Wood shelf "Sag-ulator"

[8ntruck 6,999]

What @formariz is doing with his tensioners rope idea is making the shelf into a truss.  The shelf is mainly in compression.

 

When suspending things from threaded rods attached to the ceiling, we need to pay attention to a walkway collapse in a Hyat Regency hotel sometime back in the 70's, I think it was.  There were two or three levels of walkways suspended over a large common area in the centre of the building.  On a New Year's Eve, the walkways were loaded up with lots of people.  Tragically, one of the connections between the threaded rod style support from the ceiling to the walkway failed, plunging many people to their deaths.

 

The accident investigation revealed that the original design specified a single piece support rod from the ceiling to the lowest walkway.  What the contractor built were individual support rods between the highest walkway and the ceiling, then another support rod to the next level walkway and so on.  This allowed the walkway to fail in shear between the two support rods on the highest walkway instead of the load being transmitted directly to the support rod on each walkway.  Had things been built as specified, that accident probably would not have happened.

 

The lesson here is that a single rod (properly sized for the total load) through all of the shelves to the ceiling is the better solution.  Granted, we are talking about shelving here, not walkways that need to support people safely.

[formariz 11,987]

7 hours ago, ebinmaine said:

How do you attach at the ends? 

One easy way is as per photo below. Just to illustrate the types of fasteners not having the correct sized ones at hand. One half illustrated the left end of rod having a turnbuckle preferably a long one. U bolt should be long enough to allow unobstructed tightening of turnbuckle. Mount u bolt with legs across shelf grain and not along it using nuts and washers on both sides. In this system shelf should be loosely resting on end supports so it does not restrict flexing. I usually only screw it loose on predrilled oversized holes just so shelf cannot be brought forward accidentally.