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October 2007

The Magic of Hoists

By | Hoists, Resources, Scaffolding | No Comments

What connection do hoists have with scaffolding?  Can they be classified as scaffolds?  Hoists, after all, support workers and materials, as the scaffold definition specifies.  Typically, they are temporary, thus qualifying for another portion of the scaffold definition.  The hoist car has a supporting structure, thus qualifying with still another portion of the scaffold definition.  But are they really scaffolds?  The short answer is no.  The longer answer is still no. No matter how long you make the answer, the answer is still no.  A hoist transports workers and materials.  (View a hoist as a pick-up truck that drives vertically up and down the building and you’ll understand why hoists are not scaffolds.)

Hoists, just as scaffolding, are critical pieces of equipment on the modern jobsite.  Without them, it would be near impossible to economically construct a multi-story building.  The adjacent photo dramatically illustrates the importance of hoists on a jobsite in New York City.  Universal Builders Supply, who supplied the hoists for this project, did a fantastic job of demonstrating the versatility and importance of these machines.  Sure there is a crane on the job; but it can do only so much in a day.  And besides, cranes cannot easily transport workers.

Generally hoists can be cable supported or mast supported.  They can transport materials only or workers and materials.  They can be designed to be supported by a scaffold, they can be designed to be free standing, and they can be designed to be supported by the adjacent structure.  They can be single or multiple platforms or cars, and they are designed for a broad range of capacities.  They can be assembled by hand (if they aren’t very large), and they can be so large that a crane may be needed to erect them.  Without question, hoists are the workhorse of the project.

A mast supported hoist is an engineering marvel, similar to tower cranes and mast climbing scaffolds.  The mast supports the track or guideway for the hoist car and transfers the weight of the car and payload down to the base.  Obviously the base must support the load; reshoring for the base may be required.  If designed for it, a mast can be free standing for a certain height; otherwise, the mast is supported, or tied, to an adjacent structure to keep it from falling over.  These ties are structural ties, that is, the ties are a very critical part of the construction and must be designed and installed very carefully.  While the tie does not transfer any vertical loads to the adjacent structure, it does supply the lateral or sideway stability so the car load will be transferred through the mast.  The frequency of the ties is dependent on the design of the mast.  More frequent ties may result in a lighter mast.  Conversely, fewer ties means the mast must be more rigid and therefore more robust (you can’t get something for nothing!).  As with scaffolds, bracing is the key to the design and operation of a hoist.  Interior bracing in the mast provides the stiffness and components to keep the mast from bending too much while also providing the means to transfer loads down through the mast.

The next time you take a ride on a hoist think about what’s happening.  Transporting workers and goods vertically up the building is just as important as getting those workers and goods to the jobsite.  In fact, it can be much more difficult, once you think about it.  You can always take a side street to get to the job.  Climbing 50 flights of stairs however doesn’t sound like a very appealing alternative to taking a ride.