Warehouse Storage Racks - A Primer

If you own, work in, or manage a warehouse you are certainly aware of the importance of efficient storage systems. Without a doubt, the most common type of warehouse storage available today comes in the form of component based racking systems. These types of systems have grown in complexity over the past decades and as such a need has arisen for a lay-person's guide that can explain all of the options currently available.

After reading this guide, you'll be able to make an informed decision on the various benefits & advantages of several common storage rack types.

While this guide is meant to assist you in choosing your rack, it is still beneficial to consult with one of our professional solutions specialists. They have been working with this material every day for years and are aware of ALL the tips and tricks concerning storage racks. Please feel free to call us at 800-598-5532 to discuss your planned layout.

Table of Contents:

• Selective Pallet Rack
• Selective Pallet Rack Brands
• Drive-In Rack
• Pushback Rack
• Pallet Flow
• Carton Flow
• Cantilever Rack

Selective Pallet Rack

Selective Pallet racking is by far the most common type of warehouse storage rack and is what is typically thought of when the need arises for industrial type storage racking. All selective rack is made from component pieces that are usually priced & purchased seperately.

Uprights

Uprights (also called Frames, or less commonly, legs) are the support columns that hold up individual shelves in a section of rack. Pallet Rack uprights form the ends of what are commonly known as 'bays' of pallet racking. Each pallet rack bay must have at least two uprights, however if multiple bays will be placed in a row they may share uprights (see figure 1).

Beams

Beams are used to create the actual 'shelf levels' that support loads and are held up by pallet rack uprights. Pairs of beams form each individual shelf level (see figure 1). Shelf capacity is determined by the height of the beam, length of the beam and the number of shelves per bay. Most modern beams feature end clips that attach directly to the upright without the use of specialized hardware, however there are many different brands available that feature unique designs (see section on selective rack brands.)

Putting it all together

Now that you're familiar with the individual components, let's take a look at configuring a rack installation that's right for you.

Step 1: Size the product

The first step in determining what is needed is to size the product to be stored. The product's width, depth and height are important to know, however you must also include the height, depth and width of your pallet if you are using them (see figure 2). In addition to the size of the product, the maximum weight of the product must also be determined. These measurements are key to determining the correct rack for your needs.

Step 2: Rows & Bays

Most often, static racks are configured in rows to make maximum use of available space. Rows can be configured in single or double (back to back) runs (see figure 3). The number of rows created will be determined by the width of the bays needed (see figure 1).

Determining the width of the bays is accomplished by using the product measurements taken in Step 1. A good rule of thumb is to add 6" to the width of each load to get overall bay width (also beam length - see below.) For example, if the product width is 42" and is to be stored as two pallets per shelf, this is the correct equation: (42+6) x 2 = 96" wide bays. To determine the depth of your uprights, subtract 6" from the depth of the product to allow the proper pallet overhang. For example, if the pallets are 48" deep, subtracting 6" gives an upright depth of 42". This overhang is adequate to insure that the weight of the product will be evenly distributed on the beams however, a lesser overhang is allowable as a function of aesthetics. If this is the case be sure that the pallets are in good condition. In this situation we would also recommend the use of additional supports; ie. Pallet Supports or Wire Decking (see figure 5 below).

As mentioned above, the beam length will be the exact same as the width of the bays. The length of beams is always measured from the insides of the upright frames.

Step 3: Shelf Spacing & Overall Rack Height

To get the overall rack height, again use the load measurements taken at the beginning. To each load, add 6" to get the distance between shelves. The beam height will also need to be accounted for here and a rough estimate of 4", 5" or 6" per shelf level (depeding on shelf capacity needed) will leave enough room for the beams. An equation to use for this height would read as follows:

((Load Height + 6") x # of Shelf Levels) + ([4", 5" or 6"] x # of Shelf Levels) = Upright Height

Please note - The top of the upright should be more than 1/2 the height of the pallet + load to prevent loads from tipping over and falling off the rack. The bottom of the top load should never be at the top of the upright.

Other items to take into account when determining the overall rack height are the overall height of the ceiling, sprinkler system, lights and any other obstructions. Make sure to also account for the maximum reach of the lift truck that will retrieve the pallets. Also of note when determining aisle width is the turning radius of the lift truck.

Step 4: Rack Accessories

A Note About Wire Decking
Wire Decking is typically used as a "fail-safe" when used in conjunction with static pallet rack. If you have pallets loaded with loose boxes, cartons or other materials the decking will act to catch items knocked off of the pallet to prevent injury to persons on the ground (provided the items are no smaller than the deck's mesh size). Wire decking will also not prevent an item from falling off the front or back of the racking system. Although wire decking can be used as a "shelf level" to hold assorted goods, please note that most wire decks are NOT RATED FOR POINT LOADING. What this means is that if a deck's overall capacity rating is 2000#, the deck will support a 2000# load evenly distributed over the entire surface of the deck. The palletized load must still be entirely supported by the front and rear pallet rack beams.

Pallet Rack Identification Guide

Below are some of the most common types of pallet racking found today. If you have something not on this list, please contact us at 800-598-5532 and we'll be happy to help you identify it.

Teardrop	Interlake (New)	Structural
Ridg-U-Rak	Sturdibuilt	Speedrack
T-Bolt	Republic	Hiline
Unarco II	Paltier	Palmer Shile
Husky	Prest	Slide & Lock
Frick Gallagher	Amrack	Mirak

Drive-In & Drive-Through Rack

Traditional pallet rack is a great solution for many warehouses, but if you have a lot of inventory that shifts on a regular basis, drive in or drive through rack is a storage solution you may want to consider. While traditional static rack storage allows for many rows of pallet racking with aisles between the individual rows, drive in and drive thru racking allows for a much denser arrangement of your stored product. Both drive-in and drive through rack systems allow more efficient use of available space than traditional multi-aisle selective racks systems. In fact, when compared to a conventional selective rack system, the same amount of storage can be acheived with a high density drive in or drive thru system in 80% less space.

High density storage racks work by utilizing standard pallet rack uprights in conjunction with rail beams or more simply, rails to store the pallet loads in a very dense configuration. The key difference between these racks and selective pallet racks is that the forklift truck operates inside of the rack itself and there are no specified lanes between the rows. The forklifts enter into the individual bays of the rack and the bays themselves can be as long or as short as needed.

Drive in rack and Drive through rack systems decrease storage and retrieval time while increasing efficiency and productivity among workers. Not only do they benefit your operations, they can also decrease your bottom line by giving you more storage room per dollar spent on racking. Because these racks create a more uniform load in a confined storage area, your forklift operators working in the system become more skillful drivers. In addition to these benefits, consider this - drive-in & drive-thru systems are very energy efficient. Since the product is so densly loaded in this type of system, there is less air to be heated or cooled between your pallets and your forklifts don't need to drive as far to pick or place loads thereby using less fuel.

Pallet Rack/Drive-In Rack Comparison

Clearly, Drive-in or Drive-Through is not for everybody however, it is exceptionally good at storing large quantities of palletized materials in a smaller space than would be afforded by selective pallet rack (see figure 6).

Types of High-Density Storage Rack

Within the class of drive-in or drive-through racks are several notable configurations - most commonly defined by the length of storage time and ease of retrieval needed for the product being stored (see figure 7).

One Way Drive In - Last in First Out (LIFO)
Material is both stored and retrieved from the same side (entry point) in several aisles. For this reason, the first material put in this system is the last to come out. This works well where shelf life is at a minimum or not a major concern. This system also works well in cold storage environments or warehouse freezers.

Two-Way Drive In - Multi First-In Last Out System
Arranging drive-in to be enterable from two sides allows for maximum space usage and easy product accessability from two seperate sides.

Drive-Thru - First in First Out (FIFO)
Free access from both sides allows materials to be stored from one end and retrieved from the other. With this capability, a first in first out storage arrangement is made possible. This system is used where there is expiration dated material or wherever shelf life is of major concern.

Pushback Rack

A push-back racking system can be a great option when you're tight on space. In a push back rack system, the pallets each sit in a tray that rides along rails in the rack frame itself. The push back rails are supported on an incline and gravity moves the trays along the rails towards the front of the rack. From the front, the loads are both picked and deposited while the back of the rack remains closed. When a load is deposited to the front of the rack, it will "push back" the previosuly placed load, thus decreasing picking times but keeping the number of picking faces to choose from high.

Push-back racks can store multiple sized pallets up to six deep and four high making push-back rack a very efficient LIFO (last in, first out) system. This type of dynamic storage system allows you to have all the benefits of a high-density storage system without the drawbacks of a drive-in system. Let's look at this further.

With a typical high-density drive-in system, each bay will typically be filled same type of product. That way, when retrieving products one need only go to that 'pick-face' to get any one item. If dissimilar items were to be placed in the same bay that entire bay may potentially need to be unloaded to get at the needed product, thus wasting a large amount of time and resources. However, with a pushback system many different products can be placed in lanes within the same bay allowing for a larger quantity of pick faces. With each individual lane being a seperate product, those products will still be accessible without first unloading the rack.

Pallet Flow Rack

Similar in concept to pushback rack is a pallet flow system. The pallets move from back to front and as they are removed from the rack, the next in line takes the previous pallet's place. Unlike pushback rack however, the rack is usually loaded from the back and picked from the front.

Almost any static pallet rack system can be retrofitted to be a more efficient dynamic storage system because the pallet flow rails drop into place using the existing racking components as their support structure. Lanes of pallet flor rails usually have built-in 'brakes' that work to slow the pallets to a smooth gentle pace as they glide down the lane. One of the biggest strengths of pallet flow rails over pushback is that flow rails will allow a longer lane. For example, while pushback may be able to store pallets 5 deep, a pallet flow system will allow as many as 10-15 pallets deep.

Carton Flow Rack

Put simply, the main advantage of carton flow rack is that merchandise remains better organized and easier to find/pick. With carton flow rack, the product is automatically rotated on a first in first out basis. The concept is simple and effective. Merchandise is stocked in the rear of the carton flow rack and moves toward the picking station in front on an inclined shelf equipped with specially designed roller track. When a carton is removed from the picking station, the next one in line rolls to the front. Carton flow is a great system that always keeps items within reach. Inventory is easier to monitor and control since products are fully visible at all times.

Restocking and picking typically offer the greatest opportunity for improving efficiency. With carton flow rack systems labor savings of up to 75% can be realized almost immediately. Because items are picked from the front and stocked from the rear, both functions can be performed without interference and with minimized travel.

In a static storage system such as standard shelving, the stockers and pickers are often doing a lot of unnecessary work, leading to decreased productivity. Although the static storage systems may be less expensive in the short term, in the long run they can cost you more than they initially save, especially compared with a flow rack system.

Static vs. Dynamic Storage Systems

Figure 9 shows a very clear comparison between static and dynamic racks. In the static system, the stockers and pickers are taking far more steps than are necessary to accomplish their tasks. They may not always take the most efficient path to the product and they will almost certainly get into each others' way at some point. In the dynamic system, the first thing to notice is that both the stockers AND the pickers have much less distance to walk. This allows them to concentrate on stocking and picking and will allow them to get more work done. Also notice that in the same amount of space that was designated for static storage there is far more storage space available because the space is used much more efficiently. Since stocking and picking operations are now seperate, neither worker will interfere with the others' work.

Pick Modules

Carton Flow Rack can be used either as free standing units or as part of a system in conjunction with conveyor, static storage, and multi-level mezzanines. A typical pick-module layout is shown here in a cutaway view. This multilevel system consists of two facing rows of carton flow rack with conveyor running down the middle. Pallet Rack is placed behind the carton flow aisle for restocking. The conveyors are used for staging orders, take-away for finished orders, and also to haul away empty cartons.

In an alternate version of this layout, (see figure 10, Layout 1) pallet rack can be placed over the rear of the carton flow rack, offering additional storage directly above the carton flow rack. To support the additional weight, pallet rack posts replace the standard carton flow posts and beams are substituted for sway braces. Pallet storage over the flow storage can also be used to achieve two and three tier storage systems.

Figure 10, Layout 2 shows a combination of pallet rack and carton flow supplying product of varying volume to pickers at a central conveyor aisle. Orders move away from the flow rack and enable pickers to continue order selection.

Figure 10, Layout 3 demonstrates a layout where fast moving items are stored on main picking aisles for easy access and maximum picker productivity. Restocking occurs from the center aisle without interrupting order picking flow.

Carton Flow Rack Components

Like pallet rack, carton flow rack is modular and consists of many individual components. Units can be strung together utilizing 'starter' and 'adder' sections to create entire rows of carton flow storage. There are also several distinct types of carton flow frames and shelves that can be utilized in a variety of situations (see figure 11).

The most common types of carton flow frames are square front and layback. Square front carton flow frames are useful for picking full cases. Applications include canned goods, liqour, parts, etc. Layback carton flow frames are useful when picking from open cases. Applications may include health & beauty products, books, or other situations where the cases are differently sized. Another advantage to layback frames is that it is easier for workers to access the middle and lower shelves. This is typically where you'd store your highest turnover merchandise, thus creating faster and more efficient picking.

There are also several different types of carton flow shelves that assist in different picking applications. Straight shelves are the most common type of carton flow shelf, and are most commonly used when picking full cases. Knuckled shelves are the second most common carton flow shelf type and are useful for picking individual items from the cartons. Weld-in trays are similar to knuckled shelves but provide a larger access space from which to pick items. Finally, reverse knuckled shelves are useful for split case picking when the items are picked from the front of the cartons.

Roller track is at the heart of carton flow rack's operation. It is on these tracks that the actual product (in cartons) rolls forward towards the front of the rack. Typically, these rollers are used in pairs to form 'lanes' in each carton flow shelf. These lanes keep similar products seperated. Shelf guides work with the roller track to keep product seperated. The guides are placed between laned to keep products rolling in their specific lanes so they do not cross over into other lanes on the carton flow shelves. Carton flow clips hold the carton flow shelves to the frames. Some of these clips can also be used with regular pallet rack frames to allow you to create a mix of carton flow rack and pallet rack in the same vertical space.

Cantilever Rack

Cantilever Rack, also known as furniture or pipe rack is a great solution for storage of long, bulky materials such as lumber and PVC or metal pipes. Furniture rack is a style of cantilever racking that can be decked to provide static storage similar to pallet racking, with the advantage that it provides easier storage and retreival of bulky or oddly sized material than traditional pallet rack. Cantilever rack is a very efficient means of storing material. The storage density with cantilever rack can be very high if you plan out how you will use it efficiently, but generally cantilever rack's flexibility makes it a very popular storage solution with near immediate return on investment.

Uprights

Like pallet rack, cantilever has specific components that work together to create larger bays and rows of storage. Uprights are the main structural components in any cantilever rack installation. Uprights work with bases (when referring to uprights below, we are speaking about complete upright/base combinations) to create the 'backbone' of the rack. Uprights are available in single, or double sided configurations - with the only difference between the two being that with double sided uprights, you can store material on both sides of the rack. Like pallet rack, there are many different makes and brands that do not all work together. You must match the same make arm and base to build a complete unit. Please Be Aware - NEVER put arms on the back side of single sided cantilever rack. Even if the upright has holes to hold arms on both sides, this is a very dangerous practice and should be avioded at all costs.

Arms

Similar to pallet rack beams, cantilever arms make up the actual 'levels' that are used for storage. The arms are typically adjustable on the upright to create shelf levels of whatever height are needed. Arms can be straight or inclined to hold goods that may roll off. Some arms even come with a "lip" that attaches to the end of the arm to prevent loads from slipping off the front of the rack.

Braces

The last component of cantilever rack is bracing. The braces go between uprights and stabilize the rack laterally. Braces are not intended to hold loads and should only ever be used to connect and brace the uprights in a row. The braces will be the same length as the spacing between uprights.

Putting it all together

Let's start the same way we did with pallet racking. In order to have an effective and efficient system, it is first important to think about what will be stored. We're going to start by measuring the load. The big difference between cantilever rack and pallet rack however, is that you need to make sure that if your load consists of multiple components you'll want to make sure that you take into account the measurement of the entire unit load and not just a piece of the load. (see figure 12)

Step 1 - Arm Length & Lateral Spacing

The depth that you arrive at using the above measurements will be the minimum arm length necessary for your product. Please Note - the depth of your load should not exceed the length of your arm. The rated arm capacities of cantilever rack will not be correct if you improperly load the racking. (see figure 13 for correct arm loading techniques)

Step 2 - Load Deflection & Lateral Spacing

Lateral spacing is the distance from the center of one upright to the center of the next. To determine the correct spacing between the uprights you'll also need to take into account load deflection. Load deflection is a very real concern when using cantilever rack to store long items. When designing a cantilever rack system, you should try to use the fewest number of arms to store your loads. However, since deflection may damage your load you should also strive to keep deflection to a minimum. A good method to determine the lateral spacing needed is to use blocks of wood placed on the ground. Place your load on these blocks to check for proper support. If two blocks yields too much deflection, try three - if that's too few, try four. When running these tests, you must use the correct spacing method shown in figure 14. The Load should overhang the end arms by 1/2 of the distance from the center of one upright to the center of the next upright.

Taking this into account, the lateral arm spacing of an 8' load supported by two arms (as in the figure above) would be 4' as this would allow for 2' unsupported on each end.

Step 3 - Determining Upright Height

As with other rack types, to determine the height of your uprights, you must consider ceiling height, lift truck reach and any other items that may interfere with the top of your racking. This can incluude sprinklers, ceiling joists, and lighting, among other things. Figure 15 shows the measurements you need to arrive at the total upright height. These measurements include the actual load height, the clearance between the top of the load and the bottom of the next shelf (6" is recommendedand), the height of the arms and the height of the base. Adding these numbers will give the overall upright height needed.

Notice in the figure that a load has been placed directly on the base. This is not only acceptable, it is recommended and does not diminish the capacity of the upright. A commonly recommended practice is to place your heaviest load on the base because it doesn't subtract from the overall upright capacity.

Step 4 - Determining Capacities Needed

In a properly loaded cantilever rack, each arm supports an equal part of the load's weight. To arrive at the necessary arm capacity, first determine the number of arms needed to hold the load and divide the load's weight by that number. In figure 16 below, there are three arms supporting an equal part of a 6000 pound load. This would give you a needed arm capacity of 2000 pounds.

To determine upright capacity, simply multiply the number of arms per side by the load on each arm. In figure 16 below, since there are four arms each holding a weight of 2000 pounds, the required minimum capacity of the upright would be 8000 pounds.

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