Transcript Properties of Steel - ACE Mentor Program Chicago

PROPERTIES
OF STEEL
WHAT IS STEEL?
• An alloy of iron (Fe26) and other elements, primarily carbon (C6)
• Comes from our Earth’s crust – 6% is iron
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
STEEL
• It’s the most recycled material on the plant
• Cheaper to recycle than to mine and manipulate iron ore
STEEL IN THE U.S. & THE WORLD
• 1900 - 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
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
WHY STEEL? ADVANTAGES
• Ease of fabrication, lower production cost, its recyclable
• It also possesses desirable physical properties
WHY STEEL? ADVANTAGES
• High Strength (particularly tensile strength)
Tension –pulling force
Compression – pushing force
Concrete has
high compressive
strength and very
low tensile strength
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
WHY STEEL? ADVANTAGES
• Uniform
• Properties don’t change unlike in concrete or wood
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
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
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)
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
STEEL DISADVANTAGES
• Buckling
• As the length and slenderness of a compressive column is increased,
its danger of buckling increases
STEEL SECTIONS
• Easy to roll steel into any shape
• The I, T, and C shapes are most common
STEEL SECTIONS - AESTHETICS
• Rolled pipe or tubular cross-section
• Popular in the U.S. for architectural aesthetics in exposed structures
CONNECTIONS
• The glue that hold a steel structure together
• Historically, major structural failures often involve failed connections
• Connections fail when there’s unexpected force
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
CONNECTIONS
• Bolts – screw threads and fasteners
• Easy to do on-site, cheap, can be tightened
• High-strength bolts are available
CONNECTIONS
• Rivets – are smooth and pounded into a drilled hole with a gun
• Quick , simple, won’t shake loose
DECKING - FLOORS
• Corrugated sheets below a layer of concrete
and steel reinforcing bars
• Bars help strength and limit cracking
QUESTIONS?