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.