Steel

1. Steel

2. 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.

3. 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. Zimmerphoto

4. 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

5. 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.

6. 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.

7. 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

8. 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

9. 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

10. 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

11. 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

12. Joining Steel Members • Welding • Offers a unique and valuable capability • Can join members of steel together as if they were one

13. 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

14. Metal Decking • Sheets of steel that have been corrugated to increase its stiffness • Span determined by thickness

15. 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.