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CIVI 321 > CHAPTER 10 > Flashcards

CHAPTER 10 Flashcards

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1
Q

2 types of growth

A

endogenous

exogenous

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2
Q

What is endogenous

A

intertwined growth.

very strong and lightweight

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3
Q

What is exogenous

A

outward growth

more predictable engineering properties

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4
Q

Difference between deciduous and confierous

A 
Deciduous = hardwood
Coniferous = softwood
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5
Q

Dark vs light ring

A

Early wood : light ring

Latewood : dark ring

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6
Q

What is early wood

A

rapid spring growth of hollow thin-walled cells

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7
Q

What is late wood

A

dense summer growth of thick-walled cells which are much harder and stronger

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8
Q

from center axis outwards

A
  • pith
  • heartwood (darker)
  • sapwood (ligher)
  • cambium (very thin layer)
  • inner bark
  • outerbark
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9
Q

Longitudinal properties

A

strongest and least shrinkage

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10
Q

Radial

A

perpendicula ro the growth rings

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11
Q

Tangential

A

weakest and most shrinkage

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12
Q

The direction influences

A

strength, modulus, thermal expansion, conductivity and shrinkage

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13
Q

Definition of anisotropic

A

properties change with direction

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14
Q

Chemical composition of wood

A 
Cellulose
Lignin
Hemicellulose
Extractives
Ash-forming
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15
Q

What is cellulose

A

polymer that forms strands (fibrils) that make up cell walls.

high density indicates higher strength

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16
Q

What is the lignin?

A

The glue

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17
Q

What are extractives?

A

tannins, coloring matters, essential oils, fats, resins, waxes, starches

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18
Q

What are ash-forming?

A

calcium, potassium, phosphate, silica

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19
Q

What depends on the moisture content?

A

shrinkage
strength
weight

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20
Q

What is EMC?

A

equilibrium moisture content.

moisture content for average atmospheric conditions

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21
Q

What is the FSP?

A

fiber saturation point

moisture content when cells are completely saturated with bound water but no free water inside cell cavities.

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22
Q

what is bound water

A

water held tightly in cell cavities, wood shrinks on removal

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23
Q

what is free water

A

water inside cell cavities

doesnt affect shrinkage

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24
Q

above fsp?

A

changes affect only wet weigth

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25
below fsp?
small changes strongly affect all physical and mechanical properties
26
largest shrinkage is in
tangential direction
27
smallest shrinkage is in
longitudinal direction
28
zero shrinkage @
above fsp, regardless of direction
29
for glulam, assume
1% shrinkage per 5% change in m/c
30
wood production steps (6)
1. harvesting 2. sawing 3. seasoning (drying) 4. surfacing (planing) 5. grading 6. preservative treating
31
5 types of wood products for construction
- dimensional lumber - heavy timber - round stock - specialty items - engineered wood products
32
harvesting : 3 things
- minimal sap wanted - concerns of fire hazard - other plant growth and underbrush is minimal
33
3 types of sawings
live (plain) quarter combinatio0n
34
3 types of board cuts
flat-sawn rift-sawn quarter-sawn
35
describe flat sawn
worst quality, most problems and defects grain is
36
describe rift-sawn
45-80°
37
describe quarter-sawn
80-90° best quality, least shrinkage problem
38
moisture content of green wood when leaving mill
approximately 15%
39
3 methods of seasoning
``` air drying (cheap and slow) kiln drying (fast and expensive) combination ```
40
s4s means
surfaced 4 sides = dressed
41
planing involves taking off
1/4 inch from each side
42
4 types of grades for canadian timbers
- select structural (ss) - no 1 - no 2 - standard utility
43
causes of lumber defects (5)
- natural wood growth - seasoning too fast - wood diseases - animal parasites - faulty processing
44
what is the specific gravity of the cell wall?
1.5
45
specific gravity closer to 1.5 means
more cell walls which is denser and stronger
46
what is the R value?
1/conductivity
47
what is thermal diffusivity
rate at which material absorbs heat from surroundings
48
applying heat to wood
first expands the wood from thermal expansion then shrinks from moisture loss (when below FSP)
49
electrical properties of wood
good electrical insulator which decreases with moisture content. more water is a better electrical conductor
50
modulus of elasticity of wood depends on
- species variation - moisture content - specific gravity and - direction of grain
51
which is better : tensile or compressive?
tensile
52
which is stronger : parallel or perpendicular to grain for tensile strength?
parallel to grain 20x greater than perpendicular
53
loads over time for wood?
wood can support higher loads of short duration than sustained loads
54
load duration : what is the time assumed for design?
10 year loading and/or 90% full max load throughout life of structure
55
short-duration loads, how to design?
multiply design values by load duration factors fr short-duration loads
56
vibration damping and wood
vibration damping increases w/ moisture content up to FSP. better than structural metals
57
what are the two main testing techniques?
- testing of timbers of structural sizes (ASTM D 198) | - testing of representative, small, clear specimens (ASTM D 143)
58
3 types of tests
- 2-point, 3rd-point or center-loading
59
design considerations for wood
- load duration - temperature - size - flat use - column stability - repetitive member - wet service - beam stability - volume (glulam only) - curvature (glulam only) - bearing area
60
5 organisms that degrade wood
- fungi caused dry rot - bacteria damage black heartwood - termite damage - spruce ips beetle - marine-borer damage to a buried pile
61
wood preservation, 2 types
- petroleum-based, | - waterborn preservatives (salts)
62
2 applications techniques for wood preservation
- superficial treatment (Generally not effective) | - liquid penetration (pressure treating at high temp, heat and moisture)
63
what are engineered wood products?
- made by bonding together wood strands, veneers, lumbers or other forms of wood fibers to produce large units.
64
2 advantages of engineered wood products
- produce specific and consistent mechanical properties that are better than natural large ppieces - hard to find high quality large natural pieces
65
what is plywood
thin sheets (plies) flued together with the grain at right angles toeach other so it has the same propertiesin both direction
66
how is plywood made?
veneer is peeled from a soaked log on a giant lathe
67
what is particle board?
sawdust sized particles
68
what is chip board
randomly oriented wood chips
69
what is osb
wood chips and strand oriented in specific direction
70
how are floor joists made of wood?
two 2x4s or 2x6s as flanges and an OSB web
71
what is glulam?
lumber glued together with the parallel grain
72
advantages of glulam
- ease of manufacturing large pieces from standard commercial - can vary cross section along length - special architectural designs - can use lower wood grade in less stressed areas - minimizes shrinkage defects

CIVI 321 (7 decks)

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