Which is stronger, structural or roll formed columns?

Which design resists impact damage better, open or closed roll formed sections?

What options are available for rack frame protection and frame reinforcement?

What is rack damage?

What are Rack Manufacturers Institute (RMI) Specifications?
How does this new standard benefit the customer?
Will some systems be sold which do not conform to this standard?

What are the typical clear aisle requirements for different lift equipment?

What are the limitations for Rack stability?

When does a Rack System need to have approval for Seismic Zones?

What are typical budget prices for various types of Storage and Picking Systems?

There is one factor that determines the amount that a braced column section will bend when a load is applied, and that is an engineering calculation called the moment of inertia. It is expressed with reference to the bending axis, and in the case of fork truck impact, the deeper the column section, and the greater the bending resistance. The column depth is much more important than the material thickness or the column width, and as a result, if a structural and roll formed column of equivalent capacities have these loadings applied, the structural will temporarily bend, or deflect, up to seven times as much as would the roll formed section. In terms of failure caused by overload, this relationship holds. A roll formed column of an equivalent capacity is approximately four times as strong in failure as the structural section, meaning that the structural column will tolerate only one-quarter of the force of the roll formed column before the deflection above becomes permanent deformation. While we know that the roll formed column dents more easily than does the structural, it does not become “damaged” as defined previously until significant deformation of the material has occurred. Because of its inherent advantages over structural, it would take significant damage of the roll formed column before it would be brought to the same weakness level as the structural column. This is a surprise to many users because they have experience with denting only, and not rack failure.

In summary, greater concern should be rack failure and the danger it represents.

View Diagram

Closed sections have certain structural advantages, but not in the area of impact resistance. The moment of inertia about the bending axis in a frontal impact situation for a closed section column and an open section column are virtually identical, so their bending resistance levels are equivalent. In fact, if all else is equal, because of the structural advantages of closed sections, a closed section column of a given load-carrying ability will have a thinner wall than will an open column of the same load-carrying ability. This would decrease impact resistance. Only if the capacity of the closed section is greater (or thicker) would a user enjoy any structural advantage in it - but this holds true when comparing almost any two columns. Why don’t we see many manufacturers produce this shape? The problem lies in usability. Attachment of accessories can be difficult with closed sections, because through-bolts would have to be used, and proper tightening without column crushing would be a problem without a special type of fastener. Also, accessories attached in opposition (on each side of the column) can create an attachment problem. Because of these problems and the fact that there are no real advantages, few companies offer closed roll formed column sections.

View Diagram

Rack frame protection (stand-off type) includes structures not directly attached to the frames such as guardrail, floor-mounted column protectors, and floor angle guidance. Guardrail (posts and rail sections) provides a visual and physical barrier at rack row ends plus it absorbs impact exerted by forklifts and other mobile equipment. Column protectors (1/4" thick steel plate), like the guardrail, also provide a physical barrier and absorb impact exerted by forklifts, but they only protect rack frame columns. Floor angle guidance (structural angle) contains and guides order pickers and turret trucks down aisles which protects the rack frames from damage.

View Diagram

Frame reinforcement consists of the following options - columns with internal X-3 bracing, double columns, and heavy-duty horizontal struts. Internal X-3 bracing (1-3/4" x 1-3/4" x 1/8" angle welded inside the aisle column) adds bending resistance to the column, thereby increasing its moment of inertia. Double columns (additional column section welded to the back of the aisle column) add depth to the column, thereby increasing its moment of inertia as well. Heavy-duty horizontal struts (stronger column section welded front-to-back at the lower elevation of the frame) are beneficial in resisting force applied within their vicinity.

View Diagram

It may seem silly to ask the question, but without defining the problem it would be difficult to solve. The most important definition, and the most practical one, is “Any change in the rack’s load-carrying characteristics which compromises its ability to do its job as specified by the manufacturer”. This means that minor dents or scratches, while important indicators of how the lift equipment operators are interfacing with the rack, would not be considered damage that must be immediately acted upon. The type of damage that does affect the load-carrying capabilities of the rack system is the major material deformation on frames or beams, any damage to the beam-to-frame connection, or damage to a weld. This type of damage is almost always caused by inadvertent contact between the forklift and the rack, or the load on the forklift and the rack. It normally occurs within the lower portion of the front column facing the aisle.

In June 1997, virtually all-major U.S. rack manufacturers adopted an important new design standard. The new standard, 1997 Rack Manufacturers Institute (RMI) Specification for the Design, Testing, and Utilization of Industrial Steel Storage Racks, is the result of years of effort put forth by leading engineering consultants and industry professionals. In addition to adoption by the rack industry, this standard will be integrated into building codes across the country.

Simply put, there were no prior industry standards for the design of storage racks. Various groups put various standards forth, and it was a manufacturer’s prerogative as to which standard they would accept, if any. Without a common design standard in place to protect the customer, buyers of rack products could not make a reliable comparison between proposals put forth by multiple suppliers. More important, without a common design standard it is difficult to establish the safety of the proposed rack system without an exhaustive analysis by an independent engineering consultant. With the adoption of RMI 1997, this analysis is built-in and its cost is borne by the manufacturer. These manufacturers will need to prove on the front end that their design procedures and capacity tables conform to the standard.

There will be a few manufacturers that do not design their systems according to RMI 1997 in areas where building codes allow it.

To conform to RMI 1997 Specifications, a rack must be structurally attached to the following if the overall height from the floor to the top load beam exceeds six (6) times, but no more than eight (8) times the depth of the frame. Example: 42” deep frame with top load beam at 288” = 6.86 to 1.

a.	Replace standard frame footplates with oversized seismic footplates requiring two (2) anchors per footplate or four (4) anchors per frame.
b.	Tie frames to a concrete wall using wall ties that do not exceed 10’-0” (vertically) from each other.
c.	Tie frames to adjacent row frame using cross aisle ties.
d.	Tie frames to another row (create back to back row) using row spacers that do not exceed 10’-0” (vertically) from each other.

The following budget prices include these following assumptions:

• Prices include Materials and Engineering Services, Freight, plus Installation and Project Management Services. Note: Sales/Use Taxes are not included.
  
• Prices include floor positions for the Selective Rack and Drive-In Rack Systems.
  
• Pallets are to be 48” deep x 40” wide with a maximum load of 2,500 pounds.
  
• Cartons are to be 20” deep x 15” wide with a maximum load of 40 pounds.
  
• Prices for the Selective Rack, Drive-In Rack, Double Deep Rack, Push Back Rack, and Pallet Flow Rack assume 4-5 pallet levels high per bay.
  
• Prices for the Narrow Aisle Rack assume 8-9 levels high per bay with wire decks.
  
• Prices for the Carton Flow Rack assume 4 levels high with 4-6 lanes per bay.