What Is Form Work? | Types | Formwork Checklist | Removal Of The Formwork |

What Is Form Work? | Types | Formwork Checklist | Removal Of The Formwork |

WHAT IS FORMWORK?

Formwork is defined as a total system of support of fresh concrete to be placed it includes:

1)  Total frame/mould of various shape in which concrete remain in contact.

2)  Total system of supporting arrangement i.e. by frame, pipes, acro-span, trusses etc.

3)  Nuts, bolts tie rods, bracing including other supporting systems for satisfactory sustaining a load of concrete + live loads until the concrete attains the strength to withstand the same

 

What Are The Various Type Of Formwork Are Used In Construction?

CONVENTIONAL FORMWORK: Includes – formwork i.e. shuttering made up by steel plates and industrial plywood includes pipe support’s / wooden ball support.

DOCA FORMWORK: Specially designed formwork with simple methods for fixing in position and removing from the position. This tread name of formwork had proved confidence in various complicated structure for their satisfactory completion. This can be used for large slabs, big columns, deep beams, large size retaining walls, and hyperbolic cooling towers etc.

SLIP FORMWORK: In a structure where shapes are regular of having a uniform variation like shaft of the water tank, chimney, towers etc. and not having penetrations. This type of formwork can effectively used for rapid construction in this case formwork is design in such a way that it moves continuously ahead to receive the fresh concrete in such a way that when it leaves the concrete already placed should attain sufficient strength to withstand the load of concrete + live load, while concreting is done. In this case concreting is done continuously till the work is over for the shape

Example: The shaft of water tank for 15-20 Mtr. can be completed in 4 to 5 days.

 

JUMP FORM:  Where Shape / The geometry of the structure is not uniform and the height of the structure is more. Jump formwork can be used. For example about 100 to 110 m high and 90m to 55 m dia of cooling tower shell varying hyperbolically being constructed with the jump form at RAPP-5&6 site.

 

Site Engineer / Supervisor Must Give Attention To Following Areas While Checking The Formwork / Scaffolding.

 

PRE CONSTRUCTION REQUIREMENT:

a)   Alignment level position of formwork w.r.t permanent reinforcement.

b)  Type of finish requirement decides the type of formwork.

c)   Spacing of the support system Tightening of bolt, tie rods etc.

d)  Accuracy of dimensions.

e)  Gap in the successive shutters to avoid slurry leakage.

f)    Where penetration / EP’s are to be made, the supports are to be   re-ensured to maintain dimension, alignment and level of the same.

g)  Bracing and adequate support for projections/ cantilever must be checked.

h)  Wherever construction joints are to be left, the position of shear keys, and support arrangement to be ensured.

i)    Safety aspects to be taken care while checking the formwork the proper access to reach other portion of the formwork to ensure, a case needs attention during the concreting.

j)    Form fixing to be checked w.r.t removal of formwork point of view. It should be easily removable without damaging the final concrete.

ALSO READ: Know the Difference between Formwork, Shuttering, Centering, and Staging

 

REQUIREMENT DURING CONSTRUCTION

a)   A set of skilled carpenter to be ensured to attend the area immediately in case, support’s / forms gets displaced while concreting / vibration of concrete.

b)  Proper illumination in internal and external location of pours to be ensured.

c)  Application of surface retarder immediately before the concreting where green cutting is required.

 

POST CONSTRUCTION REQUIREMENT:

a)   In general the codal practice for removing the formwork to be strictly followed for removal of form.

b)  For special structures like dome of reactor and shell of Cooling Towers: -Specified procedure to be followed for removal of form.

c)   Specific care to be observed for safety during disturbing.

d)  Specific care to be observed while removing formwork at high structure should not damage the structure at floor.

ALSO READ: Removal of Concrete Formwork: Know the Correct Time | calculations | specification

 

Removal Of The Formwork At Various Constructions Need Attention As Summarized Below

Forms should not be removed until the concrete has achieved strength that is at least twice the stress to which the concrete may be subjected at the time of removal of formwork. However, under normal circumstances, where no significant variation in temperature is seen the following striking period should be followed:

Removal of forms and supports (As per IS456-2000)

Position of formwork	Min. period before striking formwork.
Vertical formwork to Columns, walls, beams.	16-24 hours
Soffit formwork to slabs (props left under after removal of formwork)	3 days
Soffit formwork of beams (props left under after removal of formwork)	7 days.
Props of slabs (spanning up to 4.5 m)	7 days.
Props to slabs (span over 4.5 m)	14 days.
Props to beams & arches (spanning up to 6)	14 days.
Props to beams & arches (spanning over 6m)	21 days.

 

a)   Striking should be done slowly to avoid damage to projections and without shocks or vibration.

b)  When forms are stripped, there should be no excessive deflection or distortion and no evidence of damage to the concrete due to removal of support.

c)   When forms are removed before the specified curing is completed, curing should be continued up to the specified time.

d) The concrete supporting forms and shores not be removed from beams, floors and walls until these structural units are strong enough to carry their own weight or any approved superimposed load. In no case should supporting forms and shores be removed from horizontal members before concrete strength has achieved this specific concrete strength.

e)  It is always recommended to remove forms for columns and piers before forms for beams and slabs

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