20Great Stone Bridge in China History of Bridge Development100 B.C. Romans2,104 years ago700 A.D. Asia1,304 years agoClapper BridgeRoman Arch BridgeTree trunkStoneArch designevenly distributesstressesNatural concretemade from mudand strawClapper Bridges employed all over the world, most notably in England. Originally, tree logs used, but they tended to rot. Stones were better, but difficult to maneuver. The Romans developed highways that connected the empire. Bridges helped them do this.Great Stone Bridge in ChinaLow bridgeShallow archAllows boatsand water to passthrough
21History of Bridge Development 19001920Truss BridgesMechanics of DesignWood2000Suspension BridgesUse of steel in suspending cablesPrestressed ConcreteSteel
22Basic ConceptsSpan - the distance between two bridge supports, whether they are columns, towers or the wall of a canyon.Force -CompressionTensionCompression –Tension -Concrete has good compressive strength, but extremely weak tensile strength. What about steel cables?
23Basic Concepts Beam - a rigid, usually horizontal, structural element PierPier - a vertical supporting structure, such as a pillarCantilever - a projecting structure supported only at one end, like a shelf bracket or a diving boardLoad - weight on a structure
24Types of BridgesBasic Types:Truss BridgeBeam BridgeArch BridgeSuspension BridgeFloating BridgeFloatingTrussBeamArchSuspensionThe type of bridge used depends on the obstacle. The main feature that controls the bridge type is the size of the obstacle.
25Truss BridgeTypical 40m to 500mAll beams in a truss bridge are straight. Trusses are comprised of many small beams that together can support a large amount of weight and span great distances.
26Types of BridgesBeam BridgeConsists 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.
27Types of Bridges Forces Beam BridgeForcesWhen something pushes down on the beam, the beam bends. Its top edge is pushed together, and its bottom edge is pulled apart.
28Types 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.
29Types of Bridges Forces Arch 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.
30Types of 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.
31Types of Bridges Forces Suspension BridgesForcesIn 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.
32Types of Bridges Floating Bridge Pontoon bridges are supported by floating pontoons with sufficient buoyancy to support the bridge and dynamic loads.While pontoon bridges are usually temporary structures, some are used for long periods of time.Permanent floating bridges are useful for traversing features lacking strong bedrock for traditional piers.Such bridges can require a section that is elevated, or can be raised or removed, to allow ships to pass.
33Floating BridgesRetractable!But high maintenance!
34Ground below bridge Loads Materials Shapes Bridge Engineering How do the following affect your structure?Ground below bridgeLoadsMaterialsShapes
35Some Uses of Bridges Walkways Highways/Roads Railways Pipelines Connecting landsCrossing rivers and canyons
36Types of BridgesArchTrussCantileverCable-StayedSuspension
62Other Types Truss Southern Pacific Railroad Bridge, Tempe, AZ CantileverFirth of Forth-Forth Rail Bridge, Edinburgh, Scotland
63FUNCTION OF A BRIDGEBosporus Straits Bridgeat Istanbul, Turkey –To connect two communities which are separated by streams, valley, railroads, etc.Replaces a slow ferryboat tripConnects two continentBuilt in 1973Total length is 5000 ft
64COMPONENTS OF A BRIDGE Deck or Slab: supported roadway on abridge Beam or Girder: A rigid, usually horizontal,structural elementAbutment: The outermost end supports on abridge, which carry the load fromthe deckPier: A vertical supporting structure, such as apillarFoundation
66TYPES OF BRIDGES Beam or Girder Bridge Truss Bridge Rigid Frame Bridge Arch BridgeCable Stayed BridgeSuspension Bridge
67Chesapeake Bay Bridge, Virginia GIRDER BRIDGETypical span length 30 to650 ftWorld’s longest: Ponte Costae Silva, Brazil with a centerspan of 1000 ftChesapeake Bay Bridge, Virginia
68Firth of Forth Bridge, Scotland TRUSS BRIDGETypical span length150 to 1500 ftWorld’s longest:Pont de Quebec, Canadawith a center span of1800 ftFirth of Forth Bridge, Scotland
69RIGID FRAME BRIDGE Girders and piers act together Cross-sections are usually I-shaped or box-shaped.Design calculations for rigidframe bridges are moredifficult than those of simplegirder bridges.
70ARCH BRIDGE Larimer Avenue Bridge, Pittsburgh After girders, arches are the second oldest bridge type.Arches are good choices for crossing valleys and riversArches can be one ofthe more beautifulbridge types.Typical span length130 ft – 500 ft.World’s longest:New River Gorge Bridge, U.S.A. with a center span of1700 ft.Larimer Avenue Bridge, Pittsburgh
71CABLE STAYED BRIDGE Continuous girder with one or more towers erected above in themiddle of the span.From these towerscables stretch downdiagonally and supportthe girder.Typical span length350 to 1600 ft.World’s largest bridge:Tatara Bridge, Japancenter span: 2900 ft.Normandie Bridge
72Golden Gate Bridge, California SUSPENSION BRIDGEContinuous girder with one or more towers erected above in the middle of the span.At both ends of the bridge, large anchors or counter weights are placed to hold the ends of the cables.Typical span length250 to 3000 ft.Golden Gate Bridge, California
73Factors Describe a Bridge Four main factors are used in describing a bridge:Span (simple, continuous, cantilever)Material (stone, concrete, metal, etc.)Placement of the travel surface in relation to thestructure (deck, through)Form (beam, arch, truss, etc.).
75LOADS ON BRIDGES Permanent Loads: remain on the bridge for an extended period of time (self weight of the bridge)Transient Loads: loads which are not permanent- gravity loads due to vehicular, railway andpedestrian traffic- lateral loads due to water and wind, ice floes,ship collision, earthquake, etc.
76VEHICULAR DESIGN LOADS (HL 93) AASHTO – American Association of State Highwayand Transportation OfficialsThis model consists of:Design TruckDesign TandemDesign Lane
77DESIGN TRUCK145 kN35 kN4.3 to 9.0 m4.3 m9.3 N/mDESIGN TRUCK
79DESIGN PRINCIPLES Resistance ≥ effect of the applied loads Strength of the Member ≥ Factor of Safety x Applied LoadAllowable Stress Design (ASD):Load and Resistance Factor Design (LRFD):η ∑γiQi ≤ φi RnWhere, Qi = Effect of loadsRn = Nominal resistanceγi = Statistically based resistance factorapplied to the force effectsφi = Statistically based resistance factor applied tothe nominal resistanceη = Load modification factor
81CONCRETE BRIDGESRaw materials of concrete: cement, fineaggregate coarse aggregate, waterEasily availablecan be designed to satisfy almost any geometricalignment, straight to curvedcan be cast-in-place or precastCompressive strength of concrete range from5000 psi to 8500 psiReinforced concrete and prestressed concrete
82STEEL BRIDGES Minimum construction depth Rapid construction Steel can be formed into any shape or formPredictable lifeEase of repair and demolition
83WOOD BRIDGES Convenient shipping to the job site Relatively light, lowering transportation and initialconstruction costLight, can be handled with smaller constructionequipmentApprox. 12% of the bridges in US are wood bridgesCommonly used for ft span
84Wood Bridge on Concrete Abutments Three Span Wood Bridge