design of an underground water tank for gegele …
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DESIGN OF AN UNDERGROUND WATER TANK
FOR GEGELE COMMUNITY IN KWARA STATE
BY
AFODUN, MUHAMMAD MUKHTAR
(08/30GB017)
JULY 2013
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DESIGN OF AN UNDERGROUND WATER TANK FOR GEGELE COMMUNITY IN KWARA STATE
BY
AFODUN, Muhammad Mukhtar (08/30GB017)
DEPARTMENT OF CIVIL ENGINEERING
UNIVERSITY OF ILORIN, NIGERIA.
A Project submitted to the Department of Civil Engineering,
University of Ilorin, in partial fulfillment of the requirement for the award
Of Bachelor of Engineering Degree in Civil Engineering.
JULY 2013
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CERTIFICATION
This is to certify that this project has been read and approved as part of the requirement of
the Department of civil engineering, University of Ilorin, for the award of Bachelor of
Engineering Degree (B. Eng.) in Civil Engineering.
________________ _________________
Dr. O.G. Okeola DATE Project Supervisor
________________ _________________
Prof. Y.A. Jimoh DATE Head of Department
________________ _________________ External Examiner DATE
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DEDICATION
This project is dedicated to Almighty Allah, the All-Knowing, the All-Wise,
The Lord of the Worlds and the Master of the Day of Recompense.
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ACKNOWLEDGEMENT
My sincere gratitude goes to Almighty God for the priceless life given to me and for granting
me the grace to complete my first degree in Civil Engineering.
Due appreciation also goes to my project supervisor Dr. O. G. Okeola, for his profound
supervision, kindness, generousity, care and most importantly, for giving me the design text
on which the copious part of this project is based - Anchor, R. D. (1992), Design of Liquid
Retaining Concrete Structures, 2nd edition. Your support and contribution to my success is
indeed great.
I am extremely grateful to my parents, Alhaji and Alhaja Afodun for their unrepayable love,
guidance and care throughout my life. I also thank my siblings for their advice and prayers.
I thank the following people whose efforts and assistance has helped me in writing this
project:
Prof. Y. A. Jimoh of the Civil Engineering department, University of Ilorin, who
introduced earth retaining structures in the 400 level course work,
Dr. S. A. Raji of the Civil Engineering department, for his keen interest and his
assistance on tank safety accessories,
Engr. AbdulHamid Ayomaya of Index Consultants for his explanation of detailing
concrete structures,
Engr. Akinola of Makins consultant who made available the subsoil parameters of
the project site,
Akinola Olakunle Kenneth for his illustrative tutorials on structures,
Agboola Asimiyu, for his tutorial on Global Mapper,
Alao, Ameen and Wusu for the wonderful time we had together as fellow project
students,
I am also greatly indebted to Prof. J. A. Olorunmaiye for his fatherly concern throughout my
undergraduate years. I thank TOTAL E&P Nigeria Ltd. for the scholarship I was awarded as it
assisted me financially throughout my undergraduate study. Lastly, I thank the multitude of
people who might have helped me and are not mentioned herein.
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NOTATION
As area of steel reinforcement
c nominal concrete cover
d effective depth
fb average bond strength between concrete and steel
fct tensile strength in concrete
fcu characteristic cube strength of concrete at 28days
fs Service steel stress
fy strength of steel
H depth of liquid
Ka active earth pressure coefficient
L length of member
M bending moment
n total load per unit area, number of years
Pn Future population
Po Present population
q Distributed imposed load per unit area
r population growth rate
R Restraint Factor
smax estimated maximum crack spacing
T1 fall in Temperature from Hydration peak to ambient,
T2 Variation in temperature
v shear stress
vc critical concrete shear stress for ultimate limit state
V total shear force
wmax maximum allowable crack width
αc Coefficient of linear expansion of concrete
ɣ Density of Soil
ɣf Partial safety factor for load
ɣm Partial safety factor for material strength
ɣw Unit weight of water
ρ steel ratio
ρcrit critical steel ratio
ɸ Angle of repose, diameter of reinforcement steel
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ABSTRACT
This project is aimed at designing an underground water tank which is to be synchronized
with or to augment existing and insufficient overhead water tanks in Gegele community,
Kwara state. The project methodology involves mapping and Geo-information, survey and
siting of tank, population estimation, water demand estimation, structural analysis and
design. The design approach of the liquid retaining structure is limit state design using BS
8007 and BS8110. The design caters for strength, floatation flexural and thermal cracking.
The calculated volume of the tank needed to augment the existing overhead tanks is 600m3
and it has two compartments of 300m3 each. The wall, roof slab and floor slab thicknesses
are 350mm, 250mm and 400mm respectively. Provision of reinforcement in walls: vertical
bars: T20 @ 175mm c/c Each Face (1800mm2), horizontal bars: T20 @ 175mm c/c Each Face
(1800mm2), floor slab: Top face- T25 @150 c/c Top Face Shortspan, T25 @175 c/c Top Face
longspan, Bottom face- T20 @ 100 c/c Each Way Bottom face, top Slab: T16 @150 c/c both
faces. It is expected that the Underground water reservoir will improve water accessibility
and distribution in Gegele community. The structure is designed to meet stability, strength
and serviceability requirements as stated by BS8007 and BS8110.
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TABLE OF CONTENTS
Title page i
Certification iii
Dedication iv
Acknowledgement v
Notations vi
Abstract vii
Table of Contents viii
List of Tables xi
List of Figures xii
CHAPTER ONE: INTRODUCTION 1
1.0 Introduction 1
1.1 Problem Statement 1
1.2 Aim and Objectives 2
1.3 Justification 2
1.4 Scope of Work 2
1.5 Description of Study Area 3
CHAPTER TWO: LITERATURE REVIEW 6
2.0 Introduction 6
2.1 Water Demand 6
2.1.1 Introduction 6
2.1.2 Population Forecast 7
2.1.3 Arithmetical progression of population 7
2.1.4 Water Demand 7
2.2 Types of Water Tanks 8
2.3 Objectives of Structural Design 11
2.4 Fundamental Design Methods 11
2.5 Impermeability 11
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2.6 Site Conditions 12
2.7 Tension, compression and flexural resistance of walls 12
2.8 Exposure classification 13
2.9 Structural Layout 14
2.10 Joints in Liquid retaining structures 14
2.11 Civil Engineering Standard Method of Measurement (CESMM) 16
2.11.1 Preparation of Bill of quantities 17
2.11.2 Project Cost Estimation 18
2.12 Review of past works 18
CHAPTER THREE: METHODOLOGY 20
3.1 Preliminary Studies 20
3.1.1 Mapping and Geo-information 20
3.1.2 Survey and Siting of Tank 20
3.2 Population Estimation 21
3.2.1 Average Population per building 21
3.2.2 Future population Estimation 21
3.3 Tank sizing 21
3.3.1 Water demand estimation 21
3.4 Structural analysis and Design 23
3.4.1 Limit State Design 23
3.4.2 Ultimate limit state 23
3.4.3 Serviceability limit state 23
3.5 Loading 23
3.6 Wall thickness 23
3.6.1 Ease of construction 24
3.6.2 Structural arrangement 24
3.6.3 Adequate strength in shear 24
3.6.4 Cracking due to tensile forces 25
3.7 Floatation 25
3.8 Rate of Materials 25
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3.9 Design of Underground Tank 26
3.10 Structural Drawings and detailing 47
3.11 Bar bending schedules 56
3.12 Bill of Engineering Measurement and Evaluation. 58
3.12.1 Quantity of Materials 58
CHAPTER FOUR: CONCLUSION AND RECOMMENDATION 62
4.1 Conclusion. 62
4.2 Recommendations 62
References 63
APPENDIX 65
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LIST OF FIGURES
Figure Title Page
1.1 Aerial Photograph of Gegele community showing the location of the existing insufficient overhead tanks and the location of the proposed underground tank. Source: Google Earth
4
1.2 Map of Kwara State showing its constituent local Governments
5
1.3 Map of Nigeria showing Kwara State. 5
2.1 tension and compression in a cylindrical tank 13
2.2 Walls of a rectangular tank 13
2.3 complete contraction joint 15
2.4 partial Contraction joint 15
2.5 Expansion joint 16
2.6 Sliding joint 16
3.1 Image of digitalized buildings using global mapper (Buildings are easier
to count in this image as compared to satellite imagery).
22
3.2 Plan view of tank 48
3.3 Sectional Elevation of Tank 48
3.4 Top Slab detailing 49
3.5 Floor Slab Detailing 50
3.6 Walls D&E detailing 51
3.7 Wall A Detailing 52
3.8 Cross sectional Elevation showing reinforcements 53
3.9 Sectional Side Elevation 54
3.10 Access plan detailing 55
3.11 Sectional elevation of access showing detailing 55
3.12 3D model of Tank 56
B.1(b) Bending Moment Coefficient for walls 66
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LIST OF TABLES
Table Title Page
3.1 Approximate minimum thickness of R. C. Cantilever wall subjected
to water pressure
24
3.2 Roof slab Bar Bending schedules 57
3.3 Floor slab Bar Bending schedules 57
3.4 Wall D&E Bar Bending schedules 57
3.5 Wall A Bar Bending schedules 58
3.6 Access Bar Bending schedules 58
3.7 Reinforcement quantities of various members 60
3.8 BEME of Construction Materials (Labour and profit overhead of 25%
is included)
61
C.1 Sectional Areas per metre width for various bar spacing 66
3.14 Bending moment Coefficients for rectangular panels 67
A2.3 Limiting Moments tables 68
A2.6 Limiting Moments tables 68
A2.7 Limiting Moments tables 69
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CHAPTER ONE: INTRODUCTION
1.0 Introduction
The necessity to store and supply purified water has been a major source of civil engineering
activity for many civilizations (Ian and Roger, 1991). The growing need for water tanks was
impelled by climate change, water scarcity and rapid population explosion within the last
decade. Climate change has a major effect on the amount of water flowing in rivers and has
strained the level of water stored in the water supply reservoirs.
Underground tanks are liquid containing vessels that accommodate the internal pressure
from the containing fluid and the lateral earth pressure from the surrounding soil.
Underground water tanks are used to store water, petroleum products and similar liquids.
The force analysis of the tanks is about the same irrespective of the chemical nature of the
content. All tanks are designed as crack free and water proof structures to eliminate any
leakage to the soil and also to prevent seepage into the tank there by causing contamination
(Sahoo, 2008).
Water is one of the basic necessities for a human being. Different sectors of the society use
water for different purposes, for example drinking, cooking, bathing, and washing clothes
and sanitation. Water requirements for a society varies upon factors such as number of
buildings in the society, number of floors in each building, number of flats on each floor, etc.
swimming, gardening have become additional factors for increased water demand
nowadays (Gupta, 2010).
1.1. Problem Statement
The Nigeria water sector is faced with a lot of challenges which have made the sector
perform below expectations. Of these problems is lack of adequate infrastructure for water
storage and distribution. For quality water to be made available for all, water distribution
infrastructures like underground and overhead tanks water tanks must be placed in every
community to meet daily water demand at a relatively low cost and with ease.
Gegele is a community that has a problem of poor water supply and distribution and it has
also been faced with a problem of low pressure water from the supply mains in the past,
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though this problem no longer exists. The supply is also erratic, which calls for water storage
to cater for peak and off-peak demand. Gegele community is usually supplied by 12
municipal overhead water tanks about a year ago. However, the number has been reduced
to 4. The overhead tanks are situated near the Ilorin Central mosque. The numbers of the
tanks were reduced due to concern over the aesthetics of the newly rehabilitated mosque.
1.2 Aim and Objectives.
The aim of this project is to design for a durable, reliable, economic and functional
underground water tank for Gegele community in Kwara State. The specific objectives to
accomplish the aim are:
Estimation of water demand for Gegele community.
Structural analysis of underground water tanks.
Economic design and detailing of the concrete underground water tank.
Carry out BEME for the designed tank.
1.3 Justification.
Water is one of the basic necessities for human survival and making it available for
consumption requires infrastructures like underground tanks. Nigeria is a country that
needs to invest more in water supply and distribution infrastructures to be able to achieve
the millennium development goals (MDG). Therefore the justification of this project is to
improve water supply and distribution by the optimum synchronization of an underground
water reservoir with the existing distribution network.
1.4 Scope of Work
The scope of the project will be limited to the design of an underground tank for Gegele
community in Kwara State to augment the existing overhead tanks. The general idea is to
collect and store water from the supply mains in the proposed underground tank and then
distribute it to Gegele community under gravity. The Northern and higher part of Gegele can
be supplied water from the existing overhead tanks efficiently through pipe isolation.
However, this project does not detail the technique of pipe isolation. The design approach
of the liquid retaining structure is limit state design under BS 8007 and BS8110.
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1.5 Description of Study Area
The study area is Gegele community situated within Ilorin West Local Government Area. It is
an urban settlement in the heart of Ilorin metropolis of Kwara State (see Figures 1.1, 1.2 and
1.3). Gegele has a global coordinate of 8° 29ʹ 41.89ʺ N and 4° 32 ʹ 53.24ʺ E. Gegele is grossly
populated by indigenes though most commercial activities are along the major roads. The
gradient is relatively high with elevations of 318m in the northern part to 310 m in the
Southern part.
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Figure 1.2: Map of Kwara State showing local Government of the study area (hatched)
Figure1.3: Map of Nigeria showing Kwara State
(Source: upload.wikimedia.org/Wikipedia/commons/8/82/Nigeria_Kwara_State_map.png)
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Chapter Two: Literature Review
2.0 Introduction
The water supply facility for each person must be continuous and sufficient for personal and
domestic uses. Domestic uses ordinarily include drinking, personal sanitation, washing of
clothes, food preparation and personal and household hygiene. According to the World
Health Organization (WHO), between 50 and 100 litres of water per person per day are
needed to ensure that most basic needs are met and few health concerns arise. The water
required for personal or domestic use must be safe, therefore free from micro-organisms,
chemical substances and radiological hazards that constitute a threat to health. Measures of
drinking-water safety are usually defined by national and local standards. WHO’s Guidelines
for drinking-water quality provide a basis for the development of national standards that, if
properly implemented, will ensure the safety of drinking-water (United Nations, 2010).
Factors such as Population explosion, Expansion of business activity, Rapid urbanization,
Climate change, Depletion of aquifers have caused increasing demand for water.
Water resources are sources of water that are useful or potentially useful. Uses of water
include agricultural, domestic, industrial etc. Virtually all of these human uses require fresh
water. 97% of the water on the Earth is salt water. However, only three percent is fresh
water; slightly over two thirds of this is frozen in glaciers and polar icecaps. The remaining
unfrozen fresh water is found mainly as groundwater, with only a small fraction present
above ground or in the air. Nigeria is blessed with abundant water resources which have not
been adequately harnessed. Water resources development evolved with the urbanization
that followed the advent of western form of administration that tended to concentrate
efforts on large scale programme by creation of artificial lakes and emphasis later on
boreholes in areas removed from the man-made lakes. (Fagoyinbo, 1998)
2.1 Water Demand
2.1.1 Introduction
According to World Health Organization (WHO) the average consumption for every human
being to have access to sufficient water for personal and domestic use is between 0.05 and
0.1 cubic metre of water per day (United Nations, 2010). In a recent study by Sule et. al.,
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(2010), it was found out that most Ilorin residents use between 0.046 to 0.115 cubic metre
of water per person per day. Before designing proper water works project, it is essential to
determine the quantity of water that is required daily. This involves the determination of
the following items.
2.1.2 Population Forecast
There are several methods for population forecast, these include:
1. Arithmetic progression method
2. Geometrical progression method
3. Incremental increase method
4 Decreased rate of growth method
2.1.3 Arithmetical progression
This method population forecast, gives lower results. In this method the increase in
population from decade to decade is assumed constant. This method should be used for
forecasting population of large cities which have reached their saturation population.
(Punmia et. al.,1995). Generally, water supply projects are designed for a design period of
20 to 40 years after their completion. The population at the end of the design period would
be used to design the tank capacity. Mathematically,
rategrowthpopulationr
yearsofNumbern
populationInitialP
yearsatPopulationP
Where,
Eqn(3.1) nr)(1PP
0
n
0n
n
2.1.4 Water Demand
An average person may consume no more than 5to 8 litres a day in liquid and solid foods,
including 3 to 6 litres in the form of water, milk and other beverages. However, the per
capita consumption of water drawn from public supply is quite large (Punmia et. al., 1995).
Total water requirements may be divided into five categories some of the categories are:
1. Residential or domestic use
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The residential or domestic use includes water requirements for drinking, cooking, bathing,
washing of clothes, utensils and house, and flushing of water closets. Provision is sometimes
made for domestic animals. According to World Health Organization (WHO) the average
consumption for every human being to have access to sufficient water for personal and
domestic use is between 0.05 and 0.1 cubic metre of water per day (United Nations, 2010).
2. Water systems losses
Losses from a water distribution system consist of (Punmia et. al., 1995):
i. Leakage and overflow from service reservoirs
ii. Leakage from main and service pipe connections
iii. Leakage and losses on consumer’s premises when they get unmetered household
supplies
iv. Under-registration of supply meters
v. Large leakage or wastage from public taps.
Losses in supply lines are mainly due to defective pipe joints , cracked pipes, and loose valve
and fittings.
2.2 Types of Water Tanks
A water tank is used to store water to tide over the daily requirements. In general, there are
three types of water tanks:
(i) Surface tanks
(ii) Elevated tanks, and
(iii) Underground tanks.
Water tanks could also be made from ranges of materials such as (Woolhether, 2012):
1. Plastic: A plastic underground water tank is lightweight, easy to handle and easy to
install. Plastic water tanks present no health risks. Water can be kept fresh and
uncontaminated for long periods. Plastic tanks are used in many countries where
fresh water is scarce. In Nigeria, for instance, plastic tanks are used to store
rainwater for drinking purposes. Other areas may use the stored water for
agricultural needs such as irrigation or for watering livestock.
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2. Concrete: Precast or cast-in-place concrete is an exceptionally strong and durable
material used for underground water tanks. Concrete tanks are built to withstand
the gases and chemicals emitted from the soil. Underground concrete tanks work
well where space is a challenge. Concrete works especially well in fire-prone areas. If
placed underground, there is minimal risk of damage from fire or environmental
factors.
3. Fiberglass: Underground water tanks made of Fiberglas are lightweight and versatile.
They are durable and are not susceptible to corrosion or leakage. Fiberglas tanks are
less expensive than steel or concrete. Installation is much simpler and less time-
consuming. Fiberglass underground water tanks can safely store fresh water for
short- or long-term use.
4. Steel: Underground water tanks can be constructed of carbon steel, lined carbon
steel or stainless steel. These steel tanks receive a corrosion resistant polyurethane
coating. Steel tanks are considered safe and contamination-free for storing potable
or non-potable water. They come in a variety of shapes and sizes for both
commercial and residential use.
From the shape point of view, water tanks may be of several types, such as:
1. Circular tanks
2. Rectangular tanks
3. Spherical tanks
4. Circular tanks with conical bottoms (Intze tanks).
5. Conical tanks
Rectangular tanks are usually used when small capacity or volume of water is required. For
small capacities circular tanks prove uneconomical as the shuttering (formwork) for circular
tank is very costly. The rectangular tanks should be preferably square in plan so as to
economize construction material. It is desirable that the longer side should not be greater
than twice the smaller side (Mohammed, 2011).
However rectangular tanks are not used for large capacities since they are not economical
and also, its exact analysis is difficult. For a given capacity perimeter is least for a circular
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tank (Punmia et al, 2003). The choices of concrete as the material for constructing the
underground water tank have many advantages over other materials, including: (Gibson
2010)
Inherent strength making them naturally rigid and durable.
Durability with no danger of rusting, corroding or being damaged by tree roots.
Availability in a variety of different sizes.
Concrete tanks are not liable to ‘float’ like a plastic tank may under high Hydrostatic
pressure.
Concrete is made from natural materials and is therefore easily recycled.
Concrete tanks save space by being buried underground.
Keeping water cool.
In the construction of concrete structures for the storage of liquids, the imperviousness of
concrete is an important basic requirement. Hence, the design of such construction is based
on avoidance of cracking in the concrete. In addition, concrete tanks require low
maintenance. Concrete construction makes for a substantial, sturdy tank structure that
easily contain the internal liquid pressure while comfortably resisting external forces such as
earthquake, wind, and lateral earth pressure. The water tank has to be far away from
sanitary structures such as soak-away and septic tanks.
Since the capacity of the tank is likely to be large, it would be economical to use a cylindrical
shape for the tank; otherwise a rectangular tank is preferred. The dimension, capacity or
volume of the tank will be determined by multiplying the standard average consumption of
water per person multiplied by the population of the community.
When tanks are situated underground, the walls of the tank are to be designed for earth
pressure as well as water pressure acting separately, and also acting simultaneously.
Similarly the floors of the tank are to be designed for hydrostatic water pressure (if water
table is higher) acting upwards. The walls of underground tanks are designed for earth
pressure, especially when the tank is empty. Such a condition is very frequently experienced
as and when the tank is emptied for cleaning purposes. The active earth pressure, which
varies triangularly along the depth of tank wall, depends upon the conditions of side fill. If
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the water table rises up to ground, or even up to the level above the tank, additional
hydrostatic pressure due to subsoil water will be experienced (Punmia et al, 2003)
2.3 Objectives of Structural Design
A structure that is designed to retain liquids must fulfill the requirements for normal
structures in having adequate strength, durability, and freedom from excessive cracking or
deflection. In addition, it must be designed so that the liquid does not percolate or leak
through the concrete structure. In the design of liquid retaining structures, if the structure
has been proportioned and reinforced to be leak-proof, then the strength is more than
adequate. The requirements for ensuring a reasonable service life for the structure without
undue maintenance are more onerous for liquid retaining structures than for normal
structures, and adequate concrete cover is also essential. Equally the concrete itself must be
of good quality and well compacted (Anchor, 1992).
2.4 Fundamental Design Methods
Historically, the design of structural concrete has been based on elastic theory with
specified maximum design stresses in the materials at working loads. More recently limit
state philosophy has been introduced providing a more logical basis for determining factors
of safety. In limit state design, the working or characteristic loads are enhanced by being
multiplied by a partial safety factor (Anchor, 1992).
Formerly, the design of liquid-retaining structures was based on the use of elastic design
with material stresses so low that no flexural tensile cracks developed. This led to the use of
thick concrete sections with copious quantities of mild steel reinforcement. The probability
of shrinkage and thermal cracking was not dealt with on a satisfactory basis, and nominal
quantities of reinforcement were specified in most code of practice (Anchor, 1992).
2.5 Impermeability
Concrete for liquid retaining structures must have low permeability. This is necessary to
prevent leakage through concrete and also to provide adequate durability, resistance to
frost damage and protection against corrosion for reinforcement and other embedded steel.
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The minimum thickness of concrete for satisfactory performance in most structures is
200mm (Anchor, 1992).
Liquids loss may occur at joints that have been badly designed or constructed and also at
cracks. It is however found that cracks of limited width do not allow liquid to leak and the
problem for the designer is therefore to design the structure so that surface crack widths
are limited to a predetermined size (Anchor, 1992).
2.6 Site Conditions
The choice of site for a reservoir or tank is usually dictated by requirements outside the
structural designer’s responsibility, but the soil conditions may significantly affect the
design. A well-drained site with under lying soils having a uniform bearing pressure at
foundation level is ideal. A high level ground water must be considered in designing the
tanks in order to prevent flotation and poor bearing capacity may give rise to increased
settlement (Anchor, 1992).
The soil investigation must also include chemical tests on the soils and ground water to
detect the presence of sulphates or other chemicals in the ground which could attack the
concrete and eventually cause corrosion of the reinforcement (Anchor, 1992).
2.7 Tension, compression and flexural resistance of walls
Generally, there are two fundamental ways in which the pressures subjected to the tank can
be contained:
1. By forces of direct tension and compression (Fig 2.1).
2. By flexural resistance (Fig 2.2).
Anchor (1992) explained that structures designed using tensile or compressive forces are
normally circular and may be prestressed. Rectangular tanks rely on the flexural action using
cantilever walls, propped cantilever walls, or walls spanning in two directions.
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Figure2.1: tension and compression in a cylindrical tank (Source: Anchor, 1992)
Figure2.2: Walls of a rectangular tank (Source: Anchor, 1992)
2.8 Exposure classification
Structural concrete elements are exposed to varying types of environmental conditions. The
roof of a pump house is waterproofed with asphalt or roofing felt and, apart from a short
period during construction, is never exposed to wet or damp conditions. The lower section
of the walls of a reservoir are always wet (except for brief periods during maintenance), but
the upper sections may be alternately wet and dry as the water level rises. The underside of
the roof of a closed reservoir is damp from condensation (Anchor, 1992).
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Precautions should be taken to ensure that moisture and air do not penetrate to the
reinforcement and cause corrosion which in turn will cause the concrete surface to spall.
Adequate durability can be ensured by providing a dense well-compacted concrete mix with
a concrete cover of 40mm, but it is also necessary to control cracking in the concrete and
prevent percolation of liquid through the member (Anchor, 1992).
Presently, the faces of liquid retaining structure are designed for a crack width of 0.2mm or
0.1 mm in some members where appearance is very important. Previous designed used
different exposure classes A, B and C for various faces under different situations. The Code
of practice for Design of concrete structures for retaining aqueous liquids (BS 8007) requires
that all liquid-retaining structures should be designed for at least “severe conditions of
exposure.
2.9 Structural Layout
Generally, assuming member sizes precede any form of detailed analysis of the structure.
Generally, structural design should be considered from the viewpoints of strength,
serviceability, ease of construction and cost. In liquid-retaining structures, it is particularly
necessary to avoid sudden changes in section since they cause concentration of stress and
hence increase the possibility of cracking (Anchor, 1992).
It is a good principle to carry the structural loads as directly as possible to the foundation,
using the fewest structural members. It is preferable to design cantilever walls as tapering
slabs rather than as counterfort walls with slabs and beams (Anchor, 1992).
2.10 Joints in Liquid retaining structures
1. Contraction Joint
It is a movement joint with deliberate discontinuity without initial gap between the concrete
on either side of the joint. The purpose of this joint is to accommodate contraction of the
concrete (Sahoo, 2008). The joint is shown in Fig.2.3.
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Fig 2.3 complete contraction joint (Source: Sahoo, 2008)
A contraction joint may be either complete contraction joint or partial contraction joint. A
complete contraction joint is one in which both steel and concrete are interrupted and a
partial contraction joint is one in which only the concrete is interrupted, the reinforcing
steel running through (Sahoo, 2008) as shown in Fig.2.4
Fig 2.4 partial Contraction joint (Source: Sahoo, 2008)
2. Expansion Joint
It is a joint with complete discontinuity in both reinforcing steel and concrete and it is to
accommodate either expansion or contraction of the structure. A typical expansion joint is
shown in Fig.2.5
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Fig 2.5 Expansion joint (Source: Sahoo, 2008)
This type of joint requires the provision of an initial gap between the adjoining parts of a
structure which by closing or opening accommodates the expansion or contraction of the
structure.
3. Sliding Joint
It is a joint with complete discontinuity in both reinforcement and concrete and with special
provision to facilitate movement in plane of the joint. This type of joint is provided between
wall and floor in some cylindrical tank designs (Sahoo, 2008). A typical joint is shown in
Fig.2.6
Fig 2.6 Sliding joint (Source: Sahoo, 2008)
2.11 Civil Engineering Standard Method of Measurement (CESMM)
The main purpose the Bill of Quantities is to assist the contractors to produce an accurate
tender figure efficiently and to enable post contract administration be carried out in an
efficient and cost effective manner. Estimation is the process of pricing based on the
~ 17 ~
available information, specification, and various drawings toward arriving at total sum
known as tender sum. This is to be done within the context of form of contract and terms in
which the sum will apply or may vary (Okeola, 2012).
2.11.1 Preparation of Bill of quantities
The phrase ‘Bills of Quantities’ is more appropriate to a building contract where the General
Summary contains a list of individual Bills. In civil engineering documents the equivalent Bills
are called Parts so the overall document is a Bill of Quantities. The pre-contract exercise of
measuring the work also applies to the post-contract task of measurement. The correct
term for this task is re-measurement where the work is physically measured on site or
admeasurement where the actual quantities are calculated from records (Okeola, 2012).
There are five sections in the Bill of Quantities:
1. Preamble
2. List of Principal Quantities
3. Day work Schedule
4. Work Items (divided into parts)
5. Grand Summary
1. Preamble
The Preamble is an extremely important section of the Bill of Quantities and is the
potentially vital source of information to the estimator. If any other Methods of
Measurement have been used in the preparation of the Bill of Quantities, the fact should be
recorded there (Okeola, 2012).
2. Preliminaries
The preliminaries section of the bill of quantities is the engineer or QS’s introduction to the
contract. The section provides information on the location, size, and complexity of the
project and gives details of the conditions of contract under which the project is to be
implemented (Okeola, 2012).
~ 18 ~
3. Coding and numbering
The aim of the coding is to produce a uniformity of presentation to assist the needs of
the estimator and the post-contract administration.
2.11.2 Project Cost Estimation
There are many approaches to preliminary estimates of proposed projects. They all use
some measures of gross unit costs from recently completed construction works which are
updated by the use of factors which recognizes cost differences as a result of time frame,
location or any peculiarities of the work that is being estimated. However in general the
estimating structure comprises (Okeola, 2012):
Dividing the project into small elements so as to allow a single rate or unit cost to be
applied to each element
Extending the quantities and rates to determine a cost for each element
Summing the resulting elemental costs and
Applying indirect costs to give a complete estimate.
2.12 Review of past works
Mohammed (2011) stated that the design of a tank can be more economical, reliable and
simple if optimization method is used to calculate the minimum cost of structural design of
rectangular and circular sanitary concrete tanks.
A brief theory behind design of liquid retaining structure (circular water tank with flexible
and rigid base and underground water tank) using working stress method was presented by
Sahoo (2008) as a final year project. The study also included computer subroutines to
analyze and design circular water tank with flexible and rigid base and rectangular
underground water tank. The programme was written in Microsoft excel using visual basic
programming language.
Fagbemi (2011) worked on the analysis and design of an elevated water tank to meet the
daily water demands of Tanke Akata and Tanke Iledu areas of Ilorin, Kwara State. A
concrete- Intz tank was the type of tank chosen for design from economical and capacity
~ 19 ~
point of view, the design approach was elastic design method. The project also highlighted
water demand and use.
Gupta (2010) analyzed the theory behind the design of liquid retaining structure such as
rectangular underground water tank. The report also included design requirements of water
tank, survey, excavation methods, reduced levels, average depth of UGWT, soil on which it
is constructed, depth of water table, type of mix design and capacity of the tank. The tank
was designed for Gyanganga society which is a residential settlement.
~ 20 ~
CHAPTER 3: METHODOLOGY
The methodological steps involved in executing the project are outlined below:
3.1 Preliminary Studies
The Preliminary studies are findings which are paramount to the structure to be designed.
The preliminary studies are:
3.1.1 Mapping and Geo-information
Google earth software was used to show location of catchment by aerial photographs. This
software also states the elevation of various points above sea level. For effective and
efficient distribution the tank’s proposed location is the highest in the area, with an
elevation of 319m above sea level. The elevation of the area reduces outward from the
location. The location of the existing overhead tank is about 10m away. For maximum water
pressure during distribution the buildings closer to the tank will be supplied from the
overhead tank while buildings farther away and of lower elevation will be supplied by the
Underground tank.
3.1.2 Survey and Siting of Tank
The survey was to establish the number and capacity of overhead water tanks. Four
overhead cylindrical steel overhead tanks stacked on steel stanchions exist but only three of
the tanks serve Gegele community. The parameters of the overhead tanks are:
Number of tanks = 4
Number of tanks serving Gegele = 3
Length of tank= 6.4m
Diameter of tank=3.048m
Volume of each tank=46.72m3
Total volume of tanks= 46.72m3x3 =140.16m3
Survey also shows that proposed tank location is well drained and not sunken. The tank is
sited far away from sewage and septic tanks to prevent contamination and on a soil with
good Bearing capacity. The site is also of high altitude so that effective pressure for efficient
distribution can be generated.
~ 21 ~
3.2 Population Estimation
3.2.1 Average Population per building
Global Mapper was used to digitalize the satellite imagery (fig 3.1) of Google Earth, the
digitalized imagery eases building count which is used in calculating the population of the
catchment. The average population per building was estimated from a sample. From a
research carried out by Sule et Al. most building in the medium density area of Ilorin have a
population of 5-8 people per building.
3.2.2 Future population Estimation
people7398
0.025))(204932(1P
2.5%r
Years20n
people4932P
Eqn(3.1) nr)(1PPformula, rategrowth ArithmetictheUsing
rategrowthpopulationr
yearsofNumbern
.populationInitialP
years.20atPopulationP
years20ofperiodafordesignedisStructure
2.5%NigeriaofrategrowthPopulation
n
0
0n
0
n
3.3 Tank sizing
3.3.1 Water demand estimation
Population estimate for Gegele community, arithmetic population growth rate of 2.5% and
WHO per capita water demand was used to estimate the size and geometry of the tank for a
20-year design period.
~ 22 ~
Figure3.1: Image of digitized buildings using global mapper (Buildings are easier to count in
this image as compared to satellite imagery).
~ 23 ~
3.4 Structural analysis and Design
The tank was designed and detailed to BS 8007 & 8110 using limit state design approach.
Lateral earth pressure, hydrostatic and surcharge pressures are analyzed in depth. Design
caters for strength, flotation, tensile, flexural and thermal cracking.
3.4.1 Limit State Design
Limit state design of an Engineering structure ensures that structure is safe, durable and
serviceable. In this method of design working loads are multiplied by partial factors of safety
and the material strength are divided by further partial factors of safety.
3.4.2 Ultimate limit state
This limit state satisfies strength, (i.e strength of the structure against collapse or failure.)
3.4.3 Serviceability limit state
Serviceability limit state controls of excessive deflections and crack widths when structure is
under service loads. Serviceability limit state ensures that structure is serviceable under
loads. Serviceability also ensures a structure is fire resistant. Generally, in liquid retaining
structures when the serviceability is satisfied, then strength would also have been satisfied
3.5 Loading
Liquid retaining structures are subjected to external earth pressure due to surcharge and
soil excluded. The internal loads are due the retained liquid, in this case the liquid retained
is water with an approximated density of 10 KN/m3. There are two most critical loading
cases for the external walls of the reservoir: when tank is full and when tank is empty. When
the tank is full with water, the passive resistance of the soil is neglected. Also when tank is
empty, only the lateral earth pressure is to be considered. For internal walls dividing a tank
into compartments, the most critical loading case is when a compartment is full while
another is empty. A partial factor of safety of 1.4 is used for all dead loads, water pressure
and lateral earth pressure.
3.6 Wall thickness
The main factors which affect optimum wall thickness are
1. Ease of Construction.
~ 24 ~
2. Structural arrangement.
3. Adequate strength in shear.
4. Avoidance of excessive crack width.
3.6.1 Ease of construction
300mm is the minimum wall thickness for four layers of reinforcement as required by liquid
retaining structures to have appropriate concrete cover and to be properly compacted to
prevent leaks.
3.6.2 Structural arrangement
A cantilever retaining wall requires a thicker section at the base because it is only restrained
at one edge which has high bending moment and shear forces. A rectangular panel spanning
in two directions and restrained on all edges retaining the same height of liquid will require
lesser wall thickness. If a cantilever wall is to be used to retain a 5m head of water a 700mm
thick wall would be required at the base, which would taper to 300mm at the top, but if a
two way spanning slab is used the required thickness may just be 350mm, as used in this
design (see Table 3.3).
Table 3.1: Approximate minimum thickness of R. C. Cantilever wall subjected to water pressure
(Source: Anchor, 1992)
Height of wall (m) Minimum wall thickness h (mm)
8 800
6 700
4 450
2 250
3.6.3 Adequate strength in shear
The check for strength in shear certifies if the assumed wall thickness can withstand the
critical shear stress; the point of maximum shear is the base of the wall assuming the wall is
a cantilever. The critical shear stress is given by (Anchor, 1992):
3.2) Eqn(
400100
2579,0
4
1
3
1
3
1
m
dbd
Asfcu
Vc
bd
As100=0.5%
~ 25 ~
fcu =35N/mm2
m =1.25
d -effective depth
Shear stress on the section, )3.3(Eqn bd
Vv u
Section thickness is adequate if v< vc
3.6.4 Cracking due to tensile forces
Structural tensile forces occur in rectangular tanks due to applied internal pressures, usually
in combination with flexure (Anchor, 1992). The additional provision of steel to cater for
tensile forces in walls is given by:
)4.3(Eqn 2 s
SF
TA
Where T is the tensile force.
3.7 Floatation
The check for floatation is critical before the design of the wall reservoir floor slab, because
the two methods for tackling floatation depend on the floor slab thickness or its extensions
at the side. The ground water level of the site is assumed to be the average of water level in
neighbouring wells. The average is water level of 3.5m from the ground level. Floatation
check is deemed OK when the weight of the empty tank is more than the weight of ground
water displaced. The factor of safety varies between 1.1 and 1.25 (Anchor, 1992).
3.8 Rate of Materials
The contract rate and direct labour rate for conctete, excavation, reinforcement, and other
materials used were given by Physical Planning Unit (PPU), University of Ilorin. The following
price quotations were given by the PPU (2013):
Concrete (1:1 ½:3) , 35N/mm2: 35000/ m3
Steel reinforcement: 280/ Kg
Sawn Form Work: 1150/ m2
75mm Blinding (1:3:6): 1800/ m2
Polythene sheet (1000g): 225/ m2
Excavation: 1750/ m3
Granite spread for covering roof: 9540/ m3
~ 26 ~
3.9 DESIGN OF UNDERGROUND TANK
~ 27 ~
DESIGN INFORMATION
Hypothetical Client: Ilorin West Local Government, Kwara state. Designed by: AFODUN, M. M
UNDERGROUND WATER TANK Intended use of structure
1. BS8007: Design of concrete structures for retaining aqueous liquids.
2. BS8110: The structural use of concrete. 3. Design of Liquid retaining concrete structures by Anchor
Relevant codes of Practice and design manuals
Allowable Bearing pressure =250KN/m2 Ground water level =3.5m below GL Angle of repose, ɸ = 300 Density of Soil = 18KN/m3
Subsoil conditions
Self-weight of concrete =24KN/m3 Surcharge on roof =5.0 KN/m2 Surcharge on soil due to vehicles =10 KN/m2 Unit weight of water, ɣw =10KN/m3 Partial factor of safety for loads =1.4 Partial factor at serviceability =1.0
General Loading conditions
Characteristic strength of steel, Grade of ribbed high-yield bars, fy (main bars and links) =460 N/mm2 Characteristic strength of concrete, fcu =35N/mm2 Concrete grade =Grade 35A
Material strength
Severe Concrete cover, c = 40mm maximum allowable crack width, wmax =0.2mm
Exposure condition
Variation in temperature, T2 =200C fall in Temperature from Hydration peak to ambient, T1 =300C Coefficient of linear expansion of concrete, αc =12 Restraint Factor, R = 0.5 population growth rate, r =2.5%
Other important parameters
~ 28 ~
REFERENCE CALCULATION OUTPUT
Population survey Google earth 2013 Wikipedia, 2013 Punmia et. Al., 1995 Punmia et. Al., 1995 W.H.O. Sule.et. Al., 2010
TANK OVERHEADEXISTING OF VOLUME
533
072.07398
Demand Water Capitaper Population DemandWater
0.072mareapopulatedDenselyfordemandwaterAverage
m0.1150.046residents
IlorinofdayperdemandwatercapitaperAverage
m0.10.05dayperdemandwatercapitaperAverage
DEMANDWATER
people7398
0.025))(204932(1P
2.5%r
Years20n
people4932P
nr)(1PPformula, rategrowth ArithmetictheUsing
rategrowthpopulationr
yearsofNumbern
.populationInitialP
years.20atPopulationP
years20ofperiodafordesignedisStructure
2.5%NigeriainrategrowthPopulation
people4932
41112communitytheinpeopleofNumberTotal
411communitytheinHousesofNumber
people12buildingainpeopleofNumberverage
ESTIMATIONPOPULATION
3
3
3
3
n
0
0n
0
n
m
A
Population= 4932 people Design Population= 7398 people Per capita water demand= 0.072m3
~ 29 ~
REFERENCE CALCULATION OUTPUT
Recce Survey
3
2
2
72.46
4.6524.17
22
cylinder a of volume
1.524mradiusr
3.048mdiameterd
6.4mlength l
m
hr
demand water CapitaPer V
perioddesign yr. 20 afor building ain people of NoP
VP
Volume Totalbuildings ofNumber
:forcater tank willoverhead thebuildings ofnumber thegCalculatin
140.16m
46.72 3Volume Water Total
exist. tank thisof numbers Three
PC
PB
PCPB
3
people 12 population Initial P
population Future P
years 20years ofnumber n
2.5%rategrowth population
:
)1(PP
formula rategrowth Population arithmetic theUsing
0
n
0n
r
where
nr
Buildings 108
0.07518
140.16 for cater tank willoverhead thebuilding ofnumber The
18
)100
5.2201(12
peopleP
P
n
n
392840
84.392
16.140533
Tank overhead of Volume-Demand Water Total
Tank nd Undergrouof Volume
TANK ND UNDERGROUOF VOLUME
3
litres
m
Volume of each
overhead tank=46.72m3
No of buildings overhead tank will cater for: 108 buildings
~ 30 ~
REFERENCE CALCULATION OUTPUT
side.shorter thee than twicmore benot
should sidelonger ther tanks,rectangula ofdesign EconomicFor
ts.compartmen twointo divided is tank the
available, becan overboardan that so 400m ofTank afor Designing
TANK OFNG DIMENSIONI
3
33 400397m256.36.3Volume m
capacity. bearing optimum with soil aon sited also is tank The
altitude.high relatively of also is site tank The
ion.contaminat
prevent to tanksseptic and sewage fromfar sited is tank The
TANK OFSITING
0.5m of board free a has tank The
TANK ND UNDERGROUTHE OF DESIGN STRUCTURAL
KN/m Capacity Bearing
30repose of Angle
/18Density Soil
PROPERTIES SOIL
2
o
3
mKN
~ 31 ~
REFERENCE CALCULATION OUTPUT
All dimensions are in millimeters.
2
3
2
2
/87.2
1.028.7KN/mroofon aggregate Stone ofWeight
KN/m 10soil retainedon vehiclesloaded todue Surcharge -
slab. roof on the KN/m 2.0 of load liveA -
LOADING
mKN
m
assumedis
70m).(say joint expansion an
require ch wouldlength whi than theless is structure theof size The-
STRUCTURE. OF LAYOUT
3
2
0
3
10KN/m water ofdensity Assume
1.35m i.e
depth theof 0.75m of head water ground aon based be shouldDesign
/63
118Pressure Soil
3
1
30sin1
30sin1
30
/18 density, soil
sin1
sin1 t,coefficien PressureEarth Active
pressure Soil
Loads (a)
S.ASSUMPTION DESIGN
mKN
K
mKN
K
K
a
a
a
Surcharge on soil= 2.87KN/m2
~ 32 ~
REFERENCE CALCULATION OUTPUT
460 grade bars yieldhigh ribbed-steelent Reinforcem
concrete. finished
of Kg/m 325 ofcontent cement mininum a35A with grade Concrete
Materials (c)
0.2mmh crack widtDesign
exposure. severefor Design
BS8110 and 8007 BS Design to (b)
3
structure. monolithic a as designed be willstructure The
. leakage of sources potential are they as
desirable are jointsmpovement no structure, theof size theof In view
Joints (f)
panels. spanning way two
continuous as designed are panel slab roof and wallfloor, All
(e)Design
40mm steel oflayer outer cover to (d)
pressures. surcharge and water ground soil, External
WELLS)(BOTH EMPTY WELLS(a)
CASESLOADING
~ 33 ~
REFERENCE CALCULATION OUTPUT
BS 8007 2.3
diagrams pressure theseCombining
6.67H)H3
1-(110
: thereforeis water ground of presence the todue
load extra effective The effect.buoyancy the todue reduced is
soil theofdensity effective epresent th is water ground Where
in well water todue Pressure
full Wet well(b)
soil. external theof
resistance pressure for the made be willallowance No
~ 34 ~
REFERENCE CALCULATION OUTPUT
BS8110 BS8110 Table 3.9
2
4
1
3
13
1
c
4
1
3
1
3
1
c
/60.0
25.1
300
4005.0
25
3579.0
v
d. depth, effective
300mm, of thicknessminimum aFor
0.5% be toassumed is100
400100
2579.0
v
:isnt reiforceme of 0.5% assumed
an with concrete grade 35 ofStrength Shear Ultimateallowable The
300mm. be should
thicknessminimum thehigh wall, 5m a ofon Constructi of EaseFor
Sections of Thickness
mmN
bd
A
dbd
Af
s
m
scu
mKN /121533.375.301.252
1530
2
14.1
8
5
:diagram pressure thefrom forces theofaddition The
:is loading external maximum
the todue walls theoffoot at the forceshear ultimate maximum The
Soil Water Surcharge
thick.400mmfloor and thick 350mm wallsUse
5.270
40165.12202
2d thicknessoverall
67.20110006.0
10121
bv
Vd
shear,for required wallofdepth effective minimum The
3
mm
c
mm
ondistributi
Walls, h=350mm floor, h=400mm
~ 35 ~
REFERENCE CALCULATION OUTPUT
SLAB) (ROOF SLAB COVER TOP
for. designed be need oneonly so similar, are slabsBoth
1l
65.6l
supports. itsover slab spanningway - twocontinuous a is slab roof The
free.partially assumed are walls theand roof ebetween th joints The
y
y
x
x
l
ml
~ 36 ~
REFERENCE CALCULATION OUTPUT
thick250mm slab a Using
:sizing Slab
2
kk
2
2
23
2
KN/m 20.42
1.6(5.0)1.4(8.87)
1.6QG 1.4n Load,Design
/0.5 on trafficconstructilight and excluded) are (vehicles
roofon access partial toodue load Live
/87.8 load dead Total
/87.20.1m28.7KN/mcracking) thermalreduce (to
aggregates stone ofWeight
6.0KN/m 240.25slab roof of Weight Self
Loading Slab
mKN
mKN
mKN
2
y
2
x
2
sy
2
sx
M
M Moments,Support
M
M Moments,Span Maximum
:tsCoefficienMoment Bending
xy
xx
xsy
xsx
nl
nl
nl
nl
KNm
KNm
KNm
KNm
0Medges,Shortspan
93.3765.642.20042.0Mmidspan,Shortspan
.38.5265.642.20058.0Medges,Longspan
73.3965.642.20044.0Mmidspan,Longspan
x
2
sx
2
y
2
sy
202
2
1640250
2shortspan ofdirection In
steel.diameter 16mm of use theAssuming
entReinforcemMain
mm
chd
ent.reinforcemn comoressiofor need no 156.0
026.0202100035
1093.37
93.37Mmoment,midspan Shortspan
2
6
2
sx
k
bdf
Mk
KNm
cu
Roof slab d=200mm
Gk=8.87KN/m2 Qk=5.0KN/m2
n=20.42KN/m2
Msy= 39.73KNm
My= -52.38KNm
Msx= 37.93KNm
K=0.026
~ 37 ~
REFERENCE CALCULATION OUTPUT
Table A2.3 (Anchor, 1992)
20295.0
95.0
9.0
026.025.05.0
9.025.05.0
z
la
la
kla
ladz
strength. saitsfiesent that reinforcem minimum theis this
)(566mm B c/c Y12@200mm provide
89.49320295.046087.0
1093.37
87.0
2
26
mmladf
MA
y
s
)(1340mm B c/c 150mm @ Y16 Provide
KNm 37.93 Moment
52mm barsmain cover to
250h ickness,Section th
0.2mmhcrack widt
statelimit lity serviceabi gConsiderin
2
mm
KN/m 144 capacityshear Ultimate
N/mm 186stresses steel Service
KNm 41.7moment Limiting
2
29.0120
FS-4770.55MF
4603
2FS
26slab way -2 of Ratiodepth Span Basic
SLAB ROOF FORCHECK DEFLECTION
bd
M
providedA
requiredA
s
s
52226MF ratio basicdepth effective
span limiting
293.09.0120
113.02-4770.55MF
93.02021000
1093.37
02.1131340
89.493460
3
2FS
2
6
2
bd
M
Provide Y12 @200mm c/c B (566mm2)
Provide Y16 @ 150mm c/c B (1340mm2) E F
~ 38 ~
REFERENCE CALCULATION OUTPUT
Table 5.2-Anchor Table 5.1- Anchor
OK. Deflection ratio,span Actualratiospan limiting
9.32202
6650
depth effective
span actual
0.5R factor,Restraint
12concrete ofexpansion linear oft coefficien
0.2mmhcrack widtDesign
20T ture,in temperaVariation
30T ambient, peak toHydration from turein tempera fall
13.65m3)(0.352)(6.3
onconstructi continuous of Maximum
ENTREINFORCEM MINIMUM OF NCALCULATIO
c
0
2
0
1
C
C
.1111
4
2
12
3
2
3
2
2
111110180
2.0
0.2mmhcrack widt allowable Maximum
nmicrostrai 18030125.0
strainn contractio effectiveNet
max
max
max
max
6max
1
mmS
S
S
f
f
f
fSAlso
mmTR
wS
TR
b
ct
b
ct
c
c
%35.0100460
6.1
%36.01001111
4
y
ctcrit
f
fAlso
faceEach )(905mm c/c 125mm @ T12 Provide
900
25010000.36%
lengthunit per area0.36%entreinforcem of area Minimum
slab. roof For the
2
2mm
Deflection OK
Provide T12@ 125mm c/c For distribution
~ 39 ~
REFERENCE CALCULATION OUTPUT
)(1340mm facesboth for c/c @150mm T16 provide
1260mm
3501000100
36.0
0.36%
entreinforcem of area minimum
wallsFor the
2
2
Area
WALLSON FORCES
5300mm
350mm) of thicknessbase a (assuming 2
250
2
3505000
slabfloor toslab roof of centre tocentre walls,ofheight Effective
pressures. soil
equivalent by the pressure surcharge therelace toconvenient isIt
pressure. surcharge toduerly rectangula and pressures,
soil and water toduerly triangulaloaded are panels wallsThe
5.87mheight equivalenth
5.87mx
34.38
x
31.05
5.3
approach; ianglessimilar tr usingBy
~ 40 ~
REFERENCE CALCULATION OUTPUT
Anchor, 1992 Pg. 90 Appendix B Case 2 Fig B.1
2
2
/533.510 Hpressure water Internal
2 CASE
44.38KN/m total
10.00 1.56.67H6.67r Groundwate
34.38surcharge) ncludingpressure(i soil External
1 CASE
Loading
mKN
faceloadedontensionM
faceunloadedontensionM
SpanHorizontalM
spanverticalM
H
v
30.130.5
65.6
l
l ratio
6.65m walloflength
5.3m wallofheight
A Wall
z
x
70.1565.638.44008.0
25.3965.638.4402.0
47.233.587.538.44017.0
5.633.587.538.44046.0
EMPTY)(TANK WATERSOIL
CASE1
2
2
H
H
V
v
M
M
M
M
70.1565.653008.0
88.4665.65302.0
31.253.553017.0
48.683.553046.0
FULL)(TANK WATERINTERNAL
CASE2
2
2
2
2
H
H
V
v
M
M
M
M
face.each on A, Wall2 Case As
emptyother thefull,t compartmen One :1
3.130.5
65.6
l
l
30.5l wallofHeight
650.6l wallofLength
B Wall
z
x
z
x
CASE
ratio
m
m
~ 41 ~
REFERENCE CALCULATION OUTPUT
3.13.5
65.6
65.6l wallofLength
30.5l wallofHeight
D Wall
A WallasJust :C Wall
x
z
z
x
l
lratio
m
m
A Wallas sam :G F, E, Walls
A Wall2 Case as Same
FULL)(TANK WATERINTERNAL1, CASE
A Wall1 Case as Same
EMPTY)(TANK WATERAND SOIL 1, CASE
below. evaluated is which wallsin the tension cause both wellsin
water todue load The ignored. bemay and low is stress ecompressiv
theof valueThe n.compressioin concrete by the resisted arewhich
wallsin the forces horizontal ecompressiv cause loads External All
FORCES DIRECT
2
2
/482
4.3)(5.310
wallofheight 1mlowest over the pressure water Average
KN/m 535.310pressure water Maximum
B. andA on walls pressure todue D in WallTension
D WALLIN TENSION
mKN
23
2
S
25.3312402
10159
2
/240F of stress steel service a Assuming
ve.conservati isit but neglected isfloor theofeffect The
1592
319.2F and D on Wallheight metreper Force
height 319.2KN/m6.6548Force Total
mmF
TA
mmN
KN
S
s
~ 42 ~
REFERENCE CALCULATION OUTPUT
KN00.4182Load Total
917.28KN 713.650.4024SlabFloor .4
KN8.793)24535.03.6(3C B, A, Walls
1146.6KN 24)50.352(13.65G F, E, D, Walls3.
751.98KN 713.655)(2.87liveload and aggregate Stone
roofon load 2.Imposed
KN 573.3 713.650.2524 weight self 1.Roof
:loads theanalyzing andt compartmen a Taking
structure.
theof weight imposed the todue slabisfloor under the pressure soil The
SLAB FLOOR
/66.65765.13
41825.1
Area Base
LoadFOSpressure Bearing
:is pressure soil the
area,floor over theon distributi uniform Assuming
2mKN
.floatationfor checked be tohas structure base, thedesigning Before
other. for the providing andt compartmrn one of base for the Designing
3430.98KN weight Total
917.28KNslabFloor
793.8KN C B, A, Walls
1146.6KN G F, E, D, Walls
KN 573.3 weightself Roof
:empty tank ofWeight
~ 43 ~
REFERENCE CALCULATION OUTPUT
BS8110 Table 3.14 CASE 9
satisfied. Floatation
waterground todueUplift empty tank ofWeight
274525.1
65.3545
Safety ofFactor
empty tank ofWeight
3.186395.1765.1310displaced water ofWeight
WATERGROUND TO DUE UPLIFT
KN
KN
slab. way twoa is SlabFloor
16650
6650
l
lSlab,Floor For the
x
y
KNm
KNm
60.16265.666.65056.0M
7.15965.666.65055.0M
later moments fixingfor allowing and supportedsimply Assuming
2
y
2
x
KNm
KN
KN
32.328
wlE WallformMoment
85.565.137
65.6535.0224C Wallfrom UDL
85.565.137
65.6535.0224E Wallfrom UDL
surcharge neglecting wallsfrom moments fixing minimum
2
KNm
KNm
28.13032.3260.162MMax
54.1432
32.327.159MMax
(Internal) B Wall
y
x
Floatation check Satisfied
~ 44 ~
REFERENCE CALCULATION OUTPUT
300mm10-20-40-400laverinner ofdepth Effective
40mmcover
400mmknessFloor thic
ENTREINFORCEM FLOOR
)TF(2810mm c/c 175mm @ T25 Use
28.130M
)TF(3270mm c/c 150mm @ T25 Use
54.143M
2
y
2
x
KNm
KNm
FLOOR IN STEEL MINIMUM
0.5R factor,Restraint
12concrete ofexpansion linear oft coefficien
0.2mmhcrack widtDesign
20T ture,in temperaVariation
30T ambient, peak toHydration from turein tempera fall
c
0
2
0
1
C
C
FLOOR: T25@150 TF T25@175 TF
~ 45 ~
REFERENCE CALCULATION OUTPUT
.1111
3
25
2
25
3
2
3
2
2
25
111110180
2.0spacingcrack
0.2mmhcrack widt allowable Maximum
nmicrostrai 18030125.0
strainn contractio effectiveNet
max
max
max
max
6max
1
mmS
S
S
f
f
f
fSAlso
mm
mmTR
wS
TR
b
ct
b
ct
c
c
%35.0100460
6.1
%75.010031111
25
y
ctcrit
f
fAlso
2
s 3000mm40010000.75%A
)(3140mmEW TF c/c @100mm T20 Provide
Face Bottom
)(2810mmlongspan TF c/c @175mm T25 Provide
)(3270mmshortspan TF c/c @150mm T25 Provide
Face Top
slabfloor for t arrangemen steel Final
2
2
2
40mmCover
350mm thicknessWall
ENTSREINFORCEM WALL
mm286121240350
:entreinforcem oflayer inner deth to Effective
70.6KNmMoment
c/c T16@150mmfor A2.6 Table A,Appendix toRefering
)(1340mm faceeach for c/c T16@150mm
:earlieris calculatedent reinforcem minimum The
2
T20 @100 EW
~ 46 ~
REFERENCE CALCULATION OUTPUT
2
s 1340A c/c mm 150 @ T16 use bendingfor Therefore
70.6KNm/m. than less are moments All
Steel Horizontal
A WALL
mm
)(1800mm EF c/c 175mm @ T20 Provide
25.1671mm25.331mm 1340
:siondirect tenfor cater toareaent reinforcem theAdding
2
222 mm
ent.reinforcem same with theprovided areG F, E, D, C, B, Walls
KNm/m 80.8Moment Allowable
EF. c/c 175mm @ T20 Provide
68.48KNm/mMoment Vertical Maximum
Steel Vertical
T20 @175 EF For all walls. T20 @175 EF For all walls.
~ 47 ~
3.10 STRUCTURAL DRAWINGS AND
DETAILING
~ 48 ~
Fig3.2: Plan view of tank
Fig 3.3: Sectional Elevation of Tank
~ 49 ~
Fig
3.4
: To
p S
lab
det
ailin
g
~ 50 ~
Fig
3.5
: Flo
or
Slab
Det
ailin
g
~ 51 ~
Fig
3.6
: Wal
ls D
&E
det
ailin
g
~ 52 ~
Fig3.7: Wall A Detailing
~ 53 ~
Fig
3.8
: Cro
ss s
ecti
on
al E
leva
tio
n s
ho
win
g re
info
rcem
ents
SEC
TIO
N A
- A
~ 54 ~
SECTION B-B
Fig 3.9 Sectional Side Elevation
~ 55 ~
Fig 3.10 Access plan detailing
Fig 3.11: Sectional elevation of access showing detailing
Section C-C
~ 56 ~
Fig 3.12: 3D model of tank
~ 57 ~
3.11 BAR BENDING SCHEDULES
Table 3.2: Roof slab Bar Bending schedules
Table 3.3: Floor slab Bar Bending schedules
Table 3.4: Wall D&E Bar Bending schedules
~ 58 ~
Table 3.5 Wall A Bar Bending schedules
Table 3.6 Access Bar Bending schedules`
~ 59 ~
3.12 BILL OF ENGINEERING MEASUREMENT AND EVALUATION.
3.12.1 QUANTITY OF MATERIALS
Concrete (1:1 ½:3)
Roof Slab: Volume= (length × breadth × thickness)-Access = (13.65m×7m×0.25m)-(2×1.0m×1.0m×0.25m) = 23.89m3-0.5m3 = 23.39m3
Walls A, B and C: Volume=number × length × height × thickness =3 × 6.3m × 5m × 0.35m =33.08m3 Walls D, E, F and G: Volume=number × length × height × thickness =2 × 13.65m × 5m × 0.35m =47.78m3 Floor Slab: Volume=length × width × thickness =14.25m × 7.6m × 0.4m =43.32m3
Access: Volume=number × length × breadth × height
=8×1.1m×0.2m×0.2m =0.352m3
Total volume of concrete=147.93m3
Excavation: Volume=length × breadth × height
=16.25m × 9.6m × 5.48m =854.88m3
Blinding (1:3:6): Volume=length × breadth × thickness
=14.25m × 9.6m × 0.075m =10.26m3
Granite spread: Volume=length × breadth × thickness
=13.65m × 7m × 0.1m =9.56m3
Formwork: Area=length × breadth Roof slab = 12.6m × 6.3m=79.38m2
~ 60 ~
Floor Slab= 2× (14m×0.4m) + 2 × (7.6m×0.4m) = 17.28m2 Wall A =
Internal (6.3m×5.0m ) = 31.5m2 External (7.0m×5.25m) = 36.75m2
Wall B= (6.3m×5.0m) × 2= 63m2
Wall C= Internal (6.3m×5.0m) =31.5m2
External (7.0m×5.25m) = 36.75m2
Wall D, E, F and G Internal=4×5.0m×6.3m=126m2 External=2×5.25m×13.65m=143.33m2
Total area: 565.49 m2 Polythene sheet (1000g):
Area= length × breadth
=14.25m x 7.6m
=108.3m2 Reinforcement:
Table 3.7: Reinforcement quantities of various members
S/N Member Weight=0.006165ɸ2 (kg) Number of similar member
Total weight (Kg)
1 Wall A 4196 3 12588 2 Wall D&E 5559 2 11118 3 Roof slab 3140 1 3140 4 Access 109 2 218 5 Bottom slab 11510 1 11510 Total Weight 38574
~ 61 ~
Table 3.8: BEME of Construction Materials (Labour and profit overhead of 25% is included)
S/N Description Quantity Unit Rate(N) Amount(N)
A Preliminaries 250000
B Excavation
1 Excavation to floor slab base level not exceeding 5.5m
854.88 m3 1750 1496040
Sub Total 1496040
C Concrete
1 Provide, mix and place grade 25 concrete(1:3:6) for 75mm Blinding
10.26 m2 1800 18468
2 Provide, mix and place Concrete grade 35 for floor, walls and roof (1:1 ½:3), 35N/mm2
147.93 m3 35000 5177550
Sub Total 5196018
D Formwork
1 Sawn Formwork for all floor, walls and roof
565.49 m2 1150 650314
Sub Total 650314
E Polythene Sheet
1 Polythene sheet (1000g) 108.3 m2 225 24368
Subtotal 24368
F Reinforcement
1 Steel reinforcement for floor, walls and roof of tank according to specification.
38574 Kg 280 10800720
Subtotal 10800720
G Granite
7 Granite spread for covering roof 9.56 m3 9540 91203
Subtotal 91203
H Total Amount 18508663
I Add 2% VAT 370174
J Add 5% Contingency 925434
K GRAND TOTAL 19804270
~ 62 ~
CHAPTER FOUR: CONCLUSION AND RECOMMENDATION
4.1 Conclusion.
The designed underground water reservoir will help store daily water requirements instead
of depending on the direct erratic supply form mains. Storing water in tanks for domestic
household use is very important because of great demand during peak periods. The tank
was designed using limit state design approach. The structure is designed to meet stability,
strength and serviceability requirements as stated by BS8007 and BS8110.
4.2 Recommendations
1. It is recommended that a computer program should be written to design the tank to
make accurate and faster analysis.
2. The structure should be built as designed in this report so as to improve water
availability and accessibility in all households in Gegele community.
3. After construction the structure should be maintained for long useful life.
4. Vehicular movement should be restricted on the roof slab by barb wires.
~ 63 ~
References
Anchor, R. D. (1992). Design of Liquid Retaining Concrete Structures. 2nd edition. Edward
Arnold, London, UK.
British Standards, BS 8007 (1987), Code of Practice for Design of Concrete Structures for retaining
aqueous liquids.
British Standards, BS 8110 (1987), Code of Practice for Design of Concrete Structures.
Fagbemi, O. S. (2011). Analysis and design of elevated water tank, Final Year Project,
Department of Civil Engineering, University of Ilorin, Ilorin, Nigeria.
Fagoyinbo, J. B. (1998). Improvement in Water Resources Capacity Utilization Towards the
achievement of Objectives of Vision 2010. Proceedings of the National Engineering
Conference and Annual General Meeting, Nigerian Society of Engineers, Maiduguri, Nigeria.
Pp 17
Gibson. C, (2010). Concrete Underground Water Tanks. Available at:
http://www.homeimprovementpages.com.au/article/concrete_underground_water_tanks
(Accessed October 30, 2012).
Gupta, L. (2010). Design of Underground Water Tank. Final Year Project. Department of Civil
Engineering, Walchand Institute of Technology, Solapur, India.
Ian, B. and Roger, W, (1991). Design Tables for Water retaining structures, Longman group,
UK Ltd.
Karamouz, M., Szidarovsky, M. and Zahraie, B. (2003), Water Resources Systems Analysis,
Lewis Publishers, Washington DC, USA.
Mohammed, H. J. (2011). Economical Design of Water Concrete Tanks. European Journal of
Scientific Research. (49)4, pp 510-520.
Okeola, O. (2012) Civil Engineering Practice. A monograph on the basic Civil Engineering
Practice. Department of Civil Engineering, University of Ilorin, Ilorin, Nigeria.
~ 64 ~
Physical Planning Unit, University of Ilorin (2013), Personal Communication with the Chief
Quantity Surveyor, Physical Planning Unit, University of Ilorin, Nigeria.
Punmia, B. C., Jain. A. K. and Jain. A. K, (1995). Environmental Engineering-1: Water Supply
Engineering. Laxmi Publications (P) Limited, New Delhi, India. Vol. 1 pg. 139-162.
Punmia, B. C., Jain. A. K. and Jain. A. K, (2003) Reinforced Concrete Structures. Laxmi
Publications (P) Limited, New Delhi, India. Vol 2 pg 261-262.
Sahoo, N. (2008). Design of water tank. Final Year Project. Department of Civil Engineering,
National Institute of Rourkella, India.
Sule, B.F., Ayanshola, A.M. and Salami, A.W. (2010). Water Consumption Patterns in Ilorin,
Kwara State, Nigeria. Proceeding of the 2nd Annual Civil Engineering Conference, University
of Ilorin, Nigeria, 26 – 28 July 2010 Department of Civil Engineering, University of Ilorin,
Ilorin, Nigeria. Pg. 231.
United Nations (2010). Media brief: The Human Right to Water and Sanitation. Available at:
www.un.org/waterforlifedecade (Accessed: December 9, 2012).
Woolhether. L. (2012). The Best Underground Water Tanks. Available at:
http://www.ehow.com/list_7502181_underground-water-tanks.html#ixzz2BJrZ1BbJ
(Accessed: November 5, 2012).
~ 65 ~
APPENDIX
~ 66 ~
Table C.1 (source: Anchor, 1992)
Figure B.1(b) Bending Moment Coefficient for walls. (source: Anchor, 1992)
~ 67 ~
Table 3.14 (BS 8110; 1987)
~ 68 ~
(Source: Anchor, 1992)
~ 69 ~