Flatbed truck
A flatbed truck (or flatbed lorry in British English) is a type of truck which can be either articulated or rigid. As the name suggests, its bodywork is just an entirely flat, level 'bed' with no sides or roof. This allows for quick and easy loading of goods, and consequently they are used to transport heavy loads that are not delicate or vulnerable to rain, and also for abnormal loads that require more space than is available on a closed body.
Road trucks
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A flatbed has a solid bed, usually of wooden planks. There is no roof and no fixed sides. To retain the load there are often low sides which may be hinged down for loading, as a 'drop-side' truck. A 'stake truck' has no sides but has steel upright pillars, which may be removable, again used to retain the load.
Loads are retained by being manually tied down with ropes. The bed of a flatbed truck has tie-down hooks around its edge and techniques such as a trucker's hitch are used to tighten them. Weather protection is optionally provided by manually 'sheeting' the load with a tarpaulin, held down by ropes. These manual loading techniques are slow and require some care and skill. There is also the risk that an improperly secured load may be shed in transit, often leading to accidents or road blockages. There is also little theft protection for such a load. The slowness of loading loads like this led to the development of more efficient truck designs with enclosed bodies.
Some improvement was made with the general replacement of ropes by flat webbing straps, tightened with a ratchet. These reduced the skill of 'roping up' and improved the control of tension, leading to fewer shed loads.
Decline of flatbeds
Flatbeds became rare in the 1980s as the majority of road freight changed to either containers or pallet loads carried on larger and more efficient trucks, optimised for quicker loading by fork-lift trucks. Containers are carried on specialised semi-trailers with twistlocks in the corners to retain the container. Pallet loads are carried in either box bodies, loaded through rear doors, or curtain-sided bodies loaded through the sides. Both of these protect loads from the weather and can be quickly loaded with standard loads, but are more restrictive for single bulky loads, loaded by crane. The haulage and logistics business also changed around the same time as a greater proportion became more regular in nature, such as standard daily loads of equally-sized boxes from a distribution centre to a supermarket, rather than the unpredictable ad hoc nature or earlier road transport.
Flatbeds are still in use, but are now used for more specialised cargoes, such as constructional steelwork or lighter abnormal loads, such as machinery.
Low loaders, for construction machinery and heavy plant vehicles, are not considered as flatbeds. Neither are abnormal load carriers for heavy haulage.
Configuration/design in US trailers
Most places in North America, length is commonly 48 feet or 53 feet, and width is either 96 or 102 inches (including rub rails and stake pockets on the sides, which generally placed every 2 feet). Some older trailers still in service are only 45 feet or shorter if used in sets of doubles or triples (often used to haul hay). Various lengths and combination setups can only be legally driven on turnpike/toll roads which are far too long for most roadways. Body and frame can be one of 3 general designs: the heaviest and sturdiest is all steel (usually with wood planks), Ever popular combo with steel frame and aluminium bed, these type often have wood portions for nailing down dunnage boards), and aluminium (which is the lightest allowing for more cargo to be legally carried without overweight permits). Incredibly light and very expensive to purchase, all aluminium trailers are very slippery when wet, flex more and are easily damaged. They also have a natural upwards bend so that when loaded they straighten out to be more flat, rather than to sag in the middle under a load. Another popular type of flatbed trailer is a stepdeck (or drop deck) with approximately 2 feet lower deck and low profile wheels to accommodate taller loads, without hitting low bridges or tunnels. These stepdecks can come with loading ramps to allow vehicles to roll on and off of the back from ground level. Shorter trailers used for local jobs such as landscaping and building material delivery within urban or local areas can have a "hitchhiker" type forklift truck attached to the back in order for driver alone to deliver and unload pallet/skid items. A bulkhead or "headache rack" is sometimes be attached to the front of either a straight or a stepdeck trailer for load securement at the front of the deck. In the event of long pipes or steel or lumber coming loose in a hard braking incident, they save the operator and cab/sleeper in one of two manners in theory. If attached to the trailer they bend while attempting to block forward motion of a loosened cargo, causing the long load to go above the cab and driver. If attached to the frame behind the cab or sleeper of the tractor, in theory they protect the back of the cab from impact and if unable to stop the load coming thru the cab, they cause the cab to be knocked off of.the frame, rather than impale the cab and kill or seriously injure the driver.48 and 53 ft lengths usually have two axles spread out to over 10 ft apart at the rear "California spread" in order to allow for more weight distribution on the rear of the deck (40,000 lb instead of 34,000 for a tandem axles design). So-called Cali spread was originally designed to comply with bridge weight formulas in that state but has since been adopted in most other parts of the country. These spread axles take far wider turning radius, and if turning the combination tractor/trailer too sharply, the front axle tires of the trailer may damage the road/parking lot surface, or pop a tire bead off of the rim, or both. Some trailers have the capability of lifting or lowering the front axle independently to mitigate this risk, however driver may not be able to use this feature if the trailer is loaded, but if the deck is empty the driver can lower the front axle to bring the rear axle off of the ground to significantly decrease turning radius of the rig for easy manoeuvre in tight spaces, or to reduce tire wear during empty /deadhead miles of travel. Under the deck of the trailer can be attached racks for spare tires, dunnage boards, or tire chains...as well as various tool/storage boxes. On one side (or often both sides for alternating pull on strap tension) are usually sliding (but sometimes fixed) winches to ratchet down 4 inch straps for load securement. On most 48 foot trailers, you may not place these strap/winches over a tire as when air pressure releases out of the suspension system when parked, the deck lowers down and will likely pop a trailer tire. Some trailers have an air scale which when the driver learns how to interpret properly through experience, combined with his knowledge of how much his/her rig weighs when empty and can interpret how much cargo can safely and legally be loaded onto the trailer. With different varying loads of cargo, driver can have an idea how much his gross total weight is (and if he is legal to avoid ticket) (80,000 without a permit in most states, but slightly lower in others). Some decks have pop up chain systems which have a higher WLL (working load limit) than attaching chains to either the stake pocket/spools, or the frame. Other decks of trailers can have sliding detachable accessories which greatly diversify your options of where and how to place a chain hook for securement. Besides axles which raise/lower as needed, some spread axle trailers can slide one or both axles forward, or back to create a tandem setup in specific situations when necessary, to comply with weight distribution requirements. Although certain amounts of front and rear cargo overhang is allowed (as well as overhang to one or both sides of the trailer) with flags/banners/flashing lights to warn drivers behind and to the side of you of impending danger of impalement if they follow too close behind you and you should have to suddenly stop...in extreme cases permit loads require escort be led front rear or both for oversize/over dimension cargo/equipment.
Tow trucks
Some vehicle recovery tow trucks have flat beds and are able to winch a recovered vehicle entirely on board. They can then drive the vehicle away for repair without needing to tow it. This allows a faster journey, does not require a driver in the vehicle being towed, and allows a damaged vehicle to be recovered when it cannot be towed. As these flat beds usually slope gradually to the rear, unlike the level bed of a cargo flatbed, they are known as 'beavertails'. Some tow truck beds are demountable and may be lowered behind the truck for easy loading, then both bed and load winched back aboard as one.
Railway flatbeds
Railways also employ flatbed trucks in engineering trains and freight trains. In Britain and the Commonwealth the term bogie flat is often applied to a bogie flatbed truck. Although less common, flatbed railway trucks on rigid frames and axles are sometimes used, with both 4-wheel and 6-wheel versions being extant. In British English, the term 'truck' most commonly relates to railway vehicles, with the word 'lorry' more commonly applied to road vehicles.
See also
References
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