BRIDGE DESIGN
BY
SAIF HAROON
Post-Doctoral Research Associate
Department of Civil & Environmental Engineering
FAMU-FSU College of Engineering
FUNCTION OF A BRIDGE
To connect two
communities which are
separated by streams,
valley, railroads, etc.
Bosporus Straits Bridge
at Istanbul, Turkey –
• Replaces a slow ferry
boat trip
• Connects two continent
• Built in 1973
• Total length is 5000 ft
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
COMPONENTS OF A BRIDGE
Deck
Girder
Abutment
Pier
TYPES OF BRIDGES
•Beam or Girder Bridge
•Truss Bridge
•Rigid Frame Bridge
•Arch Bridge
•Cable Stayed Bridge
•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.
Larimer Avenue Bridge, Pittsburgh
• Typical span length
130 ft – 500 ft.
• 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 – American Association of State Highway
and Transportation Officials
This model consists of:
• Design Truck
• Design Tandem
• Design Lane
DESIGN TRUCK
145 kN
145 kN 35 kN
4.3 to 9.0 m
4.3 m
9.3 N/m
DESIGN TRUCK
DESIGN TANDEM
110 kN
110 kN
1.2 m
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 ∑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 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
Before
Collapse
After 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
THANK YOU