Water Tower Tank Structrual Design

8/13/2019 Water Tower Tank Structrual Design

1/26

PAGE

CONTENTS

ACKNOWLEDGEMENT

CHAPTER 1

1. INTRODUCTION 012. MANAGEMENT 023. ORGANISATION AND ORGANISATION CHART 03

CHAPTER 2

2.1 DEMAND MANAGEMENT 04

2.2 DISTRIBUTION SYSTEMS 06

2.3 TESTING WATER DISTRIBUTION SYSTEM 07

2.4 PRESSURE MEASURING DEVICES 08

CHAPTET 3

3.1 WATER RETAINING STRUCTURES 06

3.2 CONSTRUCTION JOINTS 06

3.3 CONCRETE TESTINGS DONE AT SITE 10

CHAPTER 4

4.1 FORMWORK 11

4.1.1 CHARACTERISTICS OF GOOD FORMWORK 11

4.1.2 MATERIALS FOR FORMWORK 12

4.1.2.2 TIMBER FORM WORK 12

4.1.3 TOOLS USED FOR FORMWORK 12

4.1.4 COVER BLOCKS 12

4.1.5 REMOVABILITY AND STRIKING 13

4.1.6 MAINTENANCE AND STORAGE OF FORMWORK 13


2/26

4.2 TYPES OF FORMWORK 14

4.2.1 COLUMN FORMWORK 14

4.2.1.1 PLUMBING THE COLUMN 14

4.2.1.2 KICKER FORMWORK 14

4.2.2 BEAM FORMWORK 15

4.2.3 FORMWORK FOR STAIR CASE 15

CHAPTER 5

5.1 REINFORCEMENT 16

5.2 CONCRETING 17

CHAPTER 6

6 CONTROL AND SAFETY AT THE SITE 19

CHAPTER 7

PRACTICAL DIFFICULTIES ENCOUNTERED 19

CONSLUSION 19

ACKNOWLEDGEMENT

I would like to convey my special thank to all officers in National watersupply and drainage board (NWSDB), Town south office, Piliyandala and

Beijing municipal corporation (BMEC). Also I thank to the Industrial

Training Division of the faculty of engineering, University of Peradeniya andNational Apprentice and Industrial Training Authority.

Chapter 1

1.1 INTRODUCTION

The B.Sc. engineering undergraduates are employed for the industrial trainingafter first and third academic years. It is carried out by the Industrial Training

Division of the university under the approval of National Apprentice andIndustrial Training Authority. The training period is about 3 months. All thetraining appointments were handled by director training division at Telawela


3/26

office (at Ratmalana). According to my preference they asked me to go to the

Town south office at Piliyandala. Project manager at Piliyandala appointed mefor Athurugiriya - Hokkandara worksite on 31stSeptember. Until that, for

about one week I was at Piliyandala site.

At Piliyandala site pipe laying work was being done at that time (mainly atBokkundara and Borelesgamuwa) and some finishing works at Miriswatawater tower. From Piliyandala office I gathered more information about Town

south project. Following organization chart describes the town south office

structure under the project manager.

Town south of Colombo water supply project has 2 main categories. They are,

1. On- going

2. Extension

Under the first one 4 sub projects, i.e. Homagama, Kesbewa main, Kesbewa

sub and Keselwatte were carried out. Similarly under extension project there

are 5 subprojects, i.e. Mattegoda, Hokkandara, Athurugiriya, Madapatha and

Godagama. My site comes under these extension projects.

Contract for principal civil works for those projects was awarded to Beijing

Municipal Corporation (BMEC) of China on 29th March 99 and expected to befinished about December 2000.

Design of mechanical & electrical works is being carried out by NWSDB.

Consultancy services for both projects are provided by the Nippon JogesuidoSekki of Japan in association with Parson engineering science of Pasadena,California of U.S.A. . Supervision and design of these sub projects were done

by NWSDB. However consultants were doing supervision work most of thetimes as its their duty to check the construction was according to the design.

Athurugiriya project comprises of a 920m3ground reservoir, 1000m3elevated

tower/tank (30m height) 9km long transmission main, a distribution network

of pipelines 28km in length, pumping station and ancillary facilities (underdesign). Treated water for the project is obtained by tapping the Labugama

transmission main. The design capacity is 4300m3/day and the total

population to be served by the design year of 2018 will be around 12500.

Hokkandara project comprises of 920m3ground reservoir 1000m3elevatedtower, 4.5m long transmission main, a distribution network of pipe line 15km.

In length, pumping station, and ancillary facilities (under design). Treatedwater for the project is obtained by tapping the Ambatale Jubilee-Batteramulla

transmission main. The design capacity is 6200m3/day and the total

population to be served by the design year of 2018 will be around 33000.


4/26

During my training periods time most probably only pump house work and

tower work will be only carried out according to the work schedule. Mr.Thavandra kumar was the site engineer for both Athurugiriya and

Hokkandara. Mr. Mohan was Structural engineer for these sites (overall incharge).

1.2 Management

I) National water supply and drainage board (NWSDB)

Since NWSDB is a semi governmental organization, board of directors

managed it. Next to them a chairman and a general manager will be there and

balance follows as in the organization chart given above.

II) Beijing municipal engineering corporation (BMEC)

Similarly BMEC also have much similar management hierarchy. Site engineer

for this project by BMEC was Mr.Lieu(A Chinese engineer) .

III) General

NWSDB is the client for this project and BMEC is carries out the construction

works. In other words BMEC was paid by NWSDB under the contracts terms.Contract was offered by NWSDB by calling a tender world wide, and BMEC

offered the lowest cost for above specified projects.

Site office at Athurugiriya was facilitated (an air-conditioned container box

with necessary furniture). There were about 30 laborers employed by BMEC.

1.3 ORGANISATION

NWSDB comes under Ministry of urban development, housing andconstruction responsible for large development projects and system operation

and maintenance in the provision of water supply for domestic and industrial

uses. Co-ordinate rural water supply projects with the involvement of CBOsand local authorities. The National water supply and drainage board act

describes the statutory duty of the NWSDB to provide water supply for

public, domestic and industrial purposes. This is taken as right on the part of

the NWSDB to divert and use water for its purposes without other approval.The act administered by the NWSDB.

Chapter 2


5/26

2.1 Demand management

Demand management involves measures to encourage the conservation ofwater by reducing water use, obtaining higher value of production from the

unit of water used and preventing losses and wastage. Saving andconservation of water in one sector not only reduce the financial burden on thesociety by delaying or foregoing new investment, but also provide water forother productive uses. Demand management covers surface water as well as

groundwater. Lower water usage and extraction implies an increase in water

for in stream uses. This can result in additional benefits to fisheries, tourismand other non-consumptive uses. Maintenance of minimum in-stream flows

could be important for both commercial fishery production and for protectionof indigenous fish species and other forms of bio-diversity. It will promote

recreational activities like fishing and swimming, help to protect sensitive

aquatic eco-systems and improve water quality through maintenance ofgreater pollution assimilative capacity.

Demand management consists of a wide range of activities carried out by

various agencies across a number of sectors. Recovery of water resource

management costs at the basin level is not carried out. Water service fees arecharged in the water supply sector for customers with piped water service.

Development of a cost recovery or cost sharing policy, applying to both waterresource management costs and co-ordination with sectoral cost recovery, is a

high priority, which is now being investigated by the water resources

secretariat.

Infrastructure rehabilitation is an important means of reducing water losses. In

urban systems rehabilitation for reduction of non-revenue water is important.

Water metering is another important demand management tool. Most

NWSDB consumers are metered and pay for water on a volume basis. In theirrigation sector water deliveries are controlled using gates and other devices.There is generally no control on the water used by the individual farmer, other

than availability of flow, and there is no system for labour or charges onvolume used.

NWSDB conducts school and general public awareness programs regarding

the value of water. It also has formed water consumer societies to reducewater losses through standpipe connections.

All of these activities fall under various legal mandates for NWSDB. In mostcases demand management is a sectoral water management activity since, by

definition, demand occurs "downstream" of the point of diversion from

natural water bodies.


6/26

2.2 Distribution system

Water is distributed to consumers in several different ways, as local conditionsor other considerations may dictate. The methods are :

i. Gravity distributionThis is possible when the source of supply is alake or impounding reservoir at some elevation above the city so that

sufficient pressure can be maintained in the mains.

ii. By pumping with storage - This is the most common method generallyused in practice. In this method the excess of water pumped during

periods of low consumption is stored in elevated tanks. During periodsof low consumption is stored in elevated tanks. This what our sites

construction purpose.iii. Direct pumpingIn this method pumps are used for supplying water

without any storage. The water is forced into the main and then toconsumers. It is the least desirable method.

2.2.1 Pipe laying

At Bokkundara site that is on the Borelesgamuwa Piliyandala Rd., some pipelaying

works was done.

Fig 02: 250VJFA connector

2.2.2 Valves in pipe line


7/26

The importance of valves in pipe line should not be forgotten. Depending on

different situations and requirements, different types of valves are used. Someof the commonly used aresluice valves,

Sluice valvesThese are also known as gate valves and used to control the

flow of water through pipes. They facilitate the repair work in any portion ofthe distribution system.

Glove valveThis valve has a flatdisc which is parrallel to the flow directionand its seat is also parallel. Change in direction of flow through this valve

causes a rather high head loss. This valve is used in small sizes in buildingdistribution systems.

Pipe laying contract was awarded to sub contractors KDA Weerasinha andCo. Ltd. By BMEC according to the technical specification standard symbols

were used to denote specific parts as follows.

Fig 03: Standard symbols

2.3 Testing water distribution system


8/26

Field hydrostatic pressure testing (AWWA C600) was also done at

Borelesgamuwa. All pipe line shall be thoroughly flushed out with water priorto testing , except that any pipe line having concrete thrust blocks shall be

thoroughly flushed out with water prior to testing, except that any pipe linehaving concrete thrust blocks shall be filled with water until a curing period of

at least 7days. Pipeline should be filled slowly left under working pressure for

about 24hrs.

After a pipe line has been laid, fitted with all appurtenances and accessories

painted both from inside as wellas outside by means of protective paints, etc;the pipe line will be tested for the soundness in its construction. The step by

step procedure adopted for testing pipes is described below:

1. The pipe line is tested from section section , thus at a time, only one

particular section lying between 2 sluice valves is taken up for testing2. The down stream sluice valve is closed and water is admitted into the

pipe through the upstream sluice valve. The air valves will be operatedproperly during filling up of the pipe.

3. The up stream valve, through which water was admitted is closed, so asto completely isolate the pipe section from the rest of the pipe.

4. Pressure gages are then fitted along the length of the pipe section atsuitable intervals (say 1km or so) on the crown, through holes left forthis purpose.

5. The pipe section is the connected to the delivery side of a pump

through a small by-pass valve, and the pump is started, so as to developpressure in the pipe. The operation is continued till the pressure insidethe pipe reaches the designed value, which can be read from the

pressure gages fixed on the pipe.

6. The by-pass vave in the closed, and the pump dis-continued7. The pipe is thus kept under pressure for 24 hrs, and inspected for

possible defects, leakage at joints, etc. This completes the pressure test.The pipe is finally emptied through, drain valves, and the observed

defects are rectified, so as to make the line fit for use. The pipe is again

tested by repeating the test, inorder to ensure proper rectification ofdefects, already done.

2.4 Pressure measuring devices

Since water needs to be delivered with adequate pressure, pressure measuringdevices are essential . Hydrostatic testing, similar to that performed when new

pipe is installed, can also be used test existing water systems. Kocol(1972)

and McPherson(1983) described use of these tests in Milwauke and

Rochester, and reported that the tests enabled them to find weak sections of

pipe and leaks by subjecting the pipe to high pressures(300 psi). This type oftesting can only be done in areas with few customers, as all service


9/26

connections must be closed before repair crews are on hand is highly preferred

to having main fail at 3a.m on Saturday. This test can be helpful in detectinglarge leaks which enter sewers. Such water may, however indication of

infiltration of ground water.

Chapter 3

3.1 Water retaining structures

Water retaining structures are structures which are required to contain, orexclude, any or non aggressive aqueous liquid. Common structures of this

type include water towers and reservoirs storage tanks including sewage

disposal and treatment systems, and floors and walls of basements and otherunderground constructions where it is necessary to prevent ingress of

groundwater.

As it is important to restrain cracking so that leakages do not take place thedesign is generally governed by the requirements of the serviceability limitstate, but stability considerations are particularly important and design must

take careful account of the construction methods to be used.BS8007 gives the

guidance on design and construction of these water retaining structures based

on the limit state philosophy embodied in BS8110.

BS8007 recommends some modification to BS8110. They are

a. Use of f= 1.4 for liquid loads.b. Use of concrete grade 35c. Exposure classification of internal members(within water) and

recommends a minimum cover of 40mm.d. Maximum crack width limited to 0.2mm unless the aesthetic

appearance is critical, when 0.1 mm is required to avoid staining of

concrete.e. Maximum bar spacing of 300mm.f. Anchorage bond stresses for straight horiontal bars in sections

subjected to direct tesion must be reduced to70 per cent of the usual

values.g. At least 75mm blinding concrete is required below ground slabs.

3.2 Construction joints


10/26

All concrete structures must inevitably contain joints, although the need for

joints to accommodate movement in water retaining structures is governed bythe likelihood of, and need to restrict, unacceptable cracking principally due to

shrinkage and thermal movements. Frequently it may be possible to combinethe two categories of joint.

Principal characteristics of jointsare4 that they must be watertight, and in thecase of movement joints must also permit repeated movements to take place

as freely as possible. Water bars will be generally incorporated, either the

surface type in slabs, or commonly the centre bulb type in walls. These mustbe held effectively in position during concreting, while allowing good

compaction of the concrete to be still possible. Such water bars mustfurthermore be able to accommodate anticipated movement without tearing,

and with stand considerable pressure.

All movement joints must be sealed with a flexible compound which

effectively is watertight and also prevents dust and grit from entering and thusblocking the joint. Jointing materials must be durable under the condition of

exposure to which they may be subjected, but routine replacement is likely tobe necessary.

construction joints, contraction and expansion joints are possible source ofwater leakage if not made water-tight. Therefore, any such joint coming underwater should be provided

Fig 04: Construction joint

with a suitable water stop (bar). Common water bars may be classified in three

categories metal, rubber and mastic types.

Construction joint is defined as a joint in the concrete introduced, for

convenience in construction at which special measures are taken to achievesubsequent continuity without provision for any relative movement.


11/26

As per the technical specification manual, It was stressed that the contractor

(BMEC) should submit to the engineer(water board representative),construction joints should be located as not to impair the structural strength of

the completed structure.

3.3 Concrete testing done at the site

All the testing of concrete was done according to BS1881: part 2: 1970published in 1989 amended on 1983. This also complies with ISO4109.

For different levels of workability different methods were handled to evaluate

Workability Method

Very low Vebe time

low Vebe time, compacting factor

high Compacting factor, slump flow

Very high Flow

Table 01: Workability test methods

There are no unique relationships between the values yielded in 4 test.

International construction consortium (ICC) supplies all the concrete mix.

Allowed slump range was 8-12cm; even though there are 3 types of slump,top value was taken. Three types slumps are,

a. True slumpb. Shear slumpc. Collapse slump

Stringent quality control ensures have taken by BMEC. Check list anddetailing of concreting was filled out and checked by NWSDB representative.Checklist was prepared by Lieu(BMEC site engineer) and detailing of

concreting form was filled by Mr.Hikkandra. Cube test done for 7 day and 28day at Malabe lab.


12/26

Chapter 4

4.1 Formwork

Formwork is a mould or a box, temporary support to pre-cast or insitu

concrete structures. It holds the concrete and finally set to the inner profile ofthe structure. So the inner profile must be fit to the required shape and

dimensions. The Formwork should be supported until it curves sufficiently tobecome self-supporting.

The Formwork includes the actual material in contact with the concrete (form

face) and all the necessary associated supporting structure.

4.1.1 Characteristics of good Formwork

To successfully carry out its functions formwork must achieve a balance ofthe following requirements.

1. It should be sufficient in strength to support the weight of wet concreteplaced on it, the weight of workers and their equipments, the force ofvibration and the force of wind and rain.

2. It must have sufficient tight joints to prevent loosing of grout because

grout leakage cause honeycombing of the surface.3. It should be built in such a way that it can be easily removed and stripafter concreting.

4. It should be capable of being re-used. To ensure this, the formworkmay be coated with oil to permit easy striking off and it should be clean

before storing immediately after striking

4.1.2 Materials for formwork

Various factors should be concerned when selecting a material for formwork

1. It must be durable material because it should be able to re-use severaltimes. As such it is economical.

2. The material should be impervious to water to prevent loss of waterfrom the face of the formwork.

3. It should be able to form the desired shape and easy to handle4. Material surface should be even and free from knots because fair face is

important.


13/26

Normally, formwork is made in timber, plywood or metal.

4.1.2.1 Metal formworkMetal formwork has a very high reuse potential. So it is more economical than

timber where repetitive work is necessary. In these all four subprojectsdimensions are somewhat exactly same. Therefore most of formworks are

metal formworks. However it should be handled correctly and thoroughlycleaned, oiled and maintained after each use. It gives smooth concrete finish.

Metal formwork is made up from spatially made shallow rectangular pans ofvarious sizes. These are clipped or bolted together to form the required shapes.The main disadvantage is rusts under humid condition.

4.1.2.2 Timber Formwork

Timber is the most commonly used material for general formwork because it

is easy to cut in to shapes, fix and dismantle and cheap. Timber formwork is

usually made from softwood free from excessive knots and other defects.

A problem some times caused by the timber formwork is the rapid absorption

of the moisture from the concrete.

So before concrete is placed timber should wet. Therefore moisture will not be

absorbed too fast from the wet concrete. But timber should not be too wet

because the timber with high moisture content will shrink which may resultopen joints and leakage of grout. If the timber is dry it will absorb the

moisture from the wet concrete which could weaken the resultant concrete

member.

4.1.2.2.1 Plywood formwork

Thick plywood, which is, smooth, fairly rigid and in large sizes is most

suitable for formwork. The advantage of using plywood in formwork is that itgives a good surface finish. Therefore it does not require any further

treatment. Plywood formwork can be used many times and easy to handle. But

Plywood formwork can be used many times and easy to handle. But Plywoodsheets are very expensive. Curved formwork is most satisfactorily constructed

by forming plywood to the required curve and fixing it to a rigid timber frame.


14/26

4.1.5 Tools used for formwork

1. Hammers2. Plumbob

3. Chisel4. Hacksaw5. Try square6. Ruler and tape

4.1.6 Cover blocks

Cover block is a small block of cement with blinding wire in middle. It helpsto maintain the right amount of concrete cover during construction. Theyshould be made to the thickness of the clear cover required for the job.

After the reinforcement are set, the cover blocks should be tied to the outer

bars from all sides i.e. cover blocks should be placed between thereinforcements and the formwork. Cover blocks also help to keep the bars in

position when concreting.

It is very important to check the cover blocks before starting concreting.

Generally 1:2 mix proportions should be used for cover blocks. Because highstrength is required as concrete. But in the site, 1:3 mix proportions of mortar

was used. Cover blocks should be cured on time to gain the required strength.

4.1.7Removability and striking

Forms may have to remain undistributed until the concrete reaches a

minimum strength until it is sufficiently cured, of the required colour or toprotect it. Formworks should be struck slowly and must not be struck untilconcrete is strong enough to self-supporting because edges can be damaged.

The appropriate time at which it is safe to remove the formwork depends on

the type of element. The minimum striking time varies from 1-28 days.

Location Minimum

period

Sides of the slab and

staircase01 day

Sides of the walls and

beams

03 days


15/26

Soffit of beam and lintels 14 days

Soffit of the slab and staircase

21 days

Table 02: Formwork strikability periods

But striking time vary according to

1. Weather conditions2. Type, size, shape, and position of the element in the structure3. Guidance given in the B.O.Q.

4.1.8 Maintenance and storage of formwork

Provision must be made for the removal and storage large sections of

formwork. A level storage area is required to store formwork after striking.They should be well cleaned before storing because the grout remaining on

the forms become hard and stubborn. Then it is difficult to reuse. Metal panels

need a light coating of oil before storage to prevent rust.

All forms need to be carefully stacked and stored. Panels of forms should bekept horizontal and face to face. The forms need to be carefully stacked and

face to face. The forms and components should be clearly marked and kepttogether for easy identification on re-use. A tidy store reduces wastage,damage and losses.

4.2 Types of formwork

Formwork is used for beams, Staircases, Slabs, Columns, Lintels, drains,Retaining walls and etc. When striking formwork of all types of works said

above should strike slowly and must not be struck until concrete is strongenough to be self-supporting. Because edges can be damaged.

4.2.1 Column formwork

Column formwork is a vertical mould assembled by boards as shown on

figure. It is also called as column box. Usually vertical boards are 25mmthick. The widths of the boards vary depending on the section of the column.


16/26

The boards internal dimensions should be equal to the external dimensions of

the column. Timber or steel struts can be used as supports. The struts shouldbe able to resist the vibration and pressure of casting.

The side of the box are secured firmly together by using tie-bolts. Tie-bolts

are rods of about 6mm diameter, which hold the formwork in place. The endsof the rods are treated, so that the work can be steadily secured by using nuts.Important to remember to check whether the required dimensions are in the

inner profile of the column box, after plumbing and align the formwork.

Formwork should be located against a Kicker. Concrete specification forcolumn is usually 1:2:4(3/4") with a clear cover of 50 mm.

4.2.1.1Plumbing the column

The most important thing is plumbing the column in both directions. Inwooden formwork, two batons are fixed to both top and bottom ends of the

formwork. So suspending a plumbob from a baton at top to the bottom does

this. Adjustments could be done by the props should be adjusted until thedistance between form and line at top and bottom are equal. After that using

the try square should check the angles of the formwork. The plumbing shouldalso repeat to the adjacent edge. Finally all the props should be checked for

tightness.

Immediately after the concrete is poured, the column should be checked forplumb and carefully adjusted if necessary.

4.2.1.2 Kicker formwork

Kicker is a 3" height wooden frame as shown in figure. It should be made to

the dimensions of the column.

Before set the kickers first mark the centre of the column and draw two cross

lines through centre point of the column. Then mark the centres of the foursides of kicker formwork by nails and tie two crosses strings and find out the

centre of the kicker formwork. After that coincide the formwork centre with

the column centre by helping the two cross lines marked earlier. At the correctposition fix the formwork to column reinforcements by wooden pieces as

shown in figure.

Laying kicker is essential to ensure accuracy of the column and prevent

loosening of grout from the bottom edge of the form. It also acts as an


17/26

anchorage against up thrust for the column shuttering. Kicker formwork

should be removed before column box is set.

4.2.2 Beam formwork

A beam formwork consists of a three sided box which is supported by cross

members and which are propped to the under side of the soffit board. Thestrength of the soffit board should be greater than the strength of two

sideboards. In some cases the beam formwork is prepared separately to fit the

each beam length and fix the beam formwork by bamboo props.

In our site using two strings, which fixed to the columns, aligns formwork.

First mark the height to the beam from the floor, on the columns and the propsare adjusted to that height. Then two runners are fixed in between the twocolumns. After that short runners are fixed (nailed) on the runners,

perpendicularly with 4 spacing. Then two string are tied leaving the beam

width in between them, between the two columns and the soffit board is fixedon the short runners with helping the strings. Finally the two sideboards arefixed and supported as shown on figure.

4.2.3 Formwork for stairs

A stair case provides a link between floors in building s. It should constructedto provide, easy comfortable and safe access up and down with steps that arenot difficult to climb.

When constructing formwork for stairs, the landing is first set in position.

After the landing is fixed two strings are tied between the landing and theground (upper) floor. Those two strings should maintain the width and the

inclination of the flight. Then joists (2x4 timber batons) place the soffit board

underneath and the props are nailed to the joists.

The sideboards are set in positions. On the sideboards the step height is

marked leaving the waist thickness from the baton by using strings. After that

marks the going & risers in between the two lines by using chalk and trysquare and riser boards are nailed to the sideboards by supporting hangers.

The splayed bottom edges of riser boards are nailed to the sideboards by

supporting hangers. The splayed bottom edge of riser boards help to completetrowelling of the tread surfaces and to make sure that air is not trapped underthe bottom edge of riser boards. The riser boards are supported by struts to

prevent the sideboards from falling apart when concrete is poured or due to

vibration.


18/26

Chapter 5

5.1 Reinforcement

Steel reinforcement material requirements

1. Tensile strength2. Easy to bent up to any required shape3. Effect to temperature changes

Therefore steel is the most suitable 3 basic types of steel bars,

1. High yield (torque steel) which has ribbed appearance and may betwisted tensile strength of 450N/mm2. In drawing normally denoted as

Y.

Bar bending was according to design requirement by a group of labourers whowere specialised in bar bending. Main source material, i.e. Steel is Steel

Corporation of Srilanka. To bend the bars steel pipes were used and to cut a

electric cutter and some times manual cutters were used for small diameterbars. For base of bending normally following simple shapes are used.

1. Straight2. Right angle bend3. Cranked4. Stirrups

In addition to these simple shapes BS4466 shapes are also used.

5.2 Foundation

Foundation is a part of a structure which transmits loads directly to theunderlying soil.If the soil near the surface is capable of adequately supportingthe structural load it is possible to use either footings or a raft.A footing is a

relatively small slab giving separate support to the structure.

Depending on the transmission of forces , foundations can be classified intotwo:

1. Shallow foundationstermed footings, spread footings, or mats.Foundation depth is generally D < B

2. Deep foundations - piles or caissons with D > 4 to 5B


19/26

Foundation types and typical usage

Foundation type Use Applicable soil conditions

Spread footing,

wall footings

Individual columns,

walls bridge piers

Any conditions where bearing capacity is

adequate for applied load. May use onsingle stratum: Firm layer over soft layer or

soft layer over firm layer.

Mat Foundation Same as spread and

wall footings. Very

heavy column loads.

Usually reduces

differential

settlements and total

settlement

Generally soil bearing value is less than for

spread footings; Over one-half area of

building covered by individual footings.

Check settlements

Pile foundations

floating

In groups (at least 2 )

to carry heavy

column, wall loads;

requires pile cap

Poor surface soils. Soils of high bearing

capacity 2050m below basement or

ground surface, but by distributing load

along pile shaft soil strength is adequate.

Corrosive soils may require use of timber or

concrete pile material.

Bearing In groups (at least 2)

to carry heavy

column, wall loads;

requires pile cap

Poor surface and near-surface soils; soil of

high bearing capacity (point bearing on) is

8-50m below ground surface

Caissons (shafts

75cm or more in

diameter)

generally bearing

or combination of

bearing and skin

resistance

Larger column loads

than for piles cap by

using caissons as

column extension

Poor surface and near-surface soils; soil of

high bearing capacity (point bearing on) is

8-50m below ground surface.

Retaining walls ,

bridge abutments

Permanent retaining

structure

Any type of soil, but a specified zone in

back of wall usually of controlled backfill

Sheet-pile

structures

Temporary retaining

structures as

excavations,

waterfront structures,

cofferdams

Any soil; waterfront structure may require

special alloy or corrosion protection.

Cofferdams require control of fill material.

Table 03: Foundation types


20/26

In my site (Athurugiriya) 2 constructions were going on simultaneously.They

are

1. Pump house2. Elevated water tower(insitu)

In the following drawings I have illustrated their foundation details

Fig 05: Pump house front elevation

Following drawings represents the elevated tower base foundation details.

Following chart provides the information regarding the piles information.


21/26

Fig 06 : Chart of pile configuration detail

However use of piles depends on several conditions as described in Table no03.And in the Athurugiriya site no piles were used.


22/26

Fig 07: Elevated tower base details

Fig 08: Elevated tower base slab reinforcement details

5.2 Concreting

Splay area concreting:

For each part of construction BMEC will prepare a procedure detailing which

is called method statement. Method statement for splay area is asfollows.(summarised)


23/26

Section elevation 44.10(T.B.M. 27.70)

Volume of 2parts 14m3,22m3 16mm steel cables were used hold the formworks. Distance between

steel cables 300mm

Splay area was covered with 24 pieces of plywood 10 X 10m timber

supported by the top screwed steel pipe

Works of second part done after 1st900mm high flat steel forms. In onesegment 24 groups and totalling 48 for both segments.

ICC will supply the grade 30 concrete with slump 8-12cm.

Temperature 32C

Tremie pipe always is within the form and allowed free fall is 1m. Thiscondition was maintained in order to prevent segregation.

Concreting will be worked circularly in order to maintain the level of

concreting. Mark of the level was marked with red colour anticorrosive,

which was used for maintenance of formworks. At each layer of circlewas maintained 30cm as the maximum.

For curing gunny bags were used.

Method statement of construction of bottom dome and conical section.

1. Bottom dome 900X400, 900X300, 900X200 steel shutters( connectedwith 48dia. Steel pipes)

2. About 48 trusses will be fixed kickerAn extended part of previouslyconnected structure(here it is 10cm)

3. 5 mixers will supply volume of concrete 48m3, and 2 pump trucks willbe used. Detailed drawings of the constructions are as follows,


24/26

Fig 09: Elevated tower part sectional elevation

Fig 10: Elevated tower part sectional elevation


25/26

Chapter 6

6.1 Control and safety at the site

Each item of work control and safety was carefully mentioned in the contractconditions book. It is also important to have a copy of this at each site office.

Office equipment and temporary office facilities such as air-conditionedcontainer box were supplied by BMEC (contractors). BMEC has the authority

to prevent the trespassing of unauthorised persons. Land was acquired byNWSDB from Steel Corporation. Wooden ladder (as a temporary measure)

was provided along the tower for inspection of engineer (clientNWSDB).

Nylon net was used to cover almost entire tower (even covering the scaffolds)in order to prevent the personals falling from the tower in the case of

accidents. Medical expense for the labourers in the case of accidents on thesite was covered by BMEC.

Labourers were categorised by the work they are specialised and handled byseparate Chinese Forman as follows,

1. Barbending labourers -10

2. Carpentry labourers -153. General labourers -5

Basic salary was 250 per day per labourer and overtime was 100/= per hour

per labourer. Since employeeemployer contract laws are not so handledstringently there are can be seen many time that these employers are abusing

the employees. One good example is that removal/cleaning collapsed

boundary wall. Where the boundary wall had some broken glass pieces.

Chapter 7

PRACTICAL DIFFICULTIES ENCOUNTERED

As the work is given to more and more sub-contractors, it becomesmore and more difficult for the executive engineer to control the work.

All brought-in items such as cement, sand, timber etc. must be

inspected carefully, as sub-standard items can be brought in to get moreprofit by the contractors.


26/26

Documents

Water Tower Tank Structrual Design