final year project report

A

KIGALI INSTITUTE OF SCIENCE AND TECHNOLOGY

Avenue de l'Arme, B.P. 3900 Kigali, Rwanda

FACULTY OF ENGINEERING

DEPARTMENT OF CIVIL ENGINEERING AND ENVIRONMENTAL

TECHNOLOGY

PROGRAM OF CIVIL ENGINEERING

A PROJECT REPORT ON

Submitted by

Samuel BIGIRUMWAMI (REG.NO: GS 20100512)

Yvan RWAMPUNGU (REG.NO: GS 20101119)

Under the guidance of

Mr. Eric SERUBIBI

Submitted in partial fulfillment of requirements for the award of

BACHELOR OF SCIENCE DEGREE IN CIVIL ENGINEERING

May, 2013

PROJECT ID: CEET/CE/2013/08

PROJECT ID: CE/2013/08

STABILITY INVESTIGATION ON STEEL FRAMES OF

EXISTING WATER TANK SUPPORTS

B

KIGALI INSTI TUTE OF SCIENCE AND TECHNOLOGY

Avenue de l'Arme, B.P. 3900 Kigali, Rwanda

FACULTY OF ENGINEERING

DEPARTMENT OF CIVIL ENGINEERING AND ENVIRONMENTAL TECHNOLOGY

C E R T I F I C A T E

This is to certify that the Project Work STEEL

is a record of the original work done

by Samuel BIGIRUMWAMI (REG.No: GS20100512) and Yvan RWAMPUNGU

(REG.No:GS20101119) in partial fulfillment of the requirement for the award of Bachelor of

Science Degree in Civil Engineering at Kigali Institute of Science and Technology during the

Academic Year 2012-2013.

Mr. Eric SERUBIBI Dr G. Senthil KUMARAN

Project Supervisor Head, Dept. of CE&ET

2013.

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DECLARATION

STABILITY INVESTIGATION ON STEEL FRAME OF EXISTING WATER TANK

e Award of a Bachelor of Science Degree in Civil engineering

at Kigali Institute of Science and Technology (KIST), is our own work and all sources quoted

have been acknowledged by means of complete references.

BIGIRUMWAMI Samuel RWAMPUNGU Yvan

Signat

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DEDICATION

This work is dedicated to:

The Almighty God

SEMIVUMBI J. Bosco

GAHONGAYIRE Jeanne

RWAMPUNGU Isaac

MUKASAHAHA Beatrice

GATSINZI Family

KAGERUKA Family

To our brothers and sisters

To our classmates

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ACKNOWLEDGEMENT

Thanks are due to KIST administration and to the department of Civil Engineering and

Environmental Technology in particular for the knowledge acquired through these four years of

study in the department.

We offer our sincerest gratitude to Mr. Eric SERUBIBI for his effort in guiding us and for his

sincere advices during the supervision of this work.

We also wish to express our thanks to our friends and colleagues for their considerable

contribution in achieving this hard work.

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ABSTRACT

The Purpose of this project is to make investigation on steel frame of existing water tank

supports, to check if the stability requirements are met and also check if water tank supports met

the design standards.

This study was completed into two main phases. The first phase was data collection done at

several sites where water tanks are constructed, in choosing water tank supports to be

investigated the following were considered: the supports height should be greater than 3m from

the ground level to the bottom of the tank, the tank capacity should be between 2.5m3to 10m

3

and the tank should be constructed in Rwanda as it is our case study.

The second phase was to analyze the data collected, in data analysis we used Autodesk Robot

Structural Analysis for the calculations and got the results which allowed us to make conclusion,

after calculations, the results shows, 13% of water tank supports are not meeting design

requirements and some of them exhibit signs of instability.

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TABLE OF CONTENT

DECLARATION ............................................................................................................................. I

DEDICATION ................................................................................................................................ II

ACKNOWLEDGEMENT ............................................................................................................ III

ABSTRACT .................................................................................................................................. IV

TABLE OF CONTENT ................................................................................................................. V

LIST OF TABLES ....................................................................................................................... VII

LIST OF FIGURES ................................................................................................................... VIII

LIST OF SYMBOLS AND ABBREVIATIONS .......................................................................... X

CHAPTER 1. INTRODUCTION ................................................................................................. 11

1.1. GENERAL INTRODUCTION ...................................................................................... 11

1.2. PROBLEM STATEMENT ............................................................................................ 11

1.3. OBJECTIVE OF THE RESEARCH .............................................................................. 13

1.3.1. GENERAL OBJECTIVE........................................................................................ 13

1.3.2. SPECIFIC OBJECTIVES ....................................................................................... 13

1.4. HYPOTHESIS ............................................................................................................... 13

1.5. SCOPE OF THE PROJECT ........................................................................................... 13

1.6. SIGNIFICANCE AND RATIONALE ........................................................................... 14

1.6.1. Personal significance .............................................................................................. 14

1.6.2. Public and administrative significance ................................................................... 14

1.6.3. Academic significance ............................................................................................ 14

1.7. RESEARCH METHODOLOGY ................................................................................... 14

CHAPTER 2. LITERATURE REVIEW ...................................................................................... 16

2.1. INTRODUCTION .......................................................................................................... 16

2.2. TERMINOLOGIES ....................................................................................................... 16

2.3. PROPERTIES OF STEEL .............................................................................................. 16

2.3.1. PHYSICAL PROPERTIES OF STEEL ................................................................. 17

2.3.2. MECHANICAL PROPERTIES OF STEEL .......................................................... 17

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2.3.3. CHEMICAL PROPERTIES OF STEEL ................................................................ 18

2.4. STEEL CONNECTIONS ............................................................................................... 19

2.4.1. INTRODUCTION .................................................................................................. 19

2.4.2. RIVETED CONNECTIONS .................................................................................. 19

2.4.3. BOLTED AND PIN CONNECTIONS .................................................................. 21

2.4.4. WELDED CONNECTIONS .................................................................................. 22

CHAPTER 3. METHODOLOGY ................................................................................................ 30

3.1. INTRODUCTION. ................................................................................................................... 30

3.2. TOOLS. ................................................................................................................................ 30

3.3 TECHNIQUES. ........................................................................................................................ 30

3.4. STRUCTURAL STEEL SECTION AND THEIR CHARACTERISTIC TENSILE AND YIELD

STRENGTH. ................................................................................................................................. 32

3.4.1. Structural steel Sections. ......................................................................................... 32

3.4.2. Characteristic Tensile and yield Strength. .............................................................. 34

3.5. WATER TANK PROPERTIES. ............................................................................................. 35

3.6. ASSUMPTIONS. .................................................................................................................... 35

CHAP 4. DATA ANALYSIS. ...................................................................................................... 36

CHAPTER 5: CONCLUSION AND RECOMMENDATION. ................................................... 66

5.1. CONCLUSION. ................................................................................................................. 66

5.2. RECOMMENDATION. ..................................................................................................... 66

REFERENCES ............................................................................................................................. 72

BIBLIOGRAPHIC REFERENCES ..................................................................................................... 72

INTERNET REFERENCES .............................................................................................................. 72

COMPUTER REFERENCES ............................................................................................................ 72

APPENDICES .............................................................................................................................. 73

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LIST OF TABL ES

Table 2.1.Chemical composition of steel ...................................................................................... 18

Table 2.2.Maximum permissible stresses in rivets ....................................................................... 20

Table 2.3.Minimum size of single run fillet weld. ........................................................................ 27

Table 2.4.values of k for different angles ..................................................................................... 28

Table 3.1. RHS available on Rwandan market. ............................................................................ 32

Table 3.2. SHS available on Rwandan market. ............................................................................ 33

Table 3.3. Rolled steel equal angle available on Rwandan market. ............................................. 34

Table 3.4. CHS available on Rwandan market. ............................................................................ 34

Table 3.5. Properties of plastic tanks ............................................................................................ 35

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LIST OF FIGU RES

Fig1.1: Water tank support in state of instability. ......................................................................... 12

Fig.2.3.Example of bolt assembly................................................................................................. 22

Fig.2.5.Most common edge preparations ...................................................................................... 25

Fig.2.6.Different types of butt welds ............................................................................................ 25

Fig.2.7 Effective throat thickness of partial penetration butt weld ............................................... 26

Fig.2.8 Common fillet welds ........................................................................................................ 26

Fig.2.9.Specifications of fillet weld .............................................................................................. 27

Fig.3.1. Interface of Robot Structural Analysis Professionals 2012 ............................................. 31

Fig.3.1.Rectangular hollow sections ............................................................................................. 32

Fig.3.2. Square hollow section ...................................................................................................... 33

Fig.3.3. Rolled steel equal angle ................................................................................................... 34

Fig.3.4: Circular hallow section .................................................................................................... 34

Fig.4.1:case1(photo,model,3D ...................................................................................................... 36

Fig.4.2: case2(photo,model,3D).................................................................................................... 37

Fig.4.3:case3 (photo,model,3D).................................................................................................... 38


Fig.4.5: case5 (photo,model,3D)................................................................................................... 40





Fig.4.10: case10(photo,model,3D)................................................................................................ 45




Fig.4.14:case14 (photo,model,3D)................................................................................................ 49






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Fig.4.26: case26 (photo,model,3D)............................................................................................... 61

Fig.4.27: Case27 (photo,model,3D) .............................................................................................. 62


Fig4.29: case29 (photo,model,3D)................................................................................................ 64


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LIST OF SYMBOLS AND ABBREVIATIONS

o KIST: Kigali Institute of Science and Technology

o RHS: Rectangular Hollow Section

o SHS: Square Hollow Section

o CHS: Circular Hollow Section

o EWSA: Energy Water and Sanitation Agency

o Fig: Figure

o DL: Dead Load

o LL: Live Load

o 3D: Three Dimension

o CHAP: Chapter

o Fy: Yield stress

o MPa: Mega Pascal

o Lmin: Minimum length

o N: Newton

o kN: Kilo Newton

o m: metre

o mm: millimeter

o %: percentage

o oC: Degree Celcius

o CAD: Computer Aided Drawing

o EUROCODE: European Code of Practice

o tf: Allowable Stress in Shear

o vf: Allowable Stress in tension

o pf: Allowable Stress in bearing.

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CHAPTER I . GENERAL INTRODUCTION

1.1. INTRODUCTION

Stability of steel frame means to ensure the structural safety of steel frame by considering the

characteristic strength of the steel used and type of connections.

Stability Investigation on Steel Frames of Existing Water

Tanks Supports whether steel frames used in the design of water

tanks supports were meeting the standards thus ensuring the safety.

This study was done on 30 different cases, investigating on the stability of common steel used,

different frames and type of connections used.

1.2. PROBLEM STATEMENT

Nowadays, due to the lack of water and in order to decrease the amount of water lost from public

water supplier, for example EWSA, new buildings either residential or public which are

constructed in RWANDA are having water tanks. This is a preventive, safe and economic

method which is also advised by the government because the water demand is increasing while

the supplier is unable to satisfy the existing population demand. Therefore problems of lack of

water can be avoided by providing methods which can help the population to satisfy his water

demand in case the public water supply has failed. Also in order to support the public water

supplier, rainwater can be stored and used in some issues which do not need special treatment of

water. Sometimes water tanks are laid over platforms on the ground level but the other case

which is the most used and recommended is the use of supports to sustain it at a higher level and

thus maintain or increase the desired water pressure.

The common supports are made of steel or reinforced concrete and this work will focus on steel

framed supports. The problem is that steel frame of some water tank supports exhibit signs of

ant causes are

the lack of stability and natural catastrophes.

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The following is an example of water tank collapsed in GITEGA because of the steel members

which is not strong enough to supports the load applied.

Fig1.1: Water tank support in state of

instability.

Fig1.2: Water tank supports collapsed.

This work put our concern on the lack of stability of those steel framed supports which is mainly

due to the improper design, soil conditions including poor bearing capacity.

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1.3. OBJECTIVE OF THE RESEA RCH

1.3.1. GENERAL OBJECTIVE

The general objective was to investigate the stability of the steel framed supports of various

water tanks that are constructed in RWANDA.

1.3.2. SPECIFIC OBJECTIVES

To check if the steel frames design of water tank supports in Rwanda meets the design

standards.

To assess and cross-check the stability requirement of steel frame by Euro code 3, if the

stability requirement are met.

To recommend to whom it may concern in government institutions to establish and

follow up rules of design of steel framed supports.

1.4. HYPOTHESIS

As a recommended, safe and preventive method against water problems, the construction of

water tanks in our country is developing. These water tanks are often constructed with supports

to sustain it at a certain height.

The main hypotheses of this project are:

1. The designed or constructed steel framed water tank supports are stable and meet the

structural safety recommended by Euro code 3 guidelines.

2. The designed or constructed steel framed water tank supports are not stable and sometimes

they are failing, thus not meeting the structural safety recommended by Euro code 3

guidelines. This can be explained by the following reasons:

The steel framed supports are not designed taking into account the soil conditions.

The steel framed supports used are not strong enough and do not meet the recommended

strength.

The steel framed supports are not properly designed.

Water tanks supports are not designed for wind loads and earthquakes.

1.5. SCOPE OF THE PROJECT

This research was focused on assessing the stability of steel frames of the existing water tank

supports and it was carried out in RWANDA investigating 30 different water tank supports and

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the supports height should have 3m and above from the ground level to the bottom of the tank

and the capacity of the tank should be between 2.5m3 to 10m

3.

1.6. SIGNIFICANCE AND RATIONALE

1.6.1. Personal significance

There are many reasons which prompted us to carry out this study but the main motivation is that

in the field of civil engineering, we are interested in structural analysis. As civil engineers, we

need to conduct such study because we want to investigate on stability of steel frame of existing

water tank supports. Therefore in conducting this study we were able to enhance our knowledge

about steel frame analysis and structural design of steel structures according to Eurocode 3.

1.6.2. Public and administrative significance

This study will be a guide for different residential houses and public institutions and it will be

useful for many construction companies during the design and implementation of steel structures

that support water tanks.

1.6.3. Academic significance

This study is in line with the High Education requirements which suggest that every student in

his/her final year must submit and present a dissertation

addition, this study will help undergraduate students to do their researches in their final year

projects. They will also be able to use it in their academic courses such as Engineering

mechanics, strength of materials, structural analysis I&II, Design of steel structures...etc.

Scientifically this study may help other civil engineers who are interested in steel frame analysis

when they want to conduct a deep study about stability of steel frames of water tank supports.

1.7. RESEARCH METHODOLOGY

This research was done using the following methodology steps:

The documentation using internet and books was used with respect to the title of the project

to get enough theoretical information about steel frame analysis and the design procedure for

steel according to Euro code 3.

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Gaining information from different engineers and designers.

The data was collected from different site where water tanks are constructed.

Data analysis and interpretation of all investigated water tank supports was done using

Autodesk Robot Structural Analysis software.

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CHAPTER II . LITERATURE REVIEW

2.1. INTRODUCTION

Previous work has been done in the mentioned research field, but many of them have put their

concern on other different project like mechanical properties of steel and design of roof trusses

for buildings. The proposed research intends to achieve its goal by investigating the stability of

steel frames of water tank supports and further recommendations from the research will be taken

into account in the future design and implementation.

Steel is a common building material used throughout the construction industry. Its primary

purpose is to form a skeleton for the building or structure essentially the part of the structure that

holds everything up and together. Steel has many advantages when compared to other structural

building materials such as concrete, timber, plastics and the newer composite materials. Steel is

one of the friendliest environmental building materials; steel is 100% recyclable. Steel, unlike

wood, does not warp or twist and does not substantially expand and contract with the weather.

Unlike concrete, steel does not take time to cure and is immediately at full strength. Steel is

versatile, has more strength with less weight, has an attractive appearance, can be erected in most

weather conditions, is of uniform quality, and has proven durability and low life cycle costs.

These advantages make steel the building material of choice.

2.2. TERMINOLOGIES

Stability: Ability to maintain a firm position. On the other hand, the word stability

involves safety, resistance, strength of any structure.

Steel frames: usually refers to a building technique with a "skeleton frame" of

vertical steel columns, horizontal and diagonal I-beams and tubes, constructed in a

rectangular grid to support the floors, roof, water tanks, walls and any structure of a

building which are all attached to the frame.

Investigation: the act of searching inquiry for ascertaining facts; detailed or careful

examination.

2.3. PROPERTIES OF STEEL

The properties of steel depend primarily upon the carbon it contains, influenced by the quantity

and kind of the other ingredients (impurities), and further influenced by the cooling of the steel
http://en.wikipedia.org/wiki/Skeletonhttp://en.wikipedia.org/wiki/Steelhttp://en.wikipedia.org/wiki/Columnshttp://en.wikipedia.org/wiki/I-beam

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from its molten state. This last named influence determines the size and composition of crystals

which steel assumes upon cooling. The grades of steel are classed according to their hardness

due to their contained carbon. The higher the percent of carbon, the greater the strength and

brittleness, and less the elongation before breaking. Two classes are distinguished: mild steel

which will not harden when suddenly cooled, and high carbon steel which will harden when

suddenly cooled from a red heat.

2.3.1. PHYSICAL PROPERTIES OF STEEL

iron and carbon

2.3.2. MECHANICAL PROPERTIES O F STEEL

Stress-strain behavior:

The behavior of mild steel shows that it is like an elastic material directly proportional to the

stress up to the yield whereas high yield steel does not have defined yield point, but show a more

gradual change from elastic to plastic behavior.

Fig.2.1.Typical stress strain diagram for structural carbon steel (Eurocode 3, part1.1)

In the design, the strength considered depends on the yield stress for mild steel, while for high

Yield; the strength is based on specified proof stress of 0.2 per cent.

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Elastic moduli: E, G

These are commonly defined in terms of relationship between stress , and strain , in that region

where the curve is linear.

The most frequently used is the modulus in tension.

Notch-toughness:

There is always a possibility of microscopic cracks in a material or the material may develop

such cracks as a result of several cycles of loading.

Such cracks may grow rapidly without detection and lead to sudden collapse of the structure. The

material in which that does not happen is known as notch-tough steels. [5-6]

Hardness

It may be defined as the resistance of a material to indentations and scratching.

This is generally determined by forcing and indentor on to the surface. The resultant deformation

in steel is both elastic and plastic. [6]

Fatigue

Fatigue is the result of a member being subjected to reversing or fluctuating stress even when the

maximum applied stress drops below that normally required to produce fracture and ,in fact,

under the yield strength of the material.[6]

2.3.3. CHEMICAL PROPERTIES OF STEEL

Table 2.1.Chemical composition of steel

Constituents Maximum percent

Carbon (for thickness)diameter up to 20mm 0.23

Carbon ( for thickness) diameter over 20mm 0.25

Sulphur 0.055

Phosphorous 0.055

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2.4. STEEL CONNECTIONS

2.4.1. INTRODUCTION

A structure is an assembly of various elements or components which are fastened together

through some type of connection. If connections are not designed properly and fabricated with

care, they may be a source of weakness in the finished structure, not only in their structural

action but also because they may be the focus of corrosion and aesthetically unpleasing. Whereas

the design of main members has reached an advanced stage, based upon theories which has been

developed and refined, the behavior of connections is often so complex that theoretical

considerations are of little use in practical design.

Following are the requirements of a good connection in steelwork:

1. It should be rigid, to avoid fluctuating stresses which may cause fatigue failure.

2. It should be such that there is the least possible weakening of the parts to be joined.

3. It should be such that it can be easily installed, inspected and maintained.

The following are the common types of connections used for structural steelwork

a) Riveted connections

b) Bolted connections

c) Welded connections

d) Pinned connections

The first three are extensively used but this last time riveting is being superseded in importance

by welding and high strength bolting.

Throughout this project, the type of steel frame connections that has been used for the

investigation is the welded connections due to the fact that it is the most common used and is the

cheapest. The bolted connections are commonly used in wide projects which mostly has been

studied and designed according to standards thus fulfilling the safety and stability (EWSA tanks).

This is the reason why in the following, the project will emphasize on welded connections.

2.4.2. RIVETED CONNECTIONS

2.4.2.1.Rivet and Riveting

Riveting is a method of joining together structural steel components by using inserting ductile

metal pins, called rivets, into holes of the components to be connected from coming apart.

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A rivet consists of a shank of given length and diameter, and a head known as manufactured

head. The size of the rivet is defined by the diameter of the shank.Riveting is essentially a

forging process. The process of riveting consists in driving a hot rivet in its plastic state and the

formation of a head in the other hand. Depending on means used to drive rivets, they are hand

driven rivets which are driven by hand operated equipment, and power driven rivets which are

driven by power operated equipment. The diameter of unheated rivet, before driving is known as

the nominal diameter. Rivets are manufactured in nominal diameters of 12, 14, 16, 18, 20, 22,

24, 27, 30, 33, 39, 42 and 48 mm. The diameter of rivet hole is made larger than the nominal

diameter of the rivet by 1.5 mm for rivets less than or equal to 24 mm and by 2 mm for diameters

exceeding 24 mm.

2.4.2.2.Working stresses in rivets

The working stresses (or maximum permissible stresses) in mild steel shop is given in table 2.

Table 2.2.Maximum permissible stresses in rivets

Type of rivet Axial tensio tf

N/mm2 (MPa)

vf

N/mm2 (MPa)

pf

N/mm2 (MPa)

1. Power driven rivets 100 100 100

2. Hand driven rivets 80 80 250

2.4.2.3. Types of riveted joints

A riveted joint may be classified according to (a) arrangement of rivets and plates which is the

main classification (b) mode of load transmission, and(c) nature and location of load with respect

of rivet group. Here are different types according to the

a) Arrangement of rivets and plates

According to the arrangement of rivets and plates, riveted joints may be of the following types:

1) Lap joint: - Single rivet

- Double riveted

2) Butt joint: - Single riveted butt joint with single cover plate

- Single riveted butt joint with double cover plate

- Double riveted butt joint with single cover plate

- Double riveted butt joint with double cover plate

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2.4.2.4. Modes of failure of riveted joint

A riveted joint may fail in one of the following ways:

1. Shearing failure across one or more planes of the rivets

2. Tension failure (tearing) in the plate

3. Bearing failure between the plates and the rivets

4. Plate shear or shear out failure in the plate

2.4.3. BOLTED AND PIN CONNECTIONS

2.4.3.1.INTRODUCTION

A bolt is an externally threaded fastener designed for insertion through holes in assembled parts,

and is normally intended to be tightened or released by torquing a nut. For structures which are

not subjected to shock or vibrations, bolts can be used instead of rivets. In bolted connections,

bolts and nuts are used. The three types of bolts used in structural applications are (a) unfinished

or black bolts, (b) turned and fitted bolts and (c) high- strength bolts. In pinned connections, pins

are used for jointing the members.

Advantages of bolted connections

1. The bolting operation is very silent, in contrast to the hammering noise in riveting.

2. Bolting is a cold process, and hence there is no risk of fire.

3. Bolting operation is far quicker than riveting.

4. There is no risk involved in the bolting, in contrast to the risk of flying rivets in riveting work.

5. Less man-power is required in making the connections.

Disadvantages of bolted connections

1. The bolted connections, if subjected to vibratory loads, result in reduction in strength if they

get loosened.

2. Bolted connections for a given diameter of bolt, have lesser strength in axial tension since the

net area at the root of the threads is less.

3. Unfished bolts have lesser strength because of non-uniform diameter.

4. In the case of black bolts, the diameter of hole is kept 1.5 mm more than the diameter of the

bolt, and this extra clearance does not get filled up, in contrast to the riveted joints.

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2.4.3.2. Bolt types

A bolt is a metal pin with a head formed at one end and the shank threaded at the other end in

order to receive a nut. In common steel structural work, however, the following three bolt types

are recognized:

1. Ordinary unfinished or black bolts

2. Turned and fitted bolts

3. High strength bolts

.

Fig.1.3.Example of bolt assembly (www.google.com)

2.4.4. WELDED CONNECTIONS

2.4.4.1. INTRODUCTION

Welding is a process of connecting pieces of metal by application of heat (fusion) with or

without pressure. A metallic bond is established between the two pieces. This bond has the same

mechanical properties as the parent metal. The most important methods used for the process of

fusion are the oxyacetylene or gas welding and electric arc welding. The metal at the joint is

melted by the heat generated from either an electric arc or an oxyacetylene flame and fuses with

metal from welding rod. After cooling, the parent metal (base metal) and the weld metal form a

continuous and homogeneous joint.

There are numerous welding processes, but the one most commonly used in Civil

Engineering Structures is electric-arc welding.

ADVANTAGES AND DISADVANTAGES OF WELDING

The following are advantages of welded joints:

The welding joint can be made more than 100% strong. So welding joint will never failed.

With concern of welding there no need any kind of mould, pattern etc.
http://www.typesofwelding.net/weld_joints_symbol.html

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During the fabrication with welding, results in lighter construction and there are savings in

materials.

It is possible with welding technique to add the specific material with desired characteristics to

any portion of the machine parts.

In general case the welding equipments are not costly.

Designing of welding fabrication is not so tough.

Welding can be mechanized.

A wide range of metals and its alloy or dissimilar metals can be joined by welding process.

Welding joining of metals is performed in any position, so it does no need any kind of special

construction.

Portable welding machine equipments are available, so portability of welding machine can be

avoided.

The following are disadvantages of welded joints:

Produced ultra-violet light is very harmful for health and fumes and spatters also.

Edge preparation should be prominent for good weld.

A skilled welder is required to produce a good quality of welding joints.

A residual stress and distortion is occurred, as a result work piece may damage.

After welding stress relief is required of weld joint.

During heating the metallurgical changes occurred in the weld filler metal. Due to this reason the

molecular structure of base metal different from filler metal.

Jigs or fixtures are required to hold the weld jobs.

2.4.4.2. TYPES OF WELDS AND WELDING JOINTS

By means of welding, it is possible to make continuous, load bearing joints between the

members of a structure. A variety of joints is used in structural steel work and they can be

classified into four basic configurations namely, Lap joint, Tee joint, Butt joint and Corner

joint.

For lap joints, the ends of two members are overlapped and for butt joints, the two members are

placed end to end. The T- joints form a Tee and in Corner joints, the ends are joined like the

letter L. Most common joints are made up of fillet weld or the butt (also calling groove) weld.

Plug and slot welds are not generally used in structural steel work (figure 2.4). Fillet welds are
http://www.typesofwelding.net/index.htmlhttp://www.typesofwelding.net/welding_techniques.htmlhttp://www.typesofwelding.net/index.htmlhttp://www.typesofwelding.net/welding_position.htmlhttp://www.typesofwelding.net/edge_preparation.htmlhttp://www.typesofwelding.net/weld_joints_symbol.html

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suitable for lap joints and Tee joints and groove welds for butt and corner joints. Butt welds can

be of complete penetration or incomplete penetration depending upon whether the penetration is

complete through the thickness or partial. Generally a description of welded joints requires an

indication of the type of both the joint and the weld.

Fig.2.4.Common types of welds (Design of structural connections to Eurocode 3)

Though fillet welds are weaker than butt welds, about 80% of the connections are made with

fillet welds. The reason for the wider use of fillet welds is that in the case of fillet welds, when

members are lapped over each other, large tolerances are allowed in erection. For butt welds, the

members to be connected have to fit perfectly when they are lined up for welding. Further butt

welding requires the shaping of the surfaces to be joined as shown in Figure. 2.5.

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Fig.2.5.Most common edge preparations (www.google.com)

a) BUTT WELD OR GROOVE WELD

Butt weld or groove weld is used when the plates to be jointed are in the same plane, or when a

T-joint is desired. A butt weld is designated according to the shape of groove made during the

preparation of ends of the pieces to be joined. The common types of butt welds are shown in

figure 2.6.

Fig.2.6.Different types of butt welds (www.google.com)

Butt welds have high strength, high resistance to impact and cyclic stress. They are most direct

joints and introduce least eccentricity in the joint. But their major disadvantages are: high

residual stresses, necessity of edge preparation and proper aligning of the members in the field.

Therefore, field butt joints are rarely used.

26

A butt weld is specified by the size of the weld, which is defined by the effective throat

thickness. The reinforcement is the extra metal deposited proud of the surfaces of the pieces

jointed, as shown in figure 2.7 (a). The reinforcement may vary between 1 mm to 3 mm and is

not included in the throat thickness.

Fig.2.7 Effective throat thickness of partial penetration butt weld (Design of structural

connections to Eurocode 3)

The square butt joints are used for thickness less than 8 mm. The effective thickness of the weld,

called throat thickness, is less than the thickness T of the plates jointed. It is taken as T. In the

single V-built joint, the throat thickness is taken as T. In double V-butt joint, the weld is fully

effective and hence the throat thickness is taken equal to T. As a rule, in single U, single V and

single J butt welds, where welding is done from one side, full penetration is not possible and

hence effective throat thickness is taken equal to T. In double-V, double U and double J butt

welds, full penetration is possible and the effective thickness of throat is taken equal to the

thickness of plates jointed. Whenever two plates of different thickness are jointed, the thickness

of thinner plate must be taken into account.

b) FILLET WELD

When the lapped plates are to be jointed, fillet welds are used. These are generally of right

angled triangle shape. Common used fillet welds are Single-sided fillet welded joint types and

aregiven in the figure 2.8 given bellow:

Fig.2.8 Common fillet welds (www. Google.com)

27

Specifications of Fillet welds

Fig.2.9.Specifications of fillet weld (www.google.com)

A fillet weld is specified by the following:

(i) Size of weld

(ii) Throat thickness

(iii) Length of weld

1. Size of weld: the sides containing the right angle of the fillet are called legs. The size of

the weld is specified by minimum leg length. The length of the leg is the distance from

the root of the weld to the toe of the weld, measured along the fusion face. Table

2.3.Givesthe minimum size of single run fillet weld, as specified by IS: 816- 1969.

Table 2.3.Minimum size of single run fillet weld.

Thickness of thicker part Min. size

Up to 10 mm 3 mm

10 to 20 mm 5 mm

20 to 32 mm 6 mm

32 to 50 mm 8 mm (first run); 10 mm (min.)

Note: when the minimum size of the weld is greater than the thickness of thinner part, the

minimum size of the weld should be equal to the thickness of thinner part.

2. Throat thickness: The theoretical throat is the perpendicular distance between the root of

the weld, and the hypotenuse joining the two ends of the legs. Reinforcement is

28

neglected. The effective throat thickness is taken equal to the theoretical throat thickness,

and when the angle between the fusion faces is 90 (as is generally the case), we have:

Effective throat thickness,

Or Where the size of weld = minimum leg length

For angles other than 900 between the fusion faces, effective throat thickness = k x minimum leg

length.

Table 4.Gives the values of k for different angles between the fusion faces, as per IS:

816-1969:

Table 2.4.values of k for different angles

Angle 60 to 90 91 to 100 101 to 106 107 to 113 114 to 120

K 0.7 0.65 0.60 0.55 0.5

It may be noted that a fillet weld is not used for jointing parts if the angle between the fusion

faces is less than 60 or greater than 120. The maximum size of fillet weld at the square edge of

a plate (figure 2.6.a) is 1.5 mm less than the plate thickness and in case of a weld at the rounded

edges of flanges or the toe of an angle is kept three fourths the thickness of the edge (figure 2.6.b

).

When the fillet weld is placed parallel to the direction of the forces on both the sides of the

member, it is called side fillet weld. When the weld is placed at the end of the member, such that

it is perpendicular to the direction of the force, it is called end filletweld. If the axis of the weld is

inclined to the direction of force, it is known as diagonalfillet weld.

3. Effective length of weld: The effective length of the weld is taken as overall length

minus twice the weld size. The effective length should not be less than four times the size

of the weld; otherwise the weld size must be taken as one fourth of its effective length. If

only the side welds are used, the length of the each side fillet weld must not be less than

the perpendicular distance between the two. When the ends are returned, as shown in

figure 2.9.b, the ends should be carried continuous for a distance not less than twice the

size of the weld, especially when the joint is subjected to tensile force.

c) DEFECTS IN WELDING

29

Welding is highly specialized technique of jointing, and it should be done carefully so that no

defects or imperfections are left. The most important defects arising from the welding technique

are as follows:

1. Undercutting: this defect takes place due to excessive current and excessive length of

arc, resulting in the formation of groove in the base metal.

2. Overlap: it takes place when the weld metal overflows the groove, but does not fuse with

base metal.

3. Incomplete penetration: this defect takes place the weld metal does not penetrate up to

the root of the joint because of faulty groove preparation, or because of faulty technique

used during welding.

4. Lack of fusion: it takes place when the parent metal is coated with some foreign matter

and when the groove is not clean. Due to this, they will be lack of union between two

runs of weld metal.

5. Slag inclusion: it takes place because of formation of oxides due to chemical reaction

among the base metal, air end electrode coating, during welding.

6. Porosity: it takes place when a group of gas pores get entrapped in the weld. It is a defect

of gas inclusion.

7. Edge melting: this defect occurs in fillet welds because of careless welding.

30

CHAPTER III . METHODOLOGY

3.1. Introduction.

This chapter explains the methodology used to investigate the stability of steel frames of various

water tank supports in RWANDA.

It indicates techniques and tools used.

The data used in this research were collected from different sites in Rwanda where water tanks

are constructed especially in public institutions and residential houses.

In data collection, the desired data were: photo of water tank support, sketch of structural frame,

size and dimensions of steel section used and to know if it is rectangular hollow section (RHS),

circular hollow section (CHS) or any other types of section which can be used, volume of water

tank which was considered as the load to be applied, the shape of the tank and the location of

investigated water tank supports.

3.2. Tools.

Tools used during the data collection are as follows:

Digital camera: used to take the photos of the tank and the whole structure.

Meter: used to take measurements of the frames.

Drawing sheet: we used it to draw the model of water tank supports.

Note book: used to take notes of information required about the investigated water tank

such as volume, self-

After collecting all the data, AutoCAD software were used to draw the entire frame model of

water tank supports.

3.3 Techniques.

The data sheet we used in this project consists of the photo taken at the site where the tank is

constructed and the model drawn in AutoCAD software.

While analyzing the data collected Autodesk Robot Structural Analysis Professional 2012

software was used to clearly show the maximum deflection, maximum stress, and maximum

31

shear forces.

Fig.3.1. Interface of Robot Structural Analysis Professionals 2012

The following are the steps involved in analyzing the structure in Robot software:

1. Open the software and start drawing the model in 3D using the investigated hollow

steel sections. The shell design was used to simulate our steel frames.

2. Load definition: we applied the load we had in data collection excluding wind

load because all the supports we had were less than 10m height, therefore, are not

affected by wind as according to Eurocode, see appendices 1.

Dead load 1(DL1): self-weight of the structure(steel tubes)

Dead load2 (DL2): load from tank+ self-weight of the tank.

Live load (LL):(1.5 kN/m2 from Eurocode )

Combination1 (1.35DL1+1.35DL2+1.5LL)

2. Analysis :the following are the results done by the software:

Displacement

Stresses

Moments

Shear

32

Deflection

Reactions

3.4. Structural steel Section and their characteristic Tensile and yield Strength.

3.4.1. Structural steel Sections.

During our research project, a visit at SONATUBES s.a.r.l was done to know the structural steel

sections that are available on Rwandan market, so below are the following information from

SONATUBES s.a.r.l for steel sections available in Rwanda:

Rectangular Hollow Sections: It is available in different dimensions.

Fig.3.1.Rectangular hollow sections

Table3.1. RHS available on Rwandan market.

Breadth(mm) Height(mm) Thickness(mm)

30 20 1

40 20 0.9

50 30 1

60 40 1.2

80 40 1.5

30 20 3

40 20 2

40 20 1.5

40 20 3

60 40 3

80 40 2

33

80 40 3

Square Hollow Section:

Fig.3.2. Square hollow section

Table3.2. SHS available on Rwandan market.

Breadth(mm) Thickness(mm)

12 0.8

16 0.8

20 1

25 1

30 1.2

40 1.2

30 2

30 3

40 2.5

40 3

50 3

Rolled steel equal angles

34

Fig.3.3. Rolled steel equal angle

Table3.3. Rolled steel equal angle available on Rwandan market.

Breadth(mm) Height(mm) Thickness(mm)

20 20 2.5

30 30 2.5

40 40 3

50 50 4

Circular hallow sections: with specified dimensions

Fig.3.4: Circular hallow section

Table3.4. CHS available on Rwandan market.

Diameter(mm) Thickness(mm)

22 1.4

25 1.4

32 1.8

50 2.3

3.4.2. Characteristic Tensile and yield Strength.

In data analysis we considered the maximum stress obtained in the member compared to the

yield strength of the steel section we had, the nominal yield strength for structural hollow section

from Eurocode 3 is 235N/mm2 for S 235H as steel grade.

See the appendix 2

35

3.5. Water Tank Properties.

Water tank found on site were of two types: plastic tanks and steel tank. During the research

project a visit at ROTO TANK INDUSTRIES was done to know the properties of those tanks

d them to have the following properties:

Table 3.5. Properties of plastic tanks

Capacity Self-weight

10m3 300kg

5m3 150kg

3.5m3 115kg

3m3 100kg

2.5m3 75kg

3.6. Assumptions.

In analyzing the data we had in data collection, the following assumptions were considered:

All steel members are new, with yield strength of 235 MPa for S 235H as steel grade.

The steel connections are fixed (welding).

Wind load were not considered in load definition as the support heights of all water tank

supports are less than 10m height as recommended by Eurocode 3.

36

CHAPTER IV . DATA ANALYSIS.

Fig.4.1:case1(photo,model,3D)

Case Location (KIST Restaurant).

Tank Steel Tube

Cylindrical tank with 5 m3 volume RHS 60*40*3mm

Load values(kN/m2)

Results(stresses, deflection and displacement )

1.Stresses (Max and min)

Notes: The calculated maximum

stress is 206.72MPa at the bar

128, comparing this value to the

yield strength of 235MPa of

hollow section steel bars.

206.72MPa0.

1cm.

Hence safe.

3.Displacements


displacement is 0.2cm at node

461.

Hence it is stable.

37

Fig.4.2: case2(photo,model,3D)

Case Location (KIST, NUR Campus).

Tank Steel Tube

Cylindrical tank with 5 m3 volume RHS 80*40*3mm, RHS 60*40*3mm

Load values(kN/m2)



Notes: The calculated

maximum stress is 342.33MPa

at the bar 41, comparing this

value to the yield strength of

235MPa of hollow section steel

bars.

342.33MPa>235MPa, we

conclude that all steel members

of this tank are not strong

enough to resist applied loads.

2. Deflections


maximum deflection is 3.4cm

at the bar 43, comparing to the

allowable deflection from

Eurocode3: L/325, where L is

the length of member.

L= 260cm

Allowable

deflection=260/325=0.8cm

38

Fig.4.3:case3 (photo,model,3D)

Case Location (KIST, Guest House).

Tank Steel Tube


Load values(kN/m2)







235MPa of hollow section

steel bars.

65.80MPa0.0c

m

Hence safe.

3.Displacements


displacement is 0.1cm at node 13,

28&181.

Hence it is stable.

39


Case Location (KIST, FAED).

Tank Steel Tube


Load values(kN/m2)








steel bars.

169.64MPa0.2c

m.

Hence safe.

3.Displacements



230.

Hence it is stable.

40

Fig.4.5: case5 (photo,model,3D)

Case Location (Kimihurura, Rugando).

Tank Steel Tube


Load values(kN/m2)








bars.

218.55MPa0.

2cm

Hence safe.

3.Displacements


displacement is 0.0cm at node1.

Hence it is stable.

41


Case Location (Kibagabaga).

Tank Steel Tube

Cylindrical tank with 5 m3 volume RHS 80*40*3mm,RHS 60*40*3mm, RHS

40*40*3mm

Load values(kN/m2




stress is 77.44MPa at the bar 7,

comparing this value to the yield

strength of 235MPa of hollow

section steel bars.

77.44MPa0.

2cm.

Hence safe.

3.Displacements



16&21.

Hence it is stable.

42



Tank Steel Tube

Cylindrical tank with 3 m3 volume RHS 80*40*3mm, RHS 40*40*3mm

Load values(kN/m2




stress is 158.68MPa at the bar27,



section steel bars.

158.68MPa

43


Case Location (KIST, MMI).

Tank Steel Tube

Cubic tank with 7 m3 volume CHS with 10cm diameter

Load values(kN/m2








bars.

242.02MPa>235MPa, we

conclude that all steel members

of this tank are not strong

enough to resist applied loads.

2. Deflections


maximum deflection is 2cm at

the bar 42, comparing to the

allowable deflection from

Eurocode3: L/325, where L is

the length of member.

L= 190cm

Allowable

deflection=190/325=0.5cm

44


Case Location (Gitega).

Tank Steel Tube


Load values(kN/m2








bars.

664.41MPa

45

Fig.4.10:

case10(photo,model,3D)

Case Location (Muhima).

Tank Steel Tube

Cylindrical tank with 5 m3 volume RHS 60*40*3mm,RHS 40*40*3mm

Load values(kN/m2





at the bar72, comparing this



steel bars.

8.39MPa0.0

cm

Hence safe.

3.Displacements


displacement is 0.0cm at node1, 4,

13, 17&22.

Hence it is stable.

46


Case Location (CHUK).

Tank Steel Tube

Cylindrical tank with 2.5 m3 volume CHS with 8cm diameter

Load values(kN/m2








steel bars.

28.44MPa0.

1cm

Hence safe.

3.Displacements



155 in X direction and at node 16,

20 in Y direction.

Hence it is stable.

47

Fig.4.12:


Case Location (Gikondo).

Tank Steel Tube

Cylindrical tank with 2.5 m3 volume RHS 60*40*3mm

Load values(kN/m2)




maximum stress is 40.51MPa at

the bar3, comparing this value

to the yield strength of 235MPa

of hollow section steel bars.

40.51MPa0.0c

m

Hence safe.

3.Displacements


displacement is 0.1cm at node 53

in Z direction.

Hence it is stable.

48

Fig.4.13:


Case Location (Remera).

Tank Steel Tube


Load values(kN/m2)








steel bars.

30.72MPa0.0c

m.

Hence safe.

3.Displacements



in Z direction.

Hence it is stable.

49



Tank Steel Tube


Load values(kN/m2)







section steel bars.

46.16MPa0.0c

m

Hence safe.

3.Displacements


maximum displacement is

0.0cm at node1, 5, 12&17.

Hence it is stable.

50



Tank Steel Tube


Load values(kN/m2)





comparing this value to the

yield strength of 235MPa of

hollow section steel bars.

58.19MPa0.0

cm

Hence safe.

3.Displacements



106 in Z direction.

Hence it is stable.

51


Case Location (Kicukiro, El Castilo Hotel).

Tank Steel Tube

2 Cylindrical tanks with 3 m3 volume RHS 80*40*3mm

Load values(kN/m2)

Results(stresses, deflection and displacement)







bars.

164.21MPa0.

0cm

Hence safe.

3.Displacements



in Z direction.

Hence it is stable.

52

Fig.4.17:


Case Location (Kicukiro, El Castilo Hotel).

Tank Steel Tube


Load values(kN/m2)

Results(stresses, deflection and displacement)







62.64MPa0.

0cm

Hence safe.

3.Displacements



in Z direction.

Hence it is stable.

53

Fig.4.18:case18

(photo,model,3D)

Case Location (NDERA).

Tank Steel Tube

Two Cylindrical tanks with 5 m3 volume RHS 80*40*3mm

Load values(kN/m2)

Results(stresses, deflections and displacement)







bars.

67.26MPa0.0

cm

Hence safe.

3.Displacements



in Z direction.

Hence it is stable.

54

Fig.4.19:


Case Location (HUYE).

Tank Steel Tube


Load values(kN/m2)








32.77MPa0.0

cm

Hence safe.

3.Displacements



106 in Z direction.

Hence it is stable.

55

Fig.4.20:


Case Location (MUSANZE).

Tank Steel Tube


Load values(kN/m2)








44.88MPa0.0c

m

Hence safe.

3.Displacements



in Z direction.

Hence it is stable.

final year project report

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