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Quite simply, a bridge is a structure built to span a physical obstacle in order to provide an object passage over that obstacle. This obstacle could be a valley, a road or a body of water and the object could be people, vehicles or information. In the world of material handling, this obstacle is more often than not a gap and the object is materials. Sounds like easy stuff, right? Not so much. That headache-causing gap can be as small as six inches wide or two feet tall, yet passage required for a single load across that gap may be in excess of 80,000 pounds! Furthermore, the very safety and security of your company’s personnel, materials and physical plant are dependent on the structure and integrity of this bridge. Sounds more daunting now, no?
Designs of bridges vary depending on the function of the bridge and the nature of the terrain where the bridge is constructed. Narrowing our focus to the materials handling industry where a bridge is needed in the passage of materials, we are now able to more clearly assess “bridging needs”. Once a finished product or the raw materials for a product arrive from a sender to the next-in-line user, these products or materials must be “handled”. The first step in handling is the transfer of the product from the sender’s mode of transportation into the next-in-line user’s facility, whether that be a plant or warehouse. Whether this handling is from a truck to a ground level assembly plant, from a railcar to a raised loading dock, from international shipping containers to a warehouse via a fork lift, the safe passage of goods and materials requires a bridge. The bridge must be built to the unique specifications not only of the object being transported, but also to the specifications of both the location of origin (where the object begins) as well as the destination (where the product will end this phase of its passage).
Yard Ramps, Dock Boards, Dock Plates, Railboards and Dock Levelers are all, in effect, bridges for material handling. Yard Ramps, also called Portable Loading Ramps or Portable Loading Docks, perform one of two functions. They allow passage from the ground up into a truck bed or from the dock level down to the ground. This kind of passage is usually accomplished through use of a vehicle such as a motorized forklift. The height of the dock or “gap” between the dock and the ground, drives the required incline specifications of the bridge or Yard Ramp. So too, the weight of the product (plus the required vehicle) dictates the load capacity of the bridge. Ground-to-truck “bridging” requires the same decision elements plus the need for a level off zone at the top of the incline where the load enters or leaves the truck before it begins passage over or down the bridge.
Dock Boards and Dock Plates are very different from each other and are often called by the wrong name. Dock Plates are rectangles of steel or aluminum with some type of locking leg and either hand holes or handles to move them. They offer the lightest and most cost effective bridge available for light dock loading activity applications. More specifically, Dock Plates are ideal for manually moved passage using hand trucks and pallet jacks. Dock Plates should never be used with power equipment. Dock Boards are similar to Dock Plates but with the addition of structural components above the plate called “curbs”. These curbs, usually 8 inches in height, help to maintain alignment of power equipment and to provide maximum runoff protection . Additionally, Dock Boards are of an all-welded steel construction and have weight bearing capacities from 15,000 to 40,000 pounds. Bridges used in the transfer of materials from a freight car to a loading dock are a specialized kind of dock board known as a Railboard. Because the necessary capacity of a Railboard is from 15,000 to 80,000 pounds, a box understructure provides additional strength.
Dock Levelers provide a simple bridge of slight correction. The levelers correct height differences between loading docks, loading platforms and truck or trailer beds. Dock Levelers are usually designed to have a working range of 5″ above and 5″ below dock level. Because of gradability or steepness of incline problems, Dock Levelers are for forklift truck use and are generally not recommended for use with pallet jacks or stackers. Their capacities range from 20,000 to 30,000 pounds.
Now that the actual bridges in the Materials Handling Industry have been identified, it is important to note that, comparable to the use of bridges in varying terrain, every safety precaution must be taken not only to address bridge capacity, but also to address the “connection” of the bridge to both sides of the physical obstacle. Simply speaking, no matter how strong and efficient the bridge is, if it isn’t securely connected to the truck, freight car, dock, etc. it just isn’t safe. If one end of a highway bridge is built on sand and the other end is shored to concrete, the fastening requirements of the two ends are vastly different. So too are the fastening needs of the Yard Ramp, Dock Board, Dock Plate and Dock Leveler very different. Stationary Yard Ramps or Loading Dock Ramps are in a sense “fixed” bridges. They are put into place permanently at concrete or portable steel loading docks using mechanical or hydraulic leveling devices and remain in place for years. In most cases, they are secured to the dock by chains or dock chain brackets. Portable Steel Yard Ramps, also known as Mobile Loading Dock Ramps, are not fixed bridges: they are put into place anew with the arrival of each transport vehicle. Using a forklift and either ramp clamps or a tow bar, the operator positions the ramp into place then utilizes a self-contained, double-acting hydraulic pump to adjust the unit to the proper position at the dock or trailer door. Safety chains and brackets then securely hold the connection between the dock and the ramp.. [B2]
Steel Dock Boards also require placement using a fork lift and the board’s fold down lifting loops or lifting chains. Secure connection is ensured through the use of two 1″ stress-proof steel pins. When properly placed in the side pocket location holes, these pins hold the Dock Board firmly in place guarding against slippage. Because of the portable nature of these Dock Boards and the variation in the construction of the delivering vehicles (conventional, refrigerated, or container trailers to name a few), two four-hole pin pockets are placed on each edge, providing maximum flexibility in pin placement to ensure that the bridge doesn’t move! For the most difficult trailer-to-dock positions, the Red Pin Dock Board utilizes full length side pockets along with two locking pins for each side. As a kind of dock board, the Rail boards are also positioned using a fork lift and the board’s lifting loops or a lifting chain. Once a Rail board is in place, locking “D rings” automatically secure it against the dock to ensure the safety and stabilization of its positioning. Dock Levelers are installed directly and permanently on to the loading dock. Docks with embedded steel channels require only wedge anchor bolts to mount the levelers while docks without the embedded channel use an approach plate as well as bumper & mount plate and anchor bolts.
So the next time you have a 70,000 pound load and encounter a two foot wide or a five foot tall “gap” in your material handling world, do not think of it as an abyss. It CAN be bridged and Bluff Manufacturing is here to help you do just that!! For more than 40 years, Bluff has been recognized as an innovative leader in the fabrication and design of high quality dock, warehouse and safety equipment. Based in Fort Worth, Texas, Bluff Manufacturing serves the entire U.S. through a national distributor network. The company’s 11 distribution warehouses ensure quick delivery of the company’s entire product line which includes bridging devices such as Yard Ramps, Dock Boards and Dock Levelers. With our help, you may you never encounter a material handling obstacle that cannot be bridged.