring to protect the aircraft floor or aircraft loading ramps from concentrated contact or metal-to-metal contact, such as steel wheels and trailer tongue supports and wheels.
  • Most pneumatic tires do not require parking shoring. Those that do are usually very narrow or heavy (over 5,000 pounds).
  • Always use parking shoring when rolling shoring is required.
  • Always use parking shoring on 463L pallets when the items have sharp edges or protrusions that could damage the pallet's aluminum surface. Contact the affiliated AMC ALCS for guidance about specific vehicles or aircraft limitations.

Sleeper Shoring

Use sleeper shoring under the frame or axle of any special-purpose vehicle, such as a forklift, scoop loader, or grader, that weighs over 20,000 pounds and has tires that are not designed for highway travel. Depending on the type of vehicle, sleeper shoring is placed between the aircraft floor and a structured part of the vehicle, such as the frame or axle (Figure 6-5). This type of shoring prevents the vehicle horn bouncing up and down and possibly pulling the tie-down rings out of the aircraft floor. An aircraft encountering turbulence during flight may cause these vehicles to oscillate and place extreme forces on the tie-down devices and tie-down points that would exceed their rated capacities.

Special Shoring

Special shoring consists of approach shoring, ramp pedestal shoring, bridge shoring, and other nonspecific types of shoring.

Approach shoring has a specific application. Use approach shoring to decrease the approach angle of the aircraft loading ramps (Figure 6-6) because some items of cargo will strike the aircraft or ground during loading and unloading operations. Although there is no standard method to calculate when and how much approach shoring to use, most helicopters and many long vehicles that have limited ground clearance, such as lowboys, will require varying amounts of approach shoring. Plan to transport any required approach shoring aboard the same aircraft as the item that requires the shoring.

Use ramp pedestal shoring with approach shoring to adjust the height of the ramp to match requirements of the approach shoring.

Bridge Shoring

Use bridge shoring to take advantage of the greater strength of the vehicle treadways of the aircraft cargo floor. It allows heavy cargo to be positioned between the treadways without overloading the center floor area. Shoring is first placed either lengthwise (nose to tail) or laterally on the treadways (Figure 6-7). The position of the shoring on the treadways depends on the load to be supported and the strength of the aircraft floor. Planks or beams are positioned on top of the shoring planks and form the bridge. The bridge must be strong enough that any sag under the load is not readily apparent. When beams are used, they should be at least as wide as they are thick.

SIZE AND CONDITION OF SHORING

Each planned aircraft load will probably need shoring. The load configuration and weight determine the thickness and width of the shoring to be used. In general, lumber 10 or 12 inches wide and 2 inches thick is most suitable. Lengths of shoring can be cut to meet specific needs. For easier handling, however, the length of shoring should not exceed 12 feet. Plywood also makes good shoring. One 4- by 8-foot sheet of 1-inch plywood can be cut into four 1- by 8-foot or two 2- by 8-foot pieces of shoring. These are ideal for loading tracked vehicles.

All dimensions (thickness, length, and width) for required shoring must be actual size. Commercial-size lumber may not satisfy this requirement. For example, a 1 5/8- by 3 5/8-inch piece of lumber will not satisfy a 2- by 4-inch requirement.

Inspect shoring before use to ensure that it is clean, sound, free of nails, and fit for its intended use. Any defect in the lumber reduces its strength. Split lumber will not transfer the weight of the cargo past the split. The aircraft loadmaster may reject dirty, badly warped lumber, which will delay the loading of the aircraft.

Shoring requirements must be identified and obtained as soon as possible to ensure unit readiness. Units should plan on storing shoring and should be prepared to adjust unit needs as equipment changes.

TRANSPORT OF SHORING

When shoring is required to load cargo, it will also be needed to unload. If shoring is not available at the destination, then the shoring must be transported with the load. Include the weight of the shoring with the weight of the cargo to accurately determine the aircraft center of gravity. For tracked vehicles, simply load the lumber on top of the vehicle while it is being weighed. The weight of the shoring will not affect the vehicle center of balance. For rough terrain forklifts or other pieces of equipment that require sleeper shoring, weigh the shoring separately and add the weight to the vehicle weight. For trailers or other pieces of equipment that only require shoring under the tongue, do not worry about the weight, but always make sure adequate shoring is available.

A 3/4-inch thick by 4-foot wide by 8-foot long plywood panel weighs about 65 pounds. A 2-inch thick by 12-inch wide by 12-foot long plank weighs about 75 pounds.

SHORING REQUIREMENTS

*To find out how much shoring to use, find out how many pounds per square inch of pressure the cargo will put on the aircraft floor. The C-130 and C-141 aircraft have a pound-per-square-inch limitation, so the purpose of the calculations is to find the minimum amount of shoring necessary to do the job. Too much shoring may make the cargo too heavy to fly; too little shoring may allow the weight of the cargo to damage the aircraft.

To find the pressure rating of a piece of cargo, use two formulas: one to find how many square inches of the cargo will actually contact the cargo floor (area) and the second to find the actual pressure or weight of the piece of cargo.

For example, you have a trailer tongue support leg with a contact length of 3 inches and a contact width of 2 inches. The trailer tongue support leg will rest on the aircraft floor. The support leg weighs 325 pounds. Multiply the length by the width to get the area, in this case, 6 square inches.

L x W =   A

         

3 x 2 =   6 square inches

To find the psi of that trailer support leg, divide the support leg weight by the area. For this example, it is 54.2 psi.


A

  =  PSI

               

325
    6

   =  54.2 psi

If the aircraft floor limit is 25 pounds per square inch, then place shoring under the support leg to spread the load. A 1/2-inch-thick piece of shoring will not be enough, so put a 3/4-inch-thick board under the support leg.

Shoring is not effective under its entire length, but only at a 45-degree angle from the edge of the piece of cargo. So 3/4-inch-thick shoring will spread the load only 3/4 inch on each side of the cargo. This results in spreading the load over an area of 4.5 by 3.5 inches.

4.5 x 3.5 =   15.75 square inches

This reduces the psi to 20.7. Therefore, a 3/4-inch-thick board measuring 4.5 by 3.5 inches under the trailer support leg safely places it on the aircraft floor.

  325
15.75

  =  20.63 or 20.7 psi

NOTE: When rounding figures, always round pressure figures up to the next higher tenth of an inch. For example, 2.69 psi would round up to 2.7 psi. Always round area figures down to the next lower tenth (7.58 will be 7.5 square inches). This provides an increased safety factor. The psi is higher than it actually is, and the area is smaller than it actually is.

FORMULAS

The basic formulas for computing area and pounds of pressure for various shaped objects are in Figure 6-8.



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