Formwork is the system to support the plastic state concrete and to cast and keep in desired shape till it attains sufficient strength to support its own weight.
Sometimes, formwork is not removed in some of the new technologies, known as stay in place formwork or lost in place formwork.
Formwork Definition As Per IS 14687
Formwork is defined as
“the total system of support for freshly placed concrete including the mould or sheathing which contacts the concrete as well as supporting members, hardware and necessary bracing, etc.”
Thus, formwork is used as a temporary mould into which concrete is poured and formed.
It is a vertical or horizontal arrangement made to keep concrete in position until it gains strength & desired shape. Also, formwork is a system consisting of props, staging and shuttering items.
IS:14687 – Guidelines for falsework for concrete structures
Functional requirements of formwork
1. Erection and release:
Formwork must be so designed and constructed that they can be removed in parts or as planned in the desired sequence without damaging the surface of concrete or disturbing other sections or causing collapse of the formwork systems.
The connections joining various components of the formwork should be capable of being easily removed while formwork stripping.
2. Ease of inspection:
Once your formwork is ready, next step is to inspect it. Normally once formwork is ready site supervisor call site engineer to do the inspection of formwork.
Therefore, the formwork system should have adequate and safe access to all areas for easy inspection.
3. Shape and size:
The formwork shall be erected such that the shape and dimensions of the concrete structures are conforming to the drawings, the specifications and tolerances.
Chamfers, beveled edges if specified, should be provided in the forms.
For example if you are planning to construct a curved wall, then you need to use a shuttering material that can be bent to required curvature.
4. Finish:
The formwork should be hard enough so as to not to get damaged due to operations of reinforcement fixing, pouring and vibrating of concrete and removal of forms.
Also sheathing materials used in formwork must be able to give required finish to concrete structure.
5. Reuse and number of repetitions:
The formwork must be designed and planned to permit maximum reuses/repetitions to reduce the cost of concrete and the work.
If Plywood is used as sheathing/shuttering material, then it should be used properly so as to give higher repetitions.
Also Read: How to increase repetition of shuttering plywood
Summary
Thus, the essential requirements of formwork are:
- It should be strong enough to take the dead loads, live loads, incidental loads and other loads expected during construction before attaining the strength by the concrete.
- The joints in the formwork should be rigid so that the bulging, twisting, or sagging due to loadings is within permissible limits.
- The construction lines in the formwork should be true and the surface plane so that the cost finishing the surface of concrete on removing the shuttering is the least.
- The formwork should be easily removable without damage to itself or the concrete.
- It should provide ease of inspection.