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shrubflattenUrban and Civil

Nov 25, 2013 (3 years and 11 months ago)

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Steel

History


No role till 19 century


in a
structural cap.


First all metal structure
-

cast iron
bridge built in the late 18 century in
England. Still in use today.


Cast iron was first


but is very
brittle.


1850’s still came available
inexpensively with introduction of
the Bessemer process.


Bessemer process


air blown into
vess4el of molten iron to burn of the
impurities


1868


open hearth method was
developed which further reduced
the cost.

Material Steel



Steel is any range of alloys of
iron and carbon


that contains
less than 2 % carbon.


Ordinary structural steel called
mild steel contains less then
3/10 of 1% carbon


Ordinary cast iron contains 3
to 4% carbon


To much carbon makes a hard
but brittle metal


While to little produces a soft
weak material


Thus mild steel is iron whose
properties have been
optimized for structural
purposes


Iron is produced in a blast
furnace charged with
alternating layers of iron ore,
coke
-
coal without its volatile
combustibility leaving only
carbon, and limestone.

Uwe R. Zimmer

photo

Process


Coke burned by large quantity of air forced in
from the bottom


produces a gas of carbon
monoxide


which reacts with the ore to
reduce it to elemental iron.


Limestone forms a slag which reduces the
impurities of the iron


Molten iron is drawn off the bottom of the
furnace


One ton of iron requires


1 ¾ tons of iron ore


¾ ton of coke


¼ ton of limestone


4 tons of air


Today most steel is produced by basic oxygen
process


other methods can be used


In which a water cooled lance is lowered into a
constancy of molten iron.


Stream of pure oxygen at very high pressure is
blown from the lance into the metal to burn off
carbon and other impurities.


Molten steel from the furnace is cast into
molds to produce ingots

Production of structural shapes


Rolling process begins at the blooming
mill


The hot ingots is reduced in size by
squeezing it between rollers


Then brought to structural mill with temp
still above 2200 f


Here it passes through a succession of
rollers


That press the metal into progressively
more refined shapes and sizes


Typically wide flange shapes passes
through set of rollers around 40 times


Then it is allowed to cool


After cooling a straightening machine
takes out minor crookedness


And a saw cuts the lengths of steel into
shorter pieces.



Sizes and Shapes


By varying the space of the
rollers you can obtain a varied of
shapes and sizes


Wide flange uses for most
column and beams


American Standard I beam


less efficient structurally then
wide flange


because roller
arrangement that produces
them is incapable of increasing
the amount of steel to the
flanges without also adding
steel to the web


where it does
little to increase the load
carrying capacity.

Symbols


Wide flange W21 x 83


Sizes range from 4 to 18” in 2 in. increments


18 to 36” in 3” increments


American Standard S18 x 70


Sizes 3,4,5,6,7,8, 10,12, 15,18,20,24


Wide flange measurements


W12 x 24 used as a beam or girder


Depth actual 12.22 inches flanges 6.49 in.


W12 x 336 intended for columns


Depth actual 17 in.


Steel angles


extremely versatile


L4 x 3 x 3/8


Uses as lintels spanning doors and windows in masonry construction


Steel buildings cut into short pieces and used to connect wide flange shapes


Diagonal to braces steel frames


Members of steel trusses


Channels


C9 x 13.4


Used as truss members and bracing


Tees, plates and bars


WT13 x 47

Open Web Steel Joists


One of the many structural
steel products fabricated


A mass produced truss
used in closely spaced
arrays to support floors
and roof decks


Comes in three sizes


K series span 60 ft


Depth 8 to 30 inches


LH series (long span) 96 ft


Depth 18 to 48 inches


DLH series (deep long span)
144 ft


Depth 52 to 72 inches


Cold work steel


Sheets of steel can be
bent into c shaped, z
shaped sections


Channel stud


Cee stud


Double Stud


Cee Joist


Double Joist

Joining Steel Members


Rivets


a fastener
consisting of a cylinder
body and a formed head


Heated to a white color


Inserted through the holes in
the member


With a pneumatic hammer to
produce a second head
opposite the first


As the rivet cools its shrinks
and clamping the joined
pieces together tightly

Joining Steel Members


Bolts


Two categories


Carbon steel bolts


Also known as unfinished or common bolts


Similar to ordinary machine bolts that can be purchase at
hardware store


Not very strong


Highest strength bolts


Heat treated to develop necessary strength


Their connecting ability either is a shear connect


which stems
from their shear resistance


Or from being tighten to the point that the members join are kept
from slipping by the friction between the producing a fiction
connection

Joining Steel Members


Welding


Offers a unique and
valuable capability


Can join members of
steel together as if they
were one


Joining Steel Members


Shear Connections and Moment
Connections


In order to understand the respective
roles of shear connections and moment
connections necessary to understand the
means by which a building may be made
stable against the lateral forces of wind
and earthquakes


Three basic mechanisms


Diagonal bracing


Sheer panels


Moment connections


Diagonal bracing works by creating stable
trim angles within the unstable geometry
of a steel building


The connections within a diagonally brace
frame do not transfer moments


They behave like pins which is another
way of calling them shear connections


Shear panels


rectangle panels made of
steel or concrete


shear connections

Sheer connection

Moment connection

Metal Decking


Sheets of steel that
have been corrugated
to increase its stiffness


Span determined by
thickness

Fireproofing


Building fires are not hot enough to melt steel


but many are able to weaken it to cause structural
failure


Fireproofing


encasing steel in brick or concrete


but the weight added is considerably to the load
and cost


Metal lath and plaster


Boards or slabs of gypsum or other fire resistance
material


can serve as a finished surface


Spray on materials #1 today

general consists of
fibers.