Eads, Eiffel and the Forth Bridgece.jhu.edu/perspectives/protected/lectures/Lec04_Eads...Eads,...
Transcript of Eads, Eiffel and the Forth Bridgece.jhu.edu/perspectives/protected/lectures/Lec04_Eads...Eads,...
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.