Contents

Intake Design................................................................................................................................................. 5
1. Introduction .......................................................................................................................................... 5
1.1 Types of Intake Structures .................................................................................................................. 5
1.1.1 Submerged Intake Structures ...................................................................................................... 5
1.1.2 Exposed Intake Structures ........................................................................................................... 6
1.1.3 Wet Intake Structures .................................................................................................................. 6
1.1.4 Dry Intake Structures ................................................................................................................... 7
1.1.5 River Intake Structures................................................................................................................. 7
1.1.6 Reservoir Intake Structures.......................................................................................................... 8
1.1.7 Lake Intake Structures ........................................................................................................... 9
.............................................................................................................................................................. 9
1.1.8 Canal Intake Structures ................................................................................................................ 9
1.2 Site Selection for Intake Structures .................................................................................................... 9
2. Structural Design and Analysis ............................................................................................................ 10
2.1 Materials and Durability ................................................................................................................... 10
2.2 ACTIONS ........................................................................................................................................ 11
2.3 Imposed load................................................................................................................................. 11
2.4 Wind load ...................................................................................................................................... 12
2.5 Temperature ................................................................................................................................. 12
2.6 Design Scenarios ......................................................................................................................... 12
2.7 Failure Condition ............................................................................................................................... 13
2.7.1 GLOBAL STABILITY ...................................................................................................................... 13
2.7.2 INTERNAL STABILITY................................................................................................................... 13
2.7.2.1 ULTIMATE LIMIT STATES (ULS) ................................................................................................ 14
2.7.2.2 SERVICEABILITY LIMIT STATES (SLS) ........................................................................................ 14
2.8 Modeling and Analysis ...................................................................................................................... 14
Slabs .................................................................................................................................................... 15
Beams .................................................................................................................................................. 15
Base Walls ........................................................................................................................................... 15
Support Conditions ............................................................................................................................. 15
2.9 Analysis ............................................................................................................................................. 15
2.10 Codes and Standards ...................................................................................................................... 16
3. Design Example ............................................................................................................................... 17
Step- 1 Determine geometrical dimension ............................................................................................. 17
Lx=8m ...................................................................................................................................................... 17
Ly=6m ...................................................................................................................................................... 17
Lz=50m .................................................................................................................................................... 17
Intake Structure Layout .......................................................................................................................... 17
3.1 Load Calculation ................................................................................................................................ 18
3.1.1 Gravity Load and Hydrostatic Load ............................................................................................ 18
3.1.2 Seismic Load ................................................................................................................................... 18
3.1.3 Live load calculation ................................................................................................................... 22
3.1.4 Wind load ................................................................................................................................... 22
3.1.5 Concrete Grade Selection .......................................................................................................... 22
3.2 Concrete Cover Calculation............................................................................................................... 23
3.3 Load Combination ............................................................................................................................. 23
3.4 Design of 3D analysis modeling with ETABS Software ...................................................................... 25
3.4.1 Grid Creating in ETABS Modeling Processes .............................................................................. 25
3.4.2 Define Stage ............................................................................................................................... 29
3.4.2.2 Define wall section .................................................................................................................. 32
3.4.2.2 Earthquake Load ..................................................................................................................... 34
3.4.3.1 Draw Menu ......................................................................................................................... 37
3.4.4 Assign Menu ........................................................................................................................ 39
3.4.4.1 Mesh walls and slab if any ...................................................................................................... 39
3.4.4.2 Assign Load ............................................................................................................................. 40
3.4.5 Run analysis................................................................................................................................ 41
3.5 Design Check ..................................................................................................................................... 42
3.5.1 Check Global Stability of the Intake Tower ................................................................................ 42
3.5.1.1 Check for Sliding and Overturning Due to Earthquake Load .................................................. 42
............................................................................................................................................................ 42
3.5.1.2 Check for Sliding and Overturning due to Wind Load ............................................................ 44
3.5.1.2 Check Internal Stability of the Intake Tower .......................................................................... 45
3. Design of Reservoir ......................................................................................................................... 47
Introduction............................................................................................................................................ 47
Types of Reservoir Structures........................................................................................................ 47
Site Selection............................................................................................................................................... 49
Modeling of Structure ................................................................................................................................. 49
Structural design rules for reservoirs.......................................................................................................... 49
Durability..................................................................................................................................................... 49
Crack control ............................................................................................................................................... 50
Structural analysis ....................................................................................................................................... 50
Structural behavior of retaining wall ...................................................................................................... 50
Design Scenarios ......................................................................................................................................... 50
Design Load ............................................................................................................................................. 50
Design Example ....................................................................................................................................... 51
Load Calculation ...................................................................................................................................... 51
3.1.1 Gravity Load and Hydrostatic Load ..................................................................................... 51
Gravity Load and Hydrostatic Load ............................................................................................................. 51
3.1.2 Seismic Load ................................................................................................................................... 51
3.1.3 Live load calculation ................................................................................................................... 55
3.1.4 Wind load ................................................................................................................................... 55
3.1.5 Concrete Grade Selection .......................................................................................................... 55
3.2 Concrete Cover Calculation............................................................................................................... 56
3.3 Load Combination ............................................................................................................................. 56
3.4 Design of 3D analysis modeling with ETABS Software ...................................................................... 57
3.4.1 Grid Creating in ETABS Modeling Processes .............................................................................. 57
3.4.2 Define Stage ............................................................................................................................... 61
3.4.2.2 Define wall section .................................................................................................................. 64
3.4.2.2 Earthquake Load ..................................................................................................................... 66
3.4.4.1 Draw Menu ......................................................................................................................... 70
3.4.5 Assign Menu ........................................................................................................................ 71
3.4.4.1 Mesh walls and slab if any ...................................................................................................... 71
3.4.4.2 Assign Load ............................................................................................................................. 73
3.4.5 Run analysis................................................................................................................................ 73
 3.5 Design Check ..................................................................................................................................... 73
3.5.1 Check Global Stability of the Intake Tower ................................................................................ 73
3.5.1.1 Check for Sliding and Overturning Due to Earthquake Load .................................................. 73
............................................................................................................................................................ 73
.................................................................................................................................................................... 74
3.2 Analysis out Put ................................................................................................................................. 74
Check Crack Width .................................................................................................................................. 75
Intake Design

1. Introduction
Intake structures are used for collecting water from the surface sources such as river, lake, and
reservoir and conveying it further to the water treatment plant. These structures are masonry or
concrete structures and provides relatively clean water, free from pollution, sand and
objectionable floating material.

1.1 Types of Intake Structures

Intakes are classified under three categories:
Category 1:

1. Submerged intake

2. Exposed intake
Category 2:

1. Wet intake

2. Dry intake
Category 3:

1. River intake

2. Reservoir intake

3. Lake intake

4. Canal intake

1.1.1 Submerged Intake Structures

1. It is the one which is constructed entirely under water.

2. It is commonly used to obtain supply from a lake.

1.1.2 Exposed Intake Structures

1. It is in the form of a well or tower constructed near the bank of a river, or in some cases
even away from the river banks.

2. Exposed intakes are more common due to ease in operation.

1.1.3 Wet Intake Structures

1. It is a type of intake tower in which the water level is practically the same as the level of
the sources of supply.

2. It is sometimes known as Jack well and is most commonly used.

1.1.4 Dry Intake Structures

1. In case of dry intake t

2. Here is no water in the water tower.

3. Water enters through entry port directly into the conveying pipes.

4. It is simply used for the operation of valves etc.

1.1.5 River Intake Structures

1. It is a type of intake which may either located sufficiently inside the river so that
demands of water are met with in all the seasons of the year, or they may be located near
the river bank where a sufficient depth of water is available.

2. Sometimes, an approach channel is constructed and water is led to the intake tower.

3. If the water level in the river is low, a weir may be constructed across it to raise the water
level and divert it to the intake tower.
1.1.6 Reservoir Intake Structures

1. When the flow in the river is not guaranteed throughout the year, a dam is constructed
across it to store water in the reservoir so formed.

2. These are similar to river intake, except that these are located near the upstream face of
the dam where maximum depth of water is available.

3. Design of intake may vary based on the type of dam.

1.1.7 Lake Intake Structures

1. Generally submerged intakes are preferred for lake intakes.

2. These are constructed as cribs or bell mouths. The cribs are made of heavy timber frame
work which is partly or wholly filled with rip-rap to protect the intake conduit against
damage by waves etc.

3. The top of the crib is covered with cast iron or mesh grating.

1.1.8 Canal Intake Structures

1. In some cases, source of water supply to a small town may be an irrigation canal passing
nearer or through the town. Then it will be constructed.

2. Generally it consists of masonry or concrete intake chamber of rectangular shape,

admitting water through a coarse screen.

3. A fine screen is provided over the bell mouth entry of the outlet pipe.

4. The intake chamber may be constructed inside the canal bank if it does not offer any
appreciable resistance to normal flow in the canal.

1.2 Site Selection for Intake Structures

1. The site should be so selected that it may admit water even under worst condition of flow
in the river. Generally, it is preferred that intake should be sufficiently below the shore
line.

2. Site should be very close to treatment plant as possible.

 3. It should be so located that it is free from the pollution. It is better to provide intake at
upper stream of city so that water is not contaminated.

4. It should not interfere with river traffic, if any.

5. It should be located where good foundation conditions are available.

6. It should be so located that it admits relatively pure water free from mud, sand and
pollutants. Means it should be protected from rapid currents.

2. Structural Design and Analysis

2.1 Materials and Durability

In the design of Intake structure, besides the usual concerns with safety and
functionality, there is also the issue of durability. The structure needs to guarantee those
for a determined period of time or the project won’t be economic and sustainable.
Therefore, there are norms such as ES EN 1992 1-1 that determine some parameters
that should be met so the required durability is provided. Usually the design is made
taking into account a 50 year minimum lifespan for the structure, but in certain cases
such as hard to repair structures or important projects, the minimum lifespan should be
widened for 100 years. This tower is part of both of those exceptions, and therefore was
projected to have a 100 year lifespan. The choice of materials on the design of a
reinforced concrete structure, more specifically the choice of the concrete class, and the
choice of the cover for the reinforcement are the main aspects that need to be
controlled so the durability requirements are met. As mentioned before, ES EN 1992 1-1
determines some measures to be taken, based on the structures exposition to
degrading agents. First, it’s determined the structure’s class of exposition. As this
structure is inside the dam and placed on an environment that’s cyclic temperature
change occur, its reinforcement corrosion shall only happen due to carbonation.
Therefore its class of exposition is, as defined by ES EN 1992 1-1 XC4.
This norm imposes a minimum resistance class for the concrete to be used according to
its class of exposition. The type of concrete used was C30/37 and was solely
determined by this, because for the stresses generated for the static and dynamic
actions, a lower class of resistance was enough. As for the reinforcement, there is no
such thing as a minimum class of resistance because the steel is not as important as
concrete when it comes to durability issues. The steel chosen was A500 NR. The
materials used and their characteristics are specified on tables 2 and 3.

2.2 ACTIONS
The project actions that were taken into account were the imposed load, the dead load,
the permanent load, the wind action, the seismic action on full and empty reservoir and
the temperature action.
The following actions are considered:
(i) self-weight of the structure;
(ii) other permanent loads,
(iii) live loads;
(iv) soil lateral pressures,
(v) weight of water,
(vi) hydrostatic pressure,
(vii) uplift pressure,
(viii) Seismic actions.
Permanent load there are many loads beside the dead load that are permanently acting
on the structure and with values well defined. They are the ladders, grates, floodgate
and some other materials that are permanently loading the structure.

2.3 Imposed load

The platform slab has a function of supporting any works that may happen on the intake
tower. Because of this, the slab is often loaded by heavy materials such as machinery,
or other deposited materials. This document suggests the use of a distributed imposed
load of 15kN/m2 on the platform slab, and this was the only imposed load considered.
2.4 Wind load
Usually on tall, slender structures the wind action can be problematic, because the
global forces and moments generated tend to be high. This tower is one of those cases,
and therefore the correct definition of the wind load is very important. The wind load was
defined following the procedures recommended by ERA manual.

2.5 Temperature
The effects of temperature on the vast majority of structures aren’t usually concerning
for their safety, because of the loss of stiffness on the ultimate limit states. These effects
may pose problems for the serviceability limit states as the loss of stiffness isn’t as
significant. However, the thermal action is slow and as a cause of that ES EN 1991
allows the designer to consider the modulus of elasticity of concrete as half of the real
one to ease the stresses due to temperature, as the variation isn’t instantaneous. As
this structure is most of the time submerged, the change of temperature considered for
the load combinations was that of inside the water.
However the temperature below water level doesn’t change as described by ES EN
1991 1-5 because the variations mentioned in this norm are air temperature. Therefore,
studies made by University of Évora for Alqueva reservoir the temperature variation at
various levels below water level. It’s possible to see that below a certain level the
temperature is constant and with
a value but sometimes temperature changes below water level so, to simulate the
higher variation on the upper levels, on the part of the structure that’s always above
water level it need to consider variation of temperature and to consider this change
need adjust modulus of elasticity of concrete as half of the real one to ease the
stresses due to temperature.

2.6 Design Scenarios

Scenario 1 – Scenario of operation. It represents the situation of operation of the water intake, in
which the water are considered at full level of storage both in the front and back of the structure
acting along with the action of the fill and a live load on the top of it.
Scenario 2 – Scenario of construction stage
Scenario 3 – Scenario seismic in which is considered the same situation described in Scenario 1
2.7 Failure Condition
1. Global Stability Failure
2. Internal Stability Failure

2.7.1 GLOBAL STABILITY

The limit states assessed in order to check the global stability of this structure are:
 Loss of equilibrium of the structure due to overturning stability and loss of
equilibrium due to sliding;
 Loss of equilibrium of the structure due to uplift;
 Failure or excessive deformation of the ground.
In accordance with the Ethiopian Standard and other international regulations the structure in
analysis must check the following minimum safety factor shown
SLIDING The verification against failure by sliding is given by the following equation:

UPLIFT The safety of the structure against failure by uplift is assured if the following
equation is verified:

OVERTURNING STABILITY Verification against failure by toppling is given by the

following equation:

Safety Factor for Overturning=

Safety Factor For Sliding
Safety Factor for Overturning

2.7.2 INTERNAL STABILITY

According to ES EN 1990, the structure must be designed to resist to ultimate limit states (𝑈𝐿𝑆)
and serviceability limit states (𝑆𝐿𝑆). The first are related with the safety of people and of the
structure, while the second are related to the use/operation of the structure.
2.7.2.1 ULTIMATE LIMIT STATES (ULS)

ULTIMATE LIMIT STATES (ULS) The ultimate limit state of all elements must be evaluated,
according to the equation below: 𝐸𝑑 ≤ 𝑅𝑑 (1) in which

2.7.2.2 SERVICEABILITY LIMIT STATES (SLS)

In this dissertation are evaluated (i) the deflection of the members, (ii) the stress of
structural materials and (iii) the crack width. The stress of the materials are limited, in
serviceability, in order to ensure the steel is not yet in yielding and to ensure the
concrete has no micro-cracks, therefore steel stress 𝜎𝑠 is limited to a maximum value of
0,80𝑓𝑦𝑘 and concrete compression 𝜎𝑐 is limited a maximum of 0,60𝑓𝑐𝑘. The maximum
crack width is 0,20 𝑚𝑚 as recommended by ES EN 1992-1-1 and EN 1992-3. For these
𝑆𝐿𝑆 verifications are considered the characteristic combination.
PARTIAL SAFETY FACTORS For the previous combinations, the loads are multiplied by the
following load factors presented in table 1:
Table 1 – Partial safety factors

2.8 Modeling and Analysis

Finite element modelling to make a proper analysis on the behavior of the structure for
the project actions due to its complexity, the intake tower has to be modelled on a finite
elements program. The model was composed of shell elements and its geometry was
defined by the axis of the elements. Whenever any simplification was needed it was
always with the intention of reducing lever arms, increasing the resultant stresses. The
step by step modelling is as described.

Slabs
The slabs were defined as shell thin elements, so as to generate all slab and membrane
stresses, and ignoring the shear deformability of these elements. They were modelled
by the axes of the beams, and meshed into properly refined meshes, so the results
given were as accurate as possible.

Beams
The definition of the beams was very similar as that of the pillar and therefore won’t be
as detailed.
Base Walls

The base walls were modelled as shell thin elements similarly to the slabs, due to its
laminar aspect. This is the way their characteristics are best represented, however they
could also have been modelled considering beam elements. Due to its cross-section
being hard to represent, a simplification was made, considering for each wall the
thickness of the zone where it was the less thick.

Support Conditions
As the structure is founded on a massive footing on good quality rocks, its support
conditions are well described by fully fixed conditions. Therefore, these were used to
describe the support conditions of the structure.

2.9 Analysis
The main goal of this dissertation is to evaluate the global and internal stability of a
water intake tower in concrete.
Firstly, the geometrical definition of the structure is done, not only for better
comprehension of its geometry, but also for the obtainment of crucial data required for
the following analysis.
Then the global safety of the structure is verified,
The third step consists of the verifications for the internal stability, for the evaluation of
the ultimate and service limit states. In this point two procedures are presented. The first
one is done using simplified analytical models which are later compared with the results
of a three- 2 dimensional finite element model, which is the second procedure. In the
document of the dissertation the drawings for the geometrical definition and definition of
the main rebars are also presented.

2.10 Codes and Standards

Serviceability limit state design method was used for member sizing and
designing.

Codes used are:

ES EN 1991:2015 (Ethiopian Standard based on Euro Norms)

ES EN 1992:2015 (Ethiopian Standard based on Euro Norms)

ES EN 1997:2015 (Ethiopian Standard based on Euro Norms)

ES EN 1998:2015 (Ethiopian Standard based on Euro Norms)

Euro Code 2-2004 (as used by the software), almost similar to EBCS EN 1991-1-
6:2013
 3. Design Example

Step- 1 Determine geometrical dimension

Lx=8m
Ly=6m
Lz=50m

Intake Structure Layout

3.1 Load Calculation
3.1.1 Gravity Load and Hydrostatic Load
The gravity loads include dead loads (i.e. Self-weight, wall load on beams, partition wall
loads, cement screeds, plastering and other permanently attached loads to the building)
and live loads. Self-wt. of slabs, columns and walls are automatically included in the
analysis from the geometry and unit weight of reinforced concrete. Unit weight of
reinforced concrete is assumed to be 25 kN/m3.

Table 3- Values of the Permanent Load

Load on the Bottom Slab

Thickness Unit Weight Load
Water Load 2.00 9.81 19.62
Ceiling
Plaster 0.02 23.00 0.35
2.0 cm
Screed 0.02 23.00 0.46

3.1.2 Seismic Load

The earthquake value of design spectrum is calculated and used to get the total base
shear by multiplying it by the weight of the building according to EBCS EN 1998-8.

Step-1 from EBCS EN 1998 Annex D of Table-D2 select seismic zone of the city
which the intake tower constructed

City Afar seismic zone= 3

Step-2 Select design ground acceleration from EBCS EN 1998 table below

Take ground acceleration =0.1

o=0.1

Step-3 Select importance factor from Ethiopian code ES EN 1998 article 4.3.5.3
below take 1.5
Step-4 Multiply ground acceleration by importance factor

According to EBCS EN 1998 article 3.2 the design ground acceleration ag is equal to 0
times the importance factor γ, our design ground acceleration ag = 1.5 x 0.1g = 0.15g
m/s2 determined using reference peak ground acceleration of 0.15g for seismic zone4
and importance factor IV=1.5, the provision of medium seismicity will apply and
therefore the structure can be designed to meet the requirements medium ductility
class.

Step-5 Select Soil category with reference to geotechnical investigation from the
table below

For our design take ground type B

Step-6 calculate behavioral factor

Intake structure has a breakable behavior. According with articles 4.4(1) P and 4.4(3)P
of ES EN 1998-4 the behavior coefficients to water portions are respectively 1.5.
3.1.3 Live load calculation
The live load for all floors is taken from the building codes.

Take 1.5kN/m2

3.1.4 Wind load

Usually on tall, slender structures the wind action can be problematic, because the
global forces and moments generated tend to be high. This tower is one of those cases,
and therefore the correct definition of the wind load is very important. The wind load was
defined following the procedures recommended by ERA manual.
The wind load shall not be taken less than 3.9kN/m2 in plane of wind ward direction.

3.1.5 Concrete Grade Selection

According to Ethiopian new code EN 1992-1-1, a concrete structure should accomplish

some criteria, where commonly the most important is the structural strength.
Materials Known the exposure class in is chosen a concrete C30/37.
To avoid the direct contact with the soil, it is put a layer below of the bottom slab with
poor concrete, with the strength class C12/15. To the reinforcement, is chosen a steel
S500.

3.2 Concrete Cover Calculation

The concrete cover is the distance between the surfaces of reinforcement closest to the
nearest concrete surface.
The minimum cover shall be specified on the drawing it is defined as a minimum cover,
Cmin (see ES EN-1992:2015 sec 4.4.1.2) plus an allowance in the design for deviation,
Cdev (see ES EN-1992:2015 sec 4.4.1.3) which is
Cnom=Cmin+Cdev

3.3 Load Combination

The values of actions which occur simultaneously are combined as follows:

i) Persistent and transient situation

GRAVITY = 1.35  Gk + 1.5  Qk

The load combination for the gravity load can be made as below;
1-Combo1 1.35*DL + 1.5*LL
Combination of Earth Quack with Dead load and Live Loads
According to Equation 3.17 of ES EN 1998:2015 the following combination effect shall
be taken into consideration:

ii) Seismic Situation

COMB2-EQXP+0.3*EQYP+0.3LL+DL
COMB3-EQXP-0.3*EQYP+0.3LL+DL
COMB4-EQXP+0.3*EQYN+0.3LL+DL
COMB5-EQXP-0.3*EQYN+0.3LL+DL
COMB6-EQXN+0.3*EQYP+0.3LL+DL
COMB7--EQXN-0.3*EQYP+0.3LL+DL
COMB8-EQXN+0.3*EQYN+0.3LL+DL
COMB9-EQXN-0.3*EQYN+0.3LL+DL
COMB10-(-EQXP+0.3*EQYP+0.3LL+DL
COMB11-(-EQXP-0.3*EQYP+0.3LL+DL
COMB13-(-EQXN+0.3*EQYP+0.3LL+DL
COMB14-(-EQXN-0.3*EQYP+0.3LL+DL
COMB15(-EQXN+0.3*EQYN+0.3LL+DL
COMB16(-EQXN-0.3*EQYN+0.3LL+DL
COMB17-EQYP+0.3*EQXP+0.3LL+DL
COMB18-EQYP-0.3*EQXP+0.3LL+DL
COMB19-EQYP+0.3*EQXN+0.3LL+DL
COMB20-EQYP-0.3*EQXN+0.3LL+DL
COMB21-EQYN+0.3*EQXP+0.3LL+DL
COMB22-EQYN-0.3*EQXP+0.3LL+DL
COMB23-EQYN+0.3*EQXN+0.3LL+DL
COMB24-EQYN-0.3*EQXP+0.3LL+DL
COMB25(-EQYP+0.3*EQXP+0.3LL+DL
COMB26(-EQYP-0.3*EQXP+0.3LL+DL
COMB27(-EQYP+0.3*EQXN+0.3LL+DL
COMB28(-EQYP-0.3*EQXN+0.3LL+DL
COMB29(-EQYN+0.3*EQXP+0.3LL+DL
COMB30(-EQYN-0.3*EQXP+0.3LL+DL
COMB31(-EQYN+0.3*EQXN+0.3LL+DL
COMB32(-EQYN-0.3*EQXN+0.3LL+DL
Finally, envelopes have been evaluated for the purpose of determining the design
action effects at the critical regions.

3.4 Design of 3D analysis modeling with ETABS Software

3.4.1 Grid Creating in ETABS Modeling Processes
Step-1 Open ETABS

Step-2 File-New Model

Step-3 One the sample model menu click use setting from model
Step-4 Select Sample model from file and click ok button

Step-5 Click custom grid spacing

Step-6 Click Edit Grid fill X and Y coordinate of our intake structure

Step-7 Click ok

Step-8 Click custom story data

Step-9 Click custom fill story height click ok

Step-9 Click custom fill story height click ok

3.4.2 Define Stage

3.4.2.1 Material Property define

Material Define of Concrete

Step-1 Select define menu from ETABS model

Step-2 from define menu click on material property

From material menu select add new material

Next from add new material property change

1. Region to Euro
2. Material type to concrete
3. Standard En 1992-1-1per EN206-1 and select grade of material C30/37 and ok

Step-3 To consider temperature variation on the intake structure decrease the value of
modulus of Elasticity of the concrete by half

Material Define of Concrete

Step-1 Select define menu from ETABS model

Step-2 from define menu click on material property

From material menu select add new material

Next from add new material property change

1. Region to Euro
2. Material type to rebar
3. Standard En 1992-1-1per EN206-1 and select grade of material s500 and ok
3.4.2.2 Define wall section
Step-1 Select define menu from ETABS model

Step-2 from define menu click on wall section property

From wall property menu select add new property

Next from wall property menu change

1. Wall name preferred to use our section

2. Wall material –as per our defined material previously
3. Change modifiers to 0.5
 Property/ Stiffness Modification

Concrete has an inherent property of cracking and all members do cracking. This cracking
reduces stiffness. So the analysis with gross property would have overestimated support
moment and under estimated span moments and deflection, we provide more steel than really
required at supports and less at span. The laterals deflection and drift is also underestimated.
Stiffness modifier factors for cracked columns, beams, slabs and wall sections are used in this
project.

The frame is modeled using stiffness modifier recommended by Euro code which is
0.5Ig for column and 0.5Ig for beams.
3.4.2.2 Earthquake Load
Step-1 Select define menu from ETABS model

Step-2 Since the intake structure needs dynamic analysis we use response spectrum type of analysis

From define menu click on Function and click Response Spectrum

1. Change the code to Eurocode8-2004

2. Click to add new function
 1. Change ground type and
Step -3 In add new function behavioral factor

2. Fill ground acceleration

Step-4 Select Define Menu then selects Modal case data

Change
Fill load type load case to acceleration
to acceleration

Change this to response spectrum

Repeat Step 5 for Earthquck in U2 Direction

Load Combination we will take from templat

Comb1-1.35DL+1.5LL

Combination for earthquack which need dynamic analysis

COMB2-Lc1+0.3*Lc2+0.25LL+DL
COMB3-Lc1-0.3*Lc2+0.25LL+DL
COMB4-Lc1+0.3*Lc2+0.25LL+DL
COMB5-Lc1-0.3*Lc2+0.25LL+DL
COMB6 Lc2+0.3*Lc1+0.25LL+DL
COMB7 Lc2-0.3*Lc1+0.25LL+DL
COMB8-Lc2+0.3*Lc1+0.25LL+DL
COMB9-Lc2+0.3*Lc2+0.25LL+DL
COMB10-Lc2-0.3*Lc2+0.25LL+DL

3.4.3.1 Draw Menu

In the software there are two menu to draw

In short cut
Step-1 since our structure is made up of shear wall select icon to draw shear wall click on the grid we
need to draw
 3.4.4 Assign Menu

3.4.4.1 Mesh walls and slab if any

Step -1 First Select wall to be meshed and then click on assign menu next click shell Wall auto
mesh option

Step-2 Click auto mesh Click advance –modify/show auto rectangular mesh setting
 Fill max mesh size to 0.5

3.4.4.2 Assign Load

Select wall load to be assigned click assign click assigned load Click
shell load(Repeat this step for the other direction)
3.4.5 Run analysis

Deformed shape after analysis

3.5 Design Check
3.5.1 Check Global Stability of the Intake Tower

3.5.1.1 Check for Sliding and Overturning Due to Earthquake Load

From display option click show table click story force and export to excel
Export horizontal load generated to due to earthquake to excel

Overturning
Earthquake Load Force Elevation Moment=ElevationxEQx
El40 1502.5256 40 60101.024
El20 2383.6366 30 71509.098
Elev 10 2872.8631 20 57457.262
Elev 0 3034.0713 0 0
Total Destabilizing Force 9793.0966 189067.384
Sliding Moment
Stabilizing force generated by Self weight)
Step-1 Calculate Self weight of the
structure
Base Slab (Foundation) L W Depth
14 12 1.5
Unit weight of Concrete= 24 KN/m3
Load of Base slab=LxwxDx γcon 6048 KN
Thickness of
Wall Load L wall Height of Tower
36 1.2 50
Unit weight of Concrete= 24 KN/m3
Load of Base slab=LxwxDx γcon 51840 KN
Top Slab L W Thickness of slab
8 6 0.3
Unit weight of Concrete= 24 KN/m3
Load of Base slab=LxwxDx γcon 345.6 KN

Total stabilizing force=Self weight of

(Base Slab Wall Load Top Slab) 58233.6 KN
Assume frictional resistance= 0.5

Friction Resistance Force Self weight

of wall frictional resistance 29116.8
Safety factor 2.973196445 >1.5
Check for Overturning

Stabilizing Moment 232,934.40

Destabilizing Moment 189,067.38

Safety factor 1.23 >1.2

3.5.1.2 Check for Sliding and Overturning due to Wind Load
Wind load
Wind ward
From ERA Manual side Lee ward Kpa
Truss, column and Arches 2.4 1.2
Beams 2.4 Not applicable
Large Flat Surface 1.9
Table 3.-12 Base pressures, Ps corresponding to Vs160km/h(45m/s) the wind load cannot be
less than 4.4kn/m2 in the plane of wind ward chord and 2.2kn/m2 in the plane of leeward
chord on truss and arch components and not less than 4,4kn/m2 0n beam and girder
components
take design pressure=4.4 4.4 KNm2

Assume that for the intake tower the structural component can be groups as large flat surface
however the minimum design pressure is not recommended for large flat surface by beam or
girder minimum specified value
Total Length of wall(LT)= 8 M
Height of Tower (H) 50 M

Total Wind force on the tower is 1760 KN

(WT)=Wind pressure WxLtxHt
Wind Destabilizing Moment (Over turning Moment)=
Mo=WtxHt/2 44000
Wind Stabilizing force generated by Selfwt)
Self-weight of the structure
Base Slab (Foundation L W Depth
12 10.5 1.5
Unit weight of Concrete= 24 KN/m3
Load of Base slab=LxwxDx γcon 4536 KN
Thickness of
Wall Load L wall Height of Tower
5.5*2+7*2 25 0.8 50
Unit weight of Concrete= 24 KN/m3
Load of Base slab=LxwxDx γcon 24000 KN
Thickness of
Top Slab L W slab
8 5.5 0.3
Unit weight of Concrete= 24 KN/m3
Load of Base slab=LxwxDx γcon 316.8 KN
Total stabilizing force 28852.8 KN
 Assume frictional resistance= 0.5
Friction Resistance Force 14426.4
Safety factor 3.18042328 >=1.5
Overturning= 115411.2
2.622981818 >=1.5
3.5.1.2 Check Internal Stability of the Intake Tower
Step-1 Calculate Reinforcement

Select Wall Assign Shell Pier Label

Design Shear Wall Design Define General Pier Section

Click on section designer

 Change reinforcement diameter and spacing

Change Reinforcement by Right Click on the reinforcement and finally ok

Design Shear Wall Design Start Design Check Select Area of Reinforcement

Maximum Reinforcement Area=51545mm2

Since the wall detail is on both face we will divide Ast/2=51545/2=25772mm2 each face
Number of bar=As/as
Take diameter 20 rebar area=314mm2
No. bar=25772/314=82 take 82
Spacing =Length of wall/No. bar=25772mm2/82=110mm
Take dia.20c/c 110mm rebar
 3. Design of Reservoir

Introduction

Reservoirs are structures that contain fluids, in gaseous or liquid state. These could be
made of reinforced concrete, pre-stressed concrete or steel, however the first ones are
more common because of some important advantages such as the lowest cost of
construction and maintenance.
Besides the material, reservoirs can be classified regarding the following dots: function,
position, capacity, geometry, cover and tightness class.
In accordance with engineering standards of care, reservoirs are to be designed to
provide stability and durability, as well as protect the quality of the stored water. For any
particular project there may be more than one acceptable reservoir design concept.

Types of Reservoir Structures

Reservoirs are classified under two categories:
Category -1 Water reservoir on location

1. Under ground water tank

 2. Tank on ground

3. Elevated of overhead water tank

Category -2 Water tank based on shape

1. Circular tank
2. Rectangular tank
3. Intz tank

4. Conical bottom thank

5. Spherical thank

The reservoir designed on this paper has the objective to supply water against a
treatment plant. On this way, the tank is non-elevated, especially because of the lower
cost of construction. Besides that, a non-elevated tank has other advantages such as
an easier operation as well a lower impact on the landscape view.

Site Selection
The places of newly constructed reservoir are decided as considering the following
conditions.

 The place should be located in the altitude enable to do the gravity distribution.
 The location should be public space and not to harm the natural and social
conditions by the construction. ·
 The ground is recommended to be as flat and in good geological character as
possible to reduce the construction cost.

Modeling of Structure

To perform the structural design, to the ultimate limit state and serviceability state, finite
elements models have been developed. It is also verified a structural behaviour for a
seismic action according with the EN 1998-1.Finally, the structure is also designed to
control the cracks and then it is verified the safety at ultimate state.

Structural design rules for reservoirs

ES EN 1992-1-1, a concrete structure should accomplish some criteria, where
commonly the most important is the structural strength. However, a reservoir has to
ensure as well a good service behaviour, so it is given importance to durability and
cracking control [5].

Durability
According to ES EN 1990 defines that a common structure such as a reservoir should
has a lifetime of 50 years. The durability of a structure is dependent of the
environmental conditions. Those conditions are providing nominal concrete cover of the
structure to ensure a proper durability and does not contain aggressive chemicals.
Crack control

Cracking is normal in concrete structures, but those cracks should be controlled to

ensure a proper operation of the structure. To perform that control, NP EN 1992-1-1
defines that crack width (wk) should be limited to wmax,
Structural analysis

Structural behavior of retaining wall

Structural walls the slenderness of a reservoir, given by the ratio between a
characteristic dimension of the base and the maximum height of water, is an important
parameter to the structural behavior. This reservoir is in an intermediate level of
slenderness, so it is expected important stresses to both directions. Besides the
bending moments and shear forces, the hydrostatic impulse generates tension on the
walls.

Design Scenarios

Design Scenarios
The verifications of safety are done for five different scenarios.
Scenario 1 (S1) – When the reservoir Empty
Scenario 2 (S2) – When the reservoir at full stage

Design Load
The project actions that were taken into account were the imposed load, the dead load,
the permanent load, the wind action, the seismic action on full and empty reservoir and
the temperature action.
The following actions are considered:
(ix) self-weight of the structure;
(x) live loads;
(xi) weight of water,
(xii) Seismic actions.
Design Example
Load Calculation
3.1.1 Gravity Load and Hydrostatic Load

Gravity Load and Hydrostatic Load

The gravity loads include dead loads (i.e. Self-weight, wall load on beams, partition wall
loads, cement screeds, plastering and other permanently attached loads to the building)
and live loads. Self-wt. of slabs, columns and walls are automatically included in the
analysis from the geometry and unit weight of reinforced concrete. Unit weight of
reinforced concrete is assumed to be 25 kN/m3.

Load on the Bottom Slab

Thickness Unit Weight Load
Water Load 3.00 9.81 29.43
Ceiling
Plaster 0.02 23.00 0.35
2.0 cm
Screed 0.02 23.00 0.46

Load on the Side Wall

Thickness Unit Weight Load
Water Load 8.45 9.81 82.89
Wall Plaster 0.04 23.00 0.92
2.0 cm
Screed 0.02 23.00 0.46

3.1.2 Seismic Load

The earthquake value of design spectrum is calculated and used to get the total base
shear by multiplying it by the weight of the building according to EBCS EN 1998-8.

Step-1 from EBCS EN 1998 Annex D of Table-D2 select seismic zone of the city
which the intake tower constructed

City Afar seismic zone= 3

Step-2 Select design ground acceleration from EBCS EN 1998 table below

Take ground acceleration =0.1

o=0.1

Step-3 Select importance factor from Ethiopian code ES EN 1998 article 4.3.5.3
below take 1.5
Step-4 Multiply ground acceleration by importance factor

According to EBCS EN 1998 article 3.2 the design ground acceleration ag is equal to 0
times the importance factor γ, our design ground acceleration ag = 1.5 x 0.1g = 0.15g
m/s2 determined using reference peak ground acceleration of 0.15g for seismic zone4
and importance factor IV=1.5, the provision of medium seismicity will apply and
therefore the structure can be designed to meet the requirements medium ductility
class.

Step-5 Select Soil category with reference to geotechnical investigation from the
table below

For our design take ground type B

Step-6 calculate behavioral factor

Intake structure has a breakable behavior. According with articles 4.4(1) P and 4.4(3)P
of ES EN 1998-4 the behavior coefficients to water portions are respectively 1.5.
3.1.3 Live load calculation
The live load for all floors is taken from the building codes.

Take 1.5kN/m2

3.1.4 Wind load

Usually on tall, slender structures the wind action can be problematic, because the
global forces and moments generated tend to be high. This tower is one of those cases,
and therefore the correct definition of the wind load is very important. The wind load was
defined following the procedures recommended by ERA manual.
The wind load shall not be taken less than 3.9kN/m2 in plane of wind ward direction.

3.1.5 Concrete Grade Selection

According to Ethiopian new code EN 1992-1-1, a concrete structure should accomplish

some criteria, where commonly the most important is the structural strength.
Materials Known the exposure class in is chosen a concrete C30/37.
To avoid the direct contact with the soil, it is put a layer below of the bottom slab with
poor concrete, with the strength class C12/15. To the reinforcement, is chosen a steel
S500.

3.2 Concrete Cover Calculation

The concrete cover is the distance between the surfaces of reinforcement closest to the
nearest concrete surface.
The minimum cover shall be specified on the drawing it is defined as a minimum cover,
Cmin (see ES EN-1992:2015 sec 4.4.1.2) plus an allowance in the design for deviation,
Cdev (see ES EN-1992:2015 sec 4.4.1.3) which is
Cnom=Cmin+Cdev

3.3 Load Combination

The values of actions which occur simultaneously are combined as follows:

i) Persistent and transient situation

GRAVITY = 1.35  Gk + 1.5  Qk

The load combination for the gravity load can be made as below;
1-Combo1 1.35*DL + 1.5*LL
Combination of Earth Quack with Dead load and Live Loads
According to Equation 3.17 of ES EN 1998:2015 the following combination effect shall
be taken into consideration:

3.4 Design of 3D analysis modeling with ETABS Software

3.4.1 Grid Creating in ETABS Modeling Processes
Step-1 Open ETABS

Step-2 File-New Model

Step-3 One the sample model menu click use setting from model
Step-4 Select Sample model from file and click ok button

Step-5 Click custom grid spacing

 Step-6 Click Edit Grid fill X and Y coordinate of our intake structure

Step-7 Click ok

Change the dimension according to

Since the reservoir is circular change our grid system to cylindrical our drawing
Step-8 Click custom story data

Step-9 Click custom fill story height click ok

Step-9 Click custom fill story height click ok

3.4.2 Define Stage

3.4.2.1 Material Property define

Material Define of Concrete

Step-1 Select define menu from ETABS model

Step-2 from define menu click on material property

From material menu select add new material

Next from add new material property change

4. Region to Euro
5. Material type to concrete
6. Standard En 1992-1-1per EN206-1 and select grade of material C30/37 and ok

Step-3 To consider temperature variation on the intake structure decrease the value of
modulus of Elasticity of the concrete by half

Material Define of Concrete

Step-1 Select define menu from ETABS model

Step-2 from define menu click on material property

From material menu select add new material

Next from add new material property change

4. Region to Euro
5. Material type to rebar
6. Standard En 1992-1-1per EN206-1 and select grade of material s500 and ok
3.4.2.2 Define wall section
Step-1 Select define menu from ETABS model

Step-2 from define menu click on wall section property

From wall property menu select add new property

Next from wall property menu change

4. Wall name preferred to use our section

5. Wall material –as per our defined material previously
 6. Change modifiers to 0.5

Property/ Stiffness Modification

Concrete has an inherent property of cracking and all members do cracking. This cracking
reduces stiffness. So the analysis with gross property would have overestimated support
moment and under estimated span moments and deflection, we provide more steel than really
required at supports and less at span. The laterals deflection and drift is also underestimated.
Stiffness modifier factors for cracked columns, beams, slabs and wall sections are used in this
project.

The frame is modeled using stiffness modifier recommended by Euro code which is
0.5Ig for column and 0.5Ig for beams.
3.4.2.2 Earthquake Load
Step-1 Select define menu from ETABS model

Step-2 Since the reservoir structure needs dynamic analysis we use response spectrum type of
analysis

From define menu click on Function and click Response Spectrum

4. Change the code to Eurocode8-2004

5. Click to add new function
 3. Change ground type and
Step -3 In add new function behavioral factor

4. Fill ground acceleration

Step-4 Select Define Menu then selects Modal case data
Step-5 Defin Load Case

Change Load case type to response

spectrum

Change load case to acceleration

Fill load type to acceleration

Repeat Step 5 for Earthquck in U2 Direction

Load Combination we will take from templat

Comb1-1.35DL+1.5LL

COMB2-Lc1+0.3*Lc2+0.25LL+DL
COMB3-Lc1-0.3*Lc2+0.25LL+DL
COMB4-Lc1+0.3*Lc2+0.25LL+DL
COMB5-Lc1-0.3*Lc2+0.25LL+DL
COMB6 Lc2+0.3*Lc1+0.25LL+DL
COMB7 Lc2-0.3*Lc1+0.25LL+DL
COMB8-Lc2+0.3*Lc1+0.25LL+DL
COMB9-Lc2+0.3*Lc2+0.25LL+DL
COMB10-Lc2-0.3*Lc2+0.25LL+DL
 3.4.4.1 Draw Menu
In the software there are two menu to draw

In short cut
Step-1 since our structure is made up of shear wall select icon to draw shear wall click on the grid we
need to draw

3.4.5 Assign Menu

3.4.4.1 Mesh walls and slab if any

Step -1 First Select wall to be meshed and then click on assign menu next click shell Wall auto
mesh option
Step-2 Click auto mesh Click advance –modify/show auto rectangular mesh setting

Fill max mesh size to 0.5

3.4.4.2 Assign Load
Select wall load to be assigned click assign click assigned load Click
shell load(Repeat this step for the other direction)

3.4.5 Run analysis

3.5 Design Check

3.5.1 Check Global Stability of the Intake Tower

3.5.1.1 Check for Sliding and Overturning Due to Earthquake Load

From display option click show table click story force and export to excel
3.2 Analysis out Put
Moment of Wall

Moment=150kNm

Output from ETABs

Maximum Reinforcement Area=38325mm2
Since the wall detail is on both face we will divide Ast/2=38328/2=19164mm2 each face
Number of bar=As/as
Take diameter 14 rebar area=154mm2
No. bar=6150/113=124.15 take 125
Spacing =Length of wall/No. bar=53066mm/113=320mm
Take dia.12c/c 200mm rebar

Check Crack Width

Cracking is normal in concrete structures, but those cracks should be controlled to

ensure a proper operation of the structure. To perform that control, NP EN 1992-1-1
defines that crack width (wk) should be limited to wmax=0.2mm.
Since the crack width is 2.28mm>0.2mm
Since the crack width is 0.195mm>0.2mm ok
Use dia 14 c/c 110 reinforcement with thickness=350mm

Reinforcement Detailing
 4. Design of Treatment Plant
4.1 Introduction
Treatment plant structures are subjected to more complicated loads, more severe
exposure conditions, and more restrictive serviceability requirements than ordinary
building structures. The quality of materials and construction for wastewater treatment
plants are normally higher than the requirements for ordinary building structures to
satisfy public health and safety concerns.

Design of a water treatment plant concerns the location, population, future changes in
demand and various other factors. Therefore, in order to ensure proper designing of
water treatment plant, data with great precision is required.

1.1 Types of Treatment Plant

Generally, surface water treatment processes are categorized as conventional and advanced
treatment processes.

Conventional surface water treatment process mostly encompasses the following two types.

Type one: 1. Screening (Preliminary treatment )

2. Aeration

3. Coagulation, utilizing rapid mixing device of coagulating agent.

4. Flocculation

5. Sedimentation

6. Sand Filtration basins

7. PH correction 8. Disinfecting (chlorinating)

Type two 1. Screening (Preliminary treatment)

2. Aeration

3. Plain sedimentation

4. Horizontal Roughening filter

5. Slow sand filter

6. disinfecting (chlorinating)
Advanced treatment technologies are: - Membrane filtration, Ozone disinfection, ultraviolate
(UV) disinfection, adsorption, ion exchange and chemical softening ….

Site Selection Considerations

(1) quantity of water required

(2) quality of the raw water
(3) climatic conditions,
(4) potential difficulties in constructing the intake,
(5) operator safety,
(6) providing minimal operations and maintenance costs for ...

1.2 Structural Design Consideration

Water treatment plants need to be designed and detailed with considerable attention to
detail because of their service requirements. There are currently gaps in guidance for
structural engineering, construction and maintenance of wastewater treatment facilities.
The present structural engineering methodology requires interpretation of non-Ethiopian
standards in an Ethiopian setting, which might lead to unsafe assumptions in
compatibility of design and analysis factors.

1.3 Modeling of Structure

To perform the structural design, to the ultimate limit state and serviceability state, finite
elements models have been developed. It is also verified a structural behaviour for a
seismic action according with the EN 1998-1.Finally, the structure is also designed to
control the cracks and then it is verified the safety at ultimate state.

Structural Design Stage

Design Example
2.1 Design of Plain sedimentation Structural Layout

But for our design we take rectangular tank Plan and Section View of Sedimentation
Basin
Figure 1 Plan Layout of Sedimentation Tank

Figure 2 Section Layout of Sedimentation Tank

2.2 Loading of Sedimentation Basin

Gravity Load and Hydrostatic Load Calculation

The gravity loads include dead loads (i.e. Self-weight, wall load on beams, partition wall
loads, cement screeds, plastering and other permanently attached loads to the building)
and live loads.

Load on the Bottom Slab (unit weight x Thickness)

Unit
Thickness Weight Load
P.S.F. for
Sludge Load 0.75 18.00 13.50 DL 1.35
P.S.F. for
Water Load 3.00 9.81 29.43 LL 1.50
Ceiling
Plaster 0.02 23.00 0.35
2.0 cm
Screed 0.02 23.00 0.46

Load on the Longer Side Wall (unit weight x Thickness)

Thickness Unit Weight Load
Water Load 5.21 9.81 51.11 P.S.F. for LL 1.50
Ceiling
Plaster 0.04 23.00 0.92
2.0 cm
Screed 0.02 23.00 0.46
 Load on the Shorter Side Wall (unit weight x Thickness)
Thickness Unit Weight Load
Water Load 5.21 9.81 51.11 P.S.F. for LL 1.50 Take Half Length of wall
Ceiling
Plaster 0.04 23.00 0.92
2.0 cm
Screed 0.02 23.00 0.46

Aeration tank
Load on the Bottom Slab (unit weight x Thickness)
Unit
Thickness Weight Load
P.S.F. for
Water Load 3.00 9.81 29.43 LL 1.50
Ceiling
Plaster 0.02 23.00 0.35
2.0 cm
Screed 0.02 23.00 0.46

Load on the Shorter Side Wall (unit weight thickness)

Thickness Unit Weight Load
Water Load 3.15 9.81 30.9 P.S.F. for LL 1.50
Ceiling
Plaster 0.04 23.00 0.92
2.0 cm
Screed 0.02 23.00 0.46

Load on the Shorter Side Wall (unit weight thickness)

Thickness Unit Weight Load
Water Load 5.21 9.81 51.11 P.S.F. for LL 1.50 Take Half Length of wall
Ceiling
Plaster 0.04 23.00 0.92
2.0 cm
Screed 0.02 23.00 0.46
Horizontal Roughening filter
Load on the Bottom Slab (unit weight x Thickness)
Unit
Thickness Weight Load
P.S.F. for
Water Load 3.00 9.81 29.43 LL 1.50
Ceiling
Plaster 0.02 23.00 0.35
2.0 cm
Screed 0.02 23.00 0.46

Load on the Shorter Side Wall (unit weight thickness)

Thickness Unit Weight Load
Water Load 3.15 9.81 30.9 P.S.F. for LL 1.50
Ceiling
Plaster 0.04 23.00 0.92
2.0 cm
Screed 0.02 23.00 0.46

Load on the Shorter Side Wall (unit weight thickness)

Thickness Unit Weight Load
Water Load 5.21 9.81 51.11 P.S.F. for LL 1.50 Take Half Length of wall
Ceiling
Plaster 0.04 23.00 0.92
2.0 cm
Screed 0.02 23.00 0.46

Horizontal Roughening filter for filtering machine take 5kN/m2

2.3 Seismic Load

The earthquake value of design spectrum is calculated and used to get the total base shear by
multiplying it by the weight of the building according to EBCS EN 1998-8.

According to EBCS EN 1998-1, our design ground acceleration ag = 1.5 x 0.15g =

0.225g m/s2 determined using reference peak ground acceleration of 0.15g for seismic
zone4 and importance factor IV=1.5, the provision of medium seismicity will apply and
therefore the structure can be designed to meet the requirements medium ductility
class.
Live load calculation
The live load for all floors is taken from the building codes.

Take 1.5kN/m2

2.4 Wind load

The effect of wind load is since the height of the building is very short the effect of wind
load on their wall can be neglected.

2.5 Concrete Grade Selection

According to Ethiopian new code EN 1992-1-1, a concrete structure should accomplish
some criteria, where commonly the most important is the structural strength.
Materials Known the exposure class in is chosen a concrete C30/37.
To avoid the direct contact with the soil, it is put a layer below of the bottom slab with
poor concrete, with the strength class C12/15. To the reinforcement, is chosen a steel
S500.

2.7 Concrete Cover Calculation

Concrete Cover Calculation

Code requirement (ES EN-1992:2015

The concrete cover is the distance between the surfaces of reinforcement closest to the
nearest concrete surface.
The minimum cover shall be specified on the drawing it is defined as a minimum cover,
Cmin (see ES EN-1992:2015 sec 4.4.1.2)plus an allowance in the design for deviation,
Cdev(see ES EN-1992:2015 sec 4.4.1.3) which is
Cnom=Cmin+Cdev
2.8 Load Combination
2.8.1 Design Load Combinations
Design Load Combinations
The values of actions which occur simultaneously are combined as follows:

i) Persistent and transient situation

GRAVITY = 1.35  Gk + 1.5  Qk

The load combination for the gravity load can be made as below;
1-Combo1 1.35*DL + 1.5*LL
Combination of Earth Quack with Dead load and Live Loads
According to Equation 3.17 of ES EN 1998:2015 the following combination effect shall
be taken into consideration:

ii) Seismic Situation

COMB2-EQXP+0.3*EQYP+0.3LL+DL
COMB3-EQXP-.3*EQYP+0.3LL+DL
COMB4-EQXP+0.3*EQYN+0.3LL+DL
COMB5-EQXP-0.3*EQYN+0.3LL+DL
COMB6-EQXN+0.3*EQYP+0.3LL+DL
COMB7--EQXN-0.3*EQYP+0.3LL+DL
COMB8-EQXN+0.3*EQYN+0.3LL+DL
COMB9-EQXN-0.3*EQYN+0.3LL+DL
COMB10-(-EQXP+0.3*EQYP+0.3LL+DL
COMB11-(-EQXP-0.3*EQYP+0.3LL+DL
COMB13-(-EQXN+0.3*EQYP+0.3LL+DL
COMB14-(-EQXN-0.3*EQYP+0.3LL+DL
COMB15(-EQXN+0.3*EQYN+0.3LL+DL
COMB16(-EQXN-0.3*EQYN+0.3LL+DL
COMB17-EQYP+0.3*EQXP+0.3LL+DL
COMB18-EQYP-0.3*EQXP+0.3LL+DL
COMB19-EQYP+0.3*EQXN+0.3LL+DL
COMB20-EQYP-0.3*EQXN+0.3LL+DL
COMB21-EQYN+0.3*EQXP+0.3LL+DL
COMB22-EQYN-0.3*EQXP+0.3LL+DL
COMB23-EQYN+0.3*EQXN+0.3LL+DL
COMB24-EQYN-0.3*EQXP+0.3LL+DL
COMB25(-EQYP+0.3*EQXP+0.3LL+DL
COMB26(-EQYP-0.3*EQXP+0.3LL+DL
COMB27(-EQYP+0.3*EQXN+0.3LL+DL
COMB28(-EQYP-0.3*EQXN+0.3LL+DL
COMB29(-EQYN+0.3*EQXP+0.3LL+DL
COMB30(-EQYN-0.3*EQXP+0.3LL+DL
COMB31(-EQYN+0.3*EQXN+0.3LL+DL
COMB32(-EQYN-0.3*EQXN+0.3LL+DL
Finally, envelopes have been evaluated for the purpose of determining the
design action effects at the critical regions.

 Property/ Stiffness Modification

Concrete has an inherent property of cracking and all members do cracking. This cracking
reduces stiffness. So the analysis with gross property would have overestimated support
moment and under estimated span moments and deflection, we provide more steel than really
required at supports and less at span. The laterals deflection and drift is also underestimated.
Stiffness modifier factors for cracked columns, beams, slabs and wall sections are used in this
project.

For column and beam

Analysis
The structural system consists of 3D frame connected to each other at floor levels with
beams and rigid floor diaphragms. The structural model is done using ETABS V-2016
software for the frame structure as the same step specified for reservoir design
and intake structure.

Frame analysis
The lateral force resisting system consists a 3D rigid jointed frames made of reinforced
concrete which are founded on mat foundations placed below the ground floor level for
the building. The frame is modeled using stiffness modifier recommended by Euro code
which is 0.5Ig for column and 0.5Ig for beams.

Self-wt. of slabs, columns and walls are automatically included in the analysis from the
geometry and unit weight of reinforced concrete. Unit weight of reinforced concrete is
assumed to be 25 kN/m3.

The other load assigned to the slab and on the wall.

3D Modeling of the structure

3.2 Analysis out Put

Moment of Shear Wall Mmax=55kNm
 Design Reinforcement
Check Internal Stability
Step-1 Calculate Reinforcement

Select Wall Assign Shell Pier Label

Design Shear Wall Design Define General Pier Section

Click on section designer

Change Reinforcement by Right Click on the reinforcement and finally ok

 Change reinforcement diameter and spacing

Design Shear Wall Design Start Design Check Select Area of Reinforcement

Maximum Reinforcement Area=51545mm2

Since the wall detail is on both face we will divide Ast/2=51545/2=25772mm2 each face
Number of bar=As/as
Take diameter 20 rebar area=314mm2
No. bar=25772/314=82 take 82
Spacing =Length of wall/No. bar=25772mm2/82=110mm
Take dia.20c/c 110mm rebar
Maximum Reinforcement Area=12300mm2
Since the wall detail is on both face we will divide Ast/2=12300/2=6150mm2 each face
Number of bar=As/as
Take diameter 12 rebar area=113mm2
No. bar=6150/113=54.13 take 55
Spacing =Length of wall/No. bar=10439mm/55=189.5mm
Take dia.12c/c 150mm rebar

3.4 Check Crack Width

Cracking is normal in concrete structures, but those cracks should be controlled to

ensure a proper operation of the structure. To perform that control, NP EN 1992-1-1
defines that crack width (wk) should be limited to wmax=0.2mm.
Since the crack width is 0.3mm>0.2mm
Cheng the thickness of the wall
Since the cracked width is less than 0.2ok
Use dia 14 c/c 150 reinforcement with thickness=300mm
Reinforcement Detailing