Scaffolding’s “Dirty Little Secret” – Part 2
In Part 1 of this series, I suggested that we have a “Heavy Duty” problem with the lack of proper Load Calculations on North American scaffolds. It appears that I was not alone in this observation, and thanks to everyone for your overwhelming encouragement and feedback!
As the saying goes, we can be either “part of the problem or part of the solution”. And the time has come to shine a light on scaffold load calculations and what to do about them!
If you are wondering about your own site’s scaffolds and whether they are competently rated and tagged – the following definitions will help you dig deeper into your scaffold situation and find some solutions:
What is a Scaffold Load Rating?
A scaffold load rating is a simple weight rating that gets communicated to the Scaffold USER. Typically expressed on the scaffold tag, it can be given as a duty rating such as “Medium Duty” or 50 PSF or as a simple number such as 1,000 lbs. It is a number that the scaffold users must be trained to evaluate, interpret and, most importantly, to understand that it cannot be exceeded. This rating is almost always given as a “Uniformly Distributed Load” – meaning that the weight must be distributed throughout the platform area and not a “Point Load” – where the weight is focused on only one location on the platform.
What is a Scaffold Load Calculation?
The scaffold load calculation is a multi stage process of evaluating the ENTIRE SCAFFOLD STRUCTURE to determine the scaffold load rating based on factors of safety. Our teaching method is to address the scaffold as a “chain” of components – and as the cliché goes…“a chain is only as strong as it’s weakest link”. Therefore, the weakest scaffold component will determine the ultimate scaffold load rating.
What are the “links of the chain” for Scaffold Load Calculations?
For the purposes of a SUPPORTED scaffold load calculation, the main component groups are: Foundation, Standards (Posts), Ledgers (Bearers), and Platforms. The foundation, for example, could be the weakest link if the scaffold was erected on an engineered surface such as a rooftop. The ledgers, on the other hand, could be the weakest link if they are in long spans or they are bearing multiple platform loads.
For a SUSPENDED scaffold load calculation, the primary component groups are: the Suspension System, the Cables, the Hoisting Equipment and the Platform. In this case, the suspension system could be the weakest link based on counterweight calculations or rooftop strength or conversely, the platform could be the weakest link based on its size or construction.
In both cases, a trained and competent person must be able to perform separate calculations on each component group to determine the “weakest link” and therefore the scaffold load rating.
By far, the majority of most “everyday” scaffold load calculations can be performed by a properly trained scaffold erector and/or competent person. (Be careful, however, you’ll be surprised to find out that not many scaffold training programs cover scaffold load calculations!)
However, there are a large number of conditions in which additional investigation and verification may be required – typically by a professional engineer. In Part 3 of this series we will detail some of the conditions in which scaffold engineering may be required and what “scaffold engineering” should look like.
