UNIVERSITY OF NAIROBI

STRUCTURAL DESIGN OF A REINFORCED CONCRETE SINGLE LANE MOTORIZED BRIDGE AT RIVER NJORO

By: Wachira Anthony GichuruF16/36095/2010

PROJECT SUPERVISOR: ENG. S.S. Miringu

A project submitted as a partial fulfillment for the requirement for the award of the degree of

BACHELOR OF SCIENCE IN CIVIL ENGINEERING

2015

AbstractAs Kenya’s population continues to increase at an annual rate of 2.7%, there is need to construct more roads to keep up with future demand. Njoro region, being no exception, has experienced this population growth over the years and hence there was need to construct an access road to provide access to the various upcoming market centers as well as homesteads.

The proposed access road would cross River Njoro and hence the significance of construction of a single lane reinforced concrete motorized bridge. It was proposed that the bridge be a single lane as the number of homesteads owning cars in the area was minimal and subsequently the traffic volume through the road, ergo bridge, was minimal.

The objectives of this project were to carry out the structural design of a reinforced concretebridge in accordance with BS5400 (bridge design) and make detailed drawings and specifications for it.

The project was significant in that it would provide access across the river for both motorized and human traffic. Geological, traffic, hydrological and geotechnical surveys were carried out for the best possible location, type and height of the bridge.

The bridge was designed according to recommended (BS5400) standards and sufficient structural capacity to carry the loads at both ultimate and serviceability states and recommendations for maintenance given.

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Dedication

To the Almighty God who has brought me this far and to my parents, sister and friends for the love and moral support throughout the year and for keeping it real. God bless you.

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Acknowledgements

To the Almighty God for life, good health and His protection during this project period. I also wish to acknowledge the contribution of my supervisor Eng. S.S. Miringu whose comments and suggestions during the preparation of this project are sincerely appreciated.

Table of Contents

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Abstract.......................................................................................................................................iiDedication..................................................................................................................................iiiAcknowledgements....................................................................................................................ivTable of Contents........................................................................................................................vList of Plates...............................................................................................................................viList of Tables.............................................................................................................................viChapter One................................................................................................................................11.0 Introduction...........................................................................................................................1

1.1 Background Information...................................................................................................11.3 Objectives..........................................................................................................................3

1.3.1 Main objective............................................................................................................31.3.2 Specific objectives.....................................................................................................3

Chapter Two................................................................................................................................42.0 Literature Review..................................................................................................................4

2.1 Introduction.......................................................................................................................42.2 History of bridges..............................................................................................................42.3 Types of bridges................................................................................................................5

2.3.1 Beam bridges..............................................................................................................52.3.2 Truss bridge................................................................................................................52.3.4 Arch bridge.................................................................................................................62.3.5 Tied arch.....................................................................................................................62.3.6 Suspension bridges.....................................................................................................72.3.7 Fixed or movable bridges...........................................................................................72.3.8 Viaducts......................................................................................................................7

2.4 Bridge design considerations............................................................................................82.4.1 Functional...................................................................................................................82.4.2 Economic....................................................................................................................82.4.4 Aesthetics...................................................................................................................8

2.5 Construction Materials:.....................................................................................................92.5.1 Stone...........................................................................................................................92.5.2 Reinforced and Pre-stressed Concrete:......................................................................9

2.6 Blinding layer....................................................................................................................92.7 Bridge maintenance.........................................................................................................102.8 Bridge failures.................................................................................................................102.9 Bridge monitoring...........................................................................................................10

Chapter Three............................................................................................................................113.0 Methodology.......................................................................................................................11

3.1 Introduction.....................................................................................................................11Chapter Four..............................................................................................................................124.0 Hydrological analysis..........................................................................................................12

4.1 Determination of catchment area....................................................................................124.2 Calculation of land slope.................................................................................................124.3 Calculation of channel slope...........................................................................................134.4 Calculation of design rainfall..........................................................................................134.5 Calculation of peak flow.................................................................................................134.6 Calculation of maximum flood level (y)...................................................................16

Chapter Six................................................................................................................................176.1 Bar bending schedule......................................................................................................17

Chapter seven............................................................................................................................247.0 Recommendations and conclusion......................................................................................24

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7.1 Recommendations...........................................................................................................247.2 Conclusion.......................................................................................................................24

Chapter eight.............................................................................................................................258.0 References..........................................................................................................................258.1 List of references.................................................................................................................25

List of PlatesPlate 1. 1 Existing steel footbridge.............................................................................................2Plate 1. 2 completed reinforced concrete bridge.........................................................................2

Plate 2. 1 beam bridge5Plate 2. 2 truss bridge..................................................................................................................5Plate 2. 3 cantilever bridge..........................................................................................................6Plate 2.4 arch bridge...................................................................................................................6Plate 2.5 tied arch bridge............................................................................................................7Plate 2. 6 suspension bridge........................................................................................................7Plate 2. 7 viaduct.........................................................................................................................8

List of TablesTable 4. 1 Calculation of land slope..........................................................................................12Table 4. 2 Calculation of channel slope....................................................................................13Table 4. Calculation of land slope ……………………………………………………Table 4. Calculation of channel slope ………………………………………………….Table 6. Bar bending schedule …………………………………………………Table 6. Bar bending schedule summary……………………………………………………...Table 6. Cost estimates for reinforced concrete bridge at River Njoro………………………..

List of Symbols

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Symbol Meaningfcu characteristic strength of

concretefy characteristic strength of steelc reinforcement coverAsv cross sectional area of shear

reinforcementAsc cross sectional area of

compression reinforcementAst cross sectional area of tension

reinforcementb width of the sectiond effective depth of the sectionh overall depth of the sectionx depth to the neutral axise eccentricityα1,α2 lane factorsԐst strain in steelԐc strain in concreteEc static modulus of elasticity of

concreteEst static modulus of elasticity of

steelD.L dead loadL.L live loadMR restoring momentsMO overturning momentsᵞf3 partial safety factorᵞf1 partial load factorU.L.S ultimate limit stateS.L.S serviceability limit stateU.D.L uniformly distributed loadHA normal loadingHB abnormal loadingN.A neutral axisMpx longitudinal momentsMpy transverse momentsM momentT tensionSf Stiffness factordf distribution factorF.E.M fixed end momentsVp punching shearL effective spanWcr crack widthAcr distance from the crack position

to the point of zero strainV shear force

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Chapter One

1.0 Introduction

1.1 Background Information

The County Government of Nakuru in conjunction with the Ministry of Roads and Public Works has seen it viable to construct new roads in various parts of the county as population continues to increase at an enormous annual rate. Njoro region, being part of this county, has experienced this population growth over the years and hence there was need to construct an access road to provide access to the various upcoming market centers as well as homesteads.The proposed access road would cross River Njoro and hence the significance of construction of a single lane reinforced concrete motorized bridge providing motor access to both sides of the divide thus promoting regional development in line with Kenya’s vision 2030. It was proposed that the bridge be a single lane as the number of homesteads owning cars in the area was minimal and subsequently the traffic volume through the road, ergo bridge, was minimal. The proposed construction of the bridge was to replace the existing steel foot bridge which is now outdated as it does not cater for the growing increase in use of vehicular traffic in the region.Currently vehicular traffic has to navigate a distance of almost thrice as long in order to access this homesteads and therefore construction of a reinforced concrete bridge would reduce this distance and thus boost the farming practice by providing an easily accessible market to the residents for their produce as most of this homesteads practice farming

1.2 Problem statement

Continued population increase in the area and increased trading activities especially by farmers across both sides of the river has warranted the need for construction of a reinforced concrete motorized bridge in replacement of the existing steel foot bridge to provide access to vehicles not only transporting goods but also to those owning vehicles and who wish to access their homesteads with them. A single lane bridge was preferred as the traffic levels are at a minimum.

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Plate 1. 1 Existing steel footbridge

Plate 1. 2 Completed reinforced concrete bridge

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1.3 Objectives

1.3.1 Main objective.

To design and ergo construct according to specifications, a single lane motorized reinforced concrete bridge across River Njoro.

1.3.2 Specific objectives

To enable transportation of both persons and goods across the river by either motorized or non- motorized traffic thus enhancing economic development through trade in the region.

To provide access to those owning cars to their homesteads.

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Chapter Two

2.0 Literature Review

2.1 Introduction

A bridge is a structure built to span physical obstacles such as a body of water, valley, or road, for the purpose of providing passage over the obstacle. There are many different designs that all serve unique purposes and apply to different situations. Designs of bridges vary depending on the function of the bridge, the nature of the terrain where the bridge is constructed and anchored, the material used to make it, and the funds available to build it.

2.2 History of bridges

The first bridges were made by nature itself, as simple as a log fallen across a stream or stones in a river. The first bridges made by humans were probably spans of cut wooden logs or planks and eventually stones, using a simple support and crossbeam arrangement. Some early Americans used trees or bamboo poles to cross small caverns or wells to get from one place to another. A common form of lashing sticks, logs, and deciduous branches together involved the use of long reeds or other harvested fibers woven together to form a connective rope capable of binding and holding together the materials used in early bridges.The greatest bridge builders of antiquity were the ancient Romans. The Romans built arch bridges and aqueducts that could stand in conditions that would damage or destroy earlier designs. Some stand today. An example is the Alcántara Bridge, built over the river Tagus, in Spain. The Romans also used cement, which reduced the variation of strength found in natural stone. One type of cement, called pozzolana, consisted of water, lime, sand, and volcanic rock. Brick and mortar bridges were built after the Roman era, as the technology for cement was lost then later rediscovered.

During the 18th century there were many innovations in the design of timber bridges by Hans Ulrich, Johannes Grubenmann, and others. The first book on bridge engineering was written by Hubert Gautier in 1716. A major breakthrough in bridge technology came with the erection of the Iron Bridge in Coalbrookdale, England in 1779. It used cast iron for the first time as arches to cross the river Severn.

With the Industrial Revolution in the 19th century, truss systems of wrought iron were developed for larger bridges, but iron did not have the tensile strength to support large loads. With the advent of steel, which has a high tensile strength, much larger bridges were built, many using the ideas of Gustave Eiffel.

In 1927 welding pioneer Stefan Bryła designed the first welded road bridge in the world, the Maurzyce Bridge which was later built across the river Słudwia at Maurzyce near Łowicz,

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Poland in 1929. In 1995, the American Welding Society presented the Historic Welded Structure Award for the bridge to Poland.

2.3 Types of bridges

Bridges can be categorized in several different ways. Common categories include the type of structural elements used, by what they carry, whether they are fixed or movable, and by the materials used.

2.3.1 Beam bridges

Beam bridges are horizontal beams supported at each end by substructure units and can be either simply supported when the beams only connect across a single span, or continuous when the beams are connected across two or more spans. When there are multiple spans, the intermediate supports are known as piers. The earliest beam bridges were simple logs that sat across streams and similar simple structures. In modern times, beam bridges can range from small, wooden beams to large, steel boxes. The vertical force on the bridge becomes a shear and flexural load on the beam which is transferred down its length to the substructures on either side. They are typically made of steel, concrete or wood.

Plate 2. 1 beam bridge

2.3.2 Truss bridge

A truss bridge is a bridge whose load-bearing superstructure is composed of a truss. This truss is a structure of connected elements forming triangular units. The connected elements (typically straight) may be stressed from tension, compression, or sometimes both in response to dynamic loads. Truss bridges are one of the oldest types of modern bridges. A truss bridge is economical to construct owing to its efficient use of materials.

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Plate 2. 2 truss bridge

2.3.3 Cantilever bridge

A cantilever bridge is a bridge built using cantilevers, structures that project horizontally into space, supported on only one end. For small footbridges, the cantilevers may be simple beams; however, large cantilever bridges designed to handle road or rail traffic use trusses built from structural steel, or box girders built from pre-stressed concrete.

Plate 2. 3 cantilever bridge

2.3.4 Arch bridge

Arch bridges have abutments at each end. The weight of the bridge is thrust into the abutments at either side

Plate 2.4 arch bridge

2.3.5 Tied arch

Tied arch bridges have an arch-shaped superstructure, but differ from conventional arch bridges. Instead of transferring the weight of the bridge and traffic loads into thrust forces into the abutments, the ends of the arches are restrained by tension in the bottom chord of the structure. They are also called bowstring arches.

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Plate 2.5 tied arch bridge

2.3.6 Suspension bridges

Suspension bridges are suspended from cables. The earliest suspension bridges were made of ropes or vines covered with pieces of bamboo. In modern bridges, the cables hang from towers that are attached to caissons or cofferdams. The caissons or cofferdams are implanted deep into the floor of a lake or river. Sub-types include the simple suspension bridge, the stressed ribbon bridge, the under-spanned suspension bridge, the suspended-deck suspension bridge, and the self-anchored suspension bridge.

Plate 2. 6 suspension bridge

2.3.7 Fixed or movable bridges

Most bridges are fixed bridges, meaning they have no moving parts and stay in one place until they fail or are demolished. Temporary bridges, such as Bailey bridges, are designed to be assembled, and taken apart, transported to a different site, and re-used. They are important in military engineering, and are also used to carry traffic while an old bridge is being rebuilt. Movable bridges are designed to move out of the way of boats or other kinds of traffic, which would otherwise be too tall to fit. These are generally electrically powered

2.3.8 Viaducts

A viaduct is a bridge composed of several small spans for crossing a valley or a gorge. The term viaduct is derived from the Latin via for road and ducere, to lead. However, the ancient Romans did not use the term; it is a modern derivation from an analogy with aqueduct. Like the Roman aqueducts, many early viaducts comprised a series of arches of roughly equal length. Viaducts may span land or water or both.

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Plate 2. 7 Viaduct

2.4 Bridge design considerations

A bridge should be designed to satisfy the following basic design principles in its design.

2.4.1 Functional

A bridge must be usable and serve its intended purpose in its design life.

2.4.2 Economic

The cost of constructing a bridge and its maintenance costs should be within reasonable values in relation to the purpose of the bridge. This is done by assessing the relative costs of alternatives.

2.4.3 Structural

Bridges may be classified by how the forces of tension, compression, bending, torsion and shear are distributed through their structure. Most bridges will employ all of the principal forces to some degree, but only a few will predominate. The separation of forces may be quite clear. In a suspension or cable-stayed span, the elements in tension are distinct in shape and placement. In other cases the forces may be distributed among a large number of members, as in a truss, or not clearly discernible to a casual observer as in a box beam.

2.4.4 Aesthetics

High standards of architectural quality which address cultural and physical factors are expected in the construction process.Most bridges are utilitarian in appearance, but in some cases, the appearance of the bridge can have great importance. Often, this is the case with a large bridge that serves as an entrance to a city, or crosses over a main harbor entrance. These are sometimes known as signature bridges. Designers of bridges in parks and along parkways often place more importance to aesthetics, as well. Examples include the stone-faced bridges along the Taconic State Parkway in New York.To create a beautiful image, some bridges are built much taller than necessary. This type, often found in east-Asian style gardens, is called a Moon bridge, evoking a rising full moon.

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Other garden bridges may cross only a dry bed of stream washed pebbles, intended only to convey an impression of a stream. Often in palaces a bridge will be built over an artificial waterway as symbolic of a passage to an important place or state of mind. A set of five bridges cross a sinuous waterway in an important courtyard of the Forbidden City in Beijing, China. The central bridge was reserved exclusively for the use of the Emperor, Empress, and their attendants.

2.5 Construction Materials:

The traditional building materials for bridges are stones, timber and steel, and more recently reinforced and pre-stressed concrete. For special elements aluminum and its alloys and some types of plastics are used. These materials have different qualities of strength, workability, durability and resistance against corrosion. They differ also in their structure, texture and color or in the possibilities of surface treatment with differing texture and color. For bridges one should use that material which results in the best bridge regarding shape, technical quality, economics and compatibility with the environment.

2.5.1 Stone

The great old bridges of the Etruscans, the Romans, the Fratres Pontifices of the middle ages (since about 1100) and of later master builders were built with stone masonry. The arches and piers have lasted for thousands of years when hard stone was used and the foundations constructed on firm ground. With stone one can build bridges which are both beautiful, durable and of large span (up to 150 m). Unfortunately, stone bridges have become very expensive. Over a long period, however, stone bridges, which are well designed and well built, might perhaps turn out be the cheapest, because they are long-lasting and need almost no maintenance over centuries unless attacked by extreme air pollution.

2.5.2 Reinforced and Pre-stressed Concrete:

Concrete is a construction material used in almost all construction works. Having a dull grey color, usually concrete is not preferred in construction like bridges but some of concrete bridges have turned out to be beauties, if someone knows the art. Good concrete attains high compressive strength and resistance against most natural attacks, however, its tensile strength is low, so is not preferred in areas of tensile stresses. For tensile reinforcement of concrete steel bars are embedded into it. Steel bars start functioning when concrete cracks i.e. when concrete can no longer resist further tensile stresses. The cracks remain harmless called “hair cracks", if bars are designed and place correctly. A second method of resisting tensile forces in concrete structures is by pre-stressing.

2.6 Blinding layer

In case of foundations or where walls e.g. wing walls are founded on the ground, a screeded layer of plain concrete not less than 50 mm thick should be placed over the ground.In normal circumstances this concrete should have proportions weaker than that used in the remainder of the structure, but not weaker than grade C15. Where aggressive soil or

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aggressive groundwater is expected, the concrete should not be weaker than grade C25, and if necessary, a sulphate-resisting or other special cement should be specified.

2.7 Bridge maintenance

Bridge maintenance consists of a combination of structural health monitoring and testing. This is regulated in country-specific engineer standards and includes e.g. an ongoing monitoring every three to six months, a simple test or inspection every two to three years and a major inspection every six to ten years. In Europe, the cost of maintenance is higher than spending on new bridges. The lifetime of welded steel bridges can be significantly extended by after treatment of the weld transitions . This results in a potential high benefit, using existing bridges far beyond the planned lifetime. Highway bridge with steel hollow box sections, performed for lifetime extension by welding after treatment

2.8 Bridge failures

The failure of bridges is of special concern for structural engineers in trying to learn lessons vital to bridge design, construction and maintenance.

2.9 Bridge monitoring

There are several methods used to monitor the stress on large structures like bridges. The most common method is the use of an accelerometer, which is integrated into the bridge while it is being built. This technology is used for long-term surveillance of the bridge.

Another option for structural-integrity monitoring is "non-contact monitoring", which uses the Doppler effect (Doppler shift). A laser beam from a Laser Doppler Vibrometer is directed at the point of interest, and the vibration amplitude and frequency are extracted from the Doppler shift of the laser beam frequency due to the motion of the surface. The advantage of this method is that the setup time for the equipment is faster and, unlike an accelerometer, this makes measurements possible on multiple structures in as short a time as possible. Additionally, this method can measure specific points on a bridge that might be difficult to access.

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Chapter Three

3.0 Methodology

3.1 Introduction

The following steps were taken to carry out the project: The necessary surveys were carried out to determine the best possible location, type of

bridge, its vertical and horizontal alignments and whether or not it would require super-elevation.

A geotechnical survey was carried out to determine the maximum bearing capacity of the ground conditions at the point of proposed abutment footing construction and the allowable soil bearing pressure(qA) was found to be 490 KN/M2

A hydrological analysis to determine the maximum flood levels of the river was also carried out.

The proposed bridge structure was then modeled, loaded according to specifications(BS 5400), analyzed and designed manually through calculations.

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Chapter Four

4.0 Hydrological analysis

4.1 Determination of catchment area

Number of complete squares = 87Number of incomplete squares(covering more than 50%) = 40Number of complete squares(covering less than 50%) = 37

Total number of squares = 87+ 40+372

=125.5 squares ;approximate=126 squares

Actual area of one square = 1KM2

Hence total catchment area = 1*126 =126 KM2

4.2 Calculation of land slope

Table 4. 1 Calculation of land slope

Contour Height Length between contours

Slope

2660 60 900 60900

∗100=7%26002700 100 700 100

700∗100=14 %2600

2380 40 400 40400

∗100=10 %23402400 60 800 60

800∗100=8%2340

2740 80 400 80400

∗100=20 %26602740 80 700 80

700∗100=11 %2660

Average land slope =7+14+10+8+20+11

2=11.67 % ;approximately 12 %

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4.3 Calculation of channel slope

Table 4. 2 Calculation of channel slope

Contour Height Length between contours

Slope

2800 200 6100 2006100

∗100=3 .28 %26002600 200 7200 200

7200∗100=2 .78 %2400

2400 200 6500 2006500

∗100=3 .08 %2200

Average channel slope =3.28+2.78+3.08

3=3.05% ; approximately 3

4.4 Calculation of design rainfall

REFERENCE : The prediction of storm rainfall in East Africa.1. Using grid reference (35o 52.5’00”E, 0 o27.5’00” S) ,the 2 year 24 hour rainfall was located on

figure 1 of Appendix 1 as 50mm.2. From Appendix 1, figure 2, the 10 year:2 year ratio was found to be 1.49(Inland).3. From Appendix 1,figure 3,for a 10 year:2 year ratio of 1.49 and a recurrence interval of

25years,the flood factor was found to be 1.75

R1024 =10 year 24 hour point rainfall =1.75*50mm=87.5mm

4. From Appendix 1, figure 4,the areal reduction factor for 126 km2 was 0.82.

4.5 Calculation of peak flow

REFERENCE : The TRRL East African flood model1. Measured catchment as obtained from the map was 126km2.

Land slope 12% Channel slope 3% Channel length 35.3km

2. Type of catchment from table 7. Poor pasture Lag time (k)0.5 hours

3. From site inspection and using table 4 Contributing area coefficient, Cs 0.11

4. Using figure 14,antecedent rainfall zone is Nyanza and using table 3,the zone is a Dry zone.5. Catchment wetness factor, Cw from table 5 was 0.756. From site inspection and using table 6,land use factor, CL ,Grass cover,1.0.7. Contributing area coefficient (CA)

CA= Cs* Cw * CL

=0.11*0.75*1.0

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=0.08258. Area is a dry zone hence initial retention (Y) is 09. Using figure 16 and table 8,rainfall time (Tp=0.75) and “n” index was 0.96.10. Base time,TB= Tp+2.3k+TA

Assuming TA to be zero(0) initially

TB= 0.75+2.3(0.5) = 1.9 hours

11. Volume of runoff ; R.O= CA*(P-Y)*A*103(m3)P = Storm rainfall during time period equal to time base Rainfall during base time

RTB=TB24 ( 24 . 33

TB+0 . 33 )n

.R1024

R1024 =10 year 24 hour point rainfall=87.5mm as earlier obtained.

R1 .9=1.924 ( 24.33

1.9+0.33 )0.96

.87 .5=68 .69 mm

P = 68.69 * Areal reduction factor(ARF)0.82=56.32mm R.O=0.0825(56.32-0)*126*103(m3)= 585480.61

Q '=0 .93∗RO3600∗TB

Q'=0.93∗585480.613600∗1.9

=79 . 60m3/sec

12. TB (2nd approximation)

T A=0 . 028 l

Q'14 S

12

T A=0.028∗35.3

79.6014 ¿0.03

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=1 . 91

TB=1.9+1.91 =3.81hours

R3 . 85=3.8124 ( 24.33

3.81+0.33 )0.96

.87 .5=76 .05 mm

P = 76.05 * Areal reduction factor(ARF)0.82=62.36mm R.O=0.0825(62.36-0)*126*103(m3)= 648240.60

Q '=0 .93∗RO3600∗TB

Q'=0.93∗648240.603600∗3.81

=43 . 95 m3/sec

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13. TB (3rd approximation)

T A=0 . 028 l

Q'14 S

12

T A=0.028∗35.3

43.9514 ¿0.03

12

=2 . 21

TB=1.9+2.21 =4.1hours

R4 .17=4.124 ( 24.33

4.1+0.33 )0.96

.87 .5=76 .69 mm

P = 76.69* Areal reduction factor(ARF)0.82=62.88mm

R.O=0.0825(62.88-0)*126*103(m3)= 653684.01

Q '=0 .93∗RO3600∗TB

Q'=0.93∗653684.013600∗4.1

=41 .19m3/sec

14. TB (4th approximation)

T A=0 . 028 l

Q'14 S

12

T A=0.028∗35.3

41.1914 ¿0.03

12

=2 . 25

TB=1.9+2.25 =4.2hours

R4 .17=4.224 ( 24.33

4.2+0.33 )0.96

.87 .5=76 .89mm

P = 76.89* Areal reduction factor(ARF)0.82=63.05mm

R.O=0.0825(63.05-0)*126*103(m3)= 655430.43

Q '=0 .93∗RO3600∗TB

Q'=0.93∗655430.433600∗4.2

=40 .31m3/sec

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15.41.19−40.31

40.31∗100=2. 2%

Q’ is within 5% of previous estimate hence we use Q’ value of 40.31m3/sec Q=F*Q’F is the peak flood factor and was taken as 2.8 since K was 0.5 which is less than an hour.Q=F*Q’= 2.8*40.31=112.87m 3 /sec

4.6 Calculation of maximum flood level (y)

NB: Please used attached diagrams for reference.

Q=1n

[ (b+xy ) y ]¿53

[b+2 y √1+ x2 ]23

∗S0

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Where Q=112.87m3/sec n=0.045 (unlined, rock cut) x=4.1m b=2.1m

112 . 87= 10.045

[ (2.1+4.1 y ) y ]¿53

[2.1+2 y √1+4.12 ]23

∗0.0312

Substituting into the equation, the maximum flood height (y)= 2.26m

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Chapter Six

6.0 Bar bending schedule and cost estimates

6.1 Bar bending schedule

Table 6. 1 Bar bending schedule

BAR BENDING SCHEDULEREINFORCED CONCRETE BRIDGE AT RIVER NJORO

Made by: W.A. Gichuru Checked by : Eng S.S. Miringu Date: May 2015

Element Mark

No.

Bar

type

No.

of

No.

each

Total

No.

Length

each(mm)

Total

length(m)

Bar shape

Deck Slab S1 Y12 1 37 37 4700 174

S2 Y12 1 37 37 6320 234

S3 Y12 1 31 31 11920 370

S4 Y12 1 144 144 1732 249

Mid-span

crossbeam

B1 Y10 1 18 18 2180 39

B2 Y12 1 4 4 5760 23

B3 Y12 1 4 4 5760 23

B4 Y10 1 4 4 4320 17

Crossbeam at

abutments

B5 Y12 2 4 8 4320 35

B6 Y10 2 18 36 2880 104

B7 Y16 2 3 6 6060 36

B8 Y16 2 3 6 6060 36

Main

beam

B9 Y32 2 8 16 13520 216

B10 Y16 2 4 8 13520 108

B11 Y10 2 6 12 11920 143

B12 Y10 2 49 98 3080 302

Abutment

wall

A1 Y32 2 43 86 4700 404

A2 Y12 2 33 66 4200 277

A3 Y12 2 33 66 2600 172

A4 Y12 2 33 66 3200 211

A5 Y12 2 22 44 5270 232

A6 Y12 2 22 44 5270 232

A7 Y12 2 26 52 1620 84

A8 Y8 2 33 66 870 57

A9 Y12 2 6 12 6320 76

A10 Y10 2 6 12 6320 76

Wing wall

A11 Y20 4 29 116 3095 359

A12 Y12 4 29 116 2795 324

A13 Y10 4 23 92 4920 453

A14 Y10 4 23 92 4920 453

A15 Y12 4 21 84 2795 235

A16 Y12 4 21 84 2295 193

A17 Y12 4 23 92 1620 149

Wing-wall

footing

F1 Y12 4 34 136 3181 433

F2 Y20 4 34 136 3160 430

F3 Y10 4 11 44 4920 216

Abutment

Footing

F4 Y12 2 17 34 6320 215

F5 Y32 2 52 104 3660 381

F6 Y16 2 52 104 3679 383

Table 6. 2 Bar bending schedule summary

BAR BENDING SCHEDULE SUMMARYREINFORCED CONCRETE BRIDGE AT RIVER NJORO

Made by:W.A.Gichuru

F16/36095/2010

Checked by: S.S. Miringu Date : May 2015

Bar type Y8 Y10 Y12 Y16 Y20 Y25 Y32

Total

length(m)

57 1587 3941 563 789 0 1001

Full (12m)

lengths

4.75 132.25 328.42 46.92 65.75 0 83.42

Unit weight

(kg/m)

0.395 0.616 0.888 1.579 2.466 3.854 6.313

Total

weight

(kg)

22.515 977.592 3499.608 888.977 1945.674 0 6319.313

Table 6. 3 Cost estimates for reinforced concrete bridge at River Njoro

COST ESTIMATES

REINFORCED CONCRETE BRIDGE AT RIVER NJOROITEM DESCRIPTION UNIT QUANTITY RATE Amount

Kshs Cts

Structural

concrete

Provide place and compact for structural concrete Class 15 for blinding

Class 30 for all other structural members

M3

M34.43

133

13,500

17,000

59805

2261000

00

00Reinforcing

steel

Reinforcement bars of

high yield strength to

BS 4461.Rates

exclusive of labor

Y32

Y20

Y16

Y12

Y10

Y8

Kg

Kg

Kg

Kg

Kg

Kg

6319.313

1945.674

888.977

3499.608

977.592

22.515

150

150

150

150

150

150

947896

291851

133346

524941

146638

3377

95

10

55

20

80

25

Bitumen

surfacing

Provide 50mm

surfacing on

carriageway as well as

the midsection of the

footpath.

M3 5.2 25000 130000 00

Drainage

pipes

Provide 75mm

diameter plastic pipes

to drain the bridge

deck as well as for use

as weep holes

M 40 350 14000 00

Totals carried forward to the next page 4,512,856 85

COST ESTIMATES

REINFORCED CONCRETE BRIDGE AT RIVER NJOROITEM DESCRIPTION UNIT QUANTITY RATE Amount

Kshs Cts

Bearing pad

on bridge

seat

Provide elastomeric

bearing EKR 35

No 6 90000 540000 00

Guard rails Provide and install

parapet posts (1m)

height including

300*250*20 mm base

plates at 2m meters

apart .(rate inclusive

of base plate)

Provide and install

50mm galvanized iron

pipe hand rail.

Provide and install

flex beam guard rail

M

M

M

42

24

64

2000

500

700

84000

12000

44800

00

00

00

Totals carried forward to the next page 5,193,656 85

COST ESTIMATES

REINFORCED CONCRETE BRIDGE AT RIVER NJOROITEM DESCRIPTION UNIT QUANTITY RATE Amount

Kshs Cts

Preliminarie

s

Labour

Overhead

costs

Profit

Total carried forward

from the previous

page(grand subtotal)

15% of grand

subtotals

20% of grand

subtotals

15% of grand

subtotals

5% of grand subtotals

758752

1011670

758752

252917

78

37

78

59

TOTAL 8656550 37

VAT 16% 1385048 06

GRAND

TOTAL

10,041,59

8

43

Chapter seven

7.0 Recommendations and conclusion

7.1 Recommendations

The right quantities and quality of materials should be ensured during construction in order to

achieve the desired strengths and ensure that the bridge serves its intended purpose during its

design life. The reinforcing steel should be well stored to avoid excessive corrosion which

would interfere with its strength. Guard rails on the deck should be painted to avoid corrosion

and weep holes regularly cleaned to avoid blockage.

7.2 Conclusion

The bridge is to be constructed at a total cost of approximately kshs.10.1million.The

construction of the bridge will open up the region to trade as well as reduce travelling distance

to those wishing to access their homesteads via vehicles thus promoting regional

development.

Chapter eight

8.0 References

8.1 List of references

1. BS 5400 part 2 ,specifications for loads, (1978, 1st edition and 2006, 2nd edition)

2. BS 5400 part 4, code of practice for design of concrete bridges (1990, 3rd edition).

3. Road Design Manual part 4,bridge design by Ministry of Transport and

Communication (1982)

4. Adolf Putcher,1980, Influence Surfaces of Elastic Plates(2nd Edition)

5. Gerald Parke and Nigel Hewson,2008, ICE Manual of Bridge Engineering(2nd Edition)

6. Mosley J.H Bungey, 1987,Reinforced Concrete Design(3rd Edition)

7. Lian Duan and Wai-Fah Chen ,2013, Bridge Engineering Handbook(2nd Edition)

8. D. Fiddes ,1976, The TRRL East African flood model.

9. D. Fiddes,1974, The prediction of storm rainfall in East Africa.

10. http://en.wikipedia.org/wiki/Bridge