Previous Conclusions Concrete will continue to be a dominant construction material Reinforced...
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![Page 1: Previous Conclusions Concrete will continue to be a dominant construction material Reinforced concrete must crack in order for reinforcing to work lower.](https://reader035.fdocuments.net/reader035/viewer/2022081518/551502f155034693478b6612/html5/thumbnails/1.jpg)
Previous Conclusions Concrete will continue to be a dominant constructio
n material Reinforced concrete must crack in order for reinfor
cing to work → lower durability because steel can corrode
Prestressed concrete prevents cracking Two powerful design methods: moment diagrams o
r strut and tie models Environmental impact can be reduced through desi
gn: minimize material and recycle waste
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Steel Structures
Technical concepts:- Structural failure- Ductility- Buckling- Shear diagrams
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Steel Structures
Recent structures in steel Material properties – definitions Structural failure Environmental issues Conclusions
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Stuttgart Airport, 1991, Germany
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Structural Design in Steel
Can resist tension and compression Slender elements in compression may buckle Very lightweight structures, so vibrations ar
e a problem Follow moment diagram to minimize materi
al use
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Why is steel a good structural material?
High strength
Ductile material
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Ductility of Steel
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Ductility of Steel
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Importance of Ductility
Large displacements before collapse (as opposed to a brittle material, which fails suddenly)
Energy dissipation as the steel yields (important for resisting earthquakes and other overloading)
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Yield Stress of Steel
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Yield Stress of Steel
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How far down can a steel cablehang under its own weight?
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Bending Stresses in a Beam
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Steel Section Terminology
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Steel Section Terminology
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Shear Diagrams
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Shear Diagrams
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Shear Diagrams
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Shear Diagrams
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Shear Diagrams
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How to draw a shear diagram
1) Determine external reactions on beam
2) “Walk” along beam with your pen
3) Pen goes up and down with the loads
4) Must “close” diagram at the ends of thebeam
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Shear Diagrams
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Shear Diagrams
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Shear Diagrams
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Structural Failure
STRENGTH- Material failure- Buckling (due to instability of section)
SERVICEABILITY- Excessive deflections or vibrations- Cracking (usually in concrete)
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Stiffness of Steel STRENGTH
- Higher yield stress allows smaller sections
…but…
SERVICEABILITY- Stiffness of steel is constant (modulus of elasticit
y, E)- Deflections, vibrations, and buckling become mo
re common
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Shear Diagram for Uniform Load
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Shear Diagrams
Shear diagram equals the slope of moment diagram
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Is steel a green material?
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CO2 Emissions for Steel
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Recycled content for steel
Each ton of recycled steel saves 1200 pounds of coal
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Environmental Advantages of Steel
Lower weight reduces foundation requirements
Highly recycled and can continue to be recycled indefinitely
Durable, if protected from corrosion
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Environmental Disadvantages of Steel
Very high energy use, predominantly from burning coal → produces pollution
Lightweight, so lower thermal mass compared to concrete → requires more insulation
Is susceptible to corrosion
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Corrosion of Steel
Corrosion costs around 4% of GDP
Every 90 seconds, across the world, one ton of steel turns to rust; of every two tons of steel made, one is to replace rust.
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How to avoid corrosion?
Careful detailing to protect from water
Use stainless steel
Protect steel with galvanizing (zinc coating) or other protective coating
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Stainless Steel Disadvantages
High initial cost
Difficulty in fabricating can often result in costly waste
Difficulty in welding
High cost of final polishing and finishing
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Conclusions Steel offers many advantages, primarily high
strength and ductility Shear diagrams can be used to determine loc
ations of high stresses (and are helpful in drawing moment diagrams)
Lightweight structures are susceptible to vibrations and excessive deflections
Environmental impact can be reduced through design
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Ecological Profile of Materials
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Ecological Footprints