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

• 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 TrussesWhipple Bowstring Bollman Truss

Types of Trusses

Town Lattice Howe Truss

Terms• 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• Inference

– Act of deriving logical conclusions from premises known or assumed to be true• Lamination

– Layering a structure• Load

– Overall force that a structure is subjected in supporting weight• Load-bearing capacity

– Maximum load that a system can support before failing• Mass

– Amount of matter within an object• Superstructure

– Structure of the bridge that extends above the roadbed• Scale

– System of proportion• 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.