Questions are frequently asked about the correct bracing of scaffolds. Scaffold users turn to the standards looking for the answer, only to be disappointed by the lack of information that could be used as “instructions.” The standards acknowledge the necessity and importance of bracing by requiring that “uprights shall be plumb and braced to prevent swaying and displacement.” Since there are so many different ways to properly brace each type of supported scaffold, it is impossible to dictate a simple solution that would apply in all cases. This is why there are no simple, specific bracing guidelines. The question remains: What is correct bracing of scaffolds?
To appreciate the importance of bracing, you must understand its purpose and use. Bracing, as it is used in scaffolding, provides strength and stability to supported scaffolds. Simply stated, bracing provides strength by controlling the “unbraced length” of the scaffold leg and bracing provides stability by ensuring the scaffold leg doesn’t fall over. Beyond that, though, the concept of bracing can get a little more complicated. So, let’s look at strength and stability and see how bracing affects each one.
Bracing defines, and controls, the unbraced length of the leg. The unbraced length is the vertical distance between points of support. These points of support do not allow the legs to move sideways. The points of support in supported scaffolds are the cross brace studs on frame scaffolds, node points with horizontals on systems scaffolds, and the horizontal members in tube and coupler scaffolds. The unbraced length is one of the factors that determine how much a scaffold leg can support. Other factors include the shape of the leg, the size of the leg, and the material that is used. In other words, a wood leg is not as strong as the same size steel leg, a 3 inch diameter leg is stronger than a 1 inch diameter leg, and a round leg is equally strong in all directions compared to a rectangular leg that is stronger in one direction than in the other direction.
Since scaffolding equipment is assembled or erected from items that are manufactured, we typically cannot change the material, the shape or the size. Therefore, the only thing that we can do is change the unbraced length. This can be good and bad. By increasing the number of horizontal members on a tube and coupler or systems scaffold, the amount of weight the scaffold leg can support increases significantly. On the other hand, removing horizontal members will definitely decrease the capacity of the scaffold leg. Remove too many, and your scaffold collapses. The same results occur with frame scaffolds. While it is somewhat difficult to increase the frequency of cross braces, it is very easy to remove cross braces. Remove the wrong cross brace and you have a scaffold that may not be able to hold any load because you just increased the unbraced length. It is interesting to note that at least one scaffold manufacturer has additional cross braces studs (connection points) that allow the erector to install additional cross braces. This increases the capacity of the frame by reducing the unbraced length.
Bracing is also required to provide stability for the scaffold. The stability is a result of connecting adjacent legs of a scaffold together in such a way that the legs form a larger base. The connection between the brace and the leg is a very important part of this bracing. On tube and coupler scaffolds, the connection is what we call a fixed connection, provided you use a rigid right angle clamp and not a swivel clamp! A systems scaffold’s connection varies, depending on the manufacturer. Some connections are more rigid than others are, although all of them have some degree of rigidity. The diagonal braces that are installed on the scaffold supply additional rigidity. In fact, it is the diagonal braces that transfer all the loads to the legs. Too often, tube and coupler, and systems scaffolds, are constructed without any additional diagonal braces. In this case, the erector is relying on the connection between the horizontal and the leg to supply all the bracing. This is not good since scaffolds are not designed to support or transfer these loads. The scaffold will stand as long as the load is minimal, and there are no horizontal forces on the scaffold. At some point, however, the connection will become overloaded, break, and the scaffold will fall over. This is definitely not good.
On frame scaffolds, the connection is what is called a pin connection. The brace can rotate on the pin but cannot move sideways. In this case, it is the connection between the diagonal members of the cross brace that makes the scaffold stable. Remove that center rivet or bolt from the cross brace and you have nothing. Use horizontal rails, such as guardrails, in place of a required cross brace, and you have nothing. The scaffold falls down.
Can other types of bracing be used to brace scaffolds? Yes there are. Bracing the scaffold to an adjacent structure that is properly braced is one common method. We typically call this type of brace a tie. If the scaffold is surrounded by a stiff structure, diagonal or cross bracing may not be required. In other instances, the plank may provide bracing. Horizontal braces, in conjunction with additional ties to the structure, can be used. The configuration of the scaffold may provide bracing.
As you can see, there are many opportunities to provide the correct bracing for scaffolds. Unfortunately, there are an equal number of opportunities to leave out important bracing. Keep in mind that frame scaffolds don’t necessarily require continuous bracing but they certainly require the right bracing. Tube and coupler scaffolds, and system scaffolds, may stand without diagonal bracing, but you just don’t know how long they’ll stand. Do you want to take that chance?
Next month, we’ll look at various examples of adequate bracing. In the meantime, if you don’t understand bracing, leave it up to the experts. After all, the standards are very specific in requiring that a qualified person shall design each and every scaffold.