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WOOD
1.
2.
3.
4.
WOOD
Introductory notions
Physical-mechanical properties of wood
Wood building materials
Drying of wood
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1.1 Brief history of wood
constructions
- the Rhine bridge (1st century BC) 500 m long,
built in only 10 days
1. Introductory notions
- the Danube bridge (2nd century AC), 1070 m
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long
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1.2 General characteristics of the
wood
1.2 General characteristics of the
wood
• 99 of substances that form wood material are of
organic nature (carbon, hydrogen, oxygen),
 t ≥ 110°C unstable;
 t = 200°C fuel;
 t = 300°C inflammable, catching fire in air
without flame
- fibrous structure
- chemical composition varies according to:
- the species of the tree
- its age
- the place where it grew
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2.1 Density of wood
- 1500 kg/ m3 – apparent density
- hard wood material (oak – stejar, ash – frasin,
walnut – nuc, acacia – salcam) used for the
construction of load bearing and high durability
materials;
- soft wood material (fir – brad, spruce – molid, poplar
– plop, willow – salcie, linden – tei).
2. Physical-mechanical
properties of wood
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2.2 Wood moisture
Type of tree
Fir
Spruce
Pine
Oak
Beech – Fag
Ash
Linden
Apparent density for [kg/m3]
green wood
with 15% water
1000
450
740
480
700
520
1110
740
1010
750
920
760
740
460
• free water, hygroscopic water, and chemically
bound water
• hygroscopicity water influences the main
properties of wood
• relative standard moisture 15 .
dry
410
430
490
650
690
680
490
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2.3 Determination of mechanical
strengths
a) Compressive strength
Type of tree
Pine
Spruce
Birch – Mesteacan
Absolute humidity Relative humidity
 Ua
 Ur
80 – 90
44 – 47
80 – 100
44 – 50
60 – 80
37 – 44
a1) Compressive strength parallel to
fibers
Prismatic test tubes without defects
20 x 20 x 60 mm
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a) Compressive strength
a) Compressive strength
a2) Compressive strength perpendicular to fibers
- in resinous trees (rasinoase)
- Rc⊥ = 20 daN/cm2
- RcII = 80 daN/cm2
- in deciduous trees (foioase)
- Rc⊥ = 40 daN/cm2
- RcII = 100 daN/cm2
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b) Tensile strength
Type of
tree
Strength at a
15% moisture
Acacia
Oak
Beech
Ash
Pine
Linden
Spruce
Fir
750
740
750
760
520
460
480
450
Compressive strength
daN/cm2
Parallel to
Perpendicular to
fibers
fibers
590
130
540
105
525
90
480
105
460
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440
430
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400
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b1) Tensile strength parallel to the
fibers
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b2) Tensile strength perpendicular to
the fibers
Rt ⊥ = ( 1/15 …1/35) Rt II
c) Bending strength
Rt II = 2 RcII
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d) Shearing strength (Rezistenta la
forfecare)
d) Shearing strength
d1) Transverse shearing strength t
d2) Parallel longitudinal shearing strength II
d3) Perpendicular longitudinal shearing strength p
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e) Crushing strength of wood
Static compression, stretching and bending
Rt II = 2 Rc II
Ri ⊥ = 1,5 Rc II
Ri ⊥ = 2 Rc II
for resinous and deciduous trees
for resinous trees
for deciduous trees
These relations are valid only in the case of wood
without defects with 15% moisture.
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3. Wood building materials
• raw, semi-manufactured, finished products –
maintain the structure of the wood material from
which they are derived
• modern wood products – no longer maintain the
structure of the material from which they are derived
 following cutting (aşchiere), grinding (defibrare),
impregnation, pressing, gluing (încleiere).
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3.1 Raw wood products
3.1 Raw wood products
• end cutting, branch removal curãţarea de
crengi, bark removal
without other
operations on the wood cylinder.
• logs (buşteni), putlogs (bile), poles (manele),
posts (prãjini), round pitwood (lemn rotund
pentru minã), and airline pillars (stâlpi pentru
linii aeriene).
Logs:
• round wood material,
• L > 2,50 m; min = 18 cm
• for the obtaining of finished wood products and
semi-manufactured products
Putlogs, poles and posts
• round wood material – from resinous trees
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3.1 Raw wood products
Product
Putlogs
Poles
Posts
Thin end
cm
12-16
8-11
4-7
Round pitwood
• from resinous or deciduous wood
• used in mine propping
•  >18 cm , L = (1 – 5) m.
Length
m
6-9
3-6
2-4
Airline pillars
• from resinous and deciduous wood
• L = (5-14) m
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3.2 Semi-manufactured wood
products
3.2 Semi-manufactured wood
products
• from round wood hewn (cioplit) + cut
• hewing (cioplitura), fencing posts (bulumaci),
railway sleepers (traverse de cale feratã), timber
(cheresteaua), veneer (furnir), plywood (placaj)
and laminated boards (panele)
Hewing
• hewing of the 4 lateral sides of round resinous wood,
• processing with straight or chamfered (teşit) edges
• framework elements: beams (grinzi), wedges (pane),
rafters (capriori)
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3.2 Semi-manufactured wood
products
3.2 Semi-manufactured wood
products
Railway sleepers
Fencing posts
• hewing or cutting of wood (only deciduous wood)
– type A: all sides with chamfered edges cut or hewn
– the best quality, used in arches or bridges;
– type B: only three sides cut or hewn, the fourth side
maintaining its initial shape
– type C: only one side and the sole (talpa) cut or
hewn, the lateral sides having a natural curvature
• hewing of round deciduous wood
• used in fences
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3.2 Semi-manufactured wood
products
3.2 Semi-manufactured wood
products
Timber (cheresteaua)
Product
• cutting of round wood in longitudinal direction
• all sides flat and parallel in pairs, or only two
parallel flat sides
• from timber  boards (scânduri), deals (dulapi),
strips (şipci), scantlings (rigle), beams (grinzi)
Boards
Deals
Scantlings
Beams
Strips
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Thickness
g (cm)
 4
4
>4
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 4
Width
cm
>2g
>2g
<2g
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 g
Length
m
0,5-6
0,5-6
0,5-6
3-6
3-12
0,4-6
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3.2 Semi-manufactured wood
products
1. boards; 2. deals; 3. scantlings; 4. beams; 5. strips.
• Boards: roof boarding – (astereală) (cover
support), casings for concrete elements (in walls,
ceilings);
• Deals: floor material (bridges, scaffolds), for
reinforcement
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3.2 Semi-manufactured wood
products
3.2 Semi-manufactured wood
products
• scantlings – for frameworks and the
construction of wood doors and windows;
• beams – load bearing elements in floors,
pillars;
• strips – for fences, the manufacture of
furniture.
Veneer (furnir)
- cutting of deciduous logs – into thin, flat sheets
h = 0.4 – 6 mm
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3.2 Semi-manufactured wood
products
Plywood
Plywood (placaj)
• stratified wood products – gluing of the veneer
sheets (3-9)
• the fibers of two consecutive sheets should
form a right angle (sometimes angles of 30, 45
or 60° are formed)
• very high quality adhesives + hot pressing
• floors, walls, casings for concrete elements,
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furniture, false ceilings
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3.2 Semi-manufactured wood
products
3.3 Finished wood products
Laminated boards (Panele)
Cellular plates (plăci celulare)
• a core of soft wood strips, glued together and
covered with veneer sheets on both sides
• doors, separating walls
• a rigid wood framework (cadru)
• on the inside, cells formed by straight or
spiral veneer bands
• covered with veneer or plywood on both
sides
• doors, furniture panels, separating walls
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3.3 Finished wood products
Cellular plates
Rebated boards (scânduri fălţuite)
• from resinous wood boards
• planed (rindeluit) visible side
• L = (2 – 6) m, l = (8 – 10) cm, h = (1.8 – 2.5) m
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3.3 Finished wood products
3.3 Finished wood products
Tongue and groove floors
Wood tiles
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- resinous or deciduous
wood shingles
L = 30, 40, 50 cm,
l = 9 – 10 cm,
h = 1.5 cm.
from resinous boards, one planed side
with tongue and groove
L = 2- 6 m , l = 10-16 cm, h = 2,5 – 4,8 cm
floors
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3.3 Finished wood products
3.3 Finished wood products
Parquet
• Lamellar parquet; h =1 cm
• Laminated parquet – the pressing of wood
plates at a high temperature and pressure –
very compact structure
• Plinth (plintă) – element between the floor
and the wall
• for the construction of floors
• oak and beech woold
• L = 20 - 50 cm, l = 3–9 cm, h =17 – 22 mm
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3.4 Modern wood materials
3.4 Modern wood materials
• change of structure – by hot pressing, hot treatment
• change of composition – by impregnation with
synthetic resins
• wood stratified (lemn stratificat)
• impregnated and pressed (lemn impregnat şi presat)
• wood particle boards (plãci aglomerate din lemn)
• fiber building boards (fibrolemnoase)
• glued wood (lemnul încleiat)
Stratified wood
• veneer sheets
• impregnated with phenol formaldehyde resins,
p = 110 – 150 atm; t = 140 – 150°C
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3.4 Modern wood materials
3.4 Modern wood materials
Impregnated pressed wood
Wood particle boards (Plãcile aglomerate din
lemn – PAL)
• large blocks of soft wood 
impregnated with
synthetic resins
•  pressure and successive heatings  Vf = (0.45 –
0.75) Vi
- by the agglomeration of wood chips using a
synthetic adhesive
- under the simultaneous action of temperature and
pressure
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3.4 Modern wood materials
Fiber building boards
Fiber building boards (plãci din fibre de lemn –
PFL)
– isolated fibers, wood fiber fascicles  felted
(împâslite) and glued (încleiate)
• fiber building boards
– porous
– medium hard
– hard
– extra hard
• floors, separating walls, interior cladding, ceilings,
roofs, casings.
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3.4 Modern wood materials
4. Drying of wood
Glued wood
• joining by the gluing of several parts – squared
wood sheets (boards, deals, scantlings)
natural drying: 1 year  1cm thickness
• placement of boards in piles, allowing air to pass
between them
• time and space – extensive – disadvantage
• the most effective
air-conditioned drying
• a stream of hot air around the piles
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4. Drying of wood
4. Drying of wood
Chemical drying
Drying using high frequency currents
• salts are applied to the wood surface – salt, urea,
glucose
• they accelerate the drying of wood
•heating of bodies inside wood
•very short drying time (hours)
•extremely expensive procedure.
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