Gaja Mini Project

“POST-TENSIONED PRESTRESSED CONCRETE GIRDER BRIDGE FOR A HIGH LEVEL ROAD WAY -A Study” a mini- project reportsubmitted to Department of CIVIL Engineering, Chaitanya Engineering College In Partial Fulfilment of the requirements for the award of DEGREE OF BACHELOR OF TECHNOLOGY IN CIVIL ENGINEERING Y.S.G.GOVINDBABU M.MOHAN KUMAR V.BHARATH CHANDRA ANUSHA DEVI D.CHINAKONDAMMA 08L61A0150 08L61A0126 07L61A0110 08L61A0104 09L65A0106 Under the guidance of SRI N.AMMI REDDY, DEPUTY EXECUTIVE ENGINEER, ROADS AND BUILDINGS DEPARTMENT, NH-SUBDIVISION, AMALAPURAM. PROF.B.V.SARMA, B.E. (CIVIL), M.E. (STRUCTURES), ADV.PG.DIP.IN HOUSING (NETHERLANDS), PROFESSOR OF CIVIL ENGINEERING DEPARTMENT OF CIVIL ENGINEERING CHAITANYA ENGINEERING COLLEGE (AFFILIATEDD TO JNTU-KAKINADA) VISAKAPATNAM - 530048(A.P) CERTIFICATE 1 1 BATCH Y.S.G.GOVIND BABU M.MOHAN KUMAR O8L61A0150 08L61A0126 V.BHARATH 07L61A0110 Y.ANUSHA DEVI O8L61AO104 D.CHINAKONDAMMA 09L65A0106 1 Visakhapatnam (Affiliated to JNTU Kakinada) for his kind attitude.ACKNOWLEDGEMENT We express our gratitude to SRI N. We express our deep sense of gratitude to our guide Prof.BHARATH CHANDRA ANUSHA DEVI D. We are also thankful to the Staff of the Department for having helped and supported us during the progress of the work.SARMA. R&B Department. Chaitanya Engineering College. At length we would like to thank all those who have directly and indirectly contributed towards the completion of our project work. Y. Deputy Executive Engineer. immense help and encouragement which helped us in carrying out our mini-project work. Department of Civil Engineering.CHINAKONDAMMA 08L61A0150 08L61A0126 07L61A0110 08L61A0104 09L65A0106 NOMENCLATURE: 2 . friends for the constant support.GOVINDBABU M. It gives us great pleasure to acknowledge and express gratitude to our families.G. Head of Department.V.S.MOHAN KUMAR V. Amalapuram for his kind gesture and his personal involvement in guiding us at our site work. keen interest. B. invaluable guidance. NH-Subdivision.AMMIREDDY garu. Effective width of slab.Eccentricity ➢ fck.Breadth of web or rib ➢ D-Overall depth of beam or Slab or Column ➢ Df.Spacing of stirrups or standard deviation ➢ v.Development length ➢ LL-Live load ➢ Lx-Length of shorter side of slab ➢ Ly-Length of longer side of slab ➢ M.Modulus of elasticity of steel ➢ e.➢ A-Area ➢ b.Characteristic compressive strength of concrete ➢ fy.Dead load ➢ d.Modular ratio ➢ s.Breadth of beam or shorter dimension of a rectangular column ➢ bef. ➢ bw.Characteristic strength of steel ➢ Ii.Depth of compression reinforcement from the highly compressed face ➢ Ec.Bending moment ➢ m.moment of inertia of the girder ➢ k.Thickness of flange ➢ DL.Effective depth of beam or slab ➢ d’.Constant or coefficient or factor ➢ Ld.Modulus of elasticity of concrete ➢ Es.Shear force 1 . L.Full supply depth CONTENTS CERTIFICATE 1 ii .D.Permissible stress in shear reinforcement ➢ ῖcmax.B.L-Full supply depth ➢ C.Maximum flood level ➢ F.Diameter of bars ➢ M.S.Top of bank level ➢ F.Nominal stress ➢ ῖc – Shear stress in concrete ➢ Ф.Depth of neutral axis ➢ σst – Permissible stress in steel tension ➢ σsv.L.Maximum shear stress in concrete with reinforcement ➢ ῖbd – Design bond stress ➢ ῖv.➢ W-Total load ➢ WL-Wind load ➢ x.L.F.Canal bed level ➢ T.B.S. 2 Cantilever bridges iv v vii xii 1 1 2 2 3 3 4 2.5 Position of the bridge to the superstructure 2. STANDARD SPECIFICATIONS 2 5 5 6 7 .1.4 ECONOMIC RANGE OF SPAN LENGTHS FOR DIFFERENT TYPES OF STRUCTURES 2.8 Length of bridge 2.6 Movable bridges 2.2 Material of construction 2.1. BRIDGES-TYPES 2.1.6 Method of connections 2.9 Degree of redundancy 2.1.2.1Beam bridges 2.2.1.7 Method of clearance 2.1.1 ACTIVITIES INVOVED 1.2.2 TYPES OF BRIDGES 2.2.2.1 Function 2.4 Suspension bridges 2.7 Truss bridges 2.1.10 Type of service 2.3 HISTORY OF A BRIDGE 2.1.5 Cable-stayed bridges and 2.5 SELECTION OF BRIDGE SITE 3. INTRODUCTION 1.2 DEFINITION OF A BRIDGE 1.1.4 Inter-span relations 2.3 Arch bridges 2.2.2.ACKNOWLEDGEMENT NOMENCLATURE CONTENTS ABSTRACT 1.2.1 CLASSIFICATION OF BRIDGES 2.1.1.1 Beam bridges 2.3 NEED FOR INVESTIGATION 2.3 Form 2. 2.4.1 Dead Load 3.2.3 ABUTMENTS 4.2 PIERS 4.2.1Well foundations: 4.4 BEARINGS 3 10 10 11 11 13 14 15 .4 IRC Class B loading 7 7 7 7 3.3.3 IRC Class A loading 3.2 LOADS TO BE CONSIDERED IN A DESIGN 3.1.1.6 CLEARANCES 4.5 Longitudinal Forces 3.2.4 BRIDGE LOADING STANDARDS 3.4.2 Deep foundations 4.1 IRC Class AA Loading 3.3 INDIAN ROAD CONGRESS BRIDGE CODE 3.1 STANDARD SPECIFICATION FOR ROAD BRIDGES 3.2 Live load 3.2 Pile foundations 4.1 TYPE OF FOUNDATIONS 4.4 Wind Load 3.1 Shallow foundations 4.3 Impact 3.2.1.4.5 WIDTH OF CARRIAGEWAY 3.2.1. COMPONENTS OF A BRIDGE 4.2 IRC Class70 R Loading 3.4.2.2.6 Dynamic Load 3. 4 DESIGN OF CONCRETE ROAD BRIDGES 5.2 Concrete Girders 5.1.1.1 CONCRETE BRIDGES 5.4.2 Girder slab and diaphragm type 4.2.2 DESIGN PROCEDURE FOR RAILWAY BRIDGES: 5.2 DESIGN CRITERIA FOR RAILWAY BRIDGES 5.3.1 Girder and slab type 4.1.3.1 Approach to design 5.1.3 Girder.5.1 Courbon’s Method 5. DESIGN CONSIDERATIONS FOR DIFFERENT BRIDGE 5.2 TYPES OF PRESTRESSING AND ITS PROPER USE 5.3 DESIGN CRITERIA FOR ROAD BRIDGES 5.1 GENERAL ARRANGEMENT OF GIRDERS IN SUPER STRUCTURE 4.1.5. slab and cross beam type 4.1.4. STEEL USED IN CONCRETE 5.1 INTRODUCTION 5.1.3.3.1.5 SUPER STRUCTURE 16 4. WEB THICKNESS 22 22 23 5.4.5.3.2.3.3. Marcie Little Method 5.1.3.5.2.2.1 Steel Girders 5.1 DESIGN PROCEDURES FOR BRIDGE SUPERSTRUCTURE 5.5 DESIGN FEATURES OF THE PIER 4 26 29 35 . Henry-Jaegers Method 5.2.4.2.3.4.3 Road bridge design 5.1 DESIGN OF THE LONGITUDINAL GIRDERS 5.5. 1 BONDED POST TENSIONED CONCRETE 7.5 TERMINOLOGY 7. MISCLANEOUS ITEMS OF WORK 8.1.2.3 POST TENSIONED CONCRETE 7.2 Under water concreting 8.1.3.3.5Twin circular well 6.3.2 PRETENSIONED CONCRETE 7.1 DEFINITION 7.3.6 DESIGN FEATURES OF THE ABUTMENT 6.2 UNBOUNDED POST TENSIONED CONCRETE 7.3.3.1.4 ADVANTAGES OF PRESTRESSED CONCRETE 7.1.2Double D well 6.1 Material to be used 8.2 COMPARISION WITH PILE FOUNDATIONS 6.1 Concrete 8.3.3 PROCEDURE FOR TENSIONING AND TRANSFER 7.6Wells with Multiple Dredge Holes 37 38 38 38 40 7.1 INTRODUCTION 6.1Circular well 6.4Rectangular Well 6.3 WELL TYPES AND THEIR SUTABILITY 6.1. WELL FOUNDATIONS 6.5. Direct placement with pumps 2 44 44 44 45 48 50 52 53 53 . PRESTRESSED CONCRETE 7.2. Tremie 8.6 APPLICATIONS 8.3.3.2.3Double Octagonal Well 6. 6 ERECTION SCHEME OF GIRDERS 61 57 58 59 60 ABSTRACT This mini project is about a precast prestressed girder bridge located at Borduskuru in Andhra Pradesh.1. piers.8.3 FUTURE PRESTRESSING ARRANGEMENTS 8. Drop bottom bucket 8. 2 . This report also attempts to explain the design procedure of some components of this bridge structure. which involved in study of foundations adopted. The practical problems encountered along with their solutions are also illustrated. The study also includes the precasting of girders their launching and launching of launching system along with the methods of prestressing and prestressing techniques.3.2 STEEL 8.4 HIGH PERFORMANCE CONCRETE 8. abutments and bearings.2.5 ANTI CORROSIVE TREATMENT 8. tendering and execution. Also inspections.C. maintenance and repairs are continuing activities for enhancing the service life of the structure. 1. particularly the foundation conditions (which could be a guess/ interpolation at this stage) the type of bridge viz.C. submersible etc.S. So that detailed soil explorations as may be necessary could b e done. It is. approval/sanction. P. design. Generally 2-3 cross sections at prospective sites are taken and the bridge length is decided for the purpose of preparing stage-I estimate needed for obtaining Approval. 1 . necessary that site is to be finalized by the Engineer. The detailed proposal is then prepared by Engineer.1. For bridges having span more than 60m.C. ACTIVITIES INVOVED : A bridge project is required to carry out survey for the bridge location and collect requisite preliminary survey data that is required for bridge planning and design. R. The detailed proposal would generally mean giving sufficient details for preparation of estimate after working out the stability of structures i.1.. piers and abutments and deciding the tentative dimensions for superstructure and other components along with specifications. Depending on site conditions.. detailed estimate is required to be submitted to Government for obtaining administrative approval.e. therefore. high level. INTRODUCTION A bridge project from its conception to completion involves various stages of planning. is decided. the material used to make it and the funds available to build it. The Romans built arch bridges and aqueducts that could stand in conditions that would damage or destroy earlier designs. or road.1. a simple type of suspension bridge. and others. They enhance the vitality if the cities and aid the social. Bridges add beauty to the cities. Rope bridges. valley. for the purpose of providing passage over the obstacle.3 HISTORY OF A BRIDGE: The greatest bridge builders of antiquity were the ancient Romans. BRIDGES-TYPES 2. many using the ideas of Gustave Eiffel. Examples: London. Examples: the bridges across the river seine in Paris and the bridges across the river Thames in London. That is why military training puts special emphasis on learning how to destroy bridges during combat and while retreating and how to build new ones quickly while advancing. Cambridge and Innsbruck. 1. which has a high tensile strength.1 CLASSIFICATION OF BRIDGES: Function Material of construction Form Inter-span relations Position of the bridge to the superstructure 2 . but iron did not have the tensile strength to support large loads. In 1927 welding pioneer Stefan Bryła designed the first welded road bridge in the world. With the advent of steel. cultural and economic improvements of the areas around them. With the Industrial Revolution in the 19th century. The mobility of an army at war is often affected by the availability or otherwise of the bridges to across rivers. Oxford. were used by the Inca civilization in the Andes mountains of South America. Some stand today. much larger bridges were built. the nature of the terrain where the bridge is constructed. Designs of bridges vary depending on the function of the bridge. truss systems of wrought iron were developed for larger bridges. Johannes Grubenmann. just prior to European colonization in the 16th century. which was later built across the river Słudwia Maurzyce near Łowicz.2 DEFINITION OF A BRIDGE: A bridge is a structure built to span physical obstacles such as a body of water. 2.4 IMPORTANCE OF BRIDGE: Bridges have always figured prominently in human history. Poland in 1929. Great battles have been fought for cities and their bridges. Cities have sprung up at a bridgehead or where at first a river could be forded at any time of the year. 1. During the 18th century there were many innovations in the design of timber bridges by Hans Ulrich. POSITION OF THE BRIDGE TO THE SUPERSTRUCTURE: According to the position of the bridge to the superstructure as deck.8. military bridge. iron. 2. 2.1. 2. beam. steel. METHOD OF CONNECTIONS: According to the method of connections of the different parts of the superstructure. composite or Aluminium Bridge. 2.2. Arch bridges.7. minor bridge (6to60m).10. though.1.1.1. 2. truss.2.1. 2. Cable-stayed bridges and Truss bridges 3 . particularly for the steel construction as pin connected.3. reinforced concrete.1. pedestrian. temporary. TYPE OF SERVICE: According to the anticipated type of service and duration of use as permanent.9. 2.1. railway.1. FORM: According to the form or type of the superstructure as slab. half-through or suspended bridge. MATERIAL OF CONSTRUCTION: According to the material of construction of the superstructure as timber. 2. Cantilever bridges.1.1.6.4. movable-swing and transporter bridge. METHOD OF CLEARANCE: According to the method of clearance for the navigation as high-level. masonry. road-cum-rail or a pipeline. 2. cable stayed or suspension bridge. riveted or welded bridge.5. TYPES OF BRIDGES: There are six main types of bridges: Beam bridges. FUNCTION: According to function as aqueduct (canal over a river). LENGTH OF BRIDGE: According to the length of bridge as culvert (<6m). DEGREE OF REDUNDANCY: According to the degree of redundancy as determinate or indeterminate bridge.1. INTER -SPAN RELATIONS: According to the inter-span relations as simple continuous or cantilever bridge. viaduct (road or railway over a valley). Suspension bridges. 2.Method of connections Method of clearance Length of bridge Degree of redundancy Type of service Bridges may classify in many ways as below: 2. movable-bascule. highway. major bridge (>60m) or a long span bridge when the main span of the major bridge is above 120m. pre-stressed concrete. arch. 2. 2.2.3 NEED FOR INVESTIGATION: Before a bridge can be built at a particular site.2.6 Movable bridges are designed to move out of the way of boats or other kinds of traffic. or box girders. it is essential to consider many factors. Types of construction could include having many beams side by side with a deck across the top of them. The simplest beam bridge could be a slab of stone. In modern bridges. hence their structural name of simply supported. 2. prestressed or post-tensioned. Most cantilever bridges use a pair of continuous spans that extend from opposite sides of the supporting piers to meet at the center of the obstacle the bridge crosses. The caissons or cofferdams are implanted deep into the floor of a lake or river.7 A truss bridge is a bridge composed of connected elements (typically straight) which may be stressed from tension.2. or a combination of both. Cantilever bridges are constructed using much the same materials & techniques as beam bridges. trusses.2. Truss bridges are one of the oldest types of modern bridges. 2. or a plank of wood laid across a stream. or sometimes both in response to dynamic loads. The weight of the bridge is thrust into the abutments at either side.1 Beam bridges: Beam bridges are the most simple of structural forms being supported by an abutment at each end of the deck. compression. 2. aesthetics and cost. the stream. 2.2 Cantilever bridges are built using cantilevers horizontal beams supported on only one end. They could be half-through. No moments are transferred through the support hence their structural type is known as simply supported. Bridges designed for modern infrastructure will usually be constructed of steel or reinforced concrete. and include the Arkadiko Bridge. However. 2. safety and the aesthetics. at the sometime satisfying the demands of traffic.5 Cable-stayed bridges like suspension bridges are held up by cables. or braced across the top to create a through bridge. to a main beam either side supporting a deck between them. These are generally electrically powered. The 4 .1 Beam bridges are horizontal beams supported at each end by abutments.2. The main beams could be I-beams. which would otherwise be too tall to fit. the present and the future traffic stream characteristics subsoil conditions.2. The concrete used can either be reinforced.2. the cables hang from towers that are attached to caissons or cofferdams. When there is more than one span the intermediate supports are known as piers. such as the need for a bridge. alternative sites.3 Arch bridges have abutments at each end. 2. The earliest suspension bridges were made of ropes or vines covered with pieces of bamboo.2. The difference comes in the action of the forces through the bridge. The aim of the investigation is to select a suitable site at which a bridge can be built economically. less cable is required and the towers holding the cables are proportionately shorter.1. The investigation for a major bridge project should cover studies on technical feasibility and economic considerations and should result in an investigation report.4 Suspension bridges are suspended from cables. The earliest known arch bridges were built by the Greeks. in a cable-stayed bridge.2. are given be low:R.C. usually a wider choice may be available. For river bridges in rural areas. Rock or other hard in erodible strata close to the river bed level vi. 2. The characteristics of an ideal site for a bridge across a river are: i. A straight reach of the river.C.5ECONOMIC RANGE OF SPAN LENGTHS FOR DIFFERENT TYPES OF STRUCTURES Apart from the estimated cost based on schedule of rates. Economical approaches which should not be very high or liable to flank attacks of the river during floods.5 to 15 m 3 to 10 m 10 to 24 m 25 to 45 m 10 lo 15 m 15 to 30 m 10 to 20 m 25 to 50 m 35 to 75 m 75 to 150 m . sacred places.4 SELECTION OF BRIDGE SITE: This is particularly so in case of bridges in urban areas and flyovers. Absence of expensive river training works and x. the approaches should be free from obstacles such as hills. The ranges of span length within which a particular type of superstructure can be economical along with other considerations Rice type of foundation etc. graveyards or built up areas or troublesome land acquisition vii.Absence of sharp curves in the approaches ix. costs as quoted during tendering may be used for constantly updating the cost analysis data.success of the final design will depend on the thoroughness of the information furnished by the officer in charge of the investigation. single or multiple boxes Simply supported RCC slabs Simply supported RCC T beam Simply supported PSC girder bridges Simply supported RCC voided slabs Simply supported/continuous PSC voided slabs Continuous RCC voided slabs RCC box sections simply supported / Balanced cantilever continuous PSC box sections. Avoidance of excessive underwater construction 2. simply supported / Balanced cantilever 5 1. ii. Steady river flow without serious whirls and cross currents iii. A narrow channel with firm banks iv. Proximity to a direct alignment of the road to be connected viii. Suitable high banks above high flood level on each side v. frequent drainage crossings. 3 IMPACT: 6 . All highways bridges have to be built in accordance with the Indian Road Congress (IRC) CODES.Similarly Indian Railway Standard (IRS) Bridge rules should be followed for the design of railway bridges. Government of India (MOST). 3. design load of kerb is sufficient.2 LOADS TO BE CONSIDERED IN A DESIGN: 3. As the pedestrian traffic is very less. The purpose of the codes is to ensure adequate safety and afford protection against legal liability arising out of failures due to no fault of the designer.PSC cantilever construction / continuous Cable stayed bridges Suspension bridges 100 to 800 m 300 to 1500 m 3. besides specifications prescribed by the Ministry of Surface Transport (Roads Wing).2 LIVE LOAD: Class AA and a loading are adopted in the design. based on years of observation. The standards are adopted as per IRC recommendations.2.2. research and development. 3.1 STANDARD SPECIFICATION FOR ROAD BRIDGES: Standard specifications and code of practice have been evolved by the concerned government agencies and professional institutions.1 DEAD LOAD: The dead load consists of the weight of superstructure in any fixed support by the member.2. 3. Since the public roads and railways in India are owned and controlled by the government the bridges built on them should follow the instructions follow specifications laid down by the respective authorities. STANDARD SPECIFICATIONS 3. Loads and Stresses c) Section III-Cement concrete ( plain &reinforced) d) Section IV. 3.K and Europe.2. Braking effect caused due to the application of brakes to the wheels.3 INDIAN ROAD CONGRESS BRIDGE CODE: The Indian Road Congress (IRC) Bridge code as available now consists of eight sections as below: a) Section I – General features of design b) Section II. 3. such as earthquakes or strong gusts of wind. The area to be considered on which the wind force is assumed to act is.4 WIND LOAD: These forces are considered to act horizontally and in such a direction as to cause the maximum stresses in the member under consideration.4 Bridge Loading Standards: Bridge loading standards in many countries were first formulated to regulate heavy military vehicles and were generally specified by local authorities.Foundations and substructure h) Section IX.2. The loadings often considered of steam rollers and some form of traction engines. The wind loads are adopted as per IRC recommendations. The standards are adopted as per IRC recommendations. The earliest specifications of highway bridge loadings originated from the need to transport heavy military vehicles in U. an impact allowance should be made.Bearings 3.6 DYNAMIC LOAD: The force exerted on a bridge as a result of unusual environmental factors. 3. 7 .2. the area of the structure as seen in the elevation including the floor system less the area of perforations. stone and block masonry e) Section V.To take in to account the higher stresses is caused by the dynamic forces of the moving load.Steel road bridges f) Section VI. 3.5 LONGITUDINAL FORCES: Tractive effort caused due to the acceleration of the driving wheels.Composite construction g) Section VII.Brick. Resistance to the movement of bearings is due to temperature changes. C 6 code has revised to include the combination of loads forces and permissible stresses in fourth revision published in 2000. Bridges designed for class ‘AA’ loading are to be checked for class ‘A’ loading because under certain conditions class ‘A’ loading causes heavier stresses than class ‘AA’ loading.The I.C. class A loading (IRC standard loading): Adopted for permanent bridges other than those specified under class ‘AA’ loading. for 2 Lane Bridge the shear due to class AA wheeled vehicle controls the design for all spans from 1m to 8m. I. IRC Class AA Loading Two different types of vehicles were specified under this category grouped as tracked and wheeled vehicles with loadings of 700 kN and 400 kN respectively. class AA wheeled vehicle considered span up to 6m and tracked vehicle beyond 6m for single lane bridge. in certain industrial areas and on certain specified highways.3 of Live load +0.R.C. Class AA tracked vehicle span exceed 4m.0m span reinforced deck slab.C. In terms of train tracked vehicle and wheeled vehicle with standard axle loads and spacing.R.4. However. According to present practice.R. it is necessary to compute the maximum live load bending moment for three different conditions of loading.1. class B loading (IRC light loading): Used for temporary bridges. 8 . If shear is desired to be computed. I. referred here in as most.2 Dead load moment. I. and then adopt for design the greatest of three values. 3.C. The computation of live load bending moment only one loading condition need be considered namely Class AA wheeled vehicle span up to 4m. The ministry of surface transport government of India. class 70R loading (IRC heavy loading): This has been evolved to confirm to required standard loading of defence authorities. I. This government prescribed class 70R loading for bridges on national highways. This is to be used in place of class ‘AA’ loading.The first loading standards in India was published by the Indian roads congress in 1958 and subsequently reprinted in 1962 and 1963.R. has published a set of plans for 3.R. I.C class AA loading: Only adopted for bridges which are within certain municipal limits.0m to 10. evolved different standard live loads. The design moment for distribution is taken as 0.R. (a) Tracked vehicle of total load700 KN with two tracks each weighing 350Kn (b) Wheeled vehicle comprising 4 wheels.lane bridges should not constructed.5 WIDTH OF CARRIAGEWAY: The width of carriage way required will depend on the intensity and volume of traffic anticipated to use the bridge.All the bridges located on National Highways and State Highways have to be designed for this heavy loading. another type of loading designated as Class70R is specified instead of Class AA loading. each with a load of 100 kN totalling 400kN (c) Wheeled vehicle with a train of vehicles on seven axles with a total load of 1000kN. Only one lane of Class70R or Class AA load is considered whereas both the lanes are assumed to be occupied by Class A loading if that gives the worst effect. 9 . IRC Class70 R Loading IRC 70 R Loading consists of following three types of vehicles.5m For every additional lane. The minimum width of carriageway for a one-lane bridge is: 4. each lane meaning the width required to accommodate one train of class A vehicles. Alternatively.4. These loadings are also adopted for bridges located within certain specified municipal localities and along specified Highways. 3. Three.25m The minimum width of carriageway for a two-lane bridge is: 7. as these will be conducive to the occurrence of accidents.This type of loading is recommended for all roads on which permanent bridges and culverts are constructed.4. The heavy duty trucks with two trailers transmits load from 8axle varying from a minimum of 27kN to a maximum of 114kN. The various categories of loads are to be separately considered and worst effect has to be considered in design.3 IRC Class A loading IRC Class A type loading consists of a wheel load train comprising a truck with trailers of specified axle spacing and loads as shown in fig. a minimum of 3.5m must be allowed. 3. Impact has to be allowed as per the formulae recommended in the IRC:6-2000.2.The Class a loading is a 554 KN train of wheeled vehicles on eight axles. 3.4 IRC Class B loading Class B type of loading is similar to Class A loading except that the axle loads are comparatively of lesser magnitude.4. The width of carriage way is expresses in terms of traffic lanes. 3. The axle loads of Class B are a 332kN train of wheeled vehicle on eight axles as shown in fig. open excavation is feasible only up to a depth of 3 to 4 m where the subsoil is porous and water table is high. Bearings for the decking. In cases.1 Shallow foundations: Isolated open foundations are feasible where an SBC of about 15t/m2 or more is available at shallow depths with in-redouble substratum. Here again.1 Type of foundations: The subsoil characteristics obtained at a particular site and consequently "file" type of foundations feasible.In case of a wide bridge. trusses etc.in selector of type of structure and span arrangement as already mentioned: 4.. COMPONENTS OF A BRIDGE: The main of a bridge structure are: i. v.. it is desirable to provide a central verge of at least 1. d) The components below the bearing and above the foundation are often referred Sub-structure. and aprons at river bed level. is one of the major "considerations. where the SBC is still less and where ~ smaller spans arc economical from other considerations. raft foundations or box structures with floor' protection arid curtain 10 . From consideration of safety and effective utilization of carriage way it is desirable to provide footpath of at least 1. River training works. consisting of deck slab.6 CLEARANCES: The horizontal and vertical clearances required for highway traffic are given in fig.5m width on either side of the carriageway for all bridges. Approaches to the bridge to connect bridge proper to the roads on either side and vii. below wherein the maximum width and depth of a moving vehicle are assumed as 3300mm and 4500mm respectively. Decking. girders.2m width in order to separate the two opposing lines of traffic. iv. 4. 3. iii. Handrails. Foundations for the abutments and piers. parapets and guard stones Some of the components of a typical bridge are shown below: a) The components above the level of bearings are grouped as superstructure. like revetment for slopes for embankment at abutments. b) While the parts below the bearings level are classed as the substructure.1. c) The portion below the bed level of a river bridge is called the foundation. vi. Abutments and piers. 4. ii. pile foundations are not preferred within the flood zone of the river with deep scour. In some cases of. 4.2 Pile foundations: Pile foundations are another type of deep foundations which are suited for adoption in the following situations:-Availability' of good founding strata below large deep soft soil Need to have very deep foundations beyond the limit of pneumatic operations usually depth beyond 35 meters or so.1. adaptability to different subsoil conditions and difficult site conditions like deep standing water and large depths to good founding strata. Classification of piles (a) (b) (c) (d) (e) Precast driven piles Driven cast-in-situ piles Bored cast-in-situ piles Bored recast piles and Driven steel piles 11 . 4. requirement of very little of equipment's for' its execution.walls are the other options. However. highly pervious substratum and large' scour depth'/it may be "advisable to go for deep foundation like (a) well.1. or (b) piles.2 Deep foundations : Where suitable founding strata is available at a depth of 6 m or more with substantial depth of standing water.1 Well foundations : This is one of the most popular 'types of deep foundations in our Country. strata underlying deep standing water and the strata being very hard not permitting easy sinking of wells or based on economic factors deciding the use of piles as compared to wells. Caissons are an adaptation of well foundations to sites with deep standing water" 4.2. due various reasons like its simplicity.1.2. 2 PIERS: 12 .1: components of bridge structure 4.fig 4. Fig 4. Fig 4. Being one of the most visible components of a bridge. which directly supports the dead and live loads of the superstructure.2: Pier 4. the piers contribute to the aesthetic appearance of the structure. not taking loads from the superstructure c) The back wall.3-Abutment 13 . a) The Brest wall. b) The wing wall. The general shape and features of the pier depend to a large extent on the type.Piers are structures located at the ends of bridge spans at intermediate points between the abutments.3 ABUTMENTS: An abutment is the substructure which supports one terminals of the superstructure of a bridge and laterally supports the embankment which serves as an approach to die bridge. which is small retaining wall just behind the bridge seat. Which act as extensions of the breast wall in retaining the fill. size and dimensions of the super structure and also the environment in which the pier is located. The function of the piers is two-fold to transfer the vertical loads to the foundation. and retains the filling of the embankment in its rear. It consists of generally three structural elements. and to resist all horizontal forces and transverse forces acting on the bridge. no bearings arc generally provided if the span length is less than 10m. The top of piers/abutments caps are however rubbed smooth with carborandum stone.3 In case of roller-cum-rocker bearings only full circular rollers are to be 14 provided.slab superstructure resting on unyielding supports. Adequate care shall be exercised in selecting the right type of bearings based on the guidelines given below: (a) For solid/voided. neoprene bearings may be considered. . For spans larger than 25m roller and rocker bearings or PTFE bearings could be considered.4 BEARINGS: 4. 4. (b)For girder and slab spans more than 10m length and resting on unyielding supports.2 The design of metallic bearings and neoprene bearingsshall be in conformity with IRC: 8: Parts I & II respectively. 4. (d)For very large spans and where multidirectional freedom of movement and rotation are to be allowed provision of pot bearings may be considered.1 Bearings are vital components of a bridge which while allowing of longitudinal and/or transverse rotations and/ or movements of the superstructure with respect to the substructure (thus relieving stresses due to expansion and contraction).4.4.4.4. effectively transfer loads and forces from superstructure to substructure. the instructions contained in the codes and specifications and on the approved drawings. (ii) The minimum functional requirement of superstructure are specified in IRC: 5 and IRC: 21. railways. The protection shall be such that it can be dismantled after the construction is over without disturbing the bearing assembly. Superstructure: (i) It is the superstructure of a bridge that directly supports the traffic and facilitates its smooth uninterrupted passage over natural/manmade barriers like rivers.5 m to facilitate inspection. 4. roads etc.C. such that the line of bearing is as central as possible on the bearing plates at the normal temperature taken in design.4. by transmitting the loads and forces coming over it to the foundation through the bearings and substructure.5mm from a straight edge placed in any direction across the area.4 In order to cater for any possible relative undue movement of bearings over the abutment resulting in girder ends jamming against the dirt wall preferably a larger gap may be provided between the girder end and the dirt wall. necessary adjustment for temperature at the time of placement.5. (h)The bearings shall be so protected while concreting the deck in situ that there is no flow of mortar or any other extraneous matter into the bearing assembly and particularly on to the bearing surfaces. In case of box girder superstructure.C. creep and elastic shortening shall be made. oil the type of horizontal. (iii)Aesthetics will be one of the major considerations while deciding superstructure of a bridge keeping in view the criteria mentioned therein. the concrete surface shall be level such that the variation is not more than 1. In particular the following important points shall not be lost sight of: (a)All bearings shall be set truly level so as to have full and even seating. (iv)Consistent with economy and local availability of the materials. creeks. (g)Installation of multiple bearings one behind the other on a single line of Support is not permitted. (d) For elastomeric bearing pads.4. Thin mortar pads (not exceeding 12mm) may be used to meet this requirement. 4. the minimum clear height inside the box girders shall be 1. labour and technology for a particular type of superstructure selection may have to be made out of the following material options: 15 . (b)The bottoms of girders resting on the bearing shall be plane and truly (c)In case of rockers and roller bearings.4. (f)Bearings of different sizes must not be placed next to each other to support a span.5 All bearings assemblies shall be installed in accordance with. (e) For spans in grade. pedestals. shrinkage. the bearings shall be placed horizontal by using sole plates or suitably designed R. The alternative arrangement is to provide for box girders in which case a single box for both lanes or twin boxes for two lanes can be provided. Recent long-span girders have been designed with a single box per pair of lanes also. T-beam and slab. Fig 4. The typical arrangements for box for a two.5.(a) Masonry (b)Reinforcedcementconcrete (c)Pre-stressedconcrete (d) Steel (e)Composite construction (v) Reinforced cement concrete superstructure: These are the most popular type of superstructure in the present day which may take the form of solid slab.lane bridge are indicated. balanced cantilever or bow-string girder. arch. There are three different 16 . voided slab.It will be found that the main reinforcement becomes heavy and for long spans becomes inconvenient for placement.4-Superstructure ( girder and slab type) 4.1 GENERAL ARRANGEMENT OF GIRDERS IN SUPER STRUCTURE: Typical arrangements of RCC as well as PSC girder and slab type . rigid frame. box girder. They tend to tilt. 4. and (3) The ultimate load-carrying capacity for the combined superstructure of types (b) and (c) were 132 per cent and 162 per cent. the deck slab is supported on and cast monolithically with the longitudinal girders and no cross beam is provided. However. of the deflection for type (a) (2) The transverse load distribution between the girders was better with type (b) and best with type (c). three. 4. respectively. are rendered more rigid by the diaphragms.1. A few more typical arrangements of beams and boxes below the slabs for RCC/PSC bridges are indicated. the slab is supported on and cast monolithically with longitudinal girders. 4. becomes more uniform. diaphragms are provided to connect the girders at the supports and on one or more location within the length of span. Some experiments conducted by Prof. and cause uneven loading across the bottom bearing area.2. As will be seen in the arrangement the three different arrangements for T-beam girders will have differing effects on distribution of loads on slab as well as between girders. Victor at IIT Madras on ‘one-sixth micro concrete model of a bridge 20.5 times the spacing of the longitudinal girders. This has the disadvantage of providing no torsional rigidity and there will be always the danger of the girders tending to separate at the bottom level. respectively. The spacing of cross beams or diaphragms is generally kept not more than 1. 17 . particularly at bearings. the slab design is similar to the one mentioned in (a). Girder.1.’’The only disadvantage in type (c) is the complication involved in fixing form work and tying reinforcements. In this case. The cross beams provide still better stiffness than diaphragms.5. however. of the capacity for type (a).span girder bridge’’ for these types gave the following conclusions: (1) The deflection of superstructure of type (b) and (c) were only 74 per cent and 63 per cent . The girders.5. and this hence results in a still better distribution of the loads among the longitudinal girders in multiple-lane bridges. Girder and slab type: In this.1.1. and the distribution of load between the girders . The slab is designed as a one-way continuous slab spanning between the longitudinal girders. The current Indian practice is to use the type (b) or (c) with one cross beam on each support and at least three cross beams in between for long spans. slab and cross beam type: In this. the diaphragms are replaced by cross beams provided at the ends and one or more intermediate locations making any least three. Girder slab and diaphragm type: In this arrangement also. This also provides the advantage of reducing the number of longitudinal beams as spacing can be increased without the fear of the need to have a deeper slab since the slab will be designed as supported on all four sides.3.ways of providing the beams and slabs. the deck slab is thus supported on all four sides and hence it can be designed as a two.5.beam is replaced by prestressed concrete girders. Since these diaphragms’ do not extend up to the slab.way slab. These arrangements are equally applicable if the RCC T. They are cast monolithically with the deck slab. 5.5(a)-Freyssinet system Fig 4.Udall system Fig 4. Generally pretensioning is very rarely used in the state because of its limitations like proximity and availability of plant.Freyssinet system 18 .5(b) .2 TYPES OF PRESTRESSING AND ITS PROPER USE Basically two types of prestressing i. number of units etc. size of member. Post tensioning system is mainly used in the state. (c) Gifford. Various systems of prestressing are (a) Freyssinet. (b) Magnel-Blaton. pre tensioned and post tensioned are applied in bridge engineering.e.4. Udall system Many of the post tensioning devices are covered by patents. In case of Freyssinet system. cable with a fixed number of wires e.6-Gifford .Fig 4. The sheathing as specified in IRC: 18-2000 is generally (CRCA) Mild Steel of bright metal finish or corrugated High Density Polyethylene (HDPE) 19 . 12-5f or 12-7f or 19-7f are used.g. DESIGN CONSIDERATIONS FOR BRIDGES 5. IS: 456-1964 Indian standard specification and code of practice for plain and reinforced concrete. the former for small and medium spans and the latter for long spans .Reinforced concrete has been used on railways up to 10m span and pre-stressed concrete up to 24m in India but up to 35m in many countries. cement concrete (plain and reinforced). 2. standard specification and code of practice for road bridges. 5. IRS Code for concrete and pre stressed composite bridges on railways. IS: 1139-1959. section 3. IRC 21-2000. Reinforced concrete even in form of open web type of girders is being tried in longer railway spans in Japan. due to the heavy dead load to be dealt with the comparatively longer construction time and difficulty in maintaining adequate quality control at the site of construction. reluctance on the part of Indian railway engineers to adopt reinforced and pre-stressed concrete for longer spans on railways. design criteria for pre stressed concrete road bridges (post-tensioned). They are also difficult to be replaced under traffic when the loading conditions alter or major damages are caused due to derailments and the superstructure requires to be changed The various codes referred to for design of the concrete bridges and bridges elements are: 1. Indian standard specification for hot rolled mild steel and medium tensile deformed bars for concrete reinforcement. Indian standard specification for mild and medium tensile bars and hard drawn wire for concrete mix for cement. IRC: 18-2000. 3.5. They have used continuous deck type spans up to 105m. IS: 432-1966.and 20 .There is however. 4. 6.1 CONCRETE BRIDGES: Reinforced concrete and pre stressed concrete have been found most suited for the construction of highway bridges. 26fc Compression due to bending = 0.26Fc or 0.25 to 1.8 Works test strength: Preliminary test strength=1.2 DESIGN CRITERIA FOR RAILWAY BRIDGES Ordinary Concrete with nominal mix by volume is used in bed blocks. foundation and mass concrete works where the standard of specification and workmanship are likely to be lower. Indian standard specification for cold twisted steel bars for concrete reinforcement-tensile steel deformed bars for concrete reinforcement.34fc Shear (as inclined tension) = 0.34FC or 0. four times the shear above is permissible. precast piles and for all prestressed concrete work. The minimum quantity of cement to be used for controlled concrete on the railways according to the IRS concrete code is 325 kg/m3of concrete. IRC stipulates 360 kg/m3 for major bridges.034fc Where shear reinforcement is used. the relationships used for arriving at various strengths are: Fc= 28 days works test strength on cubes of size 150 mm in kg/cm2 fc= 28 days works test strength on cubes of size 150 mm in N/mm2 Cylinder strength=Cube strength*0. 5. particularly in super-structure slabs and girders. The maximum permissible stresses in concrete for various mixes Controlled concrete is used in all girder parts.7. IS: 1786-1966. When the mix design and testing is done.034FC or 0.33 The various proportions for permissible stresses used are: Direct compression = 0. column footing. 21 . 3 N/mm2 for post-tensioning.1. Plain drawn wires Heat treated alloy bars Concrete 1. i. the concrete used should have fc not less than 41.2. STEEL USED IN CONCRETE: The modulus of elasticity for steel to be used in prestressed concrete work is as follows.71×105 N/mm2 (1. or 22 .Bond average for anchorage = 0.96×105 N/mm2 (2×106 kg/cm2) 1.30Fc or fc Tensile stress in bending for plain concrete is same as permissible for shear stress 5.75 times average. The compaction and vibration should be such that the density of the concrete is not less than 2400 kg/m3.04fc Bond-local = 1. The ultimate strength of concrete at transfer should not be less than (2/3) Fc used for design.20fc Bearing pressure on plain concrete-average on an area less than one-third of full area= 0.04Fc or 0. Modular ratio is taken as 276/3 fc N/mm2 (or 2812/3 FC kg/cm2).1 N/mm2 for pretensioning and not less than 34. The quantity of cement used for prestressed concrete should preferably be equal to 530 kg/m3 the minimum being 380 kg/m3 for post-tensioning. 0.20Fc OR 0.07fc Bearing pressure on plain concrete-average on full area= 0.e.75×106 kg/cm2) 5630√fc N/mm2 18000√Fc kg/m2 Permissible stress in other steel bars used in all RCC and PSC works In prestressed concrete.07FC or 0.. Minimum cover and spacing for reinforcement: The higher of the two alternatives mentioned will apply (Ø stands for diameter of bar). Horizontal Ø if diameters are equal or a.3 per cent of the area should be provided near the face which is subject to tension when the column is to be provided with tension reinforcement also. Pitch of main slabs >300mm or > twice effective depth. Vertical spacing between two horizontal layers < 13mm. the end diaphragms in prestressed concrete girders should take the stress that may be induced due to different cracking at the ends of the girders. When lapping is required.section. Each end 25mm or 2Ø Longitudinal bars in column 38mm or Ø For columns of size 20 cm and 25mm or Ø Under Longitudinal bars in beams 25mm or Ø Bars in slabs 13mm or Ø Any others 13mm or Ø Foundation footings 50mm For structures submerged in water 75mm from surface or ends Minimum distance between bars: 1. In addition. 4. 5.2 Web thickness: Minimum diaphragm thickness should not be less than the web thickness of the girders connected the diaphragm should be designed to resist 3% of the total compressive force carried by both the girders and provided both at the bottom and top of the deformed bars with nominal reinforcement in the middle portion. The minimum diameter of the main reinforcement in the column will be 13mm. Nominal maximum size of aggregate +6 mm 2. a minimum 0. In addition. The Column reinforcement should not be less than 0. 23 .8 per cent of the cross.2. Pitch of distribution bars in slabs > 600mm or > 4 times effective depth. the maximum area should be restricted to 4 per cent of the area of crosssection. 3. Ø of largest bars or b. For calculating stresses in section a modular ratio of 10 may be adopted.18Mpa to 2. The code also prohibits maximum diameter as 40 mm or a section of equivalent area. Fig 4. In conditions of alternate wetting and drying the code requires provision of 75 mm cover. In moderate conditions of exposure. It specifies different minimum grades for culverts and major bridges. IS: 1786 subject to some minor changes. minimum cover from any exposed surface shall be 40 mm and in conditions obsevere exposure. except in special circumstances. IS: 432.5. IS: 1139. Nominal mix concrete is not included for use in road bridges.15% reinforcement for M40 and 3.7-Cross section across diaphragm wall 24 .0% for above grades of concrete. Minimum cement content for major bridges is 360 kg/cum and maximum 540 kg/cum. For bridges in severe exposure conditions one grade higher concrete is to be used. Permissible shear stress without stirrups varies with the percentage of steel provided from 0. IS: 1566. minimum size of longitudinal bar is 12 mm. Minimum cover to be provided for the reinforcement depends on the exposure conditions also. Minimum size of bar to be used is 8 mm and in columns.3 Design Criteria for road bridges: IRC– 21-2000 applies to design of road bridges in concrete. Material specifications and permissible stresses to be used for the concrete and steel generally follow the provisions in relevant IS codes IS: 456.5Mpa for M20 concrete and 0. it shall be 50 mm. 2. Minimum thickness shall not be less than that of deck slab and it should extend at least three.1 Steel Girders (a)Deck-type bridges: Generally.2. Nominal two legged stirrups of 12mm diameter at 150mm centers are provided. 3.1 Introduction: The design procedures for railway and road bridges primarily differ in consideration of loading. the determination of the forces becomes simple since each track is carried by a pair of girders.25% of gross area of steel in top. Some principles of spacing of girders have already been indicated in subsection. 5. 5. EUDL tables are available for design of not only main beams but also floor systems for railway bridges. In the matter case. In general.50% of gross area at the bottom and 0. The sleepers can be designed to carry the loads coming through the two rails as concentrated loads and for all standard spans up to 91. The procedure is briefly dealt with individually for these two in this section. The track is carried over the girders generally using timber or steel sleepers which are connected to the top flanges of the girders by means of the girders by means of hook bolts or other bolts.2 Concrete Girders As mentioned earlier.3.Cross girders monolithic with the deck slab should be provided at bearings and may be provided in intermediate locations according to design requirements. spanned by the deck slab as they are assumed to act only as stiffeners to the girders. deck-type bridges are designed with two girders carrying a track. 25 . the distribution of load between the girders is decided by using one of the standard methods evolved and mentioned subsection.3.3.3. They are designed with reinforcement equal to approximately 0. End diaphragms are designed to take up secondary forces that will be induced due to differential prestressing in girders. the highway bridge design takes into consideration individual disposition of the wheel loads of the vehicles.fourths depth of main beams. The shorter due concrete spans are provided with one pair of girders per track or a number of T beam and slabs placed side by side.2 DESIGN PROCEDURE FOR RAILWAY BRIDGES: 5.44 m and issued drawings to show general arrangements as well as details of members and joints. so far as the design of long-span concrete girders for railway loading is concerned. 5.1. On the other hand.1 DESIGN PROCEDURES FOR BRIDGE SUPERSTRUCTURE: 5. are 7. 26 .3 ROAD BRIDGE DESIGN 5. only the design procedures for concrete bridge are indicated here. For short spans up to 6m. Each component of the girder has to be designed separately by working out the worst effect on the component by the most severe pattern of placement of vehicles adopted for the particular class of loading.5. Once the worst loading moments and shear forces are determined for the severe conditions of loading on each component.5 m. The section is designed by the trial and error method starting with an assumed section and verifying if resultant stresses are within permissible limits mentioned in respective IRC Codes for RCC and PSC and IS 456 as the case may be. flat RCC slabs are adopted. With availability of computers for design. It is inconceivable to provide such a wide slab over two girders and where the lanes are more.3. road bridges are designed for IRC class AA loading and also checked for class A loading for the number of lanes can be occupied by class A load also. They contain full details and can be adopted directly. even without taking into consideration the footpath.1 Approach to design Since concrete girders are mostly used for road bridges.3. stresses are computed using Finite Element Method. the minimum width for standard road bridge is far two lanes which. In general. the design boils down to a problem of structural engineering.3. as indicated. Normally. Alternative arrangements of using precast PSC slabs are indicated IRC has issued standard drawings for standard span slabs and beams. more number of girders are to be provided. Width of tyre or track at road surface in a direction perpendicular to span. the effective width e=1. It has three provisions: (1) Determination of effective width of slab for a single concentrated load over a slab simply supported at two ends. Generally.5. Pigeaud’s method is used in India.4 DESIGN OF CONCRETE ROAD BRIDGES (a)Design of Deck Slab: This first depends on the method of dispersion of wheel load and effective width of slab to be considered for working out moments and shear.x/l)+W Where l = effective span in case of simply supported slab and clear span in case of continuous slabs x= distance of centre of gravity of load from the near support W= width of concentration of load .e. i.e. The methods used for this are based on Pigeaud’s method or Westerguard’s method. in the case of the cantilever slab. (2) Determination of effective width of slab for a single concentrated load placed on a cantilever slab. plus twice thickness of wearing coat.5.i.2x+w. and (3) Determination of effective area over which the concentrated load is dispersed and coefficients to be used for working out moments in either direction when slab is supported on four sides For (1) effective width e is given by e=kx(1. For (2). The dispersion of load on slab supported on all four sides will be shown x=a in direction L 27 . Knowing ‘e’ and the load plus impact. k= a constant depending on l’/l where l’ is the width of the slab and is tabulated in Annexure 14. BM for unit width of slab can be calculated. the ratio of the short span to the long span of the slab varying from 0.4 to 1. Otherwise.0. 2. 3.e. This method is most useful when k is more than0. Where V/L is small. The portion beyond the girder is designed as a cantilever for taking generally one track or line of wheels and or foot path loading plus parapet loading. i. the design of the slab is like any two way RCC slab reinforcement. For precast slabs.b in direction B Knowing U and V . Since a number of loads will come on a panel and only one may be at centre.15 for RCC This method has following limitations. M1= moment in short span = (m1+µm2) P M2= moment in long span =(m1+µm2) P µ= value of Pigeauds ratio. 1. It applies to loads placed at centers. Readers more interested in the method may refer to Victor’s “Essentials of bridge Engineering” where the full set of curves is reproduced. the coefficients m1and m2 are read from pairs of graphs provided by Pigeaud for values corresponding to U/B and V/L. the width of each slab is taken as the effective width. the values of m1 and m2 tend to become less accurate.The curves useful for design by this method are available in many textbooks. some approximations will have to be made while considering the effect of non-central loads.55. taken as 0. The curves have been evolved for different values of K. 28 . When there are only two girders. 5.1 COURBON’S METHOD: This is the simplest of the three methods in application.1 DESIGN OF THE LONGITUDINAL GIRDERS For the computation of the bending moments due to live load. When three or more girders are provided.4. the proportion of the load carried by a girder is given by Ri= PIi/∑Ii(1+ Ii/∑Ii di^2*edi) Where P= sum of loads at the section Ii= moment of inertia of the girder e=eccentricity of the loads with respect to axis of the bridge 29 . symmetrically spaced. has certain limitations.1.4. the distribution of the live load between the various longitudinal girders has to be first determined . and by at least five cross (3) The depth of cross girders/diaphragms is not less than 0. the load distribution is estimated by using any one of the following three methods. The longitudinal beams are interconnected beams/diaphragms.75 of the depth of main girders. This method. (a) (b) (c) Courbon’s method Henry-jaegar method Morice and Little version of Guyon and Massonnet method These three methods are briefly described below. however. as it is applicable only to cases where: (1) (2) The ratio of span to width of deck is more than 2 but less than 4. for a system of wheel (live) loads across a cross section under the loads. If these conditions are satisfied.5. the reactions can be worked out assuming the deck slab as unyielding and by determining the worst placement. It requires no reference to any tables or charts and also is applicable to majority of modern Tbeam bridges. In the absence of cross beams.di= distance of the girders under consideration from axis of the bridge 5. In a bridge with three or four longitudinal with a number of cross beams F is taken as ∞. The distribution of the loads between the girders is based on three dimensional parameters as given below: A=12/π^4*(L/h)^3*nEIT/EI E=π^2/2n(h/L)CJ/EIT where cross beams exist And F= LEIT When there is no cross beam c=EI1/EI2 Where L= Span length of bridge h= spacing of longitudinal beams n= number of cross beams EI= Flexural rigidity of one longitudinal girder CJ= Torsional rigidity of one longitudinal girder EIT= Flexural rigidity of one cross beam EI1 and EI2 are flexural rigidities of outer and inner longitudinal beams if they are different. normally these will be equal particularly in RCC T.2 Henry-Jaegar method: This method assumes that all the cross beams can be replaced by a uniform. continuous.4. 30 .beam bridges. transverse medium of equivalent stiffness. it takes into account the stiffness of the slab over its entire length. However.1. 3 Marcie Little Method: The method also calls for the use of standard graphs evolved for moment of coefficient. Values of k1 and k0 are given in separate sets of graphs for each reference station 0. -b/4. It applies the orthotropic plate theory to concrete bridge systems. the girders and position of loads are divided If the longitudinal girders are spaced at p. Some of the graphs are reproduced also by Victor.. The distribution coefficient is given by k0=k0 + (k1-k0)√α where α is torsional rigidity parameter of the bridge deck.4. Further information and graphs can be had from The Analysis of Grid Frameworks and related structures. 5.The distribution coefficients are given in a graphical form with parameter A as abscissa and moment coefficient m as ordinate. Only the basic principle is given below for an appreciation of the method. based on the approach first suggested by Guyon neglecting torsion and later extended by Massonnet including torsion. Different sets of graphs exits for F=0 and F=∞ and for different number of girders in the system. the abscissa representing θ and ordinate giving the k 0 or k1 value. For intermediate values of F the coefficient is interpolated using the formula mF= m0+(m∞-m0)√F√A/3+F√A Graphs are available for system of 3 or more girders. The span L is equated to 2a.1. k0=value is for α=0 31 . Complete details of the method are described along with graphs in the Concrete Bridge Design by R E Rowe. For arriving at various factors. b/4. the effective width of deck is mp which is equated to 2b and b is divided into four equal parts of considering reference stations for the coefficients and assumed load position. The distribution of loads between longitudinal girders is correlated to the differential deflection between the longitudinal girders at a section where load are applied which can be as indicated. etc. 32 .e. the worst position of load system longitudinally for producing maximum BM and shear over the length is determined and then the maximum BM and load in intermediate beams and end beams are calculated. longitudinal torsional stiffness per unit length J0=J0/q .25 α= a(i0+j0)/2E√j and i= I/p i. transverse torsional stiffness per unit length I0 and J0 are torsional stiffness factors of each longitudinal beam and cross beam/diaphragm respectively. The proportion of loads is worked out for the worst transverse position of each set of axles first. For applying the morice little method a system of tabulation is required to arrive at the worst effect. Then. the distribution factor for each beam and proportion of load is worked out for each beam. J= transverse MI of equivalent deck/unit length = J/q.k1= value is for α=1. i.e. θ =b/2a(i/j)^0. Values of θ and α are arrived at a follows. longitudinal moment of inertia (MI) of equivalent deck per unit width. The graphs are available in the reference quoted above and have been reproduced by Victor also. I being MI of each girder and p being their transverse spacing. and θ is parameter giving flexural properties of the bridge deck as a whole. J being MI of each transverse diaphragm or cross girder and q being their spacing E= Young’s modulus of material of deck G= modulus of rigidity of material of deck I0= I0/P. In all the above methods.e. i. The trestle type consists of columns with a bent cap at the top. and also for river crossings with a skew alignment. The stone layers should be properly bonded with the interior with bond stones. The cellular type permits saving in the quantity of concrete. and the quantity should be distributed as 60% on the outer face and 40% on the inner face. as in flyovers and the elevated roads. In an urban setting. For all trestles. single column piers provide an open and free-flowing perception to the motorists using the road below. Single column piers are increasingly used in urban elevated highway applications. The length of the pier at the top should not be less than 1. When used for a river bridge eg. The bearing plates are so dimensioned that the bearing stress due to dead and live loads does not exceed 4. The construction procedure should be arranged such that the construction joints are minimized. The lateral reinforcement of walls should not be less than 300mm. The top width of the pier depends on the size of the bearing plates on which the super structure rests. Solid piers can be of mass concrete or of masonry for heights up to about 6m and spans up to about 20m. but usually requires difficult shuttering and additional labour in placing the reinforcements.5 DESIGN FEATURES OF THE PIER: PIERS: Piers are of: ➢ Solid piers ➢ Single column piers ➢ Cellular piers ➢ Trestle piers ➢ Hammer head piers Solid and cellular piers for river bridges should be provided with semi-circular cutwaters to facilitate streamlined flow and to reduce scour. measured along the longitudinal axis of super structure. the lateral reinforcement of walls should be 0.2m in excess of the out-to-out dimension of the bearing plates measured perpendicular to the axis of the super structure. this design leads to minimum restriction of the waterway. It is permissible to use stone masonry for the exposed portions and to fill the interior with lean concrete. Cellular. Such piers when used for a skew bridge across a river results in least obstruction to passage of flood below the bridge. The thickness of the walls should not be less than 300mm. trestle.2 MPa. Other innovative designs for piers to suit urban site requirements includes H-shaped.3% of the sectional area of the wall of the pier. Jawahar setu across Sone River at Dehri. connecting diaphragms between the columns may also be provided. The hammer head type provides slender sub-structure and is normally suitable for the elevated roadways. Simple geometry of the pier leads to reduce construction costs. 33 .5. It is usually kept at a minimum of 600mm more than the out-to-out dimension of the bearing plates. hammer head and single column types use reinforced concrete and suitable for heights above 6m and span over 20m. Dead load of super structure and the pier itself. measured along the longitudinal axis of super structure. Reinforced concrete framed piers of “V” shaped supporting a short length of reinforced concrete decking have been used successfully in conjunction with suspended spans of pre-stressed concrete for bridges in hilly areas. if applicable. The length of the pier at the top should not be less than 1. It is normally sufficient to provide a batter of 1 in 25 on all sides for the portion of the pier between the bottom of the bed block and the top of the well.Piers flaring at the top provide wider base at the top pier for stability of the deck and limited use of space at the base of the pier at the ground level. Impact effect of live load.6 DESIGN FEATURES OF THE ABUTMENT An abutment is the substructure which supports one terminals of the superstructure of a bridge and laterally supports the embankment which serves as an approach to die bridge.Longitudinal force due to resistance in bearings. the portion pier located ‘between wind and water’. is particularly vulnerable to deterioration and hence needs special attention. The top width of pier depends on the size of the bearing plates on-which the super structure rests. Reinforced concrete framed types of piers have been used in recent years. The bottom width is pier usually larger than the top width so as to restrict the net stresses within the permissible values. In the case of river bridges. VIII. III.Longitudinal force due to breaking of vehicles. 34 . V. VI. Longitudinal force due to the tractive effort of vehicles. The bottom width is pier usually larger than the top width so as to restrict the net stresses within the permissible values. The effect of eccentric loading due to the live load occurring on one span only should be considered. It is usually kept at a minimum 600mm more than more than the out-to-out dimension of the bearing plates. The main advantage in their use is due to reduced effective span lengths for girders on either side of the center line of the pier leading to economic in the cost of super structure. It consists of generally three structural elements. IV. It is normally sufficient to provide a batter of 1 in 25on all sides for the portion of the pier. that is the portion of the masonry surface which lies between the extreme high and extreme low water. II. Effect of wind on moving loads and on the superstructure. The loads to be considered in the design of pier are I. Force due to wave action. VII. 5.2m in excess of the out-to-out dimension of the bearing plates measured perpendicular to the axis of the super structure. Live loads of traffic passing over the bridge. b) The wing wall.a) The Brest wall. 6. Which act as extensions of the breast wall in retaining the fill. v) Thrust on the abutment due to retained earth and effect of live loads on the fill at the rear end of the abutment. iii) Self-weight of the abutment. not taking loads from the superstructure c) The back wall. the forces considered are: i) Dead load due to superstructure. WELL FOUNDATIONS 6. which is small retaining wall just behind the bridge seat. ii) Live load on the superstructure. which directly supports the dead and live loads of the superstructure. It is important on abutment construction to replace the fill material carefully and to arrange for its proper drainage.1 Introduction: 35 . A good drainage system is secured by placing rock fill immediately behind the abutment and proper drain pipes at the bottom. iv) Longitudinal forces due to tractive effort and braking effort and due to temperature variation. In abutment design. and retains the filling of the embankment in its rear. Fig 6. construction of a large number of bridges across major rivers became necessary and it was recognized very soon that much bigger and deeper well foundations were required for their piers and abutments. The technique of sinking masonry wells for drinking water is very ancient and even today small drinking water wells are constructed all over the country using the same methods as were prevalent centuries ago.1-well foundations 6. With the advent of Railways in India.2 Comparison with Pile Foundation i) Well foundations provide a solid and massive foundation for heavy loads as against a cluster of piles which are slender and weak individually and are liable to get damaged when hit by floating trees or boulders rolling on the river bed in case of bridge piers. ii) Wells have a large cross sectional area and the bearing capacity of soil for this area is much greater than that of the same soil at the same depth for section. which were constructed in the middle of the nineteenth century.Well foundations had their origin in India and have been used for hundreds of years for providing deep foundations below the spring water level for important buildings and structures. Well foundations were used for the first time for important irrigation structures on the Ganga canal including solani aqueduct at Roorkee (India). 36 bearing piles of small cross- . where it cannot be inspected. viii) Masonry in the steining wells is done under dry conditions and the quality of masonry Or concrete is much better than in case of cast in situ piles for which concreting is done below the ground level and in many cases below the water level. not economical to use well foundations for very small loads and pile foundations are more suitable for them. They can resist large horizontal forces and can also take vertical loads even when the unsupported length individual piles in a cluster is small and cannot carry large horizontal force or vertical loads when the unsupported length is considerable as in case of bridge piers and abutments in scourable riverbeds. It cannot be said with confidence in the case of bearing piles if they have gone and rested on the strata taken into account while designing them or if they are resting only on an isolated boulder. the concrete is subjected to a lot of hammering and 37 . v) The size of well foundations cannot be reduced indefinitely as the dredge hole must be enough to enable a grab to work and the steining must have the thickness necessary to provide the required sinking effort. The section modulus of area. Even when sinking is done by dredging. It is possible to sink a well after overcoming these obstructions.iii) Well foundations can be provided up to any depth if only open sinking is involved and upto a depth of 33.5m if pneumatic sinking is required to be done. it is not possible to determine the exact strata through which each individual pile has passed. the dredged material gives a fairly good idea of the strata through which the well is sunk. Drilled piles and caisson piles also have this advantage over the driven piles. therefore. It is. This Provides a large section modulus with the minimum cross-sectional is large. it is possible to visually examine the strata through which sinking is done in its natural state and the material on which they are finally founded. Even in case of precast piles. iv) Piles cannot be driven through soil having boulders. In most cases. Pile foundations are generally economical up to a depth of 18m and in some cases for depths up to 27m. Logs of wood which are very often found buried even at great depths also obstruct a pile. In case of wells sunk by dewatering or pneumatic sinking. vi) Wells are hollow at the center and most of the material is at the periphery. vii) The bearing capacity of a pile is generally uncertain. The well is generally adopted for piers of single track railway bridges and those of bridges on narrow roads. 6. When the piers are very long the size of circular wells becomes unduly large.1Circular well This type of well is used most commonly and the main points in its favour are its strength. If the bearing capacity of the piles at the design depth is found to be less than the calculated value after testing.3 Well Types and Their Suitability: The followings are the different types of well in common use in Indian as below: 6. The advantages and disadvantages of each type have also been discussed . It requires only one dredger for sinking and its weight per sq. it may not be possible to sink them to the design depth and the piles may have to be cut which is costly and situ piles. Simplicity in construction and ease in sinking.damage to it cannot be ruled out. On the other hand if the stratum is too hard. The distance of the cutting edge from the dredge hole is uniform all over and the chances of tilting are the minimum for this type of well. which makes them costly and disadvantageous hydraulically also as they cause excessive obstruction to the flow of water. ix) In case of wells rising of the well steining and sinking are done in stages and a decision about the foundation level can be taken as the work progresses piles and the strata conditions become known.3. a decision about the depth has to be taken in advance.3. Allowing cantilever of one metre on either side the maximum length of the pier resting on this type of well is about 11 metres. Nine metres is generally considered as the maximum diameter of circular wells. In case of precast piles. it may become necessary to redesign the foundation and the piles of short length already cast may have to be rejected or additional number of piles may have to be provided in each cluster.2Double D well 38 wasteful. 6. This does not apply to cast in Railways as well as roadways. metre of surface is the highest due to which the sinking effort for this well is also high. 6. 39 account of the increased surface difficult than in case of double D wells. It is necessary to sink these wells simultaneously to ensure that the cutting edges are almost at the same level all the time.This type of well is most common for the piers and abutments of bridges which are too long to be accommodated on circular well.6 to 1 m to avoid tilting. They. offer greater resistance against sinking on area. Blind corners are eliminated and bending stresses in the steining are also reduced considerably.3Double Octagonal Well These types of wells are free from the shortcoming of double D-well. The wells have a tendency to tilt towards each other during the course of sinking on account of the fact that the sand between them becomes loose and does not offer as much resistance against sinking as on the other sides. They can be adopted very conveniently where the bridge is designed for open foundations and a change of well foundations becomes necessary during the course of construction on account of adverse conditions such as excessive in flow of water and silt into the excavation.5 Twin circular well This type of foundation consists of two independent circular wells placed very close to each other with a common well cap. . If the depth of sinking is small say up to 6 or 7 metres. the clear space between the two wells may be kept 0.3. The dimensions of the well are so determined that the length and the width of the dredge holes are almost equal. Masonry in steining is also more 6. 6. The shape is simple and it is easy to sink this type of well also. It is also recommended by some engineers that the overall length of the well should not be more than double the width.3.4 Rectangular Well These types of foundations are generally adopted for bridge foundations having shallow depths. however.3. The disadvantage of this type of well is that considerable bending moments are caused in the steining due to the difference in the earth pressure from outside and water pressure from inside which result in vertical cracks in the steining particularly in the straight portions where join the partition wall. however.8m x 55m and there are 21 dredge holes in each of them. The size of these wells is 24. If. however.2m size. advantageous where the length of the pier is considerable and the sizes of the double D or octagonal wells become unduly large to accommoda te the pier. Twin circular wells are advantageous only when the depths of sinking is small and the foundation material is soft rock or kankar or some other soil capable of taking fairly high loads.6m and they support the piers of San Okland Bridge. used for the towers of Howrah Bridge.2m x 5. wells with multiple dredge holes are used. The possibility of development of cracks in the pier due to relative settlement cannot be ruled out inspite of the heavy design of the cap except where the wells are founded on rock or other incompressible soils. In the United States wells of this type are more common. Design of well caps for the twin circular wells also requires special care. Wells of this type were. Each well has 55 square dredge holes of 5.6 Wells with Multiple Dredge Holes For piers and abutments of very large sizes. 6.5m x 29. however. Francisco 40 . the soil is weak. Wells of this type are not common in India. They are. Allowance is made for relative settlement of the two wells and this adds to its cost.For greater depth of sinking spacing of 2 to 3 meters may be necessary. The overall dimension of the largest well are 60. the larger size of double D or double octagonal wells may be required to keep the bearing pressure on the soil within limits. Since it is necessary to sink these wells simultaneously it is obligatory to have two sets of equipment for well sinking and in this respect they do not offer any advantage over double D or double octagonal wells.3. Fig 6.2-shapes of well foundations 41 . However. which both protects the tendon from corrosion and allows for direct transfer of tension.7. floor slab. It can be used to produce beams. PRESTRESSED CONCRETE 7. beams or foundation piles. The cured concrete adheres and bonds to the bars and when the tension is released it is transferred to the concrete as compression by static friction . or a method of lintels. This method produces a good bond between the tendon and the concrete.1 DEFINITION: Prestressed concrete is a method for overcoming concrete's natural weakness in tension. which limits their size.2 PRETENSIONED CONCRETE: Pre-tensioned concrete is cast around already tensioned tendons. it requires stout anchoring points between which the tendon is to be stretched and the tendons are usually in a straight line. most pre-tensioned concrete elements are prefabricated in a factory and must be transported to the construction site. Pre-tensioned elements may be balcony elements. floors or bridges with a longer span than is practical with ordinary reinforced concrete. An innovative bridge construction method using pre-stressing is described in Stressed Ribbon Bridge. Thus. 42 . 7. Prestressing tendons (generally of high tensile steel cable or rods) are used to provide a clamping load which produces a compressive stress that balances the tensile stress that the concrete compression member would otherwise experience due to a bending load. steel or aluminum curved duct. the tendons are tensioned by hydraulic jack tzhat reacts against the concrete member itself. When the tendons have stretched sufficiently. according to the design specifications (see Hooke’s law).3.3 POST TENSIONED CONCRETE: 7. 43 . Once the concrete has hardened.1 BONDED POST TENSIONED CONCRETE: Fig 7.1-pre stressing cables along with reinforcement for I -girder Bonded post tensioned concrete is descriptive term for a method of applying compression after pouring concrete and the curing process. The duct is then grouted to protect the tendons from corrosion. The concrete is cast around plastic.7. A set of tendons are fished through the duct and the concrete is poured. transferring pressure to the concrete. to follow the area where otherwise tension would occur in the concrete element. they are wedged in position and maintain tension after the jacks are removed. The transfer of the tension to the concrete is achieved by the steel cable acting against steel anchors embedded in the perimeter of slab. All stresses from seasonal expansion and contraction of the underlying soil are taken into the entire tensioned slab. which supports the building without significant flexure. each individual tendon is coated with grease (generally lithium based) and covered by a plastic sheathing formed in an extrusion process. as in the segmental bridge. The advantages of this system over unbounded post-tensioning are: 1) Large reduction in traditional reinforcement requirements as tendons cannot distress in accidents. 2) Tendons can be easily weaved allowing a more efficient design approach.2-showing base plates fixed in concrete girder This method is commonly used to create monolithic slabs for house contraction of the underlying soil is taken (such as adobe clay) create problems for the typical perimeter foundation. both after concrete is cured after support by false work and by the assembly of prefabricated sections.Fig 7. To achieve this. Post-tensioning is also used in the construction of various bridges. 4) No long term issues with maintaining the integrity of the anchor/dead end. 7. The main disadvantage over bonded post tensioning is the fact that a cable can distress itself and burst out of the slab if damaged (such as during repair on the slab).3.The advantages of this system over bonded post-tensioning are: 44 . 3) Higher ultimate strength due to bond generated between strand and concrete.2 UNBOUNDED POST TENSIONED CONCRETE: Unbounded post tensioned concrete differs from post-tensioning by providing each individual cable permanent freedom of movement relative to the concrete. care shall be taken to ensure that all such tendons are of the same length from grip to grip. Due allowance shall apparatus to measure the force ensure that they do not at any time introduce errors prestressed concrete member . The placement of cables or ducts and the order of stressing and grouting shall be so arranged that the prestressing steel.3. The be arrived at by plotting on a graph the gauge reading as abscissa and extensions as ordinates: the intersection of the curve with the Y axis when extended shall be taken to give the effective elongation during initial tensioning. 3) The ability to de-stress the tendons before attempting repair work. 2) The procedure of post-stress grouting is eliminated. The pressure gauges or devices attached to the tensioning shall be periodically calibrated to in reading exceeding 2 percent. The provision shall be more carefully observed for tendons of a length smaller than 7. when tensioned and grouted. Measurement of Prestressing Force : The force induced in the prestressing tendon shall be determined by means of gauges attached to the tensioning apparatus as well as by measuring the extension of the steel and relating it to its stress-strain curve. It is essential that both methods are used jointly so that the inaccuracies to which each is singly susceptible are be made for the frictional losses in the tensioning apparatus.5 m. When two or more prestressing tendons are to be tensioned simultaneously. No alteration in the prestressing force in any tendon shall be allowed unless specifically approved by the designer. In measuring the extension of prestressing steel. Breakage of Wires—the breakage of wires in any one 45 elongation shall be added minimized. The total tension imparted to each tendon shall conform to the requirements of the design.3 Procedure for Tensioning and Transfer: Stressing: The tensioning of prestressing tendons shall be carried out in a manner that will induce a smooth and even rate of increase of stress in the tendons. The initial tension required to remove slackness shall be taken as the starting point for measuring the elongation and a correction shall be applied to the total required extent of correction shall elongation to compensate for the initial tensioning of the wire. does not adversely affect the adjoining ducts. Any slack in the prestressing tendon shall first be taken up by applying a small initial tension. and this effective to the measured elongation to arrive at the actual total elongation. any slip which may occur in the gripping device shall be taken into consideration.1) The ability to individually adjust cables based on poor field conditions. 7. Well. and that the transfer of prestress to the concrete is uniform along the entire length of the tension line. Attractive and aesthetic fit: Because of the simple. v.developed and time tested standards: Since the first introduction of pre-stressed concrete in the US.shall not exceed 2. Low initial costs: 46 . irrespective of percentage. the design standards for bridge structures have continually evolved and are today governed by national AASHTO standards. when the transfer is made on several moulds at a time. care shall be taken to ensure that the prestressing force is evenly applied on all the moulds. Pre-stressed concrete bridges do well in both these aspects. manufacturing and quality assurance standards of the Common wealth of Pennsylvania and other states. Low life cycle costs: The overall economy of a structure is measured in terms of life cycle cost. ii. tough. application of stress to the concrete. Connections between elements are simple carefully panned details.5 percent during tensioning. the existing abutments and piers frequently can be used. In the long line and similar methods of prestressing. When using pre-stressed concrete beams for replacement of existing bridges. 7. iii. Where the total prestressing force in a member is built up by successive transfers to the force of a number of individual tendons on to the concrete. The transfer of the prestress shall be carried out gradually so as to avoid large differences of tension between wires in a tendon. durable—yet graceful bridges result from the low depth span ratios which are possible through the use of prestressed concrete. Transfer of Prestressing Force Wire breakages after anchorage. iv. Strong. account shall be taken of the effect of the successive prestressing. This includes the initial cost of the structure plus the maintenance cost. vi. ranging in size from short span bridges to some of the largest projects in the world. Adaptable to a wide variety of situations: Precast pre-stressed concrete products can be designed and manufactured for any application. pre-stressed concrete bridges offer attractive views from all sides. as well as design.4 ADVANTAGES OF PRESTRESSED CONCRETE: i. shall not be condoned without special investigations. clean shapes of the member used. severe eccentricities of prestressing force and the sudden Simple to design: A variety of components can accommodate various load carrying capabilities and span potentials. Durable: Because of high quality of materials used. • High strength steel pre-stressing strands to provide load needed. better substructure stability from increased dead loads. built in the early 50’s in Philadelphia. Fire resistance: Pre-stressed concrete bridges are not easily damaged by fire. Excellent riding characteristics: The public will not only be safe. • Concrete to give permanence &strength and good riding characteristics.Pre-stressed concrete bridges are economical as well as provide minimum down time for construction. as demonstrated by the performance of pre-stressed concrete girders. overloads and excess capacity. Fatigue problems are minimal because of minor stresses induced by traffic loads. xiii. ix. each selected only for the benefits it brings to get the job done.thaw and chloride resistance. Some engineers believe that this alone adds about 10 to 20% of the initial costs of a steel bridge over the period of its useful life. xi.prone details built in redundancy no special design. High strength pre-stressed concrete has excellent freeze. vii. Widely used and accepted: While pre-stressed concrete is a relatively new product the first use of pre-stressed concrete in US was in a bridge. • Reinforcing bars to further improve the long term quality of the concrete. Impacts local economy directly: 47 .Efficient material usage: Pre-stressed concrete is engineered high technology at its best. Inherently safe: Pre-stressed concrete has many things going for it no fatigue. Minimal maintenance: Of course no painting is needed. x. i. better deck durability because of reduced deflections. Pennsylvania today about a third of all bridges built use pre-stressed concrete beams. pre-stressed concrete members are particularly durable. Carefully planned details speed the total construction process and result in overall economy. Fires hot enough to consume metal bridge rails require only cosmetic repairs to a pre-stressed concrete bridge to its original condition. It is carefully designed using a variety of materials. xii. but also feel secure and comfortable on abridge that can hold vibrations to a minimum. viii. ii. viii. Most of its raw materials are also locally purchased and the health of the local pre-stressed concrete industry directly impacts further on the local economy. vii.Limited or partial pre-stressing: 48 . Magnel blaton & other systems. the commonly used anchorages are the Fressiynet. v. Tendon: A stretched element is used in a concrete member of structure to impart prestressed to concrete. cables are used as tendons. The tendons may be placed in the ducts formed in the concrete members or they may be placed outside the concrete section. High tensile steel wires. 7. Pre-tensioning: A method of pre-stressing concrete in which the tendons are tensioned before the concrete is placed.Pre-stressed concrete is produced by local small business employing local labor. iii. Non bonded pre-stressed concrete A method of construction in which the tendons are not bonded to the surrounding concrete. bars. Full pre-stressing: Pre-stressed concrete in which tensile stress in the concrete are entirely obviated at working loads by having sufficiently high pre-stress in the members. Bonded pre-stressed concrete: Concrete in which pre-stressed is imparted to concrete through bond between the tendons & surrounding concrete pre-tensioned members are belong to this group. Post tensioning: A method of pre-stressing concrete by tensioning tendons against hardened concrete. iv. Anchorage: A device generally used to enable the tendon to impart and maintained prestressed in the concrete.5 TERMINOLOGY: i. vi. While the curved portion is in tensile zone. Residential Concrete Magazine had a good. xv. “Guidelines for the selecting and strengthening Of Concrete Structures. The best review of this is available from the International Concrete Repair Institute (ICRI) . Debonding: Prevention of bond between the steel wires to its surrounding concrete. Moderate pre-stressing: In this type no limit is imposed upon the magnitude of tensile stress at working loads this form of construction is not really pre-stressed concrete but is to be regarded as reinforced concrete with reduced cracking and the section should be analyzed according to the rules of reinforced concrete as a case of bending combined with axial force.The degree of pre-stress applied to concrete in which tensile stress to a limited degree are permitted in concrete under working loads. A recently developed application of PT is external post-tensioning for strengthening of existing structures.6. xii. 2. Slabs on ground: Today.” 49 . Creep in concrete: Progressive increase in the inelastic deformation of concrete under sustained stress components. Jim Rogers. especially as an upgrade to resist seismic forces. Axial pre-stressing: A member in which entire cross section of concrete has a uniform compressive pre-stress in this type of pre-stressing the centroid of the tendons coincides with that of concrete section. Another good application for PT slabs is producing crack-free tennis courts. xiii. xi.Cap cable: A short curved tendon arranged at the interior supports of continuous beam. editor &publisher of the Post Tension Magazine.Degree of pre-stressing: A measure of the magnitude of the pre-stressing force related to the resultant stress occurring in the structural member at working load. says that until housing construction ground to a halt last year. Cracking load: The load on structural element corresponding to the first visible crack. xiv. 3. The anchorages are in compression zone. 7. x. PT is used extensively for slabs on grade where soils are likely to move especially in the American southwest. about half of all post-tensioning work was slabs on ground for homes. ix. APPLICATIONS: 1. 12. 5. b) Grade designation. 11. A good article on PT for masonry is available on Masonry Concrete Magazine. the following information should be included: a) Type of mix. Masonry walls can be post tensioned this is usually done with a solid steel fastened to the foundation and stressed with a nut the wall’s top. Pre-stressed concrete is the predominating material for floors in high rise buildings and concrete chambers in nuclear reactors. design mix concrete as nominal mix concrete.1. it can be used to temporarily repair a damaged building by holding up a damaged wall or floor until permanent repairs can be made. nominal size of e) Minimum cement content (for design mix concrete) f) Maximum water cement ratio. This enables the pipe to handle high internal pressures and the effects of external earth and traffic loads. that is. c) Type of cement d) Maximum aggregate. Also due to its ability to be stressed and then de-stressed.4. PT allows longer spans & keeps cracks tight. Bridge designers have used PT both for cast-in-place concrete and for precast segmental construction.1. 9. Pennsylvania. 8. 6. Concrete: In specifying a particular grade of concrete. 7. One interesting application is for a concrete countertop that needed to span 6feet and carry a heavy load. g) Workability 50 . Material to be used: 8. 10.1. High tensile strength steel wire is helically wrapped around the outside of the pipe under controlled tension and spacing which induces a circumferential compressive stress in the core concrete. The first pre-stressed concrete bridge in North America was Walnut Lane Memorial Bridge in Philadelphia. Unbounded post-tensioning tendons are commonly used in parking garages barrier cable. Concrete water tanks are often post-tensioned to crack width and leakage. MISCLANEOUS ITEMS OF WORK 8. 8. Pre-stressing can also be accomplished on circular concrete pipes used for water transmission. fcr = 0. 5. Fig 8.As guided by table No. 4 & 5 of IS-456:2000. k) Method of placing and l) Degree of supervision. The free water cement ratio is an important factor in governing the durability of concrete and should always be the lowest value.1 of IRS CBC) When the designer wishes to have an of the tensile strength from compressive strength. Cement content not including fly ash and ground granulated blast furnace slag in excess of 450 kg/m 3 should not be used unless special consideration has been given in design to the increased risk of cracking due to drying shrinkage in thin sections as to early thermal cracking and to the increased risk of damage due to alkali silica reactions.2. 51 estimate expression may be . j) Maximum temperature of concrete at the time of placing. the following used.7fck .h) Mix proportion (for nominal mix Fig8.2-fresh flowing concrete (Clause N0. The protection of the steel in concrete against corrosion depends upon an adequate thickness of good quality of concrete. of concrete i) Exposure conditions .1-Batching plant for weigh batching and mixing concrete). 1 IRC 78:2000) A 300mm thick plug of M-15 cement concrete shall be provided over the filling. 8. Under water concrete should have a very high degree of workability and confirm to IS: 9103.1. (Clause No.2.g. Concrete shall be laid in one continuous operation till dredge hole is filled to required height. e.4 of IS-456:2000) When it is necessary to deposit concrete under water. For under water concreting the concrete shall be placed gently by tremie boxes under still water condition and the cement contents of mix be increased by 10 percent. In case of plain concrete wells. concrete is used. equipment. 14. The mix used in bottom plug shall have a minimum cement content of 330 kg/m3 and a slump of about 150mm to permit easy flow of concrete through tremie to fill up all cavities. In case of marine or other similar conditions of adverse exposure. depending on the grade of concrete or the type of chemical attack.10. such as. the cement content shall be at least 350 kg/m3 of concrete. the grout mix shall not be leaner than 1:2 and it shall be ensured by suitable means. the concrete in the steining shall not be less than leaner than M-20 with cement not less than 310 kg/m3 of concrete and the water cement ratio not more than 0. controlling the rate of pumping that the grout fills up all interstices up to the top of the plug.2 & 14.6 and ma y need to be smaller. 708. If any dewatering is required it shall be carried out after 7 days have elapsed after bottom plugging. materials and proportions of the mix to be used shall be submitted to and approved by the engineer-in-charge before the work 52 .2 Under water concreting: (Clause N0.fcr is the flexural strength in N/mm2.45. the concrete mix for the steini ng shall not normally be leaner than M-15. and fck is the characteristic compressive strength of concrete in N/mm2. For aggregates of 40 mm maximum particle size. In case grouted concrete.The water cement ratio shall not exceed 0. the method. The well curb shall invariably be in reinforced concrete of mix not leaner than M-25. 1. Concrete shall be continuously until it is brought to the required height.2. the top surface shall be kept as nearly level as possible and the formation of seams avoided.started. The method to be used for depositing concrete under water shall be one of the following- 8. Concrete cast under water should not fall freely through the water.1.3-concreting using tremie pipes 53 . While Otherwise deposited depositing. it may be leached and become segregated. Tremie: Fig8. 2.2 Direct placement with pumps As in the case of tremie method. and thus avoid the formation of laitance layers.3 Drop bottom bucket 54 . Preferably. The concrete emerging from the pipe pushes the material that has already been placed to the side and upwards and thus does not come into direct contact. the lower end of the tremie pipe shall be below the top surface of the plastic concrete. This will cause to the concrete to build up from below instead of flowing out over the surface. thus establishing a continuous stream of concrete.1.2. At all times after the placing of concrete is started and until all the concrete is placed. it will be re-plugged at the top end. flanged steel pipe of adequate strength for the job should be used. so that when the concrete is forced down from the hopper to the pipe. A separate lifting device shall be provided for each tremie pipe with its hopper at the upper end. the vertical end piece of the pipe line is always inserted sufficiently deep into the previously cast concrete and should not move to the side during pumping. even if a partial vacuum develops inside the pipe. It will be necessary to raise slowly the tremie in order to cause a uniform flow of the concrete but the tremie shall not be emptied so that water enters the pipe. 8. It will force the plug (and along with it any water in the pipe) down the pipe and out of the bottom end. before refilling for depositing concrete.The concrete is placed through vertical pipes the lower end of which is always inserted sufficiently deep into the concrete which has been placed previously but has not set. if any. 8. the upper end of the pipe shall be plugged with a wedding of the gunny sacking or other approved material before delivering the concrete to the tremie pipe through the hopper. When concrete is to be deposited under water by means of tremie. Unless the lower end of the pipe is equipped with an approved automatic check valve. the top section of the tremie shall be a hopper large enough to hold one entire batch of the mix or the entire contents the transporting bucket. as at the beginning.1. the tremie shall be raised above the concrete surface and unless sealed by a check valve. The tremie pipe shall be not less than 200mm in diameter and shall be large enough to allow a free flow of concrete and strong enough to withstand the external pressure of the water in which it is suspended. If the change in the tremie is lost while depositing. 2 percent (for either mild steel as deformed bars) of the actual gross section area of the steining. 708.3.4-reinforcement provided to well staining without suffering any damage. The bottom door shall not be opened until the bucket rest on the surface upon which the concrete is to be deposited and when discharged. The well curb shall invariably be in R. (ClauseNo.2 Steel: (Clause No.4 IRC 78:2000) In case blasting is anticipated. The vertical reinforcements shall be tied up with hoop steel not less than 0. shall be withdrawn slowly until well above the concrete. The bucket shall be filled completely and lowered slowly to avoid backwash. on the inner face. a minimum of 0.708. For sinking through rock cutting edge should be suitably designed. vertical reinforcements (whether mild steel or deformed bars) in the steining shall not be less than 0. The steel shall be suitably arranged to prevent spreading and splitting of the curb during sinking and in service.The top of the bucket shall be covered with a canvas flap. it shall be considered as a column section subjected to combined axial load and bending.5IRC78:2000) In case where the well steining is designed as a reinforced concrete element. (Clause No.04 percent of the volume per unit length of the steining.06 percent of gross area steel shall be provided. the amount of vertical reinforcement provided in the steining shall not be less than 0. The mild steel cutting edge shall be facilitate sinking of the well strong enough and not less than 40 kg/m to through the types of strata expected to be encountered Fig8. 708. of mix not leaner than M-25 with minimum reinforcement of 72 kg/m3 excluding bond rods.3. The transverse reinforcement in the steining shall be provided in accordance with the provisions for a column but in no case shall be less than 0. The bottom doors shall open freely downward and outward when tripped. the inner faces of the well curb shall be protected with steel plates of thickness not 55 less than 10mm upto the top .4 IRC 78:2000) for plain concrete wells. It shall be properly anchored to the well curb.12 per cent of gross sectional area of the actual thickness provided. 8.04% of the volume per unit length of the steining. This shall be equally distributed on both faces of steining. However.C.7. The material concrete itself has changed a lot much. If the diaphragms are very wide/thick. In case of box structures. Fig8. provision of future prestressing arrangement is necessary and should be obligatory. holes are kept in the end diaphragms at top portion. For prestressed structure. Such arrangement should be for imparting about 20 % of the prestressing force originally applied. ii) When the reinforcement ratio is very high. iii) It allows to give concrete structure more complex shapes. suitable arrangement for external prestressing should be decided at design stage. Three main reasons for this are i) Placing is easier.3 FUTURE PRESTRESSING ARRANGEMENTS In case of prestressed concrete structures.5-Bluster blocks for future pre stressing 8. It is preferable to get the cable profile approved before approving the superstructure drawing. when shape does not allow for easy vibration or When there is no access in some zones-or of segregation is more limited than with traditional concrete. of course with some variation adopted to different possible applications. More and more use of high performance concrete (HPC) with characteristic strength ranging from 60 MPa to 80 MPa is being used world over.of well curb. a serious advantage when Considering some tendencies of modern architecture. We have to evoke very high performance fiber concretes. Self placing concrete which is a rather recent development is more and more preferred to classical concrete. which have been developed by 56 . allows for reducing equipment and man power and finally produces Financial benefits. Major goal of specifying HPC is drastic increase of durability and a large compactness which comes with a high concrete strength is the best solution to limit penetration of corrosive agents like chlorides. Concrete can practically be designed for many different applications. Until recently structural concrete was considered as a unique material. The reason for using high performance concrete is to increase concrete strength driving important normal and bending forces. Classical structural concrete has a characteristic strength ranging up to 50 MPa (500 kg/cm2).4 HIGH PERFORMANCE CONCRETE The last 10 or 20 years have seen an important evolution in materials and construction. If intermediate diaphragms are provided then holes should be left in these also keeping in view the alignment of external cables. 8. then holes should be rectangular in size to adjust the profile of alignment. located in severe/saline exposure conditions. Adequate care. Some structures have already been built in the world with such materials. At places the atmosphere may itself be corrosive due to heavy chemical industrialization. The anticorrosive treatment is required to be applied to concrete and reinforcement steel in case of saline and severe exposure conditions.7-Reinforcement bars with CPCC coating GALVANISATION: Recently galvanization to reinforcing bars is also considered as an alternative 57 . steel gets corroded due to electro-chemical action.R.Some companies with a characteristic Fig8. therefore.5 ANTI CORROSIVE TREATMENT Due to saline atmosphere.C. The anchorage / bond length in Case of FBEC Bars shall be increased by 50 % of normal values specified in I. The bridges lying in coastal area are most affected by corrosion. REINFORCEMENT: Anticorrosive treatment to reinforcing steel shall be CPCC (Cement Polymer Composite Coating) developed by Karaikudi or FBEC (Fusion Bonded Epoxy Coating). 8. Fig8. Not only the reinforcing steel but also the standards/wires used for prestressing gets corroded. The channel may also carry waste produce from the industries. The concrete and steel have to be provided with some anticorrosive treatment. which may lead to corrosion.6-Anti corrosive treatment strength ranging from150 to 200 MPa. need to taken to protect the bridge structure from this dangerous phenomenon. for commencement of erection / launching of the pre-cast PSC girders. Over mild steel liner to piles : One coat of zinc rich epoxy primer and two coats of coal tar epoxy to the outside surface. The first span girders (2 No’s) are lead into the span with the help of launching truss lowered on to the bed block and temporarily placed and secured properly. 8. 58 . + 0.anticorrosive Treatment CONCRETE SURFACE: A. 2 . for leading girders to further spans which are moved by trolleys running on temporary track over these girders. In case of deck / girder / box epoxy based paint with one coat of primer and further two coats are applied. The two outer girders.F. 4. C. 3.6 ERECTION SCHEME OF GIRDERS: 1. In case of parapets water proof cement based paint in three coats is applied. The girders already placed in span 1 can now be moved laterally to a desired location for providing a temporary track over these girders. In case of part of substructure exposed to atmosphere water proof cement paint. In case of part of substructure in contact with earth and upto H. since the launching truss is already in position over the first and second span.T. E. for commencing launching of girders. The piers and bed blocks must be completed in all respects from one and of the bridge.A two spans continuous launching truss may be used to span across the first two spans of the bridge.9 m or H. The launching truss can now move towards to occupy span numbers 2 and 3. Cement Polymer Composite Coating is used in our site as anti corrosive treatment for reinforcement. B. D. whichever is higher one coat of primer and two coats of coal tar epoxy. of the first span of bridge can be lead by moving the girders on a temporary rail track up to the launching truss (behind abutment) and then through the help of launching truss. they can be moved further into the first span location .L. 5.L. they are side shifted to their final positions and then the in-situ portion of the diaphragms shall be concreted in the first stage. The central girder of each of the spans is now brought with the help of trolley running over the temporary track. The girders are carried further into the second span with the help of launching truss for leading and lowering of the girders in the second span. 59 . 7. 9. The PSC girder shall be lifted only at the end diaphragm locations and from no other intermediate locations. The two outer girders of the second span can now be brought over the temporary track laid over the girders of the first span already erected.8(a)-Erection of girders using launching trusses Fig 8. 8. this sequence can continue until two girders in all spans are erected.Fig8. The deck slab shall be concreted in the second stage to complete the structural work of superstructure. and lowered into the span. After all three girders of each span are brought into the span. Now the launching truss can be moved further into 3 rd and 4th spans.8(b)-Erection of girders using launching trusses 6. 10. Conclusion: The project created awareness about the construction process of precasting of concrete elements. 60 . prestressing techniques and launching of the pre cast girders in their respective positions. The difficulties in the actual construction of well foundations are studied. The design methodologies adopted in actual field and the importance of detailed drawings are understood. Photo gallery 61 . 62 63 64 65 . New Delhi. Standard specifications and Code of practice for road bridges. 9 Bahadur Shah Zafar Marg. 4.110 011. 6. Lucknow. Bridge Engineering by Ponnuswamy.References 1.Concrete Bridge Code. New Delhi110 002. Lucknow-226 011. 66 . Shahjahan Road. Manak Bhawan. 2. IRS Code of Practice for the design of Sub-structures and Foundations of Bridges. Design of bridges by N.Plain and Reinforces Concrete Code of Practice (Fourth Revision) Bureau of Indian Standards.226011. 3.Krishna Raju.IS-456:2000. Foundation and Substructure (Second Revision). Jamnagar House. Reinforced and Prestressed Concrete for General Bridge Construction. RDSO. 5. RDSO. Section-VII.IRS Code of Practice Plain.The India Road Congress. IRC: 78-2000. 67 .