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Properties of Steel
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What is steel? An alloy of iron (Fe26) and other elements, primarily carbon (C6) -atomic number – number of electrons -raw iron ore pellets from our earth’s crust (6% of our earth’s crust is made of iron) then a steel mill Comes from our Earth’s crust – 6% is iron
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How is steel made? Relatively easy and cheap to fabricate
After iron ore is mined, its melted at 2,800 degrees F Carbon and other elements are then added
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Steel It’s the most recycled material on the plant
Cheaper to recycle than to mine and manipulate iron ore -environmentally friendly option -sculpture was made of 2,000 pounds of scrap steel
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Steel in the U.S. & THE WORLD
the U.S. was the largest producer and the lowest cost producer The predominate material for construction of bridges and buildings ASTM issues standards on materials and design -now its China and India
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Steel in buildings Steel frame – “skeleton frame”
Vertical steel columns and horizontal I-beams in a rectangular grid to support floors, roofs, and walls Made skyscrapers possible – 1st one was in Chicago -steel framework and black aluminum facing
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Why steel? advantages Ease of fabrication, lower production cost, its recyclable It also possesses desirable physical properties -
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high compressive strength and very low tensile strength
Why steel? advantages High Strength (particularly tensile strength) Tension –pulling force Compression – pushing force - Concrete has high compressive strength and very low tensile strength
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Why steel? advantages High strength (particularly tensile strength)
High density too A 2x4 steel I-beam can be designed to be stronger and lighter than a 2x4 of wood -
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Why steel? advantages Uniform
Properties don’t change unlike in concrete or wood -
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Why steel? advantages Elasticity
Can be temporarily deformed by a force and return its original shape & size Follows Hooke’s Law accurately One of the foundations of seismology – assess stresses and reactions -
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Why steel? advantages Ductility – steel is a ductile metal
Can withstand extensive deformation under tensile stress before fracture Gives you warning before failure takes place -elements and constituents will vary steel’s ductility
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Steel disadvantages Maintenance & corrosion
Susceptible to corrosion if exposed to air, water, acids, humidity, etc. Environment of location needs to be assessed Iron is oxidized (by O2 and H2O) and produces rust Can add elements like copper or chromium Or coat the steel (or galvanize) -
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Steel disadvantages Fireproofing costs Steel is incombustible
But it softens and it’s strength decreases at high temperatures Can cause building to partially collapse in the case of the columns Concrete meets stringent fire codes Asbestos was used back in the ‘70s -asbestos was a popular material for fireproofing steel structures up until the early 1970s before the health risks of asbestos fibres were fully understood
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Steel disadvantages Buckling
As the length and slenderness of a compressive column is increased, its danger of buckling increases -
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Steel sections Easy to roll steel into any shape
The I, T, and C shapes are most common -
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Steel sections - aesthetics
Rolled pipe or tubular cross-section Popular in the U.S. for architectural aesthetics in exposed structures -
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connections The glue that hold a steel structure together
Historically, major structural failures often involve failed connections Connections fail when there’s unexpected force -
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connections Welding – fusion by melting base metal and adding
filler metal that forms a joint (stronger than the base) Greater level of skill, expensive, & requires inspections -
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connections Bolts – screw threads and fasteners
Easy to do on-site, cheap, can be tightened High-strength bolts are available -
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connections Rivets – are smooth and pounded into a drilled hole with a gun Quick , simple, won’t shake loose -
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Decking - Floors Corrugated sheets below a layer of concrete
and steel reinforcing bars Bars help strength and limit cracking -
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Questions? -
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