Steel

Question 1

what is the main use of steel?

Answer 1

rebar - reinforcement bars to resist tensile stresses which could lead to failure in the brittle concrete

Question 2

describe the process of prestressing steel

Answer 2

high strength steel - pulled at high tension until stretched, placed
in the form for the concrete beam, concrete is cast around them,
after the concrete gains strength and hardens, the cables are
anchored then cut, so it releases that tension that’s built into the
steel cable beck Into the concrete and pre-stresses it in
compression. Add compressive stresses to concrete by having the steel in tension and then cut the tension

Question 3

what are the two components of steel?

Answer 3

iron and carbon
cast iron has a lot of carbon
steel has low medium and high carbon content

Question 4

what type of steel do we use most frequently? why?

Answer 4

low carbon steel
more ductile (trade strength for ductility)
we want flexibility and warning before a collapse
more weldable than high carbon

Question 5

describe the properties of cast iron

Answer 5

brittle and weak in tension
dense and heavy and relatively cheap so used as ballast (weight for stability) or for counter balance

Question 6

what does the mix of ferrite and cementite make?

Answer 6

pearlite
Ferrite is very big and cementite is very small

Question 7

GET QUESTIONS FROM MICROSCOPY LAB

Question 8

describe the different microstructures of low carbon vs high carbon content steels

Answer 8

low carbon: coarse grains, low strength, high ductility, high toughness
high carbon: fine grains, high strength, low ductility, low toughness

Question 9

what is toughness?

Answer 9

ability to absorb energy

Question 10

what are three mechanisms to strengthen steel?

Answer 10

1) alloying: introduction of interstitial and substitutional atoms
2) work or strain hardening: generation and concentration of dislocations
3) heat treatment: formation of additional grain boundaries

Question 11

why do we alloy?

Answer 11

pure iron, without other elements, is too ductile to be used. plain carbon steels are too brittle. so we mix them
Changes properties of the steel not only mechanical but durable as well
Alloying makes it softer and less hard but reduces strength but makes it more machinable

Question 12

describe alloying and steel weldability

Answer 12

Welding is most effective and least amount of work
alloying promotes hardenability and this causes problems in welding
not all steels can be welded

Question 13

what is the other method of joining steel members?

Answer 13

bolted connections
work/labour intensive so increases project costs

Question 14

what are the advantages and disadvantages of work hardening steel?

Answer 14

improves tensile strength, yielding strength ad hardness at the expense of reduced ductility and weldability. so little application in structural steels

Question 15

explain strain hardening as area under the curve

Answer 15

Area under curve is how much energy is absorbed
Toughness is area under curve
Less toughness in strain hardened
Pink is non strain hardened so more tough because more area

Question 16

rank wood steel and concrete from most variable to least. how does this affect the phi factor?

Answer 16

wood
concrete
steel
least variable means higher phi factor (steel has 0.9)

Question 17

what are some processes affecting durability of steel?
Fcfc

Answer 17

fracture, corrosion, fatigue and assisted crackin

Question 18

what is steel fracture?

Answer 18

a physical separation of a homogeneous piece into separate pieces.
ductile at 45 degrees failure. we prefer ductile steel in order to have warning

Question 19

what factors affect the mode of failure?

Answer 19

triaxiality, temperature and strain rate

Question 20

REVIEW CORROSION FROM OTHER FLASHCARDS

Question 21

describe the corrosion process

Answer 21

an electric circuit is formed (anode and cathode). happens naturally and easier to from when steel is exposed. there are various electrochemical potential differences. electrons move from anode to cathode

Question 22

what is the first stage of rust?

Answer 22

at the anode, hydrous iron oxides form, the first being ferrous oxide

Question 23

what is green or black rust?

Answer 23

in situations where oxygen is limited (areas that are fully saturated (underwater)) corrosion may stop at the Fe(OH)2 stage. may not induce cracking of the concrete cover but the steel may completely disintegrate. rust dissolves in water.

Question 24

what happens to steel rust above water?

Answer 24

ferric rust. lots of oxygen available and steel will expand and cause stresses in concrete
corrosion depends on availability of oxygen, on availability of moisture and on factors affecting the maintenance of the electrochemical cells

Question 25

name the 5 different types of corrosion
Ggcsp

Answer 25

general
pitting
stress
galvanic
crevice

Question 26

describe each type of corrosion (separate card on galvanic corrosion)

Answer 26

general: rusting, the most familiar form
pitting: nonuniform, highly localized, occurs at distinct spots where deep pits are formed
stress: brittle failure in steel since corrosion is localized
crevice: occurs when moisture and contaminants accumulate in crevices and accelerate corrosion such as connections and joints

Question 27

what is galvanic corrosion?

Answer 27

when two metals touch, the less noble metal is more reactive. this less noble metal acts as the anode and undergoes corrosion
It is an electrochemical process in which one metal corrodes preferentially when it is in electrical contact with another, in the presence of an electrolyte.
this process is useful for the sacrificial anode

Question 28

what are the two primary exposure conditions to chlorides?

Answer 28

seawater and deicing salts. when concrete cover spalls, no longer any composite action of the steel inside the concrete
Also no more passivation film

Question 29

what does galvanizing steel mean and do?

Answer 29

method of protecting steel from corroding. zinc coating. basically, sacrificial zinc oxidizes and creates zinc oxide barrie protecting steel from outer environment. galvanizing rebar is expensive

Question 30

what are the three regions in a weld?

Answer 30

parent or base metal, weld metal, heat-affected zone

Question 31

what is welding?

Answer 31

Welding generates a temperature gradient from the fusion point to the parent metal, causing microstructural alterations in the heat-affected zone and resulting in decreased mechanical properties, which are contingent on the parent metal’s composition, initial state, and cooling speed after welding.

Question 32

what is weldability?

Answer 32

how well a metal performs when it is joined to a structure by welding. generally decreases when carbon and alloy content is increased. very strong influence on fatigue strength (based on geometry of joint, type of weld, and freedom from notch effects)