How Well Are You Connected?

By David H. Glabe, P.E. / March 26, 2012

Connections play a big part in the proper erection of a scaffold. Knowing how connections work, which products to use, and their strengths are important for both erectors and users.

Being well-connected may suggest that you have a strong bond with another person or at least you may have influence over another person’s behavior and action. Unfortunately, this article is not about that type of connection-you’ll have to go somewhere else for advice on being personally well-connected. But what about your scaffold; is your scaffold well connected? And what kind of connections are we talking about?

There are all kinds of connections found in scaffolding. In engineering terms, there are shear connections, tension connections, compression connections, moment connections, and bearing connections. These connections can be provided by bolts, nails, screws, wire, welds, glue, adhesives, tape, bubble gum, string, wire rope, friction devices, u-bolts, swaged fittings, fist-grips, expansion anchors, coupling pins, retainer pins, studs, rivets and bungee cords. Well bubble gum might be a reach but the rest are legitimate; the choice of connection depends on the required strength of the connection and the application. For example, using string to attach a frame scaffold to a building will only provide a tension tie (it works only for pulling, not pushing) and the string probably does not have the required strength. On the other hand, you could weld the same scaffold to the structure but then the weld would have to be cut when the scaffold is dismantled-probably not a good choice for this application.

Myths are pervasive in the scaffold business and often include connections. Can wire, specifically # 9, 10 or 12 gauge wire be used for connections? Do we need high strength bolts for everything scaffold related? Can I use duct tape? Are friction connections bad? And can I hang a supported scaffold by its coupling pin? The easy answers, in order, are: Maybe, maybe, doubtful, no, and perhaps.

Let’s start by looking at the issue surrounding the use of wire. Wire is often used to provide a connection between a supported scaffold and a structure to provide stability so the scaffold doesn’t fall over. While the federal Occupational Safety & Health Administration, OSHA, specifies that supported scaffolds be tied to a structure at certain intervals, it does not specify the strength. Therefore, anything can be used, including wire, string and duct tape, provided it is sufficiently strong. On the other hand, California OSHA, (CalOSHA), allows the use of #10 or double wrapped #12 wire to connect the scaffold to the structure. This is an interesting concept since it assumes that these size wires are adequately strong regardless of the circumstances; this is a bad approach since wrapping the scaffold with enclosure material will probably overload the wire connection. In another common application, scaffolders frequently want to secure a scaffold leg to a coupling pin using #9 wire in place of a retainer pin. This could be a bad idea since the wire may not be able to handle the shear (karate chop) load.

Clamps/couplers are commonly used with supported scaffolds, providing a rigid or swivel connection between two tubes. The clamps primarily rely on friction to provide the connection and there are those (whoever those are) that say this is bad—you should never rely on friction for the connection. They (whoever “they” are) apparently don’t realize that they (same folks) rely on friction to walk, drive, stop, sit, or eat. In spite of the “friction myth,” scaffold clamps work because trained scaffold erectors understand that the clamp has to be properly tightened to ensure a proper connection.

And what about the myth of high strength bolts? I have no idea where this myth started but for some reason everyone (whoever “everyone” is) thinks that only high strength bolts can be used for scaffold connections. Sure, if a high strength bolt is used as a connection on an aerial lift, for example, then you better replace it with the correct high strength bolt. But, come on, regular everyday bolts work for many applications. If you want to use high strength bolts everywhere that’s fine with me; just don’t tell me it’s required.
And what about that coupling pin/connector that aligns one scaffold leg on top of another? Since its primary purpose is to provide alignment what strength is required? Well, it doesn’t have to be very strong unless you decide you want to hang your scaffold (as opposed to suspending a scaffold from a rope). Now the coupling pin must have sufficient strength to hold up the entire scaffold that’s hanging. Usually the coupling pin isn’t strong enough. And guess what– the bolts have to be strong enough too. May I suggest having a qualified person design that connection before you kill someone? By the way, don’t necessarily rely on the manufacturer; he/she may have no idea what to tell you.

As for those funny little connectors that secure a suspended scaffold wire rope to an anchor, its best to make sure that they are installed correctly. These connectors, whether u-bolts, fist grips, or swaged fittings, they all rely on friction. In this case, definitely follow the manufacturer’s recommendations for torque specifications since this is the key to safe use. And, don’t forget that the correct size and quantity of u-bolts or fist grips are required.

That brings us to the use of duct tape. Applicable standards and good engineering practice dictate that all connections must have adequate strength to support 4 times the anticipated load. If you can tell me the strength of duct tape in tension, I’ll be happy to design a suspended scaffold for your use. Will it be a single point or two point suspended scaffold platform that you want? Oh wait, I forgot that you want to go up and down with suspended scaffold. I think the hoist is going to be a tricky one to design! Perhaps we should stick (no pun intended) to something a little more conventional.

Tags: Scaffolding bolts connections erectors OSHA Resources scaffold users wire

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David H. Glabe, P.E.

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