vt report on foundation
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ACKNOWLEDGMENT
Before we get to more important things, we would like to thank numerous people,
without whom our summer training would have been very difficult.
We would like to thank National Building Construction Corporation Limited for
providing us with the necessary, whole-hearted guidance and valuable suggestions
throughout our training period, without which this endeavor would not have been
possible.
We are very grateful to Mr. M. Manna, Regional Manager & Mr. P.Saha, Project In-
charge, for their continuous support. We thank Mr Sagar Sahoo & Mr. Rajiv Rao,
Planning, for guiding us right from the start.
We profoundly express our gratitude to Mr. Kamal Bhattacharya, for being kind &
helpful in getting us the summer training.
Finally, We acknowledge each and every member of staff at the construction site , for
their wholehearted co-operation, which made our summer training comfortable and
successful.
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NATIONAL BUILDING CONSTRUCTION
CORPORATION PROFILE
YEAR OF INCORPORATION
NBCC was incorporated in November 1960 as a wholly owned Government of India
undertakingunder the erstwhile Ministry of Works, Housing & Supply ("MoWHS"), which is
now known as the Ministry of Urban Development ("MoUD").
AN ISO COMPANY
ISO 9001:2008 Certification has been awarded to NBCC for its Project Management and
Consultancy Divisions. ISO 9001:2008 certification issued by Bureau of Indian Standards is
valid up to March 2014.
AUTHORISED CAPITAL
The authorized, issued and paid-up equity share capital is Rs. 120 crore. This includes Rs.
30 crore of fully paid-up bonus shares to the existing share holder s as on 30-09-2011.
PERFORMANCE RECOGNITION
On October 14, 2008, the Government granted NBCCSchedule "A" PSU status. NBCC has
also been awarded ISO 9001:2008 from the Bureau of Indian Standards in respect of our
consultancy and project management division. NBCC has also received "Excellent" rating
from MoUD for each of the Fiscal years from 2004 to 2010 and Ministry of Heavy Industries
& Public Enterprises has awarded us with an "Excellence Award". MoUD grants us
"Excellent" rating if all the targets set out in the MoU with MoUD for the respective Fiscal
year are acheived. Further, in 2011, for one of our PMC projects, we were awarded an
"Appreciation Shield" for quality and timely completion of NSEZ Noida Project by the
Ministry of Commerce & Industry and the Development Commissioner, NSEZ.
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AREAS OF OPERATION
NBCC is one of the few public sector companies engaged in the business of
(i) project management consultancy services for civil construction projects ("PMC")
(ii) civil infrastructure for power sector and real estate development.
NBCC is headquartered in New Delhi and in addition has 10 regional / zonal offices across
India. The projects undertaken by our Company are spread across 23 states and 1 union
territory in India. In addition, NBCC has also have also undertaken projects overseas.
NBCC's PMC business segment includes providing management and consultancy services
for a range of civil construction projects including residential and commercial complexes,
redevelopment of buildings and colonies, hospitals, educational institutions; infrastructure
works for security personnel, border fencing as well as infrastructure projects such asroads, water supply systems, storm water systems and water storage solutions.
NBCC's civil Infrastructure for power sector segment includes providing engineering and
construction services for power projects, including design and execution of (i) civil and
structural works for power projects (ii) Cooling towers (iii) Chimneys.
NBCC's real estate development segment focuses on principally two types of projects,
namely, (i) residential projects, such as apartments and townships and (ii) commercial
projects, such as corporate office buildings and shopping malls.
COMPUTERIZATION AND TRANSPARENCY
NBCC makes extensive use of information and communication technologies for the
execution and management of its projects. NBCC has implemented Enterprise Resource
Planning ("ERP") system in some business processes related to accounting, salaries, HRM
system and e-Bidding system. In addition, NBCC's team has access to domain controller and
additional domain controller, cluster servers, IT security management, network
management etc. IT security management is also utilized for the continuous upkeep of
security products , solutions, products, tools. The online computer maintenance services
ensures accurate management of the organizations hardware and software complaints
electronically, including hardware management, complaint tracking, minimum problem
rectification time, better reports management and optimal performance. NBCC also
hascentralised its database and has begun digitising its records and has business continuity
servers to protect the electronic data and ensure maximum uptime.
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PROJECT MANAGEMENT CONSULTANCYFOR CIVIL
CONSTRUCTION PROJECTS ("PMC")
Our PMC business segment includes providing management and consultancy services for a
range of civil construction projects including residential and commercial complexes,
redevelopment of buildings and colonies, hospitals, educational institutions; infrastructure
works for security personnel, border fencing as well as infrastructure projects such as
roads, water supply systems, storm water systems and water storage solutions. Some of
our clients in this segment are or have been, ESIC, Ministry of Defence, Ministry of Home
Affairs (including Security forces like CRPF, CISF, NSG, BSF), Ministry of External Affairs,
MoUD, Ministry of Commerce and Industry, Ministry of Corporate Affairs, Ministry of
Finance, Haryana Urban Infrastructure Development Board, IIT Roorkee, IIT Kharagpur, IITPatna, SVNIT, amongst others.
Our key completed projects during the period April 01, 2006 tillSeptember 30, 2011, based
on the total contract value, include road works at Agartala, construction of defence campus
at Jaipur, Jodhpur, Ahemdabad, Ambala, Sulur, CBI headquarters at New Delhi, Extension of
campus of MDU university and IIT Roorkee. Our key domestic PMC Ongoing Projects based
on the total outstanding contract value, include Indo Bangladesh Border Fencing Works at
Meghalaya, ESIC Hospital, Parel (Mumbai). We presently have one overseas PMC Ongoing
Project at Male, Maldives for construction of India - Maldives Friendship Faculty of
Hospitality & Tourism Studies.
As of September 30, 2011PMC Projects
Ongoing Projects Forthcoming Projects
Number of Projects 130 59
Contract Value (in million) 162,764.24 23,786.40*
Outstanding Contract Value/ Order Book (in million)
79,240.52 23,786.40*
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REAL ESTATE DEVELOPMENT
Our real estate development segment focuses on principally two types of projects,
namely, (i) residential projects, such as apartments and townships and (ii)
commercial projects, such as corporate office buildings and shopping malls. OurCompany has undertaken real estate projects which are spread across 10 states in
India. As ofJanuary 15, 2012, our Land Reserves aggregate approximately 127.918
Acre. Our Land Reserves are located in Delhi, Uttar Pradesh, Patna, Gurgaon,
Kolkata, Kochi, Alwar and Lucknow.
As on January 15, 2012, our completed commercial projects include commercial
complex at Vadodara, Cuttack, Agartala, Ghaziabad (Uttar Pradesh) and at
BhikajiCama Place, PragatiVihar and PushpVihar in New Delhi. Further, some of our
key real estate development Ongoing Projects include residential complex at "NBCC
Heights" at Sector-89, Gurgaon, Haryana; Khekra (Phase-I), Baghpat, Uttar Pradesh;residential-cum-commercial complex at Bahadurpur, Phase-I, Patna; New
Delhi,Sukias Lane at Kolkata and Hemanta Basu Sarani Complex. The following table
represents details for types of real estate projects, as of January 15, 2012:
Type ofReal
EstateDevelopm
ent
CompletedProjects
Ongoing Projects Forthcoming Projects
No. ofProjec
ts
Developable
Area
No. ofProjec
ts
Developable Area
Saleable Area
Leasable Area
No. ofProjec
ts
Developable Area
Saleable Area
Leasable Area
Residential
Nil - 4 3,732,0533,410,4
030 6 5,555,821
4,878,882
147,585
Commercial
8 1,076,65 3 407,633 239,560 66,624 6 2,323,9081,724,1
01290,78
6
Total 8 1,076,65 7 4,139,6863,649,9
6366,624 12 7,879,729
6,602,983
438,353
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CIVIL INFRASTRUCTURE FOR POWER SECTOR
Our civil Infrastructure for power sector segment includes providing engineering
and construction services for power projects, including design and execution of (i)
civil and structural works for power projects (ii) Cooling towers (iii) Chimneys.Some of our clients in this segment include NTPC Limited, BHEL, APGENCO Limited,
Uttar Pradesh RajyaVidyutUtpadan Nigam Limited, MAHAGENCO Limited and
Karnataka Power Corporation Limited.
Our completed key projects, during the period April 01, 2006 till September 30,
2011based on the total contract value, include construction of civil, structural and
architectural works for 2x250 MW at Korba, Chattisgarh;Rihand Main Plant , Civil
Works in Uttar Pradesh our key On-going PMC Projects, based on the total
outstanding contract value, include cooling tower, chimney at Farakka Super
Thermal Power Project, West Bengal, ,Koderma Thermal Power Project atJharkhand, Durgapur, Thermal Power Project at West Bengal, Rihand Super Thermal
Power Project, Uttar Pradesh, Barh Super Thermal Power Project, Patna, Mauda and
Vindhyachal Super Thermal Projectat Maharashtra & Madhya Pradesh respectively.
As of September 30, 2011 Civil Infrastructure for power projects(Ongoing Projects)
Number of projects 14
Contract Value(` in million) 7,875.43
Outstanding Contract Value / Order Book(`in million)
3,199.49
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SEQUENCE OF STRUCTURE WORK
1)Site Clearance
2)Demarcation of Site
3)Positioning of Central coordinate ie (0,0,0) as per grid plan
4)Surveying and layout
5)Excavation
6)Laying of PCC
7)Bar Binding and placement of foundation steel
8 )Shuttering and Scaffolding
9)Concreting
10)Electrical and Plumbing
11)Deshuttering
12)Brickwork
13)Doors and windows frames along with lintels
14)Wiring for electrical purposes
15)Plastering
16)Flooring and tiling work
17)Painting
18)Final Completion and handing over the project
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PROBLEMS FACED AT SITE
There were numerous problems which were faced at site. Some of these were
purely due to the human errors and poor workmanship but some were due to
unseen factors.
1. There was a problem in providing beams at one location as per the standarddrawings so the drawings were changed by consulting the structural designersand architect
2. There was problem pouring concrete in one beam due to small area availablefor pouring and compacting. The solution to this problem was that the size ofsteel was increased but the number of steel bars was decreased so as toprovide the total area same.
3. No window was there in staircases which lead to complete darkness, so it wasdecided to change the drawing by consulting the concerned authorities.
4. The depth if beam above the door was 35 earlier but to keep the size of the
door as per the standard it was changed to 3.
5.Frequent power cuts lead to increase in the cost of construction as generatorswere used to meet the power requirements
6.Laying of foundations was postponed by 1 month due to the rainy season.
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CONSTRUCTION PROCESS AND MATERIALS USED
Site Clearance- The very first step is site clearance which involves removal of grass and
vegetation along with any other objections which might be there in the site location.
Demarcation of Site- The whole area on which construction is to be done is marked so as toidentify the construction zone. In our project, a plot of 450*350 sq ft was chosen and the
respective marking was done.
Positioning of Central coordinate and layout- The centre point was marked with the help of a
thread and plumb bob as per the grid drawing. With respect to this center point, all the other
points of columns were to be decided so its exact position is very critical.
Excavation
Excavation was carried out both manually as well as mechanically. Normally 1-2 earth
excavators (JCBs) were used for excavating the soil. Adequate precautions are taken to see thatthe excavation operations do not damage the adjoining structures. Excavation is carried outproviding adequate side slopes and dressing of excavation bottom. The soil present beneath the
surface was too clayey so it was dumped and was not used for back filling. The filling is done in
layer not exceeding 20 cm layer and than its compacted. Depth of excavation was 54 from
Ground Level.
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PCCPlain Cement Concrete
After the process of excavation, laying of plain cement concrete that is PCC is done. A layer of 4
inches was made in such a manner that it was not mixed with the soil. It provides a solid bas for
the raft foundation and a mix of 1:5:10 that is, 1 part of cement to 5 parts of fine aggregates and
10 parts of coarse aggregates by volume were used in it. Plain concrete is vibrated to achieve fullcompaction. Concrete placed below ground should be protected from falling earth during and
after placing. Concrete placed in ground containing deleterious substances should be kept free
from contact with such a ground and with water draining there from during placing and for aperiod of seven days. When joint in a layer of concrete are unavoidable, and end is sloped at an
angle of 30 and junctions of different layers break joint in laying upper layer of concrete. The
lower surface is made rough and clean watered before upper layer is laid.
LAYING OF FOUNDATION
At our site, Raft foundations are used to spread the load from a structure over a large area,
normally the entire area of the structure. Normally raft foundation is used when large load is to
be distributed and it is not possible to provide individual footings due to space constraints that is
they would overlap on each other. Raft foundations have the advantage of reducing differentialsettlements as the concrete slab resists differential movements between loading positions. They
are often needed on soft or loose soils with low bearing capacity as they can spread the loads
over a larger area.
In laying of raft foundation, special care is taken in the reinforcement and construction of plinth
beams and columns. It is the main portion on which ultimately whole of the structure load is tocome. So a slightest error can cause huge problems and therefore all this is checked and passed
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by the engineer in charge of the site.
Apart from raft foundation, individual footings were used in the mess area which was extended
beyond the C and D blocks.
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ADVANTAGES OF USING PORTLAND POZZOLANA CEMENT OVEROPC
Pozzolana combines with lime and alkali in cement when water is added and forms compounds
which contribute to strength, impermeability and sulphate resistance. It also contributes to
workability, reduced bleeding and controls destructive expansion from alkali-aggregate reaction.
It reduces heat of hydration thereby controlling temperature differentials, which causes thermalstrain and resultant cracking n mass concrete structures like dams. The colour of PPC comes
from the colour of the pozzolanic material used. PPC containing fly ash as a pozzolana will
invariably be slightly different colour than the OPC.One thing should be kept in mind that is thequality of cement depends upon the raw materials used and the quality control measures adopted
during its manufacture, and not on the shade of the cement. The cement gets its colour from the
nature and colour of raw materials used, which will be different from factory to factory, and mayeven differ in the different batches of cement produced in a factory. Further, the colour of the
finished concrete is affected also by the colour of the aggregates, and to a lesser extent by the
colour of the cement. Preference for any cement on the basis of colour alone is technically
misplaced.
SETTLING OF CEMENT
When water is mixed with cement, the paste so formed remains pliable and plastic for a short
time. During this period it is possible to disturb the paste and remit it without any deleteriouseffects. As the reaction between water and cement continues, the paste loses its plasticity. This
early period in the hardening of cement is referred to as setting of cement.
INITIAL AND FINAL SETTING TIME OF CEMENT
Initial set is when the cement paste loses its plasticity and stiffens considerably. Final set is the
point when the paste hardens and can sustain some minor load. Both are arbitrary points andthese are determined by Vicat needle penetration resistance
Slow or fast setting normally depends on the nature of cement. It could also be due to extraneous
factors not related to the cement. The ambient conditions play an important role. In hot weather,
the setting is faster, in cold weather, setting is delayed Some types of salts, chemicals, clay, etc ifinadvertently get mixed with the sand, aggregate and water could accelerate or delay the setting
of concrete.
STORAGE OF CEMENT
It needs extra care or else can lead to loss not only in terms of financial loss but also in terms ofloss in the quality. Following are the dont that should be followed -
(i) Do not store bags in a building or a godown in which the walls, roof and floor are notcompletely weatherproof.
(ii) Do not store bags in a new warehouse until the interior has thoroughly dried out
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(iii) Do not be content with badly fitting windows and doors, make sure they fit properly and
ensure that they are kept shut.
(iv) Do not stack bags against the wall. Similarly, dont pile them on the floor unless it is a dry
concrete floor. If not, bags should be stacked on wooden planks or sleepers.
(v) Do not forget to pile the bags close together
(vi) Do not pile more than 15 bags high and arrange the bags in a header-and-stretcher fashion.
(vii) Do not disturb the stored cement until it is to be taken out for use.
(viii) Do not take out bags from one tier only. Step back two or three tiers.
(ix) Do not keep dead storage. The principle of first-in first-out should be followed in removing
bags.
(x) Do not stack bags on the ground for temporary storage at work site. Pile them on a raised, dry
platform and cover with tarpaulin or polythene sheet.
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COARSE AGGREGATE
Coarse aggregate for the works should be river gravel or crushed stone .It should be hard, strong,
dense, durable, clean, and free from clay or loamy admixtures or quarry refuse or vegetable
matter. The pieces of aggregates should be cubical, or rounded shaped and should have granular
or crystalline or smooth (but not glossy) non-powdery surfaces.Aggregates should be properlyscreened and if necessary washed clean before use.
Coarse aggregates containing flat, elongated or flaky pieces or mica should be rejected. The
grading of coarse aggregates should be as per specifications of IS-383.
After 24-hrs immersion in water, a previously dried sample of the coarse aggregate should not gain in
weight more than 5%.
Aggregates should be stored in such a way as to prevent segregation of sizes and avoid
contamination with fines.
Depending upon the coarse aggregate color, there quality can be determined as:
Black => very good quality
Blue => good
Whitish =>bad quality
FINE AGGREGATE
Aggregate which is passed through 4.75 IS Sieve is termed as fine aggregate. Fine aggregate is
added to concrete to assist workability and to bring uniformity in mixture. Usually, the natural
river sand is used as fine aggregate. Important thing to be considered is that fine aggregatesshould be free from coagulated lumps.
Grading of natural sand or crushed stone i.e. fine aggregates shall be such that not more than 5percent shall exceed 5 mm in size, not more than 10% shall IS sieve No. 150 not less than 45%
or more than 85% shall pass IS sieve No. 1.18 mm and not less than 25% or more than 60% shall
pass IS sieve No. 600 micron.
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Unit Weight of Materials Used at ConstructionSite
Following table shows unit weight of materials used at construction site. Please note
this is for reference purpose only and may vary from place and type of material.
We are thankful to Engineer Prince Saha for submitting this very useful information
to us.
S.No Material Theoretical
Weight
in(KG/M)
Approx Weight at Site
in
Remarks
Kg Per
1 Cement 1440 50 Bag
2 Steel 7850 d/162 d -dia in mm
3 Sand-
Dry 1600 50 to 55 farma 1 farma=1.25cft
River 1840 57 to 63 farma 1 farma=1.25cft
4 Stone(basalt) 2850 to 2960 48 to 52 farma metal 12mm to 20mm
5 Water 1000 1 liter
6 PCC 2240 8.24 to 8.5 Cubemould
cube mouldsize=15x15x15cm
7 RCC 2% Steel 2420
8 Bricks 1600 to 1920 1.9 to 2 no 9x4x2 3/4
4.8 to 4.9 no 9x6x3 3/4
9 Brick Masonry 1920
10 Soil(damp) 1760 50 to 55 cft Black cotton
11 Cement concrete
block(solid)
1800 18 to 20 cft 30x15x20 cm
10 to 11 no 30x10x20 cm
12 Cement Mortar 2080 57 to 62 cft
13 Lime Mortar 1760 48 to 52 cft14 Lime 640 30 bag
15 Glass 2530 0.9 to 0.95 sft 4mm tk plain
16 Teak Wood 670 to 830 18 to 20 cft
17 Sal Wood 990 22 to 24 cft
18 Marble mosaic tile 2.8 to 3.2 no 25x25x22mm
4.8 to 5.2 no 30x30x25mm
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19 Chequered tile 2.5 to 2.8 no 25x25x22mm
20 Glazed tile15x15cm 0.20 to 0.25 no 5mm tk
21 Marble Stone 2620 5.1 sft 3/4tk
22 Granite Stone 2460-2800 5.35 sft 3/4tk
23 Coddappa 2720 6.4 sft 1 1/4tk
24 A.C.sheet corrugated 16 1.2 sft
25 Bitumen 1040 220 Drum 200liter drum
26 Window frame (simpledesign)
1.9 to2.1 sft
27 Door Frame
a)30070 25 to 27 no section 4x2 1/2
b)26x70 24 to 26 no section 4x2 1/2
BRICKWORK
Brickwork is masonry done with bricks and mortar and is generally used to build partition walls.
In our site, all the external walls were of concrete and most of the internal walls were made ofbricks. English bond was used and a ration of 1:4 (1 cement: 4 coarse sand) and 1:6 were used
depending upon whether the wall is 4.5 inches or 9 inches. The reinforcement shall be 2 nos.
M.S. round bars or as indicated. The diameter of bars was 8mm. The first layer of reinforcement
was used at second course and then at every fourth course of brick work. The bars were properlyanchored at their ends where the portions and or where these walls join with other walls. The in
laid steel reinforcement was completely embedded in mortar.
STRENGTH OF BRICK MASONRY
The permissible compressive stress in brick masonry depends upon the following factors:
1. Type and strength of brick.
2. Mix of motor.
3. Size and shape of masonry construction.
The strength of brick masonry depends upon the strength of bricks used in the masonry
construction. The strength of bricks depends upon the nature of soil used for making and the
method adopted for molding and burning of bricks .since the nature of soil varies from region toregion ,the average strength of bricks varies from as low as 30kg/sq cm to 150 kg /sq cm the
basic compressive stress are different crushing strength.
There are many checks that can be applied to see the quality of bricks used on the site.Normally
the bricks are tested for Compressive strength, water absorption, dimensional tolerances and
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efflorescence. However at small construction sites the quality of bricks can be assessed based on
following, which is prevalent in many sites.
Visual check Bricks should be well burnt and of uniform size and color.
Striking of two bricks together should produce a metallic ringing sound.
It should have surface so hard that cant be scratched by the fingernails.
A good brick should not break if dropped in standing position from one metre above ground
level.
A good brick shouldnt absorb moisture of more than 15-20% by weight, when soaked in water
For example; a good brick of 2 kg shouldnt weigh more than 2.3 to 2.4 kg if immersed inwater for 24 hours.
PRECAUTIONS TO BE TAKEN IN BRICK MASONRY WORK
Bricks should be soaked in water for adequate period so that the water penetrates
to its full thickness. Normally 6 to 8 hours of wetting is sufficient.
A systematic bond must be maintained throughout the b rickwork. Vertical joints
shouldnt be continuous but staggered.
The joint thickness shouldnt exceed 1 cm. It should be thoroughly filled with the
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cement mortar 1:4 to 1:6 (Cement: Sand by volume)
All bricks should be placed on their bed with frogs on top (depression on top of the
brick for providing bond with mortar).
Thread, plumb bob and spirit level should be used for alignment, verticality and
horizontality of construction.
Joints should be raked and properly finished with trowel or float, toprovide good bond.
A maximum of one metre wall height should be constructed in a day.
Brickwork should be properly cured for at least 10 days
REINFORCEMENT
Steel reinforcements are used, generally, in the form of bars of circular cross section in concrete
structure. They are like a skeleton in human body. Plain concrete without steel or any otherreinforcement is strong in compression but weak in tension. Steel is one of the best forms of
reinforcements, to take care of those stresses and to strengthen concrete to bear all kinds of loads
Mild steel bars conforming to IS: 432 (Part I) and Cold-worked steel high strength deformed bars
conforming to IS: 1786 (grade Fe 415 and grade Fe 500, where 415 and 500 indicate yield
stresses 415 N/mm2 and 500 N/mm2 respectively) are commonly used. Grade Fe 415 is beingused most commonly nowadays. This has limited the use of plain mild steel bars because of
higher yield stress and bond strength resulting in saving of steel quantity. Some companies havebrought thermo mechanically treated (TMT) and corrosion resistant steel (CRS) bars with added
features.
Bars range in diameter from 6 to 50 mm. Cold-worked steel high strength deformed bars start
from 8 mm diameter. For general house constructions, bars of diameter 6 to 20 mm are used
Transverse reinforcements are very important. They not only take care of structural requirementsbut also help main reinforcements to remain in desired position. They play a very significant role
while abrupt changes or reversal of stresses like earthquake etc.
They should be closely spaced as per the drawing and properly tied to the main/longitudinalreinforcement
TERMS USED IN REINFORCEMENT
BAR-BENDING-SCHEDULE
Bar-bending-schedule is the schedule of reinforcement bars prepared in advance before cutting
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and bending of rebars. This schedule contains all details of size, shape and dimension of rebars to
be cut.
LAP LENGTH
Lap length is the length overlap of bars tied to extend the reinforcement length.. Lap length about50 times the diameter of the bar is considered safe. Laps of neighboring bar lengths should be
staggered and should not be provided at one level/line. At one cross section, a maximum of 50%
bars should be lapped. In case, required lap length is not available at junction because of spaceand other constraints, bars can be joined with couplers or welded (with correct choice of method
of welding).
ANCHORAGE LENGTH
This is the additional length of steel of one structure required to be inserted in other at thejunction. For example, main bars of beam in column at beam column junction, column bars infooting etc. The length requirement is similar to the lap length mentioned in previous question or
as per the design instructions
COVER BLOCK
Cover blocks are placed to prevent the steel rods from touching the shuttering plates and there by
providing a minimum cover and fix the reinforcements as per the design drawings. Sometimes it
is commonly seen that the cover gets misplaced during the concreting activity. To prevent this,tying of cover with steel bars using thin steel wires called binding wires (projected from cover
surface and placed during making or casting of cover blocks) is recommended. Covers should bemade of cement sand mortar (1:3). Ideally, cover should have strength similar to the surroundingconcrete, with the least perimeter so that chances of water to penetrate through periphery will be
minimized. Provision of minimum covers as per the Indian standards for durability of the whole
structure should be ensured.
Shape of the cover blocks could be cubical or cylindrical. However, cover indicates thickness of
the cover block. Normally, cubical cover blocks are used. As a thumb rule, minimum cover of 2in footings, 1.5 in columns and 1 for other structures may be ensured.
Structural element Cover to reinforcement (mm)
Footings 40Columns 40
Slabs 15
Beams 25
Retaining wall 25 for earth face
20 for other face
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THINGS TO NOTE
Reinforcement should be free from loose rust, oil paints, mud etc. it should be cut, bent and fixedproperly. The reinforcement shall be placed and maintained in position by providing proper
cover blocks, spacers, supporting bars, laps etc. Reinforcements shall be placed and tied such
that concrete placement is possible without segregation, and compaction possible by animmersion vibrator.
Three types of bars were used in reinforcement of a slab. These include straight bars, crank barand an extra bar. The main steel is placed in which the straight steel is binded first, then the
crank steel is placed and extra steel is placed in the end. The extra steel comes over the support
while crank is encountered at distance of (1-distance between the supports) from thesurroundings supports.
For providing nominal cover to the steel in beam, cover blocks were used which were made ofconcrete and were casted with a thin steel wire in the center which projects outward. These keep
the reinforcement at a distance from bottom of shuttering. For maintaining the gap between themain steel and the distribution steel, steel chairs are placed between them
SHUTTERING AND SCAFFOLDING
DEFINITION
The term SHUTTERING or FORMWORK includes all forms, moulds, sheeting, shuttering
planks, walrus, poles, posts, standards, leizers, V-Heads, struts, and structure, ties, prights,
walling steel rods, bolts, wedges, and all other temporary supports to the concrete during theprocess of sheeting.
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FORM WORK
Forms or moulds or shutters are the receptacles in which concrete is placed, so that it will have
the desired shape or outline when hardened. Once the concrete develops adequate strength, the
forms are removed. Forms are generally made of the materials like timber, plywood, steel, etc.
Generally camber is provided in the formwork for horizontal members to counteract the effect ofdeflection caused due to the weight of reinforcement and concrete placed over that. A proper
lubrication of shuttering plates is also done before the placement of reinforcement. The oil film
sandwiched between concrete and formwork surface not only helps in easy removal of shutteringbut also prevents loss of moisture from the concrete through absorption and evaporation.
The steel form work was designed and constructed to the shapes, lines and dimensions shown on
the drawings. All forms were sufficiently water tight to prevent leakage of mortar. Forms wereso constructed as to be removable in sections. One side of the column forms were left open and
the open side filled in board by board successively as the concrete is placed and compacted
except when vibrators are used. A key was made at the end of each casting in concrete columnsof appropriate size to give proper bondings to columns and walls as per relevant IS.
CLEANING AND TREATMENT OF FORMS
All rubbish, particularly chippings, shavings and saw dust, was removed from the interior of theforms (steel) before the concrete is placed. The form work in contact with the concrete was
cleaned and thoroughly wetted or treated with an approved composition to prevent adhesion
between form work and concrete. Care was taken that such approved composition is kept out ofcontact with the reinforcement.
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DESIGN
The form-work should be designed and constructed such that the concrete can be properly placedand thoroughly compacted to obtain the required shape, position, and levels subject
ERECTION OF FORMWORK
The following applies to all formwork:
a) Care should be taken that all formwork is set to plumb and true to line and level.
b) When reinforcement passes through the formwork care should be taken to ensure close
fitting joints against the steel bars so as to avoid loss of fines during the compaction of
concrete.
c) If formwork is held together by bolts or wires, these should be so fixed that no iron is
exposed on surface against which concrete is to be laid.
d) Provision is made in the shuttering for beams, columns and walls for a port hole of
convenient size so that all extraneous materials that may be collected could be
removed just prior to concreting.
e) Formwork is so arranged as to permit removal of forms without jarring the concrete.
Wedges, clamps, and bolts should be used where practicable instead of nails.
f) Surfaces of forms in contact with concrete are oiled with a mould oil of approved
quality. The use of oil, which darkens the surface of the concrete, is not allowed. Oiling
is done before reinforcement is placed and care taken that no oil comes in contact with
the reinforcement while it is placed in position. The formwork is kept thoroughly wet
during concreting and the whole time that it is left in place.
Immediately before concreting is commenced, the formwork is carefully examined to
ensure the following:
a) Removal of all dirt, shavings, sawdust and other refuse by brushing and washing.
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b) The tightness of joint between panels of sheathing and between these and any hardened core.
c) The correct location of tie bars bracing and spacers, and especially connections of
bracing.
d) That all wedges are secured and firm in position.
e) That provision is made for traffic on formwork not to bear directly on reinforcement
steel.
VERTICALITY OF THE STUCTURE
All the outer columns of the frame were checked for plumb by plumb-bob as the work proceeds
to upper floors. Internal columns were checked by taking measurements from outer row of
columns for their exact position. Jack were used to lift the supporting rods called props
STRIPPING TIME OR REMOVAL OF FORMWORK
Forms were not struck until the concrete has attained a strength at least twice the stress to whichthe concrete may be subjected at the time of removal of form work. The strength referred is that
of concrete using the same cement and aggregates with the same proportions and cured under
conditions of temperature and moisture similar to those existing on the work. Where so required,
form work was left longer in normal circumstances
Form work was removed in such a manner as would not cause any shock or vibration that would
damage the concrete. Before removal of props, concrete surface was exposed to ascertain that theconcrete has sufficiently hardened. Where the shape of element is such that form work has re-
entrant angles, the form work was removed as soon as possible after the concrete has set, to
avoid shrinkage cracking occurring due to the restraint imposed. As a guideline, withtemperature above 20 degree following time limits should be followed:
Structural Component Age
Footings 1 day
Sides of beams, columns, lintels, wall 2 days
Underside of beams spanning less than 6m 14 days
Underside of beams spanning over 6m 21 days
Underside of slabs spanning less than 4m 7 daysUnderside of slabs spanning more than 4m 14 days
Flat slab bottom 21 days
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CONCRETE MAKING
Just mix cement, aggregates and water, cast this mix in a mould, open the mould next
day. A uniform hard mass will be found, which is known as concrete, any body can makeit. The simplecity in making concrete make this material to be look like very simple in its
production, yet it as not so simple. Due to ignorance about concrete no other building
materials ever mis-used as concrete in the construction. In India concrete is being used
in the construction since the last 70 years. Yet 80% of the builders have no proper
understanding of this materials. Go to any construction site (except big construction
sites) you will find that sand and aggregates are being taken in iron tasla or cane baskets
to charge the mixer without the consideration of site aggregates actual grindings,
moisture content and bulking of sand. The water is poured in the mixer without any
measured quantity. It could be well imagine what sort of concrete structure will be
made with the concrete being produced in this crude method.
Most of the contractors, builders, masons etc. still follow 1:2:4 or 1:1.5:3 mixes they are
not aware of Design Mixes and Concrete Admixtures. This paper described how Design
Mixes can be converted into volume with 1 Bag Cement, 2 Boxes of sand and 4 Boxes of
Aggregate. The site practical problem is the dispersion of water and liquid admixtures
into the mixer. For this the site should fabricate a plastic circular graduated measuring
container of 30 lit capacity with a tap fitted at its bottom. This container is to be fitted
on top of the mixer. From this container water and liquid admixtures can conveniently
poured direct into the mixer in a measured quantity.
EXAMPLE OF MIX DESIGN
1. For a construction site M-25 Grade of concrete is required to be designed as per IS:
456-2000. The mix will be taken by volume. Workability required is 50 mm slump.
Normal Superplasticizer will be used in the mix. The materials will be mixed at site in atilting drum mixer of one cement bag capacity.
2. For durability consideration, maximum free W/C ration = 0.50 minimum cement
content 300 kg/m3
including Fly ash.
3. Test datas of aggregates are as given in table-1.
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4. Cement will be used PPC, having 7 days average compressive strength of 37.5 N/mm2
5. Mean design target strength:
25 + 1.65 x 5 = 33.3 N/mm2 at 28 days age
Table-1 Test Data of Dehradun Aggregates:
I.S. Sieve Size Percentage Passing
River Sand 20 mm Crushed Aggregate
40 mm 100 100
20 mm 100 86
10 mm 95 3
4.75 mm 79 0
2.36 mm 72
1.18 mm 56
600 micron 47
300 micron 27
150 micron 6
Specific Gravity 2.65 2.65
Water absorption % 0.80 0.50
Bulk density kg/lit 1.78 1.40
Note : The sand is not falling to any grading Zone of IS : 383-1970. The aggregate grading
is 20 mm single sized as per IS: 383-1970.
If 95% this sand passes on 4.75 mm sieve, then the sand will become of Zone-II as per IS
: 383-1970. The following mix is worked out as per Zone-II sand. For detail calculations
refer reference of No. 1.
a) For the target strength and given cement and Aggregate W/C ration found to be =
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0.49
b) Water for OPC 190 kg/m3. For PCC 5/100 x 190 = 9.5 , Say 10
190 10 = 180 kg/m3
to give 50 mm of Slump with the given aggregates. Normal
Superplasticizer at a dosages of
7 ml/kg cement will give 15% water reduction without loss of workability.
Water = 180 27 = 153 kg/m3
c) Cement = 153/0.49 = 312 kg/m3
d) Density of OPC concrete = 2405 kg/m3
Density for PPC Concrete = 2405 24 = Say 2380 kg/m3
e) Aggregates = 2380 -153 312 = 1915 kg/m3
f) Sand (Zone-II) = 1915 x 0.36 = 689 kg/m3
g) 20 mm aggregate = 1915 689 = 1226 kg/m
3
Mix. No. 1 On the basis of saturated and surface dry aggregates-
Water =153 kg/m3
PCC=312 kg/m3
Sand=689 kg/m3
20 mm Aggregate=1226 ml/m3
Mix No. 2
95-79 = 16% oversized particles in the sand is to be adjusted in the above mix. The
modified mix on the basis of saturated and surface dry aggregates is given below:
Water=153 kg/m3
PCC=312 kg/m3
Sand=820 kg/m3
20 mm Aggregate =1095 kg/m3
Normal Superplasticizer=2184 kg/m3
Accordingly mix ratio by weight on the basis of saturated and surface dry aggregates is
given below:
Cement : Sand : 20 mm Agg.
1 : 2.63 : 3.51 W/C Ratio = 0.49
Mix ratio by volume on the basis of room dry aggregates is given below:
Cement : Sand : 20 mm Agg.
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1 : 2.14 : 3.63 Free W/C Ratio = 0.49
MIX RATIO BY VOLUME FOR ONE BAG OF CEMENT
1. Cement = One bag = 50 kg = 35 lit = 35000 cc
2. Sand (room dry) = 2.14 x 35 = 74.9 lit = 74900 cc
3. 20 mm Aggregate (room dry) = 3.63 x 35 = 127.05 lit = 127050 cc
4. Free Water = 24.5 lit
5. Normal Superplasticizer = 350 ml
MEASURING BOXES TO BE MADE AT SITE
1. Cement = One bag = 50 kg
2. Sand (room dry) = 33 x 33 x 34.4 cm two boxes
3. 20 mm Aggregate (room dry) = 33 x 33 x 29.2 cm .. four boxes
4. Free Water = 24.5 lit5. Normal Superplasticizer = 350 ml
In the above example M-25 Design mix is converted to the familiar 1 bag cement : 2
boxes of sand and 4 boxes of aggregate. While making concrete at site the moisture
content of site sand and aggregate must be taken into account in the mixing water and
bulking of sand. In the field trial mixes are to be carried out to finalize the mix.
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FOUNDATION
The building foundation or sub structure is that part of a structure which is placed below the surface of
the ground and which transmits the superstructure load to the underlying soil ultimately. It is the part of
a structural system that supports and anchors the superstructure of a building. Foundation is the most
important part of a building. Building activity starts with the formation of foundation. Main activities of
building foundation are:-
To distribute building load to soil beneath
To distribute the load uniformly
To grapnel the structure to the ground to resist movement due to lateral force
To prevent sinking of the structure.
Any part of a structure that serves to transmit the load to the earth or rock can be called foundation.
The higher and heavier the building is to be, the wider and deeper the supports of footings for the
foundation have to be.
PURPOSE OF FOUNDATION
To pass out building weight to the soil beneath evenly;
To prevent differential settlement of building;
To provide a plane surface for the convenience of construction;
To make building substantial and durable by continuing the structure in the soil.
TYPES OF FOUNDATION:
Depending on tthhee ddeepptthh oofftthhee llooaadd--ttrraannssffeerr mmeemmbbeerr bbeellooww tthhee ssuuppeerr--ssttrruuccttuurree and tthhee
ttyyppee ooffttrraannssffeerr llooaadd mmeecchhaanniissmm foundation can be classified into two types:
a) Shallow Foundation
b) Deep Foundation.
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The classification on foundation has been provided in flow chart as follows:
Classification of Foundation
a) SSHHAALLLLOOWWFFOOUUNNDDAATTIIOONN:A shallow foundation is a type of foundation which transfers building loads to the earth
very near the surface. The objective of shallow foundation is to distribute the structural
concentrated load over a wide horizontal area at a little depth rather than a range of
depths.
Shallow foundation is often selected when the soil has a good bearing capacity and the
structural load will not cause excessive settlement of the underlying soil layers. In
general, shallow foundations are more simple and cost effective to construct than deep
foundations because little soil is removed or disturbed.Shallow foundation construction
is typically utilized for most residential and light commercial raised floor buildings.
Foundation
Shallow
SpreadFootings
WallFootings
IsolatedColumnFootings
GrillageFoundation
CombinedFootings
MatFoundation
EccentrcallyLoaded
Footings
Deep
PileFoundation
Pre-castPiles
Cast-in -situ Piles
Cofferdams Caisson
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SPREAD FOOTINGS:
Spread footing is a common term used to
refer shallow foundations which transfers
concentrated loads to a wide range area. Itincludes reinforced concrete footings, wall
footings, isolated column footings. Spread
footing provides a stable base or platform at a
low depth and it prevents the structure from
settling into the ground.
Spread Footing
ISOLATED COLUMN FOOTINGS:
Isolated column footings are used to support single columns. Each individual isolated
footing provides support for each individual column, pier, post or other single
concentrated load. So, they act as a base for a column. They transfer the superimposed
structural load to a wide range of soil. They are the most economical types of footings
and are used when columns are spaced at relatively long distances. They can be square,
rectangular or even circular in plan view.
Isolated footings can be of brick masonry, stone masonry or of Reinforced Cement
Concrete (R.C.C.) depending on amount of load, project expanses and materials
available. The base of the footing depends on the load bearing capacity of soil and the
superimposed load. They are also known as pad footing or individual column footing.
Generally isolated footings are used in case of reinforced concrete structure buildings.
WALL FOOTINGS:
This type of shallow footing supports a wall by providing footing beneath the entire wall
structure. This type of footing is used when columns are made of bricks.
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GRILLAGEFOOTINGS:In case of low bearing capacity of soil and avoiding deep excavation grillage
foundation can be used. Grillage foundation can reduce the superimposed load
of column within the safe bearing capacity of the soil. The grillage can be made
of steel or timber.
COMBINED FOOTINGS:A combined footing is nothing but a combination of pad footings having a
common base. A combined footing is constructed when (i) a column lies very
close to the property line and (ii) to prevent overlapping of footings when
columns are very adjacent. They can be rectangular or trapezoidal in plan.
Combined footing proves to be more cost effective than a single column footing.
MATFOUNDATION:
A mat is a slab that supports multiple columns. It is typically used when thebearing capacity of soil is very low. When required footings will cover more than
half the area beneath a structure, it is often desirable to enlarge and combine
the footings to cover the entire area. A mat foundation may be cheaper than
individual footings because of reduced forming costs and simpler excavation
procedures. Although mat foundations are more difficult and more costly to
design but they prove to be more effective.
ECCENTRICALLYLOADED FOOTINGS:
It is a spread or wall footing that must resist a moment in addition to the axial
column load.
b) DDEEEEPPFFOOUUNNDDAATTIIOONN:A deep foundation is used when the bearing capacity of soil is low near ground. When a
building structure transmits excessive loads to a soil with low bearing capacity near
ground, settlement of the foundation takes place which endangers the stability of the
structure. In that case deep foundation is used to ensure good bearing capacity of soil at
a considerable amount of depth. A deep foundation requires considerable amount of
materials and earthwork resulting increased cost and effort. Piles, cofferdams and
caissons are some the familiar forms of deep foundations.
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IISSOOLLAATTEEDDCCOOLLUUMMNNFFOOOOTTIINNGG
Dependingon structural load and soil isolated footing can be of following types:
BBRRIICCKKPPIILLLLAARRFFOOOOTTIINNGG: When the structural columns are made of bricks this type ofisolated footing is often used. This is the most economic type of isolated columnfooting. The width and the depth of the footing depend on load to be carried and
bearing capacity of the soil. The width is found by offsets running symmetrical round
the column.
SSttoonnee PPiillllaarr FFoooottiinngg: Stone pillar footings are stronger than brick pillars.Construction of this type of footing is similar to brick pillar footing. The width and the
depth of this footing is a bit bigger because of the stone sizes. This type of footing is
weak in resisting bending. So they are not used against long heavy structural loads.
RR..CC..CC.. CCoolluummnn FFoooottiinngg: In case of column subjected to heavy loading and bendingthis type of column footing provides a superior solution in shallow foundation. Made
with reinforcement and concrete this type of footing is high on strength and bending.
The footing is reinforced cross ways by re-bar placed at right angles to one another.
This type footing is capable of transmitting massive loads with a reduced footing
depth. This type is used as a most effective form of isolated footing. Due to its strong
structure this footing is used against high building structures provided that the soil
has sufficient bearing capacity.
INDEPENDENT COLUMN FOOTING REQUIREMENTS:The main requirements of an independent footing are as follows:
i. Must distribute loads evenly to the soil;
ii. Must be well drained to prevent wash-out;
iii. Must bear on engineered soil.
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Foundation Alternatives and Cost Evaluation
As noted earlier, the two major alternate foundation types are the shallow and
deep foundations. Shallow foundations are discussed in this chapter. Deep
foundation alternatives including piles and drilled shafts are discussed in the next
chapter. Proprietary foundation systems should not be excluded as they may be the
most economical alternative in a given set of conditions. Cost analyses ofall feasible
alternatives may lead to the elimination of some foundations that were otherwise
qualified under the engineering study.
Other factors that must be considered in the final foundation selection are the
availability of materials and equipment, the qualifications and experience of local
contractors and construction companies, as well as environmental
limitations/considerations on construction access or activities. Whether it is for
shallow or deep foundations, it is recommended that foundation support cost be
defined as the total cost of the foundation system divided by the load the foundation
supports in tons. Thus, the cost of the foundation system should be expressed in
terms of dollars per ton loadthat will be supported. For anequitable comparison, the
total foundation cost should include all costs associated with a given foundation
system including the need for excavation or retention systems,environmental
restrictions on construction activities, e.g., vibrations, noise, disposal of
contaminated excavated spoils, pile caps and cap size, etc. For major projects, if the
estimated costs of alternative foundation systems during the design stage are within
15 percent of each other, then alternate foundation designs should be considered
for inclusion in contract documents. If alternate designs are included in the contract
documents, both designs should be adequately detailed. For example, if two pile
foundation alternatives are detailed, the bid quantity pile lengths should reflect the
estimated pile lengths for each alternative. Otherwise,material costs and not the
installed foundation cost will likely determine the low bid. Use of alternate
foundation designs will generally provide the most cost effective foundation system.
A conventional design alternate should generally be included with a proprietary
design alternate in the final project documents to stimulate competition and to
anticipate value engineered proposals from contractors.
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STEPS OF ISOLATED FOOTING
SOIL EXCAVATION
LEVELLING & DRESSING OF SOIL SURFACE
PLACEMENT OF BRICK FLAT SOLING LAYER
GIVING A CEMENT CONCRETE LAYER ON IT
PLACEMENT OF CEMENT CONCRETE BLOCK
PLACING OF REINFORCEMENT
SHUTTERING
CONCRETE CASTING
REMOVAL OF FORMWORK
CURING
BACKFILLING OF EXCAVATED AREA
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SOIL EXCAVATION
To set a footing, the first step is to excavate the soil of respective area. At first the area should
be located. The depth of excavation depends on the desired strength as strength increases with
depth. We see the tools that are used in excavation below,
PICS
In most cases, baskets & spades are used for excavation. Deep excavation damages adjacent
constructions. In this phase, shore piles or other preventive means are used. Soil sloping can also
reduce this damage. The picture below shows how workers dig soil during excavation,
Fig: Excavation
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The area of footings are chosen according to design. First the C.G of footings is located.
The excavated soil is kept near the footing as later it can be used for backfilling.
PIC: excavated soil nearby the footing
LEVELLING & DRESSING OF SOIL SURFACE
After excavation, the most important step is to level the soil surface. The load of the construction
should be vertical & for this, leveling & dressing is must. Otherwise the construction might be
subjected to tilting to one side. Sand layer & brick chips are often used for leveling & dressing.
In our site LEVELLING & DRESSING were done by sand layer.
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PLACEMENT OF BRICK FLAT SOLING LAYER
Now a hard & plane surface is needed. For this purpose we place a brick layer on previous layer.
It is called BRICK FLAT SOLLING. In this layer bricks are arranged in a regular combination.
The upper surface of the layer should be uniformly planed. Below we see a brick flat soling.
CEMENT CONCRETE LAYER
Generally a C.C (cement concrete) layer having 3 height is kept on the brick layer. It is named
as CEMENT CONCRETE LAYER. It provides a smooth, uniform & strong surface for
reinforcement frame. The mix ratio for C.C layer is cement:sand:aggregate=1:3:6.
But sometimes it is avoided to reduce expenses.
PLACING OF CEMENT CONCRETE BLOCK
Usually some CC blocks are kept on the CC layer to maintain the clear cover between CC layer
& reinforcement. It is also very important to prevent the reinforcement from corrosion. There is
no standard size of blocks. It varies with size of footing & clear cover.
Sometimes brick or half brick can be used instead of CC block. But bricks are not uniformly
smooth plane. Its strength is also less than CC block. So, it is better to use CC blocs as clear
cover. Generally its size is 3x3x3.
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PLACING OF REINFORCEMENT
Now it is a very important step to place reinforcements. First we should maintain available clear
cover by using CC blocks. We must tie rebars with G.I wires or welding. It is done so that
rebars remains intact in all the time even during the casting. First a single frame of horizontal
reinforcement is kept upon the CC block. The number & diameter of reinforcements depends
upon the strength of construction. And it is determined by design engineer.
The rebars are tied by hand at the outer place if the case is respectively small. But for large case,it is done on the brick flat soling. Because it is difficult to move & place a large case.
Fig: Formation of a case Fig: Tied by G.I wire
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Fig: Preparing column
The case must remain horizontal. It is done by plumb bob. The figure below we see how a case is
being horizontal by plumb bob.
Fig: Making horizontal
After placing the case, the centre of case is marked as the column can be placed.
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Fig: Fixing the column position
Now the column is placed upon the marking space. It must be vertical. Then it is also tied with
case. After making vertical the column is supported to remain fixed.
Fig: Placing of column
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Fig: making it vertical
SHUTTERING
Shuttering means the solid boundary around the concrete. It resists water flow. It also bears the
load of concrete. So a shuttering should be enough water tight & strong. The amount of water
should remain constant in order to get a proper hydration. There are two kinds of shuttering,
1. Wooden shuttering &
2. Steel shuttering
Wooden shuttering is more chip than steel shuttering. But it is less water proof & less strong. It
also lasts a short time. On the other hand steel shuttering is strong enough. It also can be used
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more times. But it is costly. Side shuttering can be removed after 3 days as after this time
concrete get required strength.
Fig: Wood shuttering
The minimum requirements of a shuttering:
*It should be enough strong to bear the load
*It should be water tight
*It should be economical
*Its inner surface should be plane
*Its joints should be made carefully
*It should retain the concrete shape from all types of distortions.
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Problems in isolated footing
1. Segregation: Separationof constituents of a heterogeneous mixture so that their distribution
is no longer uniform is termed as segregation. In case of concrete casting when it is thrown
from a large height
Figure: segregation.
Segregation occurs due to the difference in particles size (sometimes in the specific gravity of
the mix ingredients) .There are two types of segregation. In the first, the coarser particles tend
to separate out since travel further long distance. In the second, segregation is occurred by
separation of grout (water &cement). Here in our project aggregates were thrown from a
remarkable height. As a result the ingredients were separated as they hit the lower rebar layer.This segregation will ultimately decrease the strength of the concrete. So proper arrange should
be taken to prevent segregation.
Concrete is being thrown fro about 10 h
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2. Compaction: In our observed site, for compacting concrete they used both rodding &
vibration procedure.
In case of using vibrator, it should kept in mind that vibrator must be vertical. But in our project
vibrator was used aligned.
Roding
withbamboo
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Figure:
Aligned vibrating.
3.Improper clear cover maintainance: Clear cover is a very important fact in structure. For the
structure under the ground clear should be maintained at least 3. If clear cover is not
maintained properly then the moisture content around the structure will penetrate into the
structure & cause corrosion to the reinforcement . Finally collapse the structure.
Figure: Improper clear cover maintainance
Aligned
vibrating
Improperclear cover
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4. Water logging during casting: Mix proportion is very much important for the design strength.
In our site during casting, water logged continuously. The source of water may be rain water or
leakage from nearby pipes or drains.
Figure: Water logging during casting
5. Brick as C.C block & no C.C layer: In isolated footing we normally use BFS & C.C layer to
provide a flat surface. But in our project BFS was used with no mortar. Here they also did not
use C.C layer as well as C.C block. For maintenance of the clear cover between the BFS bricks
were directly used as C.C block that is shown in the following figure.
Loggedwater
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Figure: Brick as C.C block & no C.C layer
Bricks as
C.C
top related