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1.TIMBER 1
Degree of Bachelor of Science (Honours) in BuiltEnvironment
StudiesYEAR 2 SEMESTER 1MATERIALS !R "!#STR$"TI!# %
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Nomenclature
Timbers are botanically divisible into twoclasses: softwoods
gymnosperms !"bein# $rod%ced by coni&ero%s trees andhardwoods
angiosperms) by broadleaved trees. 'ote t(at some so&twoodsare
(arder t(an (ardwoods e.#. balsawood Ochroma lagopus ! is a
(ardwoodw(ile yew Taxus baccata ! is a so&twood.Bot( classes
contain timbers w(ic( varyin wei#(t" stren#t(" resistance to
decayand colo%r.
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Timber speciesS$eci&ications s(o%ld state t(e
c(aracteristics re)%ired and"&re)%ently" name t(e s$ecies. T(e
common names %sed &ortimber s$ecies is o&ten misleadin# or
ambi#%o%s. It is best tos$eci&y timber by some reco#nised
standard e.#. BS **1 and
+*,! or by t(e -atinised s$eci&ic name. It is #enerally
s%$er&l%o%sto name t(e ori#in o& t(e timber.
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In most develo$ed co%ntries abo%t * / o& all timber %sed in
t(e
constr%ction ind%stry consists o& so&twoods. Ty$ical
so&twoods andt(eir re#ion o& ori#in incl%de: $ine European
redwood ! and s$r%ceEuropean whitewood ! 0 'ort( and entral E%ro$e
(emloc3"
s$r%ce" $ine" &ir" western red cedar" American redwood 0
'ort(
America $itc( $ine 0 entral America 4arana $ine 0 Bra5il.
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6ver 1 (ardwoods are %sed commercially" alt(o%#( over
(al&t(e re)%irements consist o& as(" beec(" iro3o" ramin"
ma(o#any"meranti" oa3 and tea3. As(" beec( and oa3 come &rom
t(etem$erate &orest o& 'ort( America and E%ro$e" t(e rest
&romtro$ical &orests.
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Tree growthT(e tree" a com$le7 livin# or#anism" can be
considered in t(ree main sections:t(e branc(es wit( t(eir leaves"
t(e tr%n3 or bole and t(e roots. T(e rootsanc(or t(e tree to t(e
#ro%nd and absorb water wit( dissolved minerals &romt(e soil.
T(e leaves absorb carbon dio7ide &rom t(e air adn in t(e
$resence o&s%nli#(t" to#et(er wit( c(loro$(yll as a catalyst"
combine carbon dio7ide wit(water to $rod%ce s%#ars. T(e s%#ars in
a)%eo%s sol%tion are trans$orted downt(e branc(es and t(e tr%n3 to
be s%bse)%ently converted" w(ere re)%ired &or#rowt(" into t(e
cell%lose o& t(e tree. T(e tr%n3 #ives str%ct%ral stren#t( to
t(e
tree" and acts as a store &or minerals and &ood s%c( as
starc( and also as atwo0way trans$ort medi%m.
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T(e tree is $rotected &rome7tremes o& tem$erat%re
anddama#e by t(e bark " insidew(ic( is t(e bast layer
w(ic(trans$orts downwards t(es%#ars synt(esised in t(eleaves.
Radial rays t(en move
t(e &ood into sa$wood cells &orstora#e. Inside t(e bast
is t(et(in and delicate cambium w(ic( is t(e #rowin# layer
&or
t(e bar3 and t(e sa$wood.8rowt( ta3es $lace w(en t(ecambi%m is
active" w(ic( intem$erat%re climates is d%rin#s$rin# and
s%mmer.
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Growth ringsRin#s o& timber added to t(e tr%n3 or branc(es"
%s%ally oneevery year. T(e rin#s are wide i& #rowt( is ra$id"
and t(ewider t(e #rowt( rin#s o& a $artic%lar s$ecies" t(e less
denseand stron# is t(e timber.
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Early wood or spring wood T(e early #rowt( o& t(e rin# it is
normallywide and so&t.
Late wood orsummer wood T(e later #rowt( o&
t(e rin# it is denser"dar3er and narrowert(an t(e early
wood.
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Sapwood
T(is &orms t(e $art o& t(e tr%n3 active in t(e li&e
$rocesses o& t(etree. It is li#(ter in colo%r t(an (eartwood"
and" as it containss%#ars and starc(" tends to be more attractive
to insects.Heartwood (is occ%rs at t(e centre o& t(e tree and
is made %$ o& dead&ibres.
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GrainT(is term re&ers to t(e #eneraldirection or arran#ement
o& t(e&ibres.
Slope of grainT(e deviation in t(e direction orain ca%sed by
branc(es or bendsin t(e tree.
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Natural defects in the tree
T(ese are &eat%res w(ic( develo$
in t(e tree be&ore or soon a&ter it is&elled" and
w(ic( may detract &romt(e %se&%lness o& t(e
timber.T(ese incl%de:
Natural inclusions
Minor de&ects w(ic( occ%r w(en$eices o& bar3 (ave
become
enclosed wit(in t(e timber arecommon. 4itc( $oc3ets and
resinstrea3s" containin# &l%id resin" are&re)%ently seen
alon# t(e #rain o&
so&twoods.
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Brittleheart
T(e centre o& t(e tree pith ! brea3s wit( a brittle
&ract%re
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Sapwood
Sa$wood re)%ires better $rotectiont(an (eartwood and ta3es
%$
moist%re more readily.
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Abnormal growth rings
a%sed by ra$id #rowt( (ence lower density and stren#t(.T(e
o$tim%m n%mber ran#es aro%nd + rin#s $er cm &orso&twoods
and 9 rin#s $er cm &or (ardwoods!.
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Two ad acent limber $ine trees e7(ibit
sinistral s$iral #rain le&t! and strai#(t#rain
Spiral grain
;istorts str%ct%ral timber inseasonin#.
