4 basic concepts when forming columns or pillars
Before talking about column formwork, we first need to understand what it means meaning.
Columns or pillars are vertical elements that support compressive and bending forces, transmitting all the loads of the structure to the foundation. They are one of the most important elements for the support of a structure and therefore, their execution requires special attention.
In columns, the reinforcing steel is formed by longitudinal bars to resist flexural tension, and brackets to prevent buckling of the element.
You probably know that there are many types of columns or pillars depending on their construction type (metal pillars, prefabricated pillars, on site pillars, etc). In this article we are going to talk about cast-on-site columns.
Let’s see the 4 most important questions about pillar formwork!
1.- What type of pillars are there?
In construction, and especially in building, there are several types of columns or pillars which can be classified according to their cross-section.
- Circular pillar: It has a circular cross-section, with diameter variation according to the design and solicitations, its use is mainly in areas where a visible finish is sought, they are not usually cladded (halls of buildings, airports, shopping centers, etc.)
- Square/rectangular pillar: It is the most used cross-section, due to the simplicity of design and execution. We can find them in all types of constructions, uncladded, cladded, with cross-section changes and even combined, straight sides, with circular sides.
- Moduled pillars: Very similar to square or rectangular pillars. The main difference is that they have a long side that is usually much larger than the short one, practically like a wall. Their use is often linked to structural stresses, stiffening structures against horizontal stresses such as wind, earthquakes, etc.
2.- What types of formwork can be used?
The origins of column formwork go back to the Roman Empire, in the 1st century, when they began to use Opus caementicium or Roman concrete in their constructions, which required a mold for its containment.
The term column or pillar formwork, refers to the mold formed by a set of metal, wood or plastic panels, which are used to contain the concrete until it sets or hardens, shaping the columns.
What types of column formwork exist?
There are basically 3 types of column formwork:
1.- Wood formwork:
This is the oldest and most ‘traditional’ type of formwork. In this case the formwork consists of 4 pieces of wood cut to size, surrounded by a number ofwood (or metal) bars, cross braces or clamps the function of which is to withstand the pressure of the concrete. It is cost-effective formwork, but with lower productivity compared to the other types.
2.- Industrial formwork:
This is a type of formwork formed by panels designed to be reused to withstand certain stresses, to achieve certain on-site productivity objectives and a uniform quality finish. The assembly and disassembly processes are usually geared to achieving the above-mentioned objectives.
In the case of circular pillars, there are more options:
1.- Cardboard formwork: it is the most used formwork when there are few pillars to be built. In fact, this type of formwork allows only one (1) concreting, as it is not reusable. Occasionally, it can leave the ‘spiral’ shape of the cardboard in its finish.
2.- Fiberglass formwork: This type of formwork has the advantage of combining reusability and portability, and leaves an excellent quality finish.
3.- Metal formwork: it offers the advantage of having a very long service life, it is reusable, but it is not usually portable (it needs to be used with a crane).
3.- When should a column formwork be stripped?
Stripping consists of the removal of the formwork that has contained the cast concrete throughout the curing phase.
According to regulations, the decision on the formwork stripping time is up to the project manager: however, this operation must never take place before the concrete strength has reached the required value, in relation to the use of the structure when stripping the formwork.
In the absence of specific concrete strength tests and under normal execution and environmental curing conditions, columns are usually stripped between 24h and 72h after casting or concreting.
4.- How can I obtain the best performance?
In order to obtain a good performance in the execution of pillars, you need to supply the adequate amount of formwork equipment, defining the appropriate formwork depending on the execution schedule.
For this purpose, you should undertake a detailed study of the entire construction process, taking into account the equipment, the necessary means, the cost of assembly and disassembly times, and the curing periods.
Conclusions
The execution of pillars is perhaps the “easiest” part of the execution of a concrete structure. However, it is important to choose the most suitable type of formwork, depending on the production rates and available manpower, in order to avoid performance problems or cost overruns during execution.
