Building Materials, Third Edition

114 BuildingMaterials

4.

5.

Modulusofelasticity

Worktolimitofporoportionality Nrnm/rnrrr'

H'W/^3

2bh3~2

H'W

/ bh

where H::::: maximumheightofdropunderthegivenweight

H ::::: heightofdropat thelimitofproportionalityreadfromthecurve(inclusiveof

deflectionx+y)

W ::::: weightofthehammer

/ ::::: spanofthetestspecimen

b::::: breadthofthetestspecimen

h depthofthetestspecimen

~ ::::: (y+x) atlimitofproportionalityfromthecurve

Broominq

Compressionand

shearing

Splitting

Wedge split

Fig.4.12 FailureofTimberSpecimenUnder

CompressionParalleltoGrain

CompressiveStrengthTest
ParalleltoGrain:Thespecimenmaybe 50 x 50 x 200mmor 20 x 20 x 80mm.Theloadisapplied
continuouslyduringthetestat aconstantrateof 0.6mmperminuteforboththesizes.
For 200mmspecimenaloadof 2.5 kN isinitiallyappliedtosetthespecimen.Deformation
undercompressionisthenmeasuredovera
central gaugelengthof 150 mm. Where
possible,directpointsareobtainedona
graphsheet.Thereadingiscontinuedwell
beyond the proportionallimit.Thefinal
readingatthemaximumloadisrecorded.
For 80 mrr-specimen,final readingofthe Crushing
maximumloadonlyisrecorded.

Compression failures are recorded

accordingtotheappearanceof thefractured
surfaceasshownin Fig. 4.12. Incasetwoor
more kindsoffailuresdevelop, theyare
describedintheorderoftheiroccurrence

(for example, shearing followed by Shearing

crushing).Theloaddeformationcurvesare
drawn.Loadanddeformationat limitof
proportionalityarethenreadaccordingly.
thevariouscharacteristicsaredetermined
bythefollowingformulae:
,
S.No. Characteristic Unit Formula

1. Compressivestressathrnitof N/mm^2 PIA

proportionality

2. Compressivestressatmaximumload Nz'mrrr' P'/A
   LP

3. Modulusofelasticityincompression N/mm^2 - ~A

paralleltograin