formwork

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FORMWORK

Introduction

Formwork is a mould or box into which wet concrete can be poured and compacted so that it will flow and finally set to the inner profile of the box or mould.

It is a classic temporary structure in a sense

that:

a) It can be erected quickly

b) Highly loaded for a few hours during the concrete placement

c) And within a few days it is disassembled for future use

Forms mold the concrete to desired size and shape and control its position and alignment

Formworks also act as a temporary structure that support:

a) it’s own weight +

b) The freshly placed concrete

c) Construction live loads (material ,

human, logistic)

Function

Good formwork would have the following

characteristics that is:a) Safe

b) Cost effective or economical

c) High Quality – finished concrete surface is of acceptable quality - in the correct location - able to produce the required shape and surface

Formwork Design

Loads include in design process are as follows

a) Fresh concrete

b) Rebar

c) Formwork material

d) Wind and lateral loads

e) Live loads due to – Formwork construction

- Reinforcing installation

- Concrete placement

Material for Formwork Construction

Among the material that can be used for

construction of formwork:

a) Timber

b) Steel

c) Glass Reinforced Plastic

d) Plastic

e) Aluminium

TIMBER FORMWORK

Timber Formwork:After Concrete Was

Poured

Timber Formwork : For The Slab

Advantages

Among the advantages of this most traditional \

formwork are :

a) Easy handling because it’s light weight

b) Easy to disassemble

c) Damaged parts can be replaced with new one

d) Very flexible

e) Easy to produce

f) Easily available

Disadvantages

Among the disadvantages are :

a) Can’t be used for long. Have limited re-use.

b) If timber is dry, it will absorb moisture from wet concrete which could weaken the resultant concrete member.

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

a) High amount of waste

b) Require high quality labor force and adequate supervision

c) Time consuming when prepared for larger structure

d) Limited spans

STEEL FORMWORK

Advantages

Among the advantages of steel formwork are :

a) Very strong and able to carry heavy load

b) Easy to be fixed

c) Uniform size and surface

d) Can be used for a very long time

e) Span longer than timber

f) More durable than timber formwork

Disadvantages

Among disadvantages of steel formwork are :

a) More expensive than wood

FIBERGLASS REINFORCED PLASTIC FORMWORK

It is used in components due to its a) moldabilityb) light weightc) Strength d) Toughnesse) Reusable

The disadvantages is, this type of formwork is more expensive than timber formwork.

PLASTIC FORMWORK

Among the advantages are:a) Lightweightb) Reusable c) Chemical resistant d) Fungus and termites resistante) Can be easily cut and nail by using wood

working toolsf) Non degradableg) Working with plastic formworks does not

require the use of electric power.

Plastic Formwork

FORMWORK FAILURE

Formwork failures are the cause of many accidents and failures that occur during concrete construction which usually happen when fresh concrete is placed

Generally some unexpected event causes one member to fail, then others become overloaded or misaligned and the entire formwork structure collapses

Causes

Improper stripping and shore removalInadequate bracingVibrationUnstable soil under mudsills, shoring not

plumbInadequate control of concrete placementLack of attention to formwork details

Inadequate bracing

More frequent causes of formwork failureInadequate cross bracing and horizontal

bracing of shores is one of the factors most frequently involved in formwork accidents.

Vibration

Forms sometime collapse when their shores/ jack are displaced by the vibration caused by:

passing traffic movement of workers & equipment on the

formwork the effect of vibrating concrete to consolidate

it

SAFETY PRECAUTION

Among the precautions that can be taken to

ensure formwork function as it suppose to be

are as follow: Material used for the construction of

formwork must fulfill the specification. Formwork is fixed firmly & 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.

Permanent Formwork

It’s a part of the permanent structure of the building.

It is a structural element that is used to contain the placed concrete, mould it to the required dimensions and remain in place for the life of the structure.

Permanent Formwork

Advantages

Among the advantages are:

a) Reducing the skill level needed on site.

b) Increase the potential for standardization and repetition.

c) Permitting off-site fabrication in factory conditions followed by scheduled and appropriate deliveries.

d) reduces construction waste

d) Speeding up erection times, particularly in building works. Save time

e) Eliminating the need to strike formwork and falsework.

f) Allowing early access for following or concurrent operations.

g) Eliminating the programme limitations of reuse of formwork.

h) reduce construction and maintenance costs

i) improve safety by reducing hazards during construction.

Plan your affairs and take proper precaution