Formwork is used to hold the concrete in any structural element before hard it. The weight of the wet concrete is higher than the dry concrete. Therefore the formwork should be strong enough to carry the load of the wet concrete. So also formwork should be free of voids and concrete or grout should not be going out from the formwork. So also it should be straight enough to maintain the shape of the structural element and can be withstand against the vibration of the equipment used. Therefore the form work is very important in the concreting works.
Formwork of Slabs and Beams
18mm plywood sheets were used as the material of the formwork and table formwork system is used in the construction of the building. In the construction of the slab and beam formwork, it is need to give a proper attention to the levels, shape and the alignment of the particular structural element. Due to the importance of the levels of slab and beams, it is need to check the level at the initial state of erecting the formwork and before the concreting is done. Because. The initial levels can change due the reinforcement loads and the movement of the formwork or jack system. Otherwise the level of the slab can change after the cast it.So also, thestop boards at drops should be well positioned and fixed correctly before the concreting. Diesel should be applied inside of the formwork which is touched the concrete surface to easy removal of formwork.
Fixing the formwork for slab (left) and support of the slab formwork (right)
Formwork of Columns and Walls
“Doka” formwork is used as the formwork of the rectangular columns and walls of the building and steel formwork is used as the formwork in the circular columns of the building. Before fixing the columns and walls formwork reinforcement need to be well positioned and cleaned. If steel are corroded it is need to wire brushed those bars. To have a proper construction joint the slab or kicker should be hacked out and need to remove the grout from the top surface of the concrete. Then all the grout and rust should be removed thoroughly using the vacuum and water in order to provide a proper bond with concrete. After getting approval for the reinforcement and hacking of the concrete take the formwork panels cover the reinforcement to provide the formwork for the column or wall. Then using the jacks and thread bars the formwork were properly fixed. Then using the plumbs formwork makes vertical inboth four direction. In this case it is need to have two plumbs for a direction. In the verticality inspection each and every column and wall were checked before concreting for verticality. So also need to check the size and the positioning of the formwork. To do that they used the marking that marked by the survey team. In the circular columns contractor used steel formwork and due that the shape of the column is not change as normal formwork.
Formwork of the rectangular column, circular column and RC wall
Formwork of Lift Core
Lift core construction of the project are in two floor upper than the slab. Due to that the form work cannot have a support from the constructed slab as in the RC walls. Therefore they used a special system for the lift core formwork. In this case “Doka” formwork is fixed to the below lift core walls using nuts and bolts and special supporting system.
Lift core formwork and its supporting system
“Doka” Formwork System
Due to the high load bearing capacity the Doka formwork is used in high rise buildings. So also, Doka climbing system provides opportunity of casting walls up to any height safely and more efficiently. Therefore using the Doka formwork gave more advantages than other conventional formwork methods. Those are,
- Reduces labor costs for formwork positioning and retraction.
- Reduces crane time as entire unit repositions quickly.
- Offers speedy, precision adjustment of the form work in all directions.
- No need of scaffoldings to make the plat form for concreting of the structure
- Least damage to the plywood sheets whiles the removal of the form work.
- Easy to maintain the verticality than in the conventional form work.
- High efficiency in erection of form work than in conventional form wok.
- Offers complete safety in all phases of the operation.
- Wider plat forms increases the efficiency of work.
- Permit quick installation as platforms are preassembled.
- Finishing the concrete of RC walls or columns. the form work should kept for 24 hours to avoid shrinkage cracks on the walls or columns.
“Alumalite” Truss Table Form Work System
Table formwork system is used for slabs. It can be fixed at the site. But in the building they remove the table from below floor and lifted the full table to the upper floor using the cranes. The table formwork reduces the formwork fixing time. Due that efficiency, the floor to floor completion cycle is 10-14 days.
Table formwork system
Table formwork cannot use in the places with little space. In those places scaffoldings and GI pipes are used as the formwork support. Plywood is used for the side boards of the formwork and timber and GI pipes used to provide supports at those places. So also side boards are fixed using the threaded bars. Pre-cone and PVC pipes used as the cover of the threaded bars.
Table formwork detailed diagram
Removal of the Formwork
According to the specifications, minimum removal time of the formwork is shown in the below.
Slab (need to provide props) - 4 days
Beam sides, walls & columns (unloaded) - 24 hours
Beam soffits (need to provide props) - 7 days
Props to slabs between beams - 14 days
Props to beams and flat slabs - 14 days
Props to cantilever - 28 daysSlab formwork is removed in 4 days after concreting and provides props to the slab. To do that it is need to check the strength of the concrete before remove the formwork. Therefore in this building test cubes are test after 3 days of concrete. After removing the formwork of specific area they used it as the upper floor formwork. The consultant need to check the props and give the approval before the concreting of the upper floor slab and beam.