Bridges
History of Bridges
• The earliest bridges were primitive.
– Logs falling across a stream are considered the
earliest bridge.
– Following that was the practice of stringing large
vines across the two areas needing to be bridge
• Engineered arches originated in the Middle
East approximately 4,000 BC
Rome
• Romans applied the arch for bridges and
aqueducts around 800 BC
• Though they constructed many kinds of bridges
such as wooden and beam bridges
– They are known for their stone arch bridge
• Stone arch bridge withstood heavy use and can still be seen
today in Europe
• Civil Engineering
– Branch of engineering relating to the building of
municipal systems, such as roads, bridges, dams, and
communication towers.
London Bridge
• Notable bridge of the medieval period
• Massive stone bridge that replaced an older
wooden bridge
• Built by Peter Colechurch
• Completed in 1209 AD
• Featured 19 arches
• Lasted 600 years
• Needed frequent repairs
– “London Bridge is Falling Down”
Ponte Vecchio
• Florence, Italy
• Architects:Taddeo Gaddi and Neri di
Fioravante
• Spans 276’ over the Arno River
• Arch/Deck arch Bridge
Jean Perronet
• “Father of Modern Bridge Building”
• Best known Bridge
– Pont de la Concorde in Paris
• Arch Bridge
• Completed in 1791
• Still stands today
Civil Engineering Education
• Drafting
– Skills and knowledge needed to visually communicate
ideas on paper or a computer program
• Surveying
– Accurately gather information about Earth’s surface
• Soil Science
– Determines the characteristics of the type of
foundation needed
Civil Engineering Education
• Mathematics
– Calculating stresses on a structure or analyzing the
material requirements of each member.
• Materials and processes
– Provides an understanding of the strength and other
characteristics of metals, woods, plastics, etc.
• Transportation
– Awareness of all laws relating to transportation and
construction of roadways, bridges, and other highway
systems
Civil Engineering Education
• Environmental Issues
– Examines how the environment effects
construction and provides information necessary
to protect people and the environment
• Physics
– Explores physical principals and mathematical
equations that are key to designing sound
structures
Factors in Bridge Design
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What is the span of the bridge?
What will be the load of the bridge?
What type of load will the bridge have?
What environmental factors will affect the
bridge?
What is the budget allowance for the bridge?
What are the soil characteristics of the banks?
What are the soil characteristics for the bottom
of the river is support columns are needed?
What is the construction time frame?
Truss
• King Post
– A central vertical post used in architectural or
bridge designs
• Warren
– Consists of longitudinal members joined only by
angled cross-members
• Pratt
– Consists of longitudinal members joined only by
angled cross-members
Truss
• K Truss
– A truss in the form of a K due to the orientation of the
vertical member and two oblique members in each
panel
• Whipple
– Considered a subclass of the Pratt truss because the
diagonal members are designed to work in tension.
The main characteristic of a Whipple truss is that the
tension members are elongated, usually thin, at a
shallow angle and cross two or more bays
Types of Trusses
King Post Truss
Warren Truss
Types of Trusses
Pratt Truss
K-Truss
Types of Trusses
Whipple Bowstring
Bollman Truss
Types of Trusses
Town Lattice
Howe Truss
Terms
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Bridge
– Structure that spans a gap
Design
– Process of creating
Angle
– Figure formed by two lines extending from the same point
Limit
– Constraint
Critical load
– Weight a structure can support before failing
Compression
– Tendency to push, squash, or squeeze a material
Average
– Value provided by dividing the sum of a set of quantities in a set
Criteria
– Set of standards or rules on which a judgment or decision can be based
Beam
– Horizontal supporting member
Conclusion
– Reasoned judgment
Terms
• End grain
– Grain of wood as seen from the end of a wood strip
• Dimension
– Measure in one direction
• Hypothesis
– Prediction based on prior knowledge made in order to test
its consequences
• Efficiency
– Strength to weight ratio
• Force
– Capacity to do work or cause physical change; energy,
strength, or active power
Terms
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Inference
– Act of deriving logical conclusions from premises known or assumed to be true
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Lamination
– Layering a structure
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Load
– Overall force that a structure is subjected in supporting weight
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Load-bearing capacity
– Maximum load that a system can support before failing
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Mass
– Amount of matter within an object
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Superstructure
– Structure of the bridge that extends above the roadbed
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Scale
– System of proportion
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Modification
– Change the properties, form, or function
Terms
• Truss
– Rigid framework, designed to support a structure
• Sketch
– Drawing
• Substructure
– Structure of the bridge that extends below the roadbed
• Model
– Small object built to scale
• Timber
– Wood used for building materials
• Span
– Distance between supports
• Tension
– Force pulling apart materials
Truss
• Bollman
– Only surviving example of a revolutionary design in
the history of American bridge
engineering. Employs wrought iron tension members
and cast iron compression members.
• Town Lattice
– This type of bridge uses a substantial number of
lightweight elements, easing the task of construction.
Truss elements are usually of wood, iron, or steel.
• Howe Truss
– Includes vertical members and diagonals that slope up
towards the center, the opposite of the Pratt truss.