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Building Materials > Timber > Flashcards

Timber Flashcards

1
Q

Production of Timber

A
  1. Felling (tronzado): Production of a Stem (tallo)
  2. Bucking (tala): Production of the log (smaller pieces).
  3. Sawing (aserrado): Production of green and rough lumber (madera)
  4. Drying: Production of dry and rough lumber
  5. planing and sorting: Production of graded finished lumber
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2
Q

Chemical composition of timber (component and element)

A

Components:

  • C 48 - 50 % mass
  • O 43 - 45 % mass
  • H 5 - 6 % mass
  • mineral substances 0,2-0,6 % mass

Elements:

  • Cellulose 40- 50 weight%
  • Hemicellulose 20-25 weight%
  • Lignin 25-30 weight%
  • Extractives 0-10 weight%
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3
Q

Timber types

A
  • Softwood (Spruce, pine)
  • Hardwood (Maple, birch, poplar, oak, beech)
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4
Q

How is defined Moisture content?

A

Moisture content M (expressed in percent) is defined as:

M = {(Wa – Wo) / Wo} • 100 [%]

Wo: oven-dry weight of wood sample

Wa: weight of sample prior to drying

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5
Q

Which are the directions of the Shrinkage ?

A
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6
Q

Possible distortion of various cut sections after drying

A

twist. bow, cup, crook

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7
Q

How are the stress-strain curves of pine wood under loads?

A

Parallel and perpendicular to the grains at a moisture content (u) of 15%

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8
Q

Failure modes of timber under compression parallel to grain

A

Failure types of non-buckling clear wood:

a) Crushing
b) Wedge splitting
c) Shearing
d) Splitting
e) Crushing and splitting
f) Brooming or end rolling

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9
Q

Failure modes of timber in tension parallel to grain

A

Failure types of clear wood:

a) Splintering tension
b) Combined tension and shear
c) Shear
d) Brittle tension

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10
Q

Failure modes of timber in bending with span parallel to grain

A

Failure types of clear wood:

a) Simple tension
b) Cross-grain tension
c) Splintering tension
d) Brash tension
e) Compression
f) Horizontal shear

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11
Q

Influence of knots on the strength of pine timber loaded parallel to the grain.

A
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12
Q

The relation of strength to loading angle (schematically)

A
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13
Q

Influence of moisture content on the strength

A
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14
Q

Effect of moisture content on the rigidity in Sitka spruce

A
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15
Q

The interaction of temperature and moisture content on the modulus of elasticity.

A

Results are averaged for six species of timber and the modulus at 20°C and 0% moisture is taken as unity.

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16
Q

Effect of grain angle on the modulus of elasticity

A

The theoretical line has been calculated by transformation of the stresses and strains from the rotated to the principal

17
Q

Quality classification parameters

A

Independently from the type of timber, the quality class is determined according to the following parameters:
• Knots
• Inclination of fibers (wane)
• Pith
• Cracks
• Resin pockets
• Bending
• Insects frass

18
Q

Influence on Timber Durability

A

The timber durability can be negative influenced by:

  • Fungi
  • Insect infestation
  • Fire

By moisture content equal to 0.0 % (dry) or to 100 % (water immersion) no attack by fungi or insect infestation is possible
With lower moisture content the degree of inflammability increases
Oxygen, Temperature and moisture are required for fungi and / or insect attack

19
Q

Preventing fungi attack

A
  • Good designed column base
  • Correct design of a bedding of a timber beam into a masonry wall
20
Q

Timber fire behavior

A

Glued beam section after exposure to fire of 30 and 60 minute
Timber carbonization, approx. 0.7-0.8 mm/min (EC 5)

21
Q

Timber fire protection

A
  • Light timber: Protection through fire resistance cladding materials.
  • Heavy timber: Protection through proper design. Burning point of approx. 300 °C
  • Outer burned layer looses strength, but act as insulating layer for the core
  • The moisture evaporation leads to a slight loss of strength and stiffness of the core
22
Q

Timber connections

A
  • Screws for timber connections
  • Connections with nailing strips
  • Wooden connections with perforated plates and perforated form parts
  • Timber truss connected with perforated plates
  • Timber connected with steel angles
  • Timber connection with steel dowels
  • Timber connection with wooden dowels
23
Q

Stiffness of connections (graph)

A
24
Q

Production of glued laminated timber

A
  • Drying of the boards
  • Strength grading - Visual and/or mechanical tests
  • Cutting off knots and other wood-defects and repetition of strength grading
  • Planning of the lamellas - Max thickness 45 mm
  • The glue is applied on the broader edge of the lamella
  • Pressing - At least three lamellas are stacked and pressed in an either straight or curved press
  • Planning of the gluelam
  • Factory assembly and further detailing

Building Materials (12 decks)

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