Scaffold Legs Under Duress

By David H. Glabe, P.E. / February 28, 2013

An Introduction to Panel Points and Why They are Important

After reviewing many user manuals for scaffold, it is clear that scaffold manufacturers understand the strong and weak locations of each of their respective systems.  However, I have not seen any scaffold user or technical manual attempt to explain to their users why they always show scaffold tie placements at the intersection of horizontal and vertical diagonal members (typical for system scaffold).  In this brief article, I’ll attempt to demonstrate some reasoning behind tie location placement.  We will be introducing the concept of “panel points” and their importance in scaffold construction.

The typical definition of a panel point is “the point of intersection where a web (or webs) meets a chord”.

Okay, that probably doesn’t help you much.  See Figures 1 & 2 for a better graphical representation of what we’re talking about here (note the deflected shape of the scaffold for effect).  As the above definition is generally used for structural trusses, a better way to define panel points for scaffolding would be as follows: “the intersection where horizontal bearers, runners, or vertical diagonals meet a vertical leg”.

Now that you know what a panel point is, let’s dig into why it is important.  The magic (physics) of a panel point is straightforward.  If a load is applied directly to the panel point, the supporting members are loaded primarily in tension or compression with little or no member bending forces.  Members have larger capacities when they are only required to transfer tension/compression forces compared to bending and tension/compression forces.

As a simple illustrative example, pretend you are a scaffold leg.  Now pretend you need to hold Dave Glabe’s prized “D. Victor Saleeby Bronze Eagle Award” over your head, say 150 lbs (Dave feeds his award three solid meals a day and it has reached an impressive girth).  In this instance, you would be a compressive member transferring weight of the bronze Eagle through your body and into the ground.  If you wanted to mimic a combination compression and bending member, have someone tie a rope around your waist and pull on you.  Not so easy to hold that 150 lbs. eagle over your head now, is it?  With this image in your head, you are now one with the scaffold leg and a step closer to scaffold enlightenment!

So remember, panel points keep scaffold members in tension/compression, not bending plus tension/compression.  Therefore, slapping a significant load bearing tie in the middle of a 10 foot scaffold tube would probably not be the best idea!  Attaching or directing a load to a panel point is better than attaching or directing a load at any other spot.  Of course, we are talking aboutscaffold in general terms and there are always exceptions.  Don’t think this article gives you the knowledge to do anything in violation of the OSHA standards or the manufacturer’s recommendations.  When in doubt, always consult with a Qualified Person.





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