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Bridge structureByDINESH

700 A.D. Asia100 B.C. RomansNatural Bridges

Clapper BridgeTree trunkStoneThe ArchNatural Cement

Roman Arch BridgeHistory of Bridge Development

Great Stone Bridge in ChinaLow BridgeShallow Arch1300 A.D. RenaissanceStrength of MaterialsMathematical TheoriesDevelopment of MetalFirst Cast-Iron BridgeCoalbrookdale, England

1800 A.D.History of Bridge Development

Britannia Tubular Bridge1850 A.D.Wrought IronTruss BridgesMechanics of Design

Suspension BridgesUse of Steel for the suspending cables

1900 A.D.1920 A.D.Prestressed ConcreteSteel2000 A.D.

Every passing vehicle shakes the bridge up and down, making waves that can travel at hundreds of kilometers per hour. Luckily the bridge is designed to damp them out, just as it is designed to ignore the efforts of the wind to turn it into a giant harp. A bridge is not a dead mass of metal and concrete: it has a life of its own, and understanding its movements is as important as understanding the static forces.How Bridges Work?

CompressionTensionBasic Concepts Span - the distance between two bridge supports, whether they are columns, towers or the wall of a canyon. Compression - a force which acts to compress or shorten the thing it is acting on.Tension - a force which acts to expand or lengthen the thing it is acting on.

Force - any action that tends to maintain or alter the position of a structureBasic Concepts Beam - a rigid, usually horizontal, structural elementPier - a vertical supporting structure, such as a pillarCantilever - a projecting structure supported only at one end, like a shelf bracket or a diving boardBeamPierLoad - weight distribution throughout a structureBasic Concepts Truss - a rigid frame composed of short, straight pieces joined to form a series of triangles or other stable shapesStable - (adj.) ability to resist collapse and deformation; stability (n.) characteristic of a structure that is able to carry a realistic load without collapsing or deforming significantlyDeform - to change shape

To dissipate forces is to spread them out over a greater area, so that no one spot has to bear the brunt of the concentrated force. To transfer forces is to move the forces from an area of weakness to an area of strength, an area designed to handle the forces.Basic Concepts Buckling is what happens when the force of compression overcomes an object's ability to handle compression. A mode of failure characterized generally by an unstable lateral deflection due to compressive action on the structural element involved.Snapping is what happens when tension overcomes an object's ability to handle tension.Loads consideredLoads considered Indian road congress bridge loadingIRC class AA loading(tracked-700 and wheeled)IRC class 70R loading loading (tracked-700 and wheeled)IRC class A loading (tracked-114 and wheeled)IRC class B loading (tracked-332 and wheeled)

British standard loadingHA type of loading- UDL + Knife edge loadingHB type of loading -1800kN

AASHTO (American Association of state highway transport officials) loading-320.3kN

Impact factorAccording to Indian standardsI = A/(B+L)WhereI= Impact factorA & B are constantL= Span in metresAccording to British standardsAn impact allowance of 25% has been provided for HA loading and No impact factor for HB loading is given.According to AASHTO loadingImpact allowance = 50/(L+25)Dispersion of loading

TYPES OF BRIDGESTypes of BridgesBeam Bridge

Consists of a horizontal beam supported at each end by piers. The weight of the beam pushes straight down on the piers. The farther apart its piers, the weaker the beam becomes. This is why beam bridges rarely span more than 250 feet.

ForcesWhen something pushes down on the beam, the beam bends. Its top edge is pushed together, and its bottom edge is pulled apart.Types of BridgesBeam BridgeTruss Bridge

ForcesEvery bar in this cantilever bridge experiences either a pushing or pulling force. The bars rarely bend. This is why cantilever bridges can span farther than beam bridges

Types of BridgesArch BridgesThe arch has great natural strength. Thousands of years ago, Romans built arches out of stone. Today, most arch bridges are made of steel or concrete, and they can span up to 800 feet.

Types of BridgesForcesThe arch is squeezed together, and this squeezing force is carried outward along the curve to the supports at each end. The supports, called abutments, push back on the arch and prevent the ends of the arch from spreading apart.

Types of BridgesArch BridgesSuspension BridgesThis kind of bridges can span 2,000 to 7,000 feet -- way farther than any other type of bridge! Most suspension bridges have a truss system beneath the roadway to resist bending and twisting.Types of Bridges

ForcesIn all suspension bridges, the roadway hangs from massive steel cables, which are draped over two towers and secured into solid concrete blocks, called anchorages, on both ends of the bridge. The cars push down on the roadway, but because the roadway is suspended, the cables transfer the load into compression in the two towers. The two towers support most of the bridge's weight.Types of BridgesSuspension Bridges

The cable-stayed bridge, like the suspension bridge, supports the roadway with massive steel cables, but in a different way. The cables run directly from the roadway up to a tower, forming a unique "A" shape. Cable-stayed bridges are becoming the most popular bridges for medium-length spans (between 500 and 3,000 feet).Types of BridgesCable-Stayed Bridge

Pythagorean TheoremBasic math and science conceptsBridge Engineeringagbacb c2=b2+a2 a+b+g=180Basic math and science conceptsBridge EngineeringFundamentals of StaticsSFy = R1+R2-P = 0SFx = 0FR1R2xy

Basic math and science conceptsBridge EngineeringFundamentals of Mechanics of MaterialsModulus of Elasticity (E):EesE=StressStrainF/ADL/Lo=Where:F = Longitudinal ForceA = Cross-sectional AreaDL = ElongationLo = Original LengthLoFFTo design a bridge like you need to take into account the many forces acting on it :The pull of the earth on every partThe ground pushing up the supports The resistance of the ground to the pull of the cablesThe weight of every vehicleThen there is the drag and lift produced by the windThe turbulence as the air rushes past the towersBasic conceptsBridge EngineeringTruss AnalysisBridge EngineeringStructural Stability FormulaK = 2J - RWhere:K = The unknown to be solvedJ = Number of JointsM = Number of MembersR = 3 (number of sides of a triangle)K Results Analysis: If M = K Stable Design If M < K Unstable Design If M > K Indeterminate DesignTruss AnalysisBridge EngineeringStructural Stability Formula (Example)JointsJ=9MembersM=15K = 2 (9) 3 = 1515 = M = K then The design is stable

http://www.jhu.edu/virtlab/bridge/truss.htmWest Point Bridge Software:http://bridgecontest.usma.edu/Bridge EngineeringTruss AnalysisTips for building a bridge1. Commitment - Dedication and attention to details. Be sure you understand the event rules before designing your prototype.Draw your preliminary design ALL joints should have absolutely flush surfaces before applying glue. Glue is not a "gap filler", it dooms the structure! Structures are symmetric. Most competitions require these structures to be weighed. Up to 20% of the structure's mass may be from over gluing.Stresses flow like water. Where members come together there are stress concentrations that can destroy your structure. Here is a connection detail of one of the spaghetti bridges.

The Importance of ConnectionsTacoma Narrows Failure

Prestressed ConcretePrestressed concrete is basically concrete in which internal stresses of asuitable magnitude and distribution are introduced so that the stressesresulting from external loads are counteracted to a desired degree.

Concrete is strong in compression but weak in tension. The tensile strengthof concrete is about one-tenth of its compressive strength. Since concrete isweak in tension, an R.C.C beam at times develops minute cracks in concreteon tension side of the beam, even when the stress developed in tensile steelis much less than its permissible value.Prestressing has two types:-Pre-tensioning.Post-tensioning.

Pre-tensioning:In the pretensioning the tendons are first tensioned between rigid anchorblocks cast on the ground or in a column or unit mould type tensioning bed,prior to the casting of concrete in the moulds. The tendons comprisingindividual wires or strands are stretched with constant or variableeccentricity with tendon anchorage at one end and jacks at the other end.With the forms in place, the concrete is cast around the stressed tendon.

Post-tensioning: In post tensioning the concrete units are first cast by incorporating ducts orgrooves to house the tendons. When the concrete attains sufficient strength,the high tensile wires are tensioned by means of means of jack bearing onthe end face of the member and anchored by wedges or nutsPrestressed concrete deckPrestressed concrete bridges areHigh strength concreteHigh tensile steelThey are Class I type without any tensile stresses under service load resulting in crack free structure.It Is suited for composite bridges also(precast pretensioned girder and casit in situ deck)

Post tension concrete deckPostensioning bridge decks are adopted for longer spans exceeding 20mIn Post tensioning curved cables are used to improve the shear resistance of the cable.

Methodology for pre-tensioning of the I-girder:

Laying of cablesPVC pipes are used for debonding of the cables.Cables are locked using the wedges and barrels. These wedges and barrels provide such arrangement that cable can come out of it, but cant go back.Stressing

Monostrand hydraulic jackCables Wedges and barrelsPrestressing pumpBox GirderI-girders can be used only for the spans smaller than 20-25 m or which arenot curved. For curved spans and spans which are greater than 20-25 m, boxgirders are used.

Cross-section of the box girder near the support

Design of GirderELEVATION

PRE-TENSIONED I-GIRDERS

ELEVATION

SECTION AT SUPPORTS (Y-Y)

SECTION AT CENTRE(Z-Z)

AREA -463125mm2 AREA -570069.44mm2

CLASS-A MOST ECCENTRICCLASS-A SYMMETRIC TO G2CLASS-A TWO LANECLASS 70R MOST ECCENTRICGRID IDEALISATION

Bandra worli sea linkExpress Highway and Swami Vivekanand road at Bandra and connects to Worli at Worli end with overall length of 5.6 kms for the entire project.

PARTIALLY PRECAST DECK PANNELPartially precast deck panelFor the purpose of deck cant be constructed above the sea and also in the portion of jetty Partially cast in situ and partially precastCan be used instead of scaffolding.

Design of precast deck panelLoadsOnly dead load and SIDL is considered(DL+SIDL)Considering only depth of precast deck panel aloneConsidering only self weight of deck as Uniformly distributed load

Design of cast in situ deck Both Dead load and live load are considered(DL+LL)Considering full depth of the deckDesign by using Strut and Tie

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