Metals

Question 1

Types of steel

Answer 1

steel advantages = high strength + ductility, ease/speed/precision

disadvantages = melts when heated, will corrode

low carbon steel = .06-.3%

medium carbon = .3-.5%

high carbon = .5-.8%

as carbon increases, strength increases, but ductility decreases, so medium is ‘best’

weathering steel = corten/has copper added to form patina

A36/A992 = common in W shapes (.25-.29 carbon)

A440 = high strength, for bolting, riveting

A441 = low alloy for welding

Question 2

Ornamental metals

Answer 2

handrails, guardrails, elevator interiors, metal panels, door/partition facings, signs, light fixtures, ceilings, meshes and perforations, etc.

most common: SS, Cu alloys, bronze, brass, Al

less common: carbon steel, Cu, iron, porcelain enamel

10 gauge min. in lg. sheets to avoid oil canning, unless back laminated, or embossed

Question 3

Metal fabrications

Answer 3

non-structural, like stairs, expansion jts. (both structural and seismic), gratings, ladders, etc.

Question 4

Types of stainless steel

Answer 4

302: Cr, Ni added, very strong, hard corrosion resistant
304: like 302, but more weldable, commonly used
301: less Cr, Ni, better tensile strength
316: for extremely corrosive environments
430: no Ni, less corrosion resistance, interiors only

Question 5

W_x_

Answer 5

nominal depth x weight lbm/ft

Question 6

Cast iron first reasonable

Answer 6

1709, Abraham Darby used coke not charcoal in production, decreased impurities, increased strength

Question 7

Steel first reasonable

Answer 7

1856 Henry Bessamer process makes steel inexpensive, stronger

Question 8

Types of Steel Shapes

Answer 8

wide flanges (W), I-beams (S), channels (C), structural tees (WT or ST), angles (L), tubes (TS) - round/square/rectangle, plates (PL) (more than 6”), bars (less than 6”)

Question 9

Non-ferrous metals

Answer 9

Al: soft, so alloyed w Mn, Zn, Mg, Cu, usu. extruded, high stength to wt., but high embd. energy

Cu: very non-corrosive bc of patina (oil or wax can slow this process), v. conductive, used for wiring, pipes, ornament

Bronze: Cu + Sn

Brass: Cu + Zn

Zn: non corrosive, for roofing/flashing

Pb: good acoustics, easy to form, non-corrosive, poisonous

Question 10

Types of metal decking

Answer 10

Most often steel, sometimes aluminum; composites ats structurally with concrete infill; cellular allows raceways

Question 11

Metal finishing

Answer 11

bending, brake forming, spinning, embossing

annealing = reheated + slowly cooled to make more ductile

quenching = reheated + cooled quickly in water to strengthen

tempering = reheated + medium coolest to strengthen + increase ductility

case hardening = harder surface, softer core

anodizing = electrolytic bath that does surface chemistry to help corrosion resistance

painting/coating = for protection or aesthetics

Question 12

Steel channels used for:

Answer 12

framing openings, stringers, where flush side is needed - buckle easily bc of asymmetry

Question 13

Light gauge metal framing

Answer 13

10-25 gauge; usu galv. steel, sometimes aluminum; used for interior partions, exterior walls (bearing or non), joist, rafters, etc.; NONCOMBUSTIBLE; doesn’t shrink with age

Question 14

Cast iron common

Answer 14

1876, used in roofs in France

1850-1880 = Cast Iron Age

Question 15

Levels of metal finish

Answer 15

No. 3 = dull, coarse

No. 4 = general purpose, still dull/coarse, common

No. 6 = sull satin

No. 7 = reflective

No. 8 = mirror-like

Question 16

Cast iron showcased

Answer 16

1851; Crystal Palace, Joseph Paxton

1889; Eiffel Tower, Halle des Machines

Question 17

Open-web steel joists

Answer 17

bottom chord & webs = bent rods

top chord = angles w/ bearing plate attached

Question 18

Types of open-web steel joists

Answer 18

K-series (2” increments) (spans 8-60 ft), LH-series (4” incr.) (spans 25-96 ft), DLH-series (4”) (spans 89-144 ft), e.g. 36LH13 (36” depth, LH-series, type 13 chord). Chord number increases as strength increases.

Question 19

Metal fabrication types

Answer 19

casting (molds), hot rolling (W-shapes, finer, less strong, more flexible), cold rolling (stronger, more brittle), extruding, drawing (stronger)

Question 20

Galvanic Action Index

Answer 20

Most reactive metals: Mg, Zn, Al, Mild Steel, Cast Iron

Medium: Cu, Ni, Cr, Pb, Sn, Stainless Steel (active)

Least reactive: Brass, Bronze, Stainless Steel (passive)

Question 21

Types of iron

Answer 21

wrought = low carbon, has slag, soft/ductile, corrosion resistant

cast = ~2% carbon, hard & brittle

grey cast iron = high silicon content, for plumbing uses

Question 22

Cast iron + Steel = 1st skyscraper

Answer 22

1885, cast iron int/ext cols., Bessamer girders, William LeBaron Jenny, 10-story, Home Insurance Bldg., Chicago

Question 23

Cast iron first used in buildings

Answer 23

By 1779, common in bridges and columns

Question 24

Metal joining

Answer 24

bolts, screws, welding (>800 deg F), brazing (800-500 deg F - only filler melts), soldering (used for lower melting pt. metals, only filler melts)

Question 25

Why gauge doesn’t matter

Answer 25

proprietary, different ones, too confusing, go with actual dimensions, not nominal

Question 26

Metal processing

Answer 26

smelting = refining

alloying = adding different metals to main metal to confer good properties