Lean Construction

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By Dr. Attaullah ShahSwedish College of
Engineering and Technology Wah Cantt.

• CE-407
• Lec-03
• Structural Engineering
• Bridges

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Bridges
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History of Bridge Development
100 B.C. Romans 2,104 years ago
700 A.D. Asia 1,304 years ago
Clapper Bridge

• Tree trunk
• Stone

• 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

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History of Bridge Development
1900
1920
Truss Bridges

• Mechanics of Design
• Wood

2000
Suspension Bridges

• Use of steel in suspending cables

• Prestressed Concrete
• Steel

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Basic Concepts
Span - the distance between two bridge supports,
whether they are columns, towers or the wall of a
canyon.
Force -
Compression Tension -
Concrete has good compressive strength, but
extremely weak tensile strength. What about
steel cables?
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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
Load - weight on a structure
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Types of Bridges

• Basic Types
• Truss Bridge
• Beam Bridge
• Arch Bridge
• Suspension Bridge
• Floating Bridge

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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.

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Floating Bridges
Retractable!
But high maintenance!
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Bridge Engineering

• How do the following affect your structure?
• Ground below bridge
• Loads
• Materials
• Shapes

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Some Uses of Bridges

• Walkways
• Highways/Roads
• Railways
• Pipelines
• Connecting lands
• Crossing rivers and canyons

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Types of Bridges

• Arch
• Truss
• Cantilever
• Cable-Stayed
• Suspension

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What makes a bridge stay up?

• Forces
• Compression a pushing or squeezing force
• Tension a pulling or stretching force

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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

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Arch Bridges

• Works by
• Compression

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Arch Bridges

• Where have you seen these bridges?

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Cold Spring Arch Bridge, Santa Barbara, CA
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Marsh Rainbow Arch, Riverton, KS
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Pont du Gard, Nimes, France
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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

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Cable-Stayed Bridges

• Works by Tension AND Compression

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Cable-Stayed Bridges

• Where have you seen these bridges?

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Zakim Bridge, Boston, MA
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Sunshine Skyway Bridge, Tampa, FL
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Sundial Bridge, Redding, CA
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Suspension Bridges

• Similar to Cable-Stayed
• Different construction method

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Suspension Bridges

• Works by Tension and Compression

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Suspension Bridges

• Where have you seen these bridges?

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Golden Gate Bridge, San Francisco, CA
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Brooklyn Bridge, Brooklyn, NY
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Verrazano-Narrows Bridge, New York, NY
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Other Types
Truss Southern Pacific Railroad Bridge, Tempe, AZ
Cantilever Firth of Forth-Forth Rail Bridge,
Edinburgh, Scotland
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FUNCTION OF A BRIDGE
To connect two communities which are separated by
streams, valley, railroads, etc.

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

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COMPONENTS OF A BRIDGE

• Deck or Slab supported roadway on abridge
• Beam or Girder A rigid, usually horizontal,
• structural
  element
• Abutment The outermost end supports on a
• bridge, which carry the
  load from
• the deck
• Pier A vertical supporting structure, such as a
  
• pillar
• Foundation

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COMPONENTS OF A BRIDGE
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TYPES OF BRIDGES

• Beam or Girder Bridge
• Truss Bridge
• Rigid Frame Bridge
• Arch Bridge
• Cable Stayed Bridge
• Suspension Bridge

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GIRDER BRIDGE

• Typical span length 30 to
• 650 ft
• Worlds longest Ponte Costa
• e Silva, Brazil with a center
• span of 1000 ft

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TRUSS BRIDGE

• Typical span length
• 150 to 1500 ft
• Worlds longest
• Pont de Quebec, Canada
• with a center span of
• 1800 ft

Firth of Forth Bridge, Scotland
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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.

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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.
• Worlds longest
• New River Gorge Bridge, U.S.A. with a center
  span of
• 1700 ft.

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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.
• Worlds largest bridge
• Tatara Bridge, Japan
• center span 2900 ft.

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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.

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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.).

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Basic Span Types
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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.

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VEHICULAR DESIGN LOADS (HL 93)

• AASHTO American Association of State Highway
• and Transportation
  Officials
• This model consists of
• Design Truck
• Design Tandem
• Design Lane

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DESIGN TRUCK
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DESIGN TANDEM
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DESIGN PRINCIPLES
Resistance effect of the applied loads
Load and Resistance Factor Design (LRFD) ? ??iQi
fi Rn Where, Qi Effect of loads
Rn Nominal resistance ?i
Statistically based resistance factor
applied to the force effects fi
Statistically based resistance factor applied to
the nominal resistance
? Load modification factor
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MATERIALS FOR BRIDGES

• Concrete
• Steel
• Wood

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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

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STEEL BRIDGES

• Minimum construction depth
• Rapid construction
• Steel can be formed into any shape or form
• Predictable life
• Ease of repair and demolition

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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

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Wood Bridge on Concrete Abutments
Three Span Wood Bridge
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GIRDER CROSS-SECTIONS COMMONLY USED IN BRIDGES
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COLLAPSE OF BRIDGES

• Poor design
• Inadequate stability of the foundation
• Fatigue cracking
• Wind forces
• Scour of footing
• Earthquake

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Before Collapse
After Collapse
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AKASHI KAIKYO BRIDGE, JAPAN
Completion Date 1998 Cost 4.3
billion Length 12,828 feet Type
Suspension Materials Steel Span 6,527 feet
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SUNSHINE SKYWAY BRIDGE, USA
Completion Date 1987 Cost 244
Million Length 29,040 feet Type Cable
Stayed Materials Steel, Concrete Span 1200
feet
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NEW RIVER GORGE BRIDGE, USA
Completion Date 1978 Cost 37 Million Length
4,224 feet Type Arch Materials Steel Span
1700 feet