Presentation on theme: "1. By Dr. Attaullah Shah Swedish College of Engineering and Technology Wah Cantt. CE-407 Lec-04 Structural Engineering Bridges-II ( ACI."— Presentation transcript:
By Dr. Attaullah Shah Swedish College of Engineering and Technology Wah Cantt. CE-407 Lec-04 Structural Engineering Bridges-II ( ACI
Elevation and cross section of Bridges
Arch and suspension Bridges
Some important definitions
700 A.D. Asia 1,304 years ago 100 B.C. Romans 2,104 years ago Clapper Bridge Tree trunk Stone Arch design evenly distributes stresses Natural concrete made from mud and straw Roman Arch Bridge History of Bridge Development Great Stone Bridge in China Low bridge Shallow arch Allows boats and water to pass through
History of Bridge Development Truss Bridges Mechanics of Design Wood Suspension Bridges Use of steel in suspending cables 1900 1920 Prestressed Concrete Steel 2000
Compression Tension Basic Concepts Span - the distance between two bridge supports, whether they are columns, towers or the wall of a canyon. Compression – Tension - Force - Concrete has good compressive strength, but extremely weak tensile strength. What about steel cables?
Basic Concepts Beam - a rigid, usually horizontal, structural element Pier - a vertical supporting structure, such as a pillar Cantilever - a projecting structure supported only at one end, like a shelf bracket or a diving board Beam Pier Load - weight on a structure
The type of bridge used depends on the obstacle. The main feature that controls the bridge type is the size of the obstacle. Types of Bridges Basic Types: Truss Bridge Beam Bridge Arch Bridge Suspension Bridge Floating Bridge TrussBeamArch Suspension Floating
Truss Bridge All 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.
Types of Bridges Beam 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.
Forces When something pushes down on the beam, the beam bends. Its top edge is pushed together, and its bottom edge is pulled apart. Types of Bridges Beam Bridge
Arch Bridges The 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 Bridges
Forces The 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 Bridges Arch Bridges
Suspension Bridges This 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
Forces In 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 Bridges Suspension Bridges
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. Types of Bridges Floating Bridge
Floating Bridges Retractable! But high maintenance!
How do the following affect your structure? Ground below bridge Loads Materials Shapes Bridge Engineering
Some Uses of Bridges −Walkways −Highways/Roads −Railways −Pipelines −Connecting lands −Crossing rivers and canyons
Types of Bridges −Arch −Truss −Cantilever −Cable-Stayed −Suspension
What makes a bridge stay up? −Forces −Compression – a pushing or squeezing force −Tension – a pulling or stretching force
Arch Bridges −Keystone – the wedge- shaped stone of an arch that locks its parts together −Abutments – the structures that support the ends of the bridge
Arch Bridges −Works by Compression
Arch Bridges −Where have you seen these bridges?
Cold Spring Arch Bridge, Santa Barbara, CA
Marsh Rainbow Arch, Riverton, KS
Pont du Gard, Nimes, France
Cable-Stayed Bridges −Piers – the vertical supporting structures −Cables – thick steel ropes from which the decking is suspended −Decking – the supported roadway on a bridge
Cable-Stayed Bridges −Works by Tension AND Compression
Cable-Stayed Bridges −Where have you seen these bridges?
Zakim Bridge, Boston, MA
Sunshine Skyway Bridge, Tampa, FL
Sundial Bridge, Redding, CA
Suspension Bridges −Similar to Cable-Stayed −Different construction method
Suspension Bridges −Works by Tension and Compression
Suspension Bridges −Where have you seen these bridges?
Golden Gate Bridge, San Francisco, CA
Brooklyn Bridge, Brooklyn, NY
Verrazano-Narrows Bridge, New York, NY
Other Types Truss Southern Pacific Railroad Bridge, Tempe, AZ Cantilever Firth of Forth-Forth Rail Bridge, Edinburgh, Scotland
FUNCTION OF A BRIDGE To connect two communities which are separated by streams, valley, railroads, etc. Replaces a slow ferry Replaces a slow ferry boat trip boat trip Connects two continent Connects two continent Built in 1973 Built in 1973 Total length is 5000 ft Total length is 5000 ft Bosporus Straits Bridge at Istanbul, Turkey –
COMPONENTS OF A BRIDGE Deck or Slab: supported roadway on abridge Deck or Slab: supported roadway on abridge Beam or Girder: A rigid, usually horizontal, Beam or Girder: A rigid, usually horizontal, structural element structural element Abutment: The outermost end supports on a Abutment: The outermost end supports on a bridge, which carry the load from bridge, which carry the load from the deck the deck Pier: A vertical supporting structure, such as a Pier: A vertical supporting structure, such as a pillar pillar Foundation Foundation
Deck Girder Abutment Pier COMPONENTS OF A BRIDGE
TYPES OF BRIDGES Beam or Girder BridgeBeam or Girder Bridge Truss BridgeTruss Bridge Rigid Frame BridgeRigid Frame Bridge Arch BridgeArch Bridge Cable Stayed BridgeCable Stayed Bridge Suspension BridgeSuspension Bridge
GIRDER BRIDGE Chesapeake Bay Bridge, Virginia Typical span length 30 to 650 ft World’s longest: Ponte Costa e Silva, Brazil with a center span of 1000 ft
TRUSS BRIDGE Firth of Forth Bridge, Scotland Typical span length 150 to 1500 ft World’s longest: Pont de Quebec, Canada with a center span of 1800 ft
RIGID FRAME BRIDGE Girders and piers act togetherGirders and piers act together Cross-sections are usually I-shaped or box-shaped.Cross-sections are usually I-shaped or box-shaped. Design calculations for rigidDesign calculations for rigid frame bridges are more frame bridges are more difficult than those of simple difficult than those of simple girder bridges. girder bridges.
ARCH BRIDGE After girders, arches are the second oldest bridge type. After girders, arches are the second oldest bridge type. Arches are good choices for crossing valleys and rivers Arches are good choices for crossing valleys and rivers Arches can be one of Arches can be one of the more beautiful the more beautiful bridge types. bridge types. Typical span length Typical span length 130 ft – 500 ft. 130 ft – 500 ft. World’s longest: World’s longest: New River Gorge Bridge, U.S.A. with a center span of New River Gorge Bridge, U.S.A. with a center span of 1700 ft. 1700 ft. Larimer Avenue Bridge, Pittsburgh
CABLE STAYED BRIDGE Normandie Bridge Continuous girder with Continuous girder with one or more towers one or more towers erected above in the erected above in the middle of the span. middle of the span. From these towers From these towers cables stretch down cables stretch down diagonally and support diagonally and support the girder. the girder. Typical span length Typical span length 350 to 1600 ft. 350 to 1600 ft. World’s largest bridge: World’s largest bridge: Tatara Bridge, Japan Tatara Bridge, Japan center span: 2900 ft. center span: 2900 ft.
SUSPENSION BRIDGE Continuous girder with one or more towers erected above in the middle of the span. Continuous 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. At both ends of the bridge, large anchors or counter weights are placed to hold the ends of the cables. Typical span length Typical span length 250 to 3000 ft. 250 to 3000 ft. Golden Gate Bridge, California
Factors 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 the structure (deck, through) Form (beam, arch, truss, etc.).
LOADS 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 and pedestrian traffic - lateral loads due to water and wind, ice floes, ship collision, earthquake, etc.
VEHICULAR DESIGN LOADS (HL 93) AASHTO – American Association of State Highway and Transportation Officials This model consists of: Design Truck Design Tandem Design Lane
145 kN 35 kN 4.3 to 9.0 m4.3 m 9.3 N/m DESIGN TRUCK
110 kN 9.3 N/m 1.2 m DESIGN TANDEM
DESIGN PRINCIPLES Resistance ≥ effect of the applied loads Strength of the Member ≥ Factor of Safety x Applied Load Allowable Stress Design (ASD): Load and Resistance Factor Design (LRFD): η ∑γ i Q i ≤ φ i R n Where, Q i = Effect of loads R n = Nominal resistance γ i = Statistically based resistance factor applied to the force effects φ i = Statistically based resistance factor applied to the nominal resistance η = Load modification factor
MATERIALS FOR BRIDGES Concrete Steel Wood
CONCRETE BRIDGES Raw materials of concrete: cement, fine aggregate coarse aggregate, water Easily available can be designed to satisfy almost any geometric alignment, straight to curved can be cast-in-place or precast Compressive strength of concrete range from 5000 psi to 8500 psi Reinforced concrete and prestressed concrete
STEEL BRIDGES Minimum construction depth Rapid construction Steel can be formed into any shape or form Predictable life Ease of repair and demolition
WOOD BRIDGES Convenient shipping to the job site Relatively light, lowering transportation and initial construction cost Light, can be handled with smaller construction equipment Approx. 12% of the bridges in US are wood bridges Commonly used for 20-80 ft span
Wood Bridge on Concrete Abutments Three Span Wood Bridge
GIRDER CROSS-SECTIONS COMMONLY USED IN BRIDGES
COLLAPSE OF BRIDGES Poor design Inadequate stability of the foundation Fatigue cracking Wind forces Scour of footing Earthquake