Transcript Lean Construction
1
CE-407 Lec-04 Structural Engineering Bridges-II ( ACI
By
Dr. Attaullah Shah
Swedish College of Engineering and Technology Wah Cantt.
Elevation and cross section of Bridges
Arch and suspension Bridges
Some important definitions
Bridges
History of Bridge Development Clapper Bridge
Tree trunk Stone
100 B.C. Romans 2,104 years ago 700 A.D. Asia 1,304 years ago Roman Arch Bridge
Arch design evenly distributes stresses Natural concrete made from mud and straw
Great Stone Bridge in China
Low bridge Shallow arch Allows boats and water to pass through
History of Bridge Development 1900
Truss Bridges Mechanics of Design Wood
1920 2000
Suspension Bridges Use of steel in suspending cables Prestressed Concrete Steel
Basic Concepts Span
- the distance between two bridge supports, whether they are columns, towers or the wall of a canyon.
Force
-
Compression
–
Tension
-
Compression Tension
Concrete has good compressive strength, but extremely weak tensile strength. What about steel cables?
Basic Concepts Beam
- a rigid, usually horizontal, structural element Beam Pier
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
Load
- weight on a structure
Basic Types
: •Truss Bridge •Beam Bridge •Arch Bridge •Suspension Bridge •Floating Bridge
Types of Bridges
Floating Truss Beam Arch Suspension The type of bridge used depends on the obstacle. The main feature that controls the bridge type is the size of the obstacle.
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.
Types of Bridges Beam Bridge 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 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 Arch 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 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 Suspension 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 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.
Floating Bridges Retractable!
But high maintenance!
Bridge Engineering
How do the following affect your structure?
Ground below bridge
Loads
Materials
Shapes
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.
Bosporus Straits Bridge at Istanbul, Turkey –
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Replaces a slow ferry
• • •
boat trip Connects two continent Built in 1973 Total length is 5000 ft
COMPONENTS OF A BRIDGE
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Deck or Slab: supported roadway on abridge
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Beam or Girder: A rigid, usually horizontal, structural element
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Abutment: The outermost end supports on a bridge, which carry the load from the deck
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Pier: A vertical supporting structure, such as a pillar
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Foundation
Girder COMPONENTS OF A BRIDGE Deck Abutment Pier
TYPES OF BRIDGES
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Beam or Girder Bridge
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Truss Bridge
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Rigid Frame Bridge
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Arch Bridge
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Cable Stayed Bridge
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Suspension Bridge
GIRDER BRIDGE
• Typical span length 30 to 650 ft • World’s longest: Ponte Costa e Silva, Brazil with a center span of 1000 ft
Chesapeake Bay Bridge, Virginia
TRUSS BRIDGE
• Typical span length 150 to 1500 ft • World’s longest: Pont de Quebec, Canada with a center span of 1800 ft
Firth of Forth Bridge, Scotland
RIGID FRAME BRIDGE
•Girders and piers act together •Cross-sections are usually I-shaped or box-shaped.
•Design calculations for rigid frame bridges are more difficult than those of simple girder bridges.
ARCH BRIDGE
• After girders, arches are the second oldest bridge type.
• Arches are good choices for crossing valleys and rivers • Arches can be one of the more beautiful bridge types.
• Typical span length 130 ft – 500 ft.
Larimer Avenue Bridge, Pittsburgh
• World’s longest: New River Gorge Bridge, U.S.A. with a center span of 1700 ft.
CABLE STAYED BRIDGE
• Continuous girder with one or more towers erected above in the middle of the span.
• From these towers cables stretch down diagonally and support the girder.
• Typical span length 350 to 1600 ft.
• World’s largest bridge: Tatara Bridge, Japan center span: 2900 ft.
Normandie Bridge
SUSPENSION BRIDGE
• 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.
• Typical span length 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.).
Basic Span Types Simple Span Continuous Span Cantilever Span
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 – A
merican
A
ssociation of
S
tate
H
ighway and
T
ransportation
O
fficials This model consists of: • • •
Design Truck Design Tandem Design Lane
DESIGN TRUCK
145 kN 4.3 to 9.0 m 145 kN 4.3 m 35 kN 9.3 N/m
DESIGN TRUCK
DESIGN TANDEM
110 kN 1.2 m 110 kN 9.3 N/m
DESIGN TANDEM
DESIGN PRINCIPLES
Resistance ≥ effect of the applied loads
Allowable Stress Design (ASD):
Strength of the Member ≥ Factor of Safety x Applied Load
Load and Resistance Factor Design (LRFD):
η ∑γ i Q i ≤ φ i R n Where, Q i R γ i n = Effect of loads = Nominal resistance = Statistically based resistance factor applied to the force effects φ i = Statistically based resistance factor applied to the nominal resistance η = Load modification factor
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Concrete
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Steel
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Wood MATERIALS FOR BRIDGES
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
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Minimum construction depth
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Rapid construction
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Steel can be formed into any shape or form
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Predictable life
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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
Three Span Wood Bridge Wood Bridge on Concrete Abutments
GIRDER CROSS-SECTIONS COMMONLY USED IN BRIDGES
COLLAPSE OF BRIDGES
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Poor design
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Inadequate stability of the foundation
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Fatigue cracking
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Wind forces
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Scour of footing
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Earthquake
Before Collapse After Collapse
AKASHI KAIKYO BRIDGE, JAPAN
Completion Date: 1998 Length: 12,828 feet Materials: Steel Cost: $4.3 billion Type: Suspension Span: 6,527 feet
SUNSHINE SKYWAY BRIDGE, USA
Completion Date: 1987 Length: 29,040 feet Materials: Steel, Concrete Cost: $244 Million Type: Cable Stayed Span: 1200 feet
NEW RIVER GORGE BRIDGE, USA
Completion Date: 1978 Length: 4,224 feet Materials: Steel Cost: $37 Million Type: Arch Span: 1700 feet