The suspension rope supporting a temporary platform is the single most important element of a suspended scaffold. You may not agree with this—too bad for you. What if the rope breaks? The platform can only go down and if you are at a considerable height, the result will be mostly unpleasant. Understanding this suggests that we should probably be sensitive to the condition of the rope to which we trust our lives.
What is a rope? A typical definition describes a rope as a cord that consists of twisted strands of material, such as hemp or wire. Of course, that begs the question of what cords and strands are. For that matter what is hemp? Can you smoke it? Perhaps not. How about this: a rope is a bunch of string or thread twisted together to make a bundle that can hold some weight. In the case of suspended scaffolds, the strings are normally wire although other materials such as hemp and polypropylene can be used, depending on the application.
Rope has been around just about forever. Evidence of rope’s use shows up in ancient Asia and Egypt. Wire ropes were invented about 1831 or so by Wilhelm Albert, a German involved with mining. He sought a solution to the very real problem of using chains where the failure of one link meant the failure of the whole chain. By twisting individual wires/strings into small bundles (strands) and then twisting the strands into a rope, (a big bundle), any defects are spread over more components, thus avoiding the problem of the weak link.
The industrial revolution encouraged rapid development of wire rope technology and the use of wire rope continued to increase. In 1841, John A. Roebling, designer and constructor of the Brooklyn Bridge, began manufacturing wire rope in America. Continued research and development discovered that more wires in the rope offered more flexibility and in 1884, researcher Tom Seale developed the parallel strand, where he used different diameter strands to make the rope. Figure 1 illustrates the Seale design.
While iron wire was initially used for metal ropes, steel wire began to be used in the late 1800’s. In fact, steel wire rope was first used in the construction of the Brooklyn Bridge in New York; the main ropes are still in use, demonstrating the durability and longevity of wire ropes. Over time, other wire rope designs have appeared, including the Filler strand, the Warrington strand and the Lang lay rope. Each design has its advantages and the job requirements will dictate the choice.
Wire rope is strong stuff, especially considering its relative light weight. Wire rope load capacity is governed by the rope material, configuration and diameter. While wire rope is available in an almost infinite number of diameters, normal diameters for suspended scaffolds are 5/16 or 3/8 inches. By its nature, rope can only handle tensile loads (you can’t push a rope!). However, the great advantage of a rope is that it can still handle the rated load whether the rope is 5 feet or 500 feet long. Within limits, that means the rope can hang down a 300-foot tall building and still support the same load as the rope will on a 50-foot tall building.
Adjustable suspended scaffolds typically use drum hoists or traction hoists. Drum hoists wind the wire rope on a drum or spool attached to the scaffold platform while a traction hoist passes the rope through the machine. Consequently, a drum hoist and rigging must support the weight of the wire rope while a traction hoist does not.
As with all materials, wire rope, while rather durable, can be damaged by improper handling and use and can also just wear out through continued use. Consequently, suspended scaffold erectors, and users, must be adequately trained in the potential hazards. For example, erectors must know how to handle the wire rope, including how to pay out the rope and how to wind it back up at the end of the job. The rope must be installed so the bottom end of the rope can hang free.
The attachment of the rope to its anchor is obviously critical to the strength of the suspension system. At a minimum, when loops in a rope are being made, a thimble and three fist grips (no u-bolts please) must be used, spaced at the manufacturer’s recommendations. The bolts must be tightened in compliance with the manufacturer’s recommendations; they must be re-tightened after the first loading of the suspension system, and then typically every day after that. The entire scaffold system including the suspension rope, must be inspected prior to each workshift. Properly trained suspended scaffold operators will know to inspect the suspension wire ropes every time the platform is raised or lowered to ensure that the rope is still in useable condition. It is rather undesirable to get the rope stuck in the traction hoist when 100 feet in the air. Even less desirable is having the suspension rope break when 100 feet in the air!
Suspended scaffolds get some impressive media coverage when failures occur since the incident leaves workers dangling high above the street below. Reporters nervously describe the precarious (and assume a dangerous) situation, leading the uninformed observer to believe that these devices are incredibly unsafe and a peril to the users. Since wire ropes on properly designed scaffolds can support six times the expected load, when the scaffold fails, it isn’t because the equipment is hazardous, but rather it is because somebody just plain screwed up. Don’t you be one of them!
