Formwork-natesh-160118124049.pdf

FORMWORK/SHUTTERING

CMR COLLEGE OF ENGINEERING AND TECHNOLOGY

PRESENTATION BY: N.NATESH(12H51A0142)

CONTENTS • DEFINITION OF FORMWORK • REQUIREMENTS OF A GOOD FORMWORK • CA TEGORIES OF FORMWORK • TYPES OF FORMWORK • PROCESS OF FORMWORK CONSTRUCTION • DESHUTTERING • FA ILURE OF FORMWORK • SA FETY PRECAUTION

DEFINITION OF FORMWORK  Formwork is a mould or open box, like container into which fresh concrete is poured and compacted.

 When the concrete is set, the formwork is removed and a solid mass is produced in the shape of the inner face of the formwork.

 It should be capable of carrying all imposed dead and live loads apart from its own weight.

REQUIREMENTS OF A GOOD FORMWORK  Materials should be cheap and reusable.  Swelling and shrinkage should be minimum .  Surface should be smooth , and afford easy stripping.  Light in weight, so that easy to transfer.  It should be practically water proof, so that it should not absorb water from concrete.

 The material of formwork should not warp or get distorted

when

exposed to the elements.

 The joints in the formwork should be cement grout.



Deflection should be minimum.

tight against leakage of

CATEGORIES OF FORMWORK CONVENTIONAL: The formwork is built on site out of timber or moisture resistant particle board. It is easy to produce but time -consuming for larger structures, and the plywood facing has a relatively short lifespan. It is still used

extensively where the labour costs are lower than the costs for procuring reusable formwork .

MODERN-DAY FORMWORK : This formwork system are mostly

modular, which are designed for speed and efficiency. The main types of formwork systems in used now are

 Table form/flying formwork  System column formwork  Slip formwork  Tunnel formwork

SLIP FORMWORK

ENGINEERED/PRE-FABRICATED FORMWORK: This formwork is built out of prefabricated modules with a metal frame (usually steel

or aluminium) and covered on the application (concrete) side with material having the wanted surface structure (steel, aluminium, timber, etc.).

Major objectives considered in formwork  Quality  Safety  Economy

Quality: Forms must be designed and built with sufficient stiffness and accuracy so that the size, shape, position, and finish of the cast concrete are maintained . Safety:

Forms must be built sufficient strength and factor of safety so that they have the capable of all supporting loads. Economy: Forms must be built efficiently, minimizing time cost .

and

TYPES OF FORMWORK MATERIALS  TIMBER  STEEL

 PLASTIC  ALUMINIUM

TIMBER FORMWORK:  Most common material used for bracing the member, hence called as the traditional formwork.

 Can easily be cut to size on site.

ADVANTAGES OF TIMBER FORMWORK:  Easy handling because its light weight.  Easy to disassemble.

 Damaged parts can be replaced with new one.  It has good thermal insulation which makes it

useful to be used in colder regions.  Reduced site labour.

 Can be built to exceed 60 year design life.

DISADVANTAGES OF TIMBER FORMWORK:  Can’t be used for long, have limited reuse.  If timber is dry, it will absorb moisture from wet

concrete which could weaken the resultant concrete member.

 Timber with high moisture content (more than 20% moisture content), wet concrete will shrink & cup leading to open joints & leakage of grout.

STEEL FORMWORK:  Steel forms are stronger, durable and have longer life than timber formwork and their reuses are more in number.

 Steel forms can be installed

and dismantled with greater ease and speed.

ADVANTAGES OF STEEL FORMWORK:  Very strong and able to carry loads

 Easy to be fixed.

 Uniform size and surface.  Can be used for more number of times.

 More durable than timber formwork.  No shrinkage of formwork occurs.

DISADVANTAGES OF STEEL FORMWORK:  More expensive than wood.  Due to high weight handling is difficult.

 Excessive loss of heat.  Limited size and shape.

PLASTIC FORMWORK:

ADVANTAGES OF PLASTIC FORMWORK:  Light weight.  Reusable.  Chemical resistant.  Fungus and termites resistant.  Can be easily cut and nail by using wood working.  Damages on the formwork can be easily removed.  Very useful for complex shaped and special features.

DISADVANTAGES OF PLASTIC FORMWORK:  Expensive at first.  Load carrying capacity low.  Damage the plastic by the heat.

ALUMINIUM FORMWORK:  Aluminium is strong and light,

and consequently fewer,

supports and ties are required.

ADVANTAGES OF ALUMINIUM FORMWORK:  Monolithic crack free structures.

 Doesn’t require timber or plywood for construction activities.  Casting of walls and slabs possible simultaneously.  Doesn’t required skilled labour.

DISADVANTAGES OF ALUMINIUM FORMWORK:  Architectural changes are not possible on the structure.



Due to the tremendous speed of construction, working

capital finance needs to the planned in advance.

PROCESS OF FORMWORK CONSTRUCTION FORMWORK FOR VARIOUS STRUCTURAL MEMBERS

FORMWORK FOR WALL

It consists of -Timber sheeting -Vertical posts -Horizontal member

-Rackers -Stakes -Wedges

Wall formwork and its components

Wall formwork

FORMWORK FOR COLUMN

 It consists of -Side and end planks -Yoke -Nuts and bolts

 Two end and two side planks are joined by the yokes and bolts.

Erection sequence for a column: Prior to positioning column formwork check that steel for the column has been inspected and

cleared f

or casting.

-

Position formwork for the column from predetermined grids.

-

Plumb formwork both ways and securely support using adjustable steel props.

-

The propping angle should be 45° to the floor.

-

Ensure the steel props are safely secured to the column formwork and the floor, and that adjustment for pushing and pulling is operational.

-

Set out the positions of column clamps from a storey rod.

-

Transfer the column clamp positions from the storey rod onto column formwork.

-

Use nails to support the arms of column clamps while wedging.

-

Position and wedge the bottom, middle and top clamps sets.

-

Check the formwork at the top for square.

-

Position and wedge the remainder of the column clamps.

-

Using a plumb bob suspended from a gauge block plumb the column

 When all the column formwork is securely propped a final check must be ma de for plumb and column alignment before and immediately after the concrete has been poured and vibrated.

Formwork for staircase  Points to consider when designing staircase formwork: Stair formwork must support the weight of concrete.

Because of the slope of the stair, some of the force is transmitted to the sideways. All formwork must be well tied together to prevent sideway movement.

Erection sequence for a beam:  Marking out and setting height for formwork  Assemble and position props, adjustable head jacks, formworks,

bearers and spreaders.  Construct and erect sidewalls and beam soffit.  Position of sole plates.

DESHUTTERING 

“DESHUTTERING” means the process of removing the shuttering.

Order and method of removing formwork:  Shuttering forming vertical faces of walls, beams and columns should be removed first. Shuttering forming soffit to slab should be removed next.

 Shuttering forming soffit to beams or other heavy loaded members should be removed in the end.

Time of removal of formwork: Sl. No

Structural Member

OPC (Ordinary Portland Cement)

Rapid Hardening Cement

2-3 Days

2 Days

1

Beam sides, walls & Columns

2

Slab (Vertical Supports remains intact)

4 Days

3 Days

3

Slab (Complete Formwork removal)

10 Days

5 Days

4

Beams (Removal of Sheeting, Props remains intact)

8 Days

5 Days

5

Beams & Arches (Complete formwork removal) (up to 6 m span)

14 Days

5-8 Days

6

Beams & Arches (Complete formwork removal) (more than 6 m span)

21 Days

8-10 Days

Cost of formwork: For normal works formwork costs about 30 -40% of the concrete cost.

Failure of formwork



Generally some unexpected event causes one

member to fail, then others become overloaded or misaligned and the entire formwork structure collapses. 

Vibration.



Inadequate bracing.



Unstable soil under foundations.



Inadequate control of concrete placement.



Lack of attention of formwork details.



Inadequate cross bracing and horizontal bracing of shores.



Passing traffic.



Movement of workers and equipment on the formwork.

SAFETY PRECAUTION  Material used for the construction of formwork must fulfill the

specification.

 Formwork is fixed firmly and properly.  Construction area must be protected to prevent vandalism of formwork.  Warning sign must be put up at the area where the formwork is fixed to prevent entrance of people that may damage the formwork.  The formwork must be inspected before the concrete is poured.