SteelSteel
HistoryHistory No role till 19 century – in a No role till 19 century – in a
structural cap.structural cap. First all metal structure - cast iron First all metal structure - cast iron
bridge built in the late 18 century in bridge built in the late 18 century in England. Still in use today.England. Still in use today.
Cast iron was first – but is very Cast iron was first – but is very brittle.brittle.
1850’s still came available 1850’s still came available inexpensively with introduction of inexpensively with introduction of the Bessemer process.the Bessemer process.– Bessemer process – air blown into Bessemer process – air blown into
vess4el of molten iron to burn of the vess4el of molten iron to burn of the impuritiesimpurities
1868 – open hearth method was 1868 – open hearth method was developed which further reduced developed which further reduced the cost.the cost.
Material SteelMaterial Steel Steel is any range of alloys of Steel is any range of alloys of
iron and carbon – that contains iron and carbon – that contains less than 2 % carbon.less than 2 % carbon.– Ordinary structural steel called Ordinary structural steel called
mild steel contains less then mild steel contains less then 3/10 of 1% carbon3/10 of 1% carbon
– Ordinary cast iron contains 3 to Ordinary cast iron contains 3 to 4% carbon4% carbon
– To much carbon makes a hard To much carbon makes a hard but brittle metalbut brittle metal
– While to little produces a soft While to little produces a soft weak materialweak material
– Thus mild steel is iron whose Thus mild steel is iron whose properties have been properties have been optimized for structural optimized for structural purposespurposes
Iron is produced in a blast Iron is produced in a blast furnace charged with furnace charged with alternating layers of iron ore, alternating layers of iron ore, coke-coal without its volatile coke-coal without its volatile combustibility leaving only combustibility leaving only carbon, and limestone.carbon, and limestone.
Uwe R. Zimmerphoto
ProcessProcess Coke burned by large quantity of air forced in Coke burned by large quantity of air forced in
from the bottom – produces a gas of carbon from the bottom – produces a gas of carbon monoxide – which reacts with the ore to monoxide – which reacts with the ore to reduce it to elemental iron.reduce it to elemental iron.
Limestone forms a slag which reduces the Limestone forms a slag which reduces the impurities of the ironimpurities of the iron
Molten iron is drawn off the bottom of the Molten iron is drawn off the bottom of the furnacefurnace
– One ton of iron requiresOne ton of iron requires 1 ¾ tons of iron ore1 ¾ tons of iron ore ¾ ton of coke¾ ton of coke ¼ ton of limestone¼ ton of limestone 4 tons of air4 tons of air
Today most steel is produced by basic oxygen Today most steel is produced by basic oxygen process – other methods can be usedprocess – other methods can be used
– In which a water cooled lance is lowered into a In which a water cooled lance is lowered into a constancy of molten iron.constancy of molten iron.
– Stream of pure oxygen at very high pressure is Stream of pure oxygen at very high pressure is blown from the lance into the metal to burn off blown from the lance into the metal to burn off carbon and other impurities.carbon and other impurities.
Molten steel from the furnace is cast into Molten steel from the furnace is cast into molds to produce ingotsmolds to produce ingots
Production of structural shapesProduction of structural shapes Rolling process begins at the blooming Rolling process begins at the blooming
millmill– The hot ingots is reduced in size by The hot ingots is reduced in size by
squeezing it between rollerssqueezing it between rollers Then brought to structural mill with temp Then brought to structural mill with temp
still above 2200 fstill above 2200 f Here it passes through a succession of Here it passes through a succession of
rollersrollers– That press the metal into progressively That press the metal into progressively
more refined shapes and sizesmore refined shapes and sizes– Typically wide flange shapes passes Typically wide flange shapes passes
through set of rollers around 40 timesthrough set of rollers around 40 times Then it is allowed to coolThen it is allowed to cool After cooling a straightening machine After cooling a straightening machine
takes out minor crookednesstakes out minor crookedness And a saw cuts the lengths of steel into And a saw cuts the lengths of steel into
shorter pieces.shorter pieces.
Sizes and ShapesSizes and Shapes
By varying the space of the By varying the space of the rollers you can obtain a varied rollers you can obtain a varied of shapes and sizesof shapes and sizes
Wide flange uses for most Wide flange uses for most column and beamscolumn and beams
American Standard I beam – American Standard I beam – less efficient structurally then less efficient structurally then wide flange – because roller wide flange – because roller arrangement that produces arrangement that produces them is incapable of increasing them is incapable of increasing the amount of steel to the the amount of steel to the flanges without also adding flanges without also adding steel to the web – where it does steel to the web – where it does little to increase the load little to increase the load carrying capacity.carrying capacity.
SymbolsSymbols Wide flange W21 x 83Wide flange W21 x 83
– Sizes range from 4 to 18” in 2 in. incrementsSizes range from 4 to 18” in 2 in. increments– 18 to 36” in 3” increments18 to 36” in 3” increments
American Standard S18 x 70American Standard S18 x 70– Sizes 3,4,5,6,7,8, 10,12, 15,18,20,24Sizes 3,4,5,6,7,8, 10,12, 15,18,20,24
Wide flange measurementsWide flange measurements– W12 x 24 used as a beam or girderW12 x 24 used as a beam or girder
Depth actual 12.22 inches flanges 6.49 in.Depth actual 12.22 inches flanges 6.49 in.– W12 x 336 intended for columnsW12 x 336 intended for columns
Depth actual 17 in.Depth actual 17 in. Steel angles – extremely versatileSteel angles – extremely versatile
– L4 x 3 x 3/8L4 x 3 x 3/8– Uses as lintels spanning doors and windows in masonry constructionUses as lintels spanning doors and windows in masonry construction– Steel buildings cut into short pieces and used to connect wide flange shapesSteel buildings cut into short pieces and used to connect wide flange shapes– Diagonal to braces steel framesDiagonal to braces steel frames– Members of steel trussesMembers of steel trusses
ChannelsChannels– C9 x 13.4C9 x 13.4– Used as truss members and bracingUsed as truss members and bracing
Tees, plates and barsTees, plates and bars– WT13 x 47WT13 x 47
Open Web Steel JoistsOpen Web Steel Joists
One of the many structural One of the many structural steel products fabricatedsteel products fabricated
A mass produced truss A mass produced truss used in closely spaced used in closely spaced arrays to support floors arrays to support floors and roof decksand roof decks
Comes in three sizesComes in three sizes– K series span 60 ftK series span 60 ft
Depth 8 to 30 inchesDepth 8 to 30 inches– LH series (long span) 96 ftLH series (long span) 96 ft
Depth 18 to 48 inchesDepth 18 to 48 inches– DLH series (deep long span) DLH series (deep long span)
144 ft144 ft Depth 52 to 72 inchesDepth 52 to 72 inches
Cold work steelCold work steel
Sheets of steel can be Sheets of steel can be bent into c shaped, z bent into c shaped, z shaped sectionsshaped sections
Channel studChannel stud Cee studCee stud Double StudDouble Stud Cee JoistCee Joist Double JoistDouble Joist
Joining Steel MembersJoining Steel Members
Rivets – a fastener Rivets – a fastener consisting of a cylinder consisting of a cylinder body and a formed headbody and a formed head– Heated to a white colorHeated to a white color– Inserted through the holes in Inserted through the holes in
the memberthe member– With a pneumatic hammer to With a pneumatic hammer to
produce a second head produce a second head opposite the firstopposite the first
– As the rivet cools its shrinks As the rivet cools its shrinks and clamping the joined and clamping the joined pieces together tightlypieces together tightly
Joining Steel MembersJoining Steel Members
BoltsBolts– Two categoriesTwo categories
Carbon steel boltsCarbon steel bolts– Also known as unfinished or common boltsAlso known as unfinished or common bolts– Similar to ordinary machine bolts that can be purchase at Similar to ordinary machine bolts that can be purchase at
hardware storehardware store– Not very strongNot very strong
Highest strength boltsHighest strength bolts– Heat treated to develop necessary strengthHeat treated to develop necessary strength– Their connecting ability either is a shear connect – which stems Their connecting ability either is a shear connect – which stems
from their shear resistancefrom their shear resistance– Or from being tighten to the point that the members join are kept Or from being tighten to the point that the members join are kept
from slipping by the friction between the producing a fiction from slipping by the friction between the producing a fiction connectionconnection
Joining Steel MembersJoining Steel Members
Welding Welding – Offers a unique and Offers a unique and
valuable capabilityvaluable capability– Can join members of Can join members of
steel together as if they steel together as if they were onewere one
Joining Steel MembersJoining Steel Members Shear Connections and Moment Shear Connections and Moment
ConnectionsConnections– In order to understand the respective In order to understand the respective
roles of shear connections and moment roles of shear connections and moment connections necessary to understand the connections necessary to understand the means by which a building may be made means by which a building may be made stable against the lateral forces of wind stable against the lateral forces of wind and earthquakesand earthquakes
Three basic mechanismsThree basic mechanisms– Diagonal bracingDiagonal bracing– Sheer panelsSheer panels– Moment connectionsMoment connections
Diagonal bracing works by creating stable Diagonal bracing works by creating stable trim angles within the unstable geometry trim angles within the unstable geometry of a steel buildingof a steel building
The connections within a diagonally brace The connections within a diagonally brace frame do not transfer momentsframe do not transfer moments
They behave like pins which is another They behave like pins which is another way of calling them shear connectionsway of calling them shear connections
Shear panels – rectangle panels made of Shear panels – rectangle panels made of steel or concrete – shear connectionssteel or concrete – shear connections
Sheer connection
Moment connection
Metal DeckingMetal Decking
Sheets of steel that Sheets of steel that have been corrugated have been corrugated to increase its stiffnessto increase its stiffness
Span determined by Span determined by thicknessthickness
FireproofingFireproofing
Building fires are not hot enough to melt steel – Building fires are not hot enough to melt steel – but many are able to weaken it to cause structural but many are able to weaken it to cause structural failurefailure
Fireproofing – encasing steel in brick or concrete – Fireproofing – encasing steel in brick or concrete – but the weight added is considerably to the load but the weight added is considerably to the load and costand cost
Metal lath and plasterMetal lath and plaster Boards or slabs of gypsum or other fire resistance Boards or slabs of gypsum or other fire resistance
material – can serve as a finished surfacematerial – can serve as a finished surface Spray on materials #1 today –general consists of Spray on materials #1 today –general consists of
fibers.fibers.