1. by dr. attaullah shah swedish college of engineering and technology wah cantt. ce-407 lec-04...

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

Bridges

700 A.D. Asia700 A.D. Asia

1,304 years 1,304 years agoago

100 B.C. Romans100 B.C. Romans2,104 years ago2,104 years ago

Clapper Bridge

Tree trunkStone

Arch design evenly distributesstressesNatural concrete made from mud and straw

Roman Arch Bridge

History of Bridge DevelopmentHistory of Bridge Development

Great Stone Bridge in China

Low bridgeShallow archAllows boatsand water to passthrough

History of Bridge DevelopmentHistory of Bridge Development

Truss Bridges

Mechanics of DesignWood

Suspension Bridges

Use of steel in suspending cables

1900 1900

1920 1920

Prestressed ConcreteSteel

2000 2000

Compression Tension

Basic Concepts 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 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 BridgesTypes of BridgesBasic Types:

•Truss Bridge•Beam Bridge•Arch Bridge•Suspension Bridge•Floating Bridge

Truss Beam ArchSuspension

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 BridgesTypes of Bridges

Beam BridgeBeam 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.


Beam BridgeBeam Bridge

Arch BridgesArch 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.


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.


Arch BridgesArch Bridges

Suspension BridgesSuspension 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.


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.


Suspension BridgesSuspension 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.


Floating BridgeFloating Bridge

Floating Bridges

Retractable!

But high maintenance!

How do the following affect your structure?Ground below bridgeLoadsMaterialsShapes

Bridge Bridge Engineering 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


− Works by Tension AND Compression

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


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 BRIDGEFUNCTION OF A BRIDGE

To connect two communities which are To connect two communities which are separated by streams, valley, railroads, separated by streams, valley, railroads, etc.etc.

• Replaces a slow ferry Replaces a slow ferry boat tripboat trip• Connects two continentConnects two continent• Built in 1973Built in 1973• Total length is 5000 ftTotal length is 5000 ft

Bosporus Straits Bridge Bosporus Straits Bridge at Istanbul, Turkey –at Istanbul, Turkey –

COMPONENTS OF A BRIDGECOMPONENTS OF A BRIDGE

• Deck or Slab:Deck or Slab: supported roadway on abridge supported roadway on abridge

• Beam or Girder:Beam or Girder: A rigid, usually horizontal, A rigid, usually horizontal, structural elementstructural element

• Abutment:Abutment: The outermost end supports on a The outermost end supports on a bridge, which carry the load from bridge, which carry the load from the deckthe deck

• Pier:Pier: A vertical supporting structure, such as a A vertical supporting structure, such as a pillarpillar

• FoundationFoundation

DeckDeck

GirderGirder

AbutmentAbutment

PierPier

COMPONENTS OF A BRIDGECOMPONENTS OF A BRIDGE

TYPES OF BRIDGESTYPES 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 BRIDGEGIRDER BRIDGE

Chesapeake Bay Chesapeake Bay Bridge, VirginiaBridge, Virginia

• Typical span length 30 to 650 ft

• World’s longest: Ponte Costa e Silva, Brazil with a center span of 1000 ft

TRUSS BRIDGETRUSS BRIDGE

Firth of Forth Bridge, ScotlandFirth 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 BRIDGERIGID 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 rigid Design 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 BRIDGEARCH 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 lengthTypical 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 Larimer Avenue Bridge, Pittsburgh

CABLE STAYED BRIDGECABLE STAYED BRIDGE

Normandie BridgeNormandie 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 lengthTypical span length 350 to 1600 ft.350 to 1600 ft.• World’s largest bridge:World’s largest bridge: Tatara Bridge, JapanTatara Bridge, Japan center span: 2900 ft.center span: 2900 ft.

SUSPENSION BRIDGESUSPENSION BRIDGE

• Continuous girder with one or Continuous girder with one or more towers erected above in the more towers erected above in the middle of the span.middle of the span.

• At both ends of the bridge, large At both ends of the bridge, large anchors or counter weights are anchors or counter weights are placed to hold the ends of the placed to hold the ends of the cables.cables.

• Typical span lengthTypical span length 250 to 3000 ft.250 to 3000 ft.

Golden Gate Bridge, CaliforniaGolden Gate Bridge, California

Factors Describe a Bridge 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.).

Basic Span TypesBasic Span Types

Simple Span

Continuous Span

Cantilever Span

LOADS ON BRIDGESLOADS 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)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 145 kN 35 kN

4.3 to 9.0 m 4.3 m

9.3 N/m

DESIGN TRUCK

DESIGN TRUCKDESIGN TRUCK

110 kN 110 kN

9.3 N/m

1.2 m

DESIGN TANDEM

DESIGN TANDEMDESIGN TANDEM

DESIGN PRINCIPLESDESIGN 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 ∑γiQi ≤ φi Rn

Where, Qi = Effect of loads Rn = Nominal resistance γi = Statistically based resistance factor applied to the force effects

φi = Statistically based resistance factor applied to the nominal resistance η = Load modification factor

MATERIALS FOR BRIDGESMATERIALS FOR BRIDGES

• Concrete

• Steel

• Wood

CONCRETE BRIDGESCONCRETE 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 BRIDGESSTEEL BRIDGES

• Minimum construction depth

• Rapid construction

• Steel can be formed into any shape or form • Predictable life

• Ease of repair and demolition

WOOD BRIDGESWOOD 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 Wood Bridge on Concrete AbutmentsAbutments

Three Span Wood Bridge Three Span Wood Bridge

GIRDER CROSS-SECTIONS GIRDER CROSS-SECTIONS COMMONLY USED IN BRIDGESCOMMONLY USED IN BRIDGES

COLLAPSE OF BRIDGESCOLLAPSE OF BRIDGES

• Poor design

• Inadequate stability of the foundation

• Fatigue cracking

• Wind forces

• Scour of footing

•Earthquake

BeforeBeforeCollapseCollapse

After CollapseAfter Collapse

AKASHI KAIKYO BRIDGE, JAPAN

Completion Date: 1998 Cost: $4.3 billion

Length: 12,828 feet Type: Suspension

Materials: Steel Span: 6,527 feet

SUNSHINE SKYWAY BRIDGE, USA

Completion Date: 1987 Cost: $244 Million

Length: 29,040 feet Type: Cable Stayed

Materials: Steel, Concrete Span: 1200 feet

NEW RIVER GORGE BRIDGE, USA

Completion Date: 1978 Cost: $37 Million

Length: 4,224 feet Type: Arch

Materials: Steel Span: 1700 feet

1. by dr. attaullah shah swedish college of engineering and technology wah cantt. ce-407 lec-04...

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