A colleague of mine sent me this image of some racking and I've been trying to figure out the design intent of some of the features.

Image one (key holes)

enter image description here

Looking at the keyholes on this racking the one side of the lobe is curved while the other side is straight, sloping away from where the skids are going to be placed.

Image 2 (top view paint sketch of the racking profile)

enter image description here

This image is a quick and dirty sketch of the shape of the racking profile,, sort of a W shape.

When I looked at these images I was thinking that the two shapes were made to work together, the straight side of the keyhole being made to slightly pull the shelves of the racking apart when placed in them. I.e. not fully resting on the bottom of the keyholes under their own weight, and then the 'W' shape of the racking uprights being used to act as a bit of a spring/dampener feature. My thinking/reasoning for this is so that when a forklift drops/lowers a skid onto the shelves, the racking uprights will have room to flex slightly and absorb some of the impact (forklifts not being particularly precision instruments). This way the racking pins don't get impact loaded every time a skid gets loaded, and also the flexing of the uprights would allow for a greater tolerance in the levelness of the shelving. (Shelving/racking safety requirements being remarkably strict)

My question is, does my reasoning sound accurate, or is there another reason for these somewhat 'complicated*' shapes?

note- by complicated I don't mean intricate, these are very simple shapes to make, but they appear to have more design intent because they go beyond simple holes and extrusion processes. I come from industry where all geometry requires justification and calculations not just "because it looks cool".

  • $\begingroup$ Looks like it's designed for drop-in support pins as seen in lots of home-use shelving systems. Perhaps you can provide a picture or schematic showing exactly how these are used in whatever a "racking" system is? $\endgroup$ – Carl Witthoft Sep 21 '17 at 17:25
  • $\begingroup$ The sloping side looks like it is designed to help "clamp" the shelf to the upright to help minimise the movement - a self-locking action... $\endgroup$ – Solar Mike Sep 21 '17 at 21:20

The main reason for the shape (W-shape) of one side of the rack is to improve structural strength.

See picture as reference.

As depicted in picture $a$, the system is to resist forces that will tend to bend the vertical pole in its local x-axis, see picture below.

Deflected shape of the pole.

Thus the moment of inertia of the profile shall be designed to be the maximum considering also the part of contact between the rack and the pole. This will be proven when you compare the moment of inertia of the two parts. Also, if you fold a piece of paper or cardboard into V-shape, it is harder to bend then when it is flat.

Also, if the profile is to be constructed like in picture $a$, the side in which the racks are connected will easily bulge out the frame. See image below. enter image description here

Therefore, this design gives room for the deflection to occur without compromising both the strength and the aesthetics of the racking system. See also this image.

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