A scaffold is a temporary structure that facilitates the work at heights in the fields of building construction, industry, stage spectacles, exhibition stands, among others.
There are 3 types of scaffolding systems that are used in any sort of industrial and building construction process.
Types of scaffolding?
FREE-STANDING TOWER SCAFFOLDING
An independent scaffold has a scaffolding height to base ratio of less than 4:1. This is based on OSHA scaffolding requirements.
The image stands for an independent 4m scaffold tower with a working platform of 2m x 1.4m.
To calculate the minimum required dimensions of the scaffolding base, we just need to divide 4m to 4. Therefore, the platform size of 2.07m x 1.4m complies the criteria ratio of 4:1.
No restraint against tipping such as, bracing, tying, guying in the structure is required.
INDEPENDENT-MODIFIED TOWERS WITH STABILISERS
When the requirement of the scaffolding height to base ratio is not satisfied, stabilisers are required.
Stabilisers are used to increase the frame width of the base. The image illustrates an 8m scaffold tower with a working platform area of 2m x 1.4m.
This tower has stabilisers composed of diagonal or scaffolding cross braces, ledgers, base collars and castors or caster wheels. This helps reduce the height to base ratio to 4:1 or even less.
The ratio must be equal or less than 4:1, which means that the minimum required bay length for the structure stability should be equal or higher than 2m (8/4) each side. Therefore, the current depth of the tower must be increased from 1.4 m to 2m.
Bridge scaffolding has to be well designed and installed, due to the complexity and associated-risks that may emerge during the stages of the assembly process.
OSHA, in the paragraph 1926.452(c), claims that a registered professional engineer should perform special designs.
For instance, the design of brackets that enables the support of cantilevered loads and access to construction workers.
It is a temporary structure that consists of many sections or bays, that stand together along a building façade with multiple purposes.
For example: maintenance (rehabilitation of building), construction (bricklaying, installment of thermal insulation on facades), etc.
Generally, these scaffolds are not free-standing towers because of the significant height compared to the reduced base depth. Therefore, they need to be restrained from tipping by the use of anchoring means.
This type of scaffolding is used to minimize the quantity of required material (considerable huge work height), and also when the surface conditions of the terrain do not permit a safe standing of the scaffolding system.
Mobile towers or scaffolds
They have the advantage of being able to be used, moved and relocated from place to place over a safe surface. This must bring the proper and safe conditions to move the temporary structure in site.
The typ of scaffolding should not be placed or moved while workers are on it due to mobile scaffolding safety requirements.
OSHA establishes, in the paragragh §1926.452(w), that the mobil scaffolding system can be moved only under specific guidelines and instructions from registered professional engineers.