How to Design Your Pallet Rack Layout Around Warehouse Columns

Warehouse Pallet Rack Design Challenges & Special Seismic Considerations

Engineering pallet rack around permanent facility obstructions such as building columns and equipment may be just part of the job… but it’s still a challenge. After all, the goal of pallet rack design is to maximize inventory storage while minimizing the system footprint. Safe thoroughfares for equipment and pedestrians are also imperative. So, what’s typically the best plan of attack for column/rack positioning?

Ideally, the best approach to pallet rack design and the one with which we have the most success is to get the customer to build/place the columns around the rack layout when possible for a new build. We’ve found that optimal column spacing for new construction is on 58’ centers providing the flexibility to bury the building column within the flue space for a variety of rack designs, including:

• VNA selective
• Narrow aisle selective
• Narrow aisle double-deep
• Narrow aisle push-back

When we can’t dictate building column layout, which is the majority of the time, several approaches minimize the loss of storage opportunity while keeping the integrity of the racking system. We’ll look at it from the perspective of the rack system types to explain.

Challenges

• Columns cannot impede the aisle throughway for vehicle or pedestrian traffic
• Building rack around columns may diminish storage capacity
• Columns positioned within rack systems may challenge system integrity

Special Note: In seismic areas, RMI specifies to separate rack bays and building columns by a distance equivalent to 5% of the rack height in the longitudinal (down-aisle) and 2% of the rack height in the cross-aisle. For example, a 360” tall frame at 2% is 7.2” distance on both sides. This can have a major impact on the layout. Providing an additional space allowance between the rack and building column ensures that the rack system and building move independently in the event of an earthquake and with enough distance to prevent a collision.

A Systems Approach to Playing “Hide the Column”

Back-to-back selective pallet rack allows for a smart approach to incorporating the warehouse columns within the pallet rack system layout without losing storage capacity. As selective systems are single-deep with single-aisle access, the forklift only needs access from the front. Two rows can be placed back to back with the columns between them, allowing each to have clear forklift access from the pick aisle. The area between the rack rows is called the flue space. This area must remain open – free from pallets, inventory, and any other combustible material as a fire-safety requirement. Therefore, the flue space presents an excellent opportunity to house the building columns. The important consideration with any flue area is properly tying the rack systems with row spacers for system stabilization. The formula for determining the optimal column spacing for selective pallet rack is:

(Rack Depth * 2) + Flue Aisle + Aisle Width / No. of Rack Sections Between Columns

Of course, planning for the most efficient aisle width depends on your warehouse equipment interface with the rack system. Thus it will vary from facility to facility and operation to operation.

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Drive-in pallet rack is a dense storage application with single-aisle forklift access for last-in/first-out inventory rotation (LIFO). Rack bays can be positioned to the sides of each column, sandwich-style, if you will. Typical columns are 10” x 10” (some can be 12” x 12”), but the rack system design is well-suited for the uprights to butt up to the column sides. Effectively the storage loss comes down to approx. 10” or 12” every 40’ to 50’ of system depth depending on where the columns are positioned. For standard GMA-style pallets of 40” x 48” d, that’s roughly a potential loss of a drive-in bay every 3 columns since building columns are usually located every 40’ to 50’.

You must also connect drive-in rack systems with row spacers where the column is between the bays. The row spacers add necessary stability to the system.

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Another dense storage system is push-back pallet rack. Push-back uses wheeled carts on inclined rails to hold pallets in typically a 3-4 deep lane. It is accessed from a single aisle for LIFO inventory rotation. The system design can be conducive to building the rack essentially around the columns.

Ideally, if you can position the layout to have the column farther back in the bay, you can sometimes use the positions in front of the column. For example, a 4-deep lane might turn into a 3-deep. If the column is at the front of the bay, you will have an increased loss of pallet positions.

The photo to the right illustrates a retrofit push-back installation within an existing building. The most efficient use of the space, in this case, resulted in the column placement located at the 2nd pallet position within the lane.

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Gravity Flow Storage Rack

Pallet flow rack is a dynamic, dense storage system that is loaded from one aisle (load/charge side) and discharged from an opposite (pick) aisle. You need two clear aisles on either side of the system, and systems average 2-10 pallets deep, so it can be a bit more of a challenge for planning around building columns within the system design.

The photo below shows that you can configure the rack around the column to maximize pallet flow bay space. Again, like push-back rack, the “column bay” on all levels is lost, but the storage capacity reduction is minimized. Bar grating can be used around the column to close gaps and prevent inventory from falling through.

Carton flow storage is a productive solution for case picking at the ground level. Carton flow is a dynamic storage solution similar to pallet flow and usually requires separate load/charge and discharge aisles. Carton flow comes in several wheels or roller applications, and system type is predicated on inventory specs. Your carton flow system should have the flexibility to enable you to minimize lost storage space and get as much SKU storage as possible as you design around the columns.

Apex Companies Full-Service Support

Getting the most out of your costly warehousing space is challenging, but there are tried and true methods when you’ve settled on the best storage systems for your needs. The experienced Apex team will help you design your pallet rack system, configure conveyors, prepare pedestrian spaces, dock areas, etc., to ensure you achieve your operational, safety, and ROI goals. Give our team a call and we can discuss the best solutions to the warehousing challenges you’re facing.