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CIVE 202 - Rami Questions > Steel > Flashcards

Steel Flashcards

1
Q

What is the other component in steel other than iron? Where does it come from?

A

Carbon

It comes from coal

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2
Q

What is the name given to the material when there is excessive Carbon (greater than 1.7%)?

A

Cast iron

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3
Q

Why would you not want to use cast iron in construction?

A

It is very brittle and weak in tension

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4
Q

What are the 3 ways of strengthening steel?

A
  1. Alloying
  2. Strain hardening
  3. Heat treatment (quenching/annealing)
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5
Q

What is the main downside of strengthening steel in connections besides reduced ductility?

A

Reduced weldability

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6
Q

What is the alternative connection besides welding? What is the problem with using it?

A

Bolting

It consumed more resources (expensive and time consuming) - more work and labor intensive; overall, increased project costs

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7
Q

What is toughness?

A

The ability of a material to absorb energy before failure

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8
Q

Name the most practical method of measuring toughness in structural steels.

A

Taking the area under the stress-strain curve

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9
Q

Why is taking the area under the stress-strain curve to calculate toughness not good for non-structural steels?

A

The area method only works for ductile materials

While structural steels are ductile, non-structural ones are more brittle

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10
Q

How does strain hardening affect toughness?

A

Decreased toughness

Decreased area under the stress-strain curve since you no longer count all of the area to the left of the unloading curve

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11
Q

Order the following materials from most to least variable: concrete, timber, steel. For each, explain the reasons for their variability or lack thereof.

A

Most variable: timber - random macroscopic defects since it is not manufactured but rather naturally grown

Medium variability: concrete - made in the field with usually unskilled labor BUT specific set of ingredients

Least variable: steel - made in factory with consistent controlled conditions

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12
Q

How do you account for the variability of materials in design?

A

Concrete and steel: phi factor
Concrete - 0.6 or 0.65
Steel - 0.85 or 0.9

Timber: other design adjustment factors
5% exclusion limit
Other adjustments (you can reference the slides but “probably not important”)

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13
Q

Comment on the difference in the phi factor between steel and concrete.

A

Steel is less variable so you can assume that you can use more of its strength, giving you a greater phi factor

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14
Q

If you are loading steel in tension, what is the permanent strain in the linear elastic region?

A

0

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15
Q

How do you find the Elastic modulus from a stress-strain graph?

A

It is the slope of stress over strain

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16
Q

What is a unique characteristic of steel in the linear elastic region compared to other materials?

A

For steel, the proportional limit is the same as the yielding point

17
Q

Why is ductility preferred in construction materials like steel?

A

You can get a warning before failure

18
Q

What is the mechanical property that is used to indicate failure of steel in a structure?

A

Yielding

19
Q

Why do we take yielding as failure?

A

Once a member reaches yielding, it begins to deform and collapse

These deformations are unideal for the structure but they also give a warning before ultimate collapse

20
Q

What is the physical difference between the uniform and localized plastic deformation regions of the stress-strain curve?

A

Uniform: same reduction of cross sectional area throughout the specimen (ie. the whole thing gets stretched out)

Localized: necking occurs (in one specific place along the specimen)

21
Q

What is the difference in failure planes between a ductile steel coupon and a brittle cast iron coupon?

A

Brittle: perpendicular failure plane

Ductile: 45 degrees and sloping (cup and cone)

22
Q

What is the difference in the corrosion reaction in submerged vs exposed steel?

A

Submerged: you don’t have much oxygen so you will stop at the first stage of rust

Exposed will progress beyond just the first stage

23
Q

What reactant is limited in the submerged condition of corrosion?

A

Oxygen

24
Q

Which condition of corrosion (submerged vs exposed) will have greater expansion?

A

Exposed since the reaction progresses further

25
Q

What are the effects on reinforced concrete in submerged vs exposed corrosion?

A

Submerged: will just lose tensile strength of the steel but no cracking of the concrete cover since there isn’t expansion

Exposed: will lose the tensile strength but also expansive cracking, spalling, delamination

26
Q

Why is it a bad idea to use different grades of steel for bolts and structural members? Why does the main issue occur?

A

Galvanic corrosion

This occurs due to a difference in electrochemical potential

The more reactive grade will become an anode and undergo corrosion (the other grade acting as a cathode)

27
Q

How can the concept of galvanic corrosion be used to protect steel in reinforced concrete?

A

Have a sacrificial anode (often Zinc) that will undergo galvanic corrosion

The Zinc is connected to the rebar and will corrode first instead of the rebar

Zinc’s corrosion isn’t expansive so no cracking due to that

28
Q

Why are welded connections the worst area for damage to occur?

A

Welded connections are usually under higher stresses, so they are more prone to corrosion (see stress corrosion)

Crevice corrosion can occur (where water gets into the gaps between the two metals)

You also have a lower fatigue strength due to the heat affected zone

29
Q

What are the three components of the microstructure at a weld?

A

Weld Metal (WM)
Base Metal (BM)
Heat Affected Zone (HAZ)

30
Q

Name the three crystals compromising the microstructure of steel.

A

Ferrite
Cementite
Pearlite

31
Q

Name the three grades of steel.

A

Eutectic, hypo-eutectic, hyper-eutectic

32
Q

Name the mechanical property of steel which alloys can increase.

A

Strength

33
Q

What is the heat affected zone during welding?

A

Area of reduced mechanical properties around the weld due to high temperatures during welding

34
Q

What are the types of corrosion?

A

General
Pitting
Galvanic
Crevice
Stress

CIVE 202 - Rami Questions (4 decks)

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