Eads, Eiffel and the Forth Bridge

The big 19th century

iron and steel bridges

1. How arches carry load: Eads Bridge2. Two hinged arches: Garabit3. Details of form in metal arches: Garabit and Mungstener4. Influence of structural failure on subsequent design5. Strength and safety in cantilever form: Forth Bridge

Eads Bridge - steel - 520 feet - 1874

Koblenz

James Buchanan Eads1820-1887

From a book written by Eads

Q: Why doesn’t this tip over?

Tension tie provides reaction

Pick the person on the railing, the carriage, or the locomotive -describe the load path for the force you have selected...

122 feet to bedrock

1871

July 4, 1874

Can you identify differences?

Pia Maria Garabit

Garabit Viaduct1884540 feet

http://www.structurae.de/en/photos/img3815.php

Garabit Viaduct.

Photo by Jacques Mossot

Le Corbusier

Firth of Tay

Firth of Forth

Court of inquiry proceedings, for Sir Thomas Bouch

re: collapse of the Firth of Tay Br.

Q: Sir Thomas, did you in designing this bridge, make any allowance at all for wind pressure?

A: Not specially.

Q: You made no allowance?

A: Not specially.

Firth of Forth Bridge - Benjamin Baker - 1890 - 1710 feet

120 feet

330 feet

can you identify tension and compression?

Eads Br.

Garabit Br.

Forth Br.

Social-Scientific-Symbolic

Economy-Efficiency-Elegance

Pine Grove Bridge

Chester/Lancaster County, PABurr truss (arch-truss)

Captain Elias McMellen builder1884

double span, two at 93 ft HAER PA-586 (2002)

Interpreting and using modern structural

analysis to better understand the scientific

aspects of structures.

(We will teach you later in the course how to perform these analyses yourself!)

Pine Grove Bridge

interpreting and using modern structural analysis to betterunderstand the scientific aspects of structures. We will teach

you later in the course how to perform these analyses yourself!

architectural rendering from summer 2002 HAER documentation team

Pine Grove Bridge

Q: What are all thesedifferent members doingdiscuss?

Longitudinal System

architectural rendering from summer 2002 HAER documentation team

Longitudinal System Model

Dead Load Response - Separate(shaded bars proportional to axial forces in bridge members)

33 k

47 k

Dead Load Response - Combined

35 k

9 k

Dead Load Subtleties

axial (F)

moment (M)

(shaded areas indicate magnitude of bending in a member)

46 k

-in.

Dead Load Member Demand Highlights

• Arch (at end)! = -391 (C) psi(allowable 1000 psi)

• Truss (post 4)! = -272 (C) psi(allowable 1000 psi)

• Truss (post 5)! = 261 (T) psi(allowable 925 psi)

Arch-truss synergy

arch truss

Midspan deflection (dead load)

Structural modeltruss alone = 0.96 in.arch alone = 0.91 in.

Simple parallel combinationtruss+arch = 0.47 in.

Structural modeltruss+arch = 0.25 in.

arch-truss is far stiffer than a simple addition of the two separate systems

Live Load Arch Deflections

" = 2.0 in.

" = 4.8 in.

5 k

5 k

Live Load Results

" = 0.07 in.

" = 0.06 in.

5 k

5 k

Total Load Member Demand Highlights

• Arch (at end)! = -489 (C) psi(allowable 1000 psi)

• Truss (post 4)! = -394 (C) psi(allowable 1000 psi)

• Truss (post 4)! = 458 (T) psi(allowable 925 psi)

(results for total load = dead load + quarter point live load)

• HW due next Tuesday. See

www.ce.jhu.edu/perspectives

www.ecs.umass.edu/perspectives

for all you need to know.