Formwork in construction use support structures and moulds to create structures out of concrete which is poured into the mould. Formwork can be made using moulds out of steel, wood, aluminium and prefabricated forms. The construction of formwork takes time and involves expenditure up to 20-25% of the cost of the structure or even more.
Various components of Formwork are:
Heavy-duty towers (HDT), walers, U-heads, H-beams, plywoods, splice for connecting walers, Tower Spindle, Footplate, Flange claw assembly, climbing cone, head adapter assembly.
The type of formwork used in Hydropower Project Project sites is already pre-manufactured by the company in Chennai. The formwork used in Hydropower Project sites has a specified dimension of walers, heavy-duty towers, H-beams, etc.
Main Types Of formwork system:
- Formwork arrangement for walls and columns
- Formwork arrangement for flat slabs
- Formwork arrangement for beams
- Heavy-duty tower system
- Stair tower system
Formwork Arrangement for walls and Columns:
For both walls and columns, plywood sheathing is supported by H-beams, backed by steel walers. This assembly facilitates fixing working platforms for access, checking of reinforcement, concreting, etc.
The entire panel, along with the platform and alignment system can be shifted using cranes as a single unit. Panels are created in workshops at the site and the assembly of components is reduced, enhancing the accuracy throughout. Since the entire unit is handled as a whole, the loss of smaller components is reduced and contributes to material productivity.
Formwork arrangement for flat slabs:
- The formwork arrangement provides flexible spacing and arrangement options.
- Simplicity in shuttering and de-shuttering results in high labor productivity.
- The formwork arrangement guarantees a clean, accurate, and smooth concrete finish.
- Suitable re-propping increases material productivity.
Salient features of H-beams
- The beams used in any Project site’s formwork system reduce timber consumption to a significant level.
- The simplicity of not only H-beams but the whole system contributes to minimizing the labor.
- The H-beams are dimensionally stable, uniform in size, and consistent in strength.
- The H-beams used are much more economical and long-lasting.
Heavy duty tower system
The Heavy-duty tower system is widely used as staging for heavy floors at higher altitudes and also serves as scaffolds o certain occasions. Heavy-duty frames are braced using standard bracing, forming the heavy-duty tower system. Couplers and pins connect frames together, ensuring verticality. Spindles provided at the bottom can be used to adjust height and level. At every 6m interval, the towers are braced with permanent structures that prevent the tower from twisting under abnormal loading conditions.
Heavy Duty tower System used in the Bridge construction in Powerhouse
Tunnel Formwork System:
In the concrete lining of the tunnel, a CIFA gantry has been used in providing the shuttering to the tunnel. It consists of a movable Gantry and the Shuttering for the Lining of the Tunnel. The gantry used in this project is 2.5 crores
The gantry operates inside the whole formwork system. It consists of 2 main parts that are inverted and overt. Overt further consists of 3 parts that are:
It also has jacks which are used to fold and unfold the shutter and place them and align them where the concreting is required.
Vibrators are also present in the gantry for proper compaction so that no air voids are left while concreting.
Gantry Shifts 4-shutters at a time of total length 6m on both the sides and the total length of the shutters is 24m. So, the Length of one shutter is 1.5m each.
Hydraulic cylinders Shrinks and the shutters also shrink Downwards at the time of De-shuttering and expand at the time of Shuttering.
The invert of the Formwork rests on the Stool post which is Tightened with the help of Impactor.
Deshuttering Of gantry:
Firstly the invert de shuttering starts in which the working platform is brought from the backside to the front side. The deshuttering work of the overt starts from the end toe which is lifted up by unlocking the hydraulic cylinder and fixing them with the traveler. Then the piers are folded and finally, the vault is closed and shifted to the front side for shuttering purpose
Disadvantage of Gantry:
The major disadvantage of Gantry is that it can be used only once. Once the work
is over then it can’t be used again at another site because It is designed for a
particular diameter of the tunnel.