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Welcome you all, so today’s class we are going to discuss about concrete in construction and demolish and operation. So these 2 operations have a major hazard if you look at is primary falls. So in the last class itself in regard to falls we have discussed about scaffolds. Scaffolds, is where
workers tend to move and complete their work. So in general it is a referred as workers platform. So the other one is primarily the form work which we will see in today’s class. So as a result of some failures or the way in which form work is not putting place in
constructions they are lot of fall hazards they are lot of failures in constructions also.
(Refer Slide Time: 01:06)
So; now a quick an introduction to what is concrete? Everyone knows what is cement? And
when it is mixed with water generally we get something as a cement paste. And this actually
used as a glue or a binder in construction. And the cement plus fine aggregate so plus water
when it is mixed you call what is called mortar. And the mortar you know very well it is used for
brick masonry construction and again it serves as a binder.
Than cement plus fine aggregate plus what you call coarse aggregate and little of admixture
where ever it is required. So with all these combination you call what is called concrete. So this
concrete is what we are going to see in today’s class.
(Refer Slide Time: 02:02)
Now if you see general concerting operation involves 3 steps primarily but we also say 4 steps. I
will tell you what is the 3 and 4 step? So number 1 process is primarily called shuttering of form
work. And number 2 is primarily reinforcement and third one is placing or pouring concrete. So
these are the 3 steps when the concrete has attained the strength we primarily do de-shuttering
that is termed as a fourth operation, fourth step.
So these are the 3 processor, we have and we are going to talk more about shuttering only other
than these 2. This concrete related hazard we will discuss along with the health issues because
more health problems are related to concrete. And reinforcement we will discuss along with
hazards with caught in between or struck by or so on. So this we will discuss along with the
crane operations. So these 2 I am not touching upon today.
So what we are going to discuss is form work or shuttering. So what is a form work? Form work
is a temporary mould that acts as a support for the fresh concrete. Otherwise concrete is a flow
able material unless you give some support and proper shape than we would not get concrete into
desired shape. So form work in very simpler form it act like a support so that it get the desired
shape of the building.
So than now they are so many ways of concreting form work available these days it can be
partially fabricated or it can be completely fabricated. You also get manufactured commercial
products available these days. Or you can also go directly and do conventional ways of you
know customizing and doing the form work also for small-small construction jobs, so all ways
are available.
(Refer Slide Time: 04:00)
Now let us talk about the temporary structures. There are lot of terminology that are comes
together we generally is confusing when you talk about form works. So along with the form
work the term comes together; which are all inter-exchangeable used are form work, centering,
shuttering, staging and scaffolding. So what is a form work? As I told this is a nothing but a
mould to actually pour in the concrete. So this is a primary a bridged pear construction.
So primarily you create all the form work structures. So when you pour the concrete it gets the
shape of the inside of the form work. Centering is the nothing but the horizontal temporary
arrangement. In a way slab form works are generally called as centering.
(Refer Slide Time: 04:44)
The next one is shuttering all your vertical temporary arrangements are primarily called
shuttering. So columns or your wall form works are generally called shuttering. So this is a
picture to show you wall form work, which is also called shuttering. Than next one is staging are
all your props and supports either for centering or for shuttering which implies either for vertical
support or your horizontal supports. All your props and supports are nothing but here called
staging.
And scaffolding is actually I said it is a workers platform. Wherein; workers try to reach the
construction site or the place of work where they have to do. And it is primarily like a helping
the workers and material movement. So these are the different terminology and all these are
called temporary structures. The minute the actual building construct is completed then all these
structures will be removed from the site.
(Refer Slide Time: 05:47)
So now what are the requirements of false work? So again if I have to recap and tell, there are lot
of types of form work for example jump formworks, slip form work. Than we also have climbing
form work, tunnel form work, table form work. So like this they are so many varieties available
and I am not going to talk about all those specialized varieties. We are only going to discuss
about general strengths and safety issues on form works.
So what are the requirements of form work? Because it is only a temporary structure and once
the permanent construction comes in place all these temporary structures will be removed. So,
why to worry much on this form work? No that is not the way it should be looked at because the
strength of the form work also affects the quality of construction or even the strength of the
actual construction also.
So the first requirement the form work should have enough strength and stability should
withstand all type of possible loads that comes on to the form work. It should be very safe; it
should support the concrete weight it should support the workers weight. And also it should be
you know primarily having a lot of integrity with the structure. So that even with whatever
lateral forces or vertical forces or any way the force comes in it actually stands firm and stable.
It should be rigid which is achieved by lot of braces and ties and it should be having a sufficient
amount of deflection, which is within the permissible limits. There can be lot of deflections
which can happen because of the dead load coming on to the farm work. When the load of the
fresh concrete live load because of the movement of workers and equipments. And also forces
caused by pumping in of concrete or vibration of concrete as a result of compaction.
So, all these should be taken into account so the form work should be very much very rigid and
stabile. Erection and release obviously form work is not like a use and through purpose. It should
be serving for multiple rounds of construction. So based on the lifecycle of material of
construction, the life cycle of the form work also depends on. There are lots of materials with
which the farm work are generally coming these days.
Starting from; timber or even aluminum or steel form works and so on. So based on the initial
cost and maintenance cost these form work life cycles are decided. So accordingly the form work
should be so designed and constructed. That it can be removed in parts without collapsing the
structure or without collapsing the form work system as such so that it can be reused. And this
should also facilitate ease of inspection.
Where ever the inspections are planned it should have may be a small window or something so
that you can actually inspect the actual concrete if you want to do so. Should also permit
maximum reuses so thereby the cost of concrete is reduced. And also should be designed in such
a way that it requires minimum cutting, wastage and assembling. So accordingly the form work
structures should be designed and even.
And the actual construction also should be designed in such a way that there is no complex shape
or a very particular shape wherein you are actually doing lot of waste of cutting and using of the
reuse of the form work. So, all these are the basic requirements for form work.
(Refer Slide Time: 09:18)
Now I have been keeping on saying there is lot of load acting on the form work. So what are the
different forms of load which comes onto the form work? Let us discuss one after the other dead
load. So if you talk about the dead load the self weight of the form work. Which is not like
changing, it just acts on to the structure. This actual, self weight of the form work, the weight of
fresh, concrete and any other temporary works, which is supported by the form work.
Which can even be scaffolds or anything which; actually knows integrated part of the whole
temporary structure. The imposed load it can be storage of materials, lateral pressure on the fresh
concrete or unsymmetrical placement of concrete. Generally what happens when you pour in the
concrete through pumps it is actually poured in one particular place only and the concrete starts
spreading ahead.
So there can be unsymmetrical imbalance of concrete load and as a result you may have different
load acting on to the whole structure. Than environmental load it can be wind, it can be seismic,
it can be water pressure, earth pressure and so on. As far as possible the water table should be
kept tight when you are using the form work, because that water is really dangerous when it
comes on to the form work and to the structure.
(Refer Slide Time: 10:38)
So let us talk about form work in foundations. So precautions should be taken to prevent burying
of forms due to the collapse of the soil. So what happens is generally the form work need not be
taken too much of precaution when it comes to foundation only the strength aspects are generally
seen. Otherwise the other form works the neatness of the structure also depends on the quality of
the form work, but as far as when you talk about foundation.
It is not a too much of a worry for any contractor, but the other issue is the water table can cause
serious problems and accidents or incidents and so on. And the forms may also be damaged if
there is water table and as a result there can be collapse of the whole structure also. That you
should keep in mind. So, proper planning and dewatering is most required when you are working
below ground levels.
And also, this is also can result in accidents or incidents that you have to keep in mind. Now if
you see the types of foundations there are so many types. But we are going to only talk about 2
here. One is stepped footing and other one is sloped footing and these are common terminology
in any civil engineering. So stepped footing just like your steps you have different layer wherein
the load acting on the above is spread across onto the foundation and to the soil below.
In sloped footing there is a tapering portion from where the load acting on the column is spread
onto the foundation and to the soil below. That is primarily called sloped footing. In sloped
footings the top forms are not a serious concern but it is based on the angle of repose that the top
forms may be there. In stepped footing it is very simpler actually you have to know vary the
dimensions.
Now a day’s form work comes with different you know series of dimension wherein you can
alter the size accordingly. And the form works can be placed to make a quick easy steps ahead.
That is primarily called stepped footing.
(Refer Slide Time: 12:46)
Now let us talk about form work for super structure. So, the first one is wall or the column form
which is also called shuttering. So this is primarily a picture of an, wall form work. In the same
way we have for column form work and as such we call it as a mould also. When it wants to
have a desired shape it is primarily, called as a mould or shuttering. So, columns forms should be
capable of easily being stripped away in no seconds.
In tall forms it is desirable to provide windows at appropriate levels for proper inspection and
also for to checking on to placement of concrete, to do vibration and so on. So there should be an
adequate window for doing all these small-small activities of the concreting work. So any
method which is applicable for a can be used for connecting the panels in place and these are all
called panels.
So these panels can be connected in place not by broken reinforcement rods with is available in
the site and so on. There should be a proper procedure for connecting the panels. Which can be
adjustable clamps or it can be bolts or any other standard practice which is supposed to be done.
Can be used because they also should take care of the load acting on to the temporary structure
Walls the 2 faces of shutters so what happens is this form work first is they place the shutter than
the place the reinforcement in between the shutters than they pour the concrete. So the 2 faces of
the shutters of the wall should be kept in place by appropriate ties. And these widths of the 2
faces of shutter should be maintained uniformly all across the wall form works. And the spacing
can be maintained by means of tubes or it can be braces or studs.
Whatever applicable practically it should be done and there should be a; proper oil also on in
order to you know remove the shutter after the concrete is placed. So this oil container should be
closed after applied on to the form work and put away from fire sources. So this will also
eliminate fire hazard and spillage of oil if there is anything should be cleaned and maintained,
also it should be avoided.
And the crane operator for lifting of the panels they should be properly experienced. Should be
aware of how to lift the panels, which should be in the design briefs. So unless the form work is
properly designed on to the lifting points and to so on, should be identified there itself and with
that places only the form work should be lifted in sites. The slings used for lifting panel should
also have adequate capacity and it should be free from defects.
And it should be ensured when the panels are lifted no loose bolts or nuts or anything is falling
off so on. So it should be properly taken care. And when the panels are lifted it should go as a
single piece and not like a, loose hanging substances should not be seen when the panels are
lifted. And when the panels are lifted again the workman should not be allowed to walk below
those places, because it is a fall hazard position.
And the lifting when; the panels are lifted unless the crane operator is assured that the panels
have been safely secured. He should not release the panel till than the panel should be held with
the cranes. And when de-shuttering happens it should be done only from the top, especially when
you are having a, tall forms. So these are the some of the safety precautions in column wall form
works.
(Refer Slide Time: 16:38)
Next is the beam slab form works, so this generally comes as a beam slab and accordingly some
provision is maintained in the slab so that it acts together. So no temporary structure or props
should be erected on the soft soil unless the soil is really you know compacted and it is ensured
that bearing is adequate below the props. And soft shuttering of slabs at upper stories should also
be protected from blowing off through the wind.
Especially when, you are going on multi-storey connections on the top shutter when there is no
load acting onto the shutter. In the sense when there is no reinforcement placed or when there is
no concrete poured in then there can be a wind force which can blow off all those shutters. So it
has to be tightly fixed and secured in place. Panel dimensions of prefabricated side shutters
should be fixed.
So that during pumping of concrete or pouring in of concrete the panels are not bulging and
leading or giving way to the pressure which comes onto the structure. So that should be
maintained otherwise there will be collapsed on the form work and the concrete. Reinforcement
steel roads or any other material should be in place with the help of lock pins and other means of
locking should not be attempted
The Scaffolding frames should be erected such that the ladders can be used for reaching on to the
form work or even otherwise the scaffolds and form work can be aligned together. So, that the
workers are having a free movement between the form work and the scaffolds. If there is any
opening in the slab or roof opening so primarily for want of anything for passing of ducts or
anything.
So that should be properly supported with planks and accordingly the slab should be casted. And
should be kept closed barricaded and provided with safety nets below. By mistake if the
movement happens still the workers should not be falling off. There should be safety net below
openings in left in the slabs. Edge of the form work should have a proper guard rails to prevent
fall of workers.
While de-staging the formworks system, the frames and bracing should be lowered only using
the rope and pulley arrangement. Although there is other means of manual handling of these de￾staging, but still it is recommended to have a rope and pulley arrangement. Workmen should not
be allowed to stand below the form works when the de-staging happens de-shuttering process is
happening. And also the area should be completely barricaded not to allow the unauthorized people into the
premises. De-shuttering materials should be stand neatly for future storage. So side precautions
common side precautions formal checks are recommended when the proposed founding level for
the false work is in preparation. So at different stages the false work has to be checked for its
strength.
When, the false work has attained a height of 10 meters than there should be a formal check. At
intermediate stages when the strength or stability of the form works has been adversely affected
with the environment conditions or loading conditions or may be unauthorized interference of
anything. So as a result it has to be checked and before applying the load in the sense before
pouring the concrete again the strength of the form work has to be thoroughly checked.
Also vibrations when happening through needle vibrators can often you know try to you know
alter the position of the props from their support base. When the needle vibrators are pocked in
the through the concrete for compassion then obviously there can be dislocation of the props. And hence so when the concreting is going on there should be a person standing for checking the
safety of props.
And also when some props are dislocated it can the load acting on that particular prop will be
transferred on to the adjacent props and yielding may very quickly happen and as a result the
other props may fail. And as a result subsequently there can be an accident or collapse of the
concrete structure. And also, there should be a means of communications between the person
operating the needle vibrator and the person standing below the level of the floor or slab.
In order to know due communications or signals that props has been dislocated. And until it is
repaired and sufficiently corrected the concreting may stop will be stopped and then renewed.
(Refer Slide Time: 21:25)
Electrical safety should be against electrocution should be taken care of when you are using
electric shutter vibrators. Fire safety should also be taken care of and accordingly fire safety
equipment should be in site especially when you are using timber form works. And so site
welding so reinforcement when your want to have a larger diameter rods are used and when you want to connect 2 rod using welding. Then accordingly it should not be done over any timber shutters the reinforcement should be
taken the welding should be taken care of ahead of your placing in above the shutters.
(Refer Slide Time: 22:06)
Some more site precaution while erecting form work there should be proper safety signs
barricades to prevent unauthorized people entering into the site. Also while you are placing you
are form work or while you are pouring in concrete or maybe you are stripping of the form work
during all precaution there should be erection and safety signs and barricades. All provisions of
designs and drawing should be complied with.
And as I said already it should not be miss understood since it is the temporary structure so the
design and the safety precautions and the constructions of details whatever is given in the
drawing should be really adhered too. And including the safety precautions because these
temporary structures are very critical for the, to give the final good or quality construction later
on to the permanent structure.
Any excavation nearby which can influence a safety of the false work should be accounted in the
planning. If you wanted to erect the form works there are few excavation which are close by than
the soil has been already disturb. So accordingly that has to be considered while you are putting
up your false works in your design and constructions. The bearing soil should be sound and
suitably prepared. And also that the there should be sole plates or base plates should be provided
in order to prevent settlement with the ground levels.
Safely measures should be taken to prevent impact of waters traffic scour due to water and so on.
And adequate bracings, struts and ties should be installed with the progress of execution. In order
to maintain, the strength and stability of form work at intermediate and final stages. There should be adequate places marked on your drawing itself where your material can be stored your
equipment can be stored.
And only in those earmarked places your material and equipment should be stored when the
concreting operation is going on. And no other places it should be done and you should be
following the design criteria for that. Inclusion of lifting points also in the design for lifting the
panels or the form work panels should be clearly indicated. And the detail of the form work also
indicated when they are crane handled.
The deterioration of materials due to storage, reuse or may be misuse should be checked and
corrective measures should be taken for safety precautions before you are using the form work.
Then incorporations of scaffolds working platforms and guard rails into the form work design at
all times should also be enabled so that you have a seamless movement of worker and equipment
into the structure. So that also should be taken care of in the form work drawing.
(Refer Slide Time: 25:01)
So during concreting, so we have talked only about erection of form works. So during concreting
adequate of access in the proper positions provided smooth movement of worker, material and
equipments so all should be enabled. All precautions should be taken care of to prevent accident
in terms of flooding in the foundation that also should be taken care off. The forms should be
very clean and free from any wood shavings or may be dirt, grit and so on. May be the earlier concrete which is available in the form work everything should be cleaned up
when form work is in place, because it may affect the strength of the concrete. The forms and
joints are in such a way that they should be preventing leakage any leakage of motor and slurry,
especially during vibrations and pouring in of concrete. Only approved coating of form or release
agent should be applied.
And this should not be touching up the reinforcement and the reinforcement should be very clean
from the same. The sequence of putting in the forms and the sequence of removal of the forms,
the rate of concreting, method of pouring in the concrete, the position of concrete joints
everything should be as per the design processes and if should not vary from that sequence. The
reinforcement and the false work should be checked.
And the permission to commence the placement of concrete should be then nodded by the side
supervise then only the concrete should be starting to pour into the structure. The thickness of the
concrete should be maintained at all times as per the drawing. And as I said the imbalance level
of concrete and one place of pouring in concrete all should be avoided as much as possible. The
props and bracing should be maintained for proper strength and especially during the placement
of concrete and vibration.
The concreting may also has to be stopped when catastrophic issues are happening in the site.
Platforms for the movement of workers and for the mechanized concrete buggies should be
separate and they are not placed and the load is not placing onto the reinforcement and it does
not go to the reinforcement reinforced steel.
(Refer Slide Time: 27:27)In spite of this there can be so many reasons for form work failures. Improper stripping and shore
removal what happens is? Initially when house or building construction happens first they put
the, first they do wall column form works after the foundation and than they do the slab or the
beam form work putting all the props and supports. After this the concrete has attained sufficient
strength so these props may be removed and the shoring generally happens.
And then the forms are actually replaced or put in into the floor above. And this shoring and re-
shoring keeps on happening unless the concrete has attained sufficient strength and so on. Now
what happens is? Before the concrete is in a particular level has reached its sufficient strength if
improper stripping happens here and there. Than actually you are collapsing the structure without
proper strength attained onto the concrete which is in the floor below.
And to start loading up the form work and start pouring in the concrete in the floor above than
obviously you may have form work failure and accident can happen. Inadequate lateral bracing
and especially when you are pushing up the form works to floors above multiple floors above.
You should take care of adequate lateral bracings, because the loads coming onto the lateral end
may start increasing apart from the load acting to the form work itself.
So that you should have adequate diagonal horizontal bracings of shores that also should be
maintained and checked for during inspections and suggested for additional lateral bracings and
ties should be maintained for the stability of the form work. Vibration due to placing equipment
so may be sometimes equipment such as vibrators which is moving around in the site forcompassion of concrete. That can create vibration to the concrete and also to the form work
itself.
So the forms sometime collapse because; when you accidently disturb the props or the support
place then the forms can accidently collapse. And so this can also be and also forms can also be
dislocated with movement of workers with the movement of vehicle moving around in the site
and also the equipment on the form work and the actual effect of vibrating concrete. So that
should be kept in mind and you should be looking for the stability of the form work at every
time.