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B A MR 0 0
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MA T E P I A L
FOR
R E I N F 0 R C I N G
course XIII
C 0 XC R E T E
may , 1914
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P R E F A CE
In the Winter of 1912, an order of bamboo
was placed with a dealer in Shanghai, China.
The
bamboo was purchased for specimens to be used in testing its strength.
Its extensive growth, its abun-
dance, and its innumerable uses,
rance of its properties,
coupled with the igno-
demand that such a test be
made.
The bamboo arrived in May of the following
year after a journey of thousands of miles on board
trans-Pacific ship and over trans-continental railroads.
The whole batch numbered thirty-five of varying size,
weight and age, of which several were injured, but
ninety per cent was sound.
Chikiang Province,
They were native of
China.
Experiments were begun in the fall
of 1913,
and extended throughout the year while f6llowing the
fourth year curriculum of the Coursee of Naval Archi-
tecture in the Massachusetts Institute of Technology,
in which these experiments were conducted.
The
great tensile strength of Bamboo inspired the author
to attempt to use it as a material for reinforcing
concrete.
In this thesis report much space has
been devoted to the discussion of the matter;
and it
is hoped that further experiments will be made to throw
more light upon the subject.
The author desires to acknowledge his indebtedness to the instructing staff in general of the De-
partment of Theoretical and Applied Mechanics of the
Massachusetts Institute of Technology;
Peabody,
Instructor in the Department,
to Mr. Dean
whose kind as-
sistance in the making and testing of concrete beams
reinforced with bamboo has been most helpful to the
author.
Thanks are also due to all those who have
bestowed their helping hand upon the author.
Massachusetts Institute of Technology,
May,
1914.
&ri
C ONTENTS
Page
iv
PREFACE
...
...
Preliminary Calculation ...
...
...
Design of Form-
..
CONCRETE REINFORCED WITH BAMBOO
...
...
...
...
1
...
... e
2
...
...
9
...
Estimate of Material, Bending of Sti rrups...
10
Pouring of Concrete ...
...
...
11
Test of Beams
...
...
...
...
.*..
Analysis of Results
...
...
Notes on the Tests
Conclusion
...
...
... 5
13
...
...
24
...
...
...
26
s..
...
...
31
...
33
...
59
.
s. ...
...
...
...
...
...
...
Tests on the Tensile Strength of Bamboo
Shearing Strength of Bamboo
...
Colurimn Tests on Bamboo
...
...
...
Specific Gravity of Split Bamboo
...
...
...
..
...
Coefficient of Friction of Bamboo...
...
Coefficient of Erpansion of Bamboo
...
Relation of Number of Toints to Diameter
Miscellaneous
.....
... *..
Veneering of Bamboo.
Bamboo in Aeroplane Work.
Gluing Quality of Bamboo.
... *..
...
...
...
...
...
...
63
...
...
67
...
69
...
e
72
...
...
71
e
74
CONTENTS
1.
V11
(continued)
Page
Carpenters'
Tools on Bamboo.
Bending of Bamboo Strips.
Cracks in Bamboo.
Cross-sectioning of Bamboo.
Review of Max Ulrich's Work
....
Review of Captain Bond's Work
...
Professor Johnson's Tests on Bamboo
Appendix II
*..
... *
*
. .o.
s.. e.
...
...
78
0 . ...
...
*.
89
...a
..
...
...
97
...
...
...
...
100
s..
...
116
...
...
Y111
LIST OF ILLUSTRATIONS.
Page
Bamboo as seen in the
Institute Laboratory
...
..
Drawing of Form - Blueprint...
Frontispiece.
.
...
...
.0
...
...
.9..
9
Wire Machine, used for testing
Tension of Bamboo ...
...
31
Shear Block, used for testing the Longitu-
dinal Shear of Bamboo.
-.
Photo and Drawing
Emery Machine,
--.
...
...
58
9...
300,000 pounds capacity
62
Bamboo Coluim Split under compression
Drawing of 5-1/2 inch Extensometer,
used in Column Test
...
...
...
Bamboo Cracks at a Joint
*.. ...
Bamboo Trestles and Bridges...
Butt of Bamboo, whole and split
Bamboo Grove in China
...
...
...
.
.9..
65
.9..
65
...
...
.0.
9
75
89
After Appendix II
"
...
"
II
V
II
Bamboo Grove in China
another view
...
...
...
V
"
V
/
/1
Y
.m
I
I
-- C
0000**
CONCRETE REINFORCED WITH BAMBOO.
The high tensile strength of bamboo led the
author to conceive the idea of applying this material
to the reinforcing of concrete beams on its tension
side.
The abundance of growth of the wood and the
ease with which it can be procured in
the land of China
would render it of practical value, should it prove to
contribute to the strength of the member to which the
reinforcement of the bamboo has been applied.
There
are several large cement factories in China that produce first grade cement at comparatively low cost.
Although reinforced concrete has been used in China
only to a limited extent, time will come when the wave
of concrete construction in the West will spread far
and wide in the East.
For structures for which steel reinforcing
will be too expensive, and where bamboo can do as well
as steel, bamboo can displace steel.
bungalows,
cottages,
watertanks,
For instance,
culvert pipes, foot
bridges, etc., can be reinforced with this material.
Preliminary Calculation.
zt
Test specimens of reinforced concrete beams
are habitually of the dimensions
40 X 8' X 6' - 8".
The beam is to be tested with a six feet span, loaded
by two loads symmetrically placed at one third of the
span from each end.
Consequently the calculation
should be made on this assumed beam.
The Joint Committee recommends " The lateral
spacing of parallel bars should not be less than two
and one-half diameters, center to center, nor should
the distance
from the side of the beam to the center
of the nearest bar be less than two diameters."
This practically fixes the design of the section as
shown in the following figure.
3
There remains, however, the calculation of maximum loads which may be expected of the beams to bear
with such reinforcement.
To do so, the common form-
las for reinforced concrete has been used.
long list
of formilas numbering sixteen,
From the
the one of
immediate application to this case is the. following:
X
where
=
3 r+2n
1/6 bd 2 Cn ----------(r + n) 2
X = bending moment due to safe loads.
b = breadth of beam.
d = distance from center of tensile steel area
to compression side of beam, or the effective depth.
C = compressive stress in the concrete.
*Brooks, John P.
"Reinforced Concrete",
p. 30.
4
n = ratio of Modulus of Elasticity of steel to
that of concrete.
r = ratio of tensile stress of steel to compres-
sive stress of concrete.
b
In this case,
concrete);
d = 7";
= 4";
n = 15;
C =650
(1 : 2 : 4
(The values of C,
r = 15.
n and r, are Joint Committee reconzrendations
.
)
3 X 15 + 2 X 15
1/6 X 4 X 7 2 X 650 X 15 -----------------
*M
(15 + 15 )2
=
26,600 inch
lbs.
(1)
.....................
The weight of concrete beam is:
41/12 X
77t. per foot
/12
222
---
=
per cu.ft.) = 220#
X 6.66 X 150 (lbs,
=
666
33.4
4//ft.
The maximum bending moments due to safe
load
W
---
and its own weight is:
2)
W
--2
X
220 X 61
+ - - - - ..
3
2'
.
.
. . . ..
(2)
Equat ing ( 1 ) and (2 ) we have
W
M
26,600 = --2
W
W
=
220 X 6
X 2 X 12 +--------- X 12
8
2050#
being the load which is expected of this beam to
S
s tand without failure.
As will be seen later, the
maximum load under which the beams fail is many times
the above figure.
This shows that in the design a
good factor of safety has been used.
There remains,
however, the calculation of
stirrup near the ends of support,
in order that the
beams will not fail by diagonal shear, and the tension in the reinforcing rods may be fully developed.
The Joint Committee recommends a working -shearing
stress of 40 lbs. per sq. in.
V
where
=
V
b
V = total shear that the concrete is capable
to bear without the help of stirrups.
v
= allowable shear stress = 40#/.'
j = vertical distance between points of application of horizontal tensile and compressive stresses.
*Brooks
"Reinforced Concrete"
page 73.
3 r + 2 n
= d -----------
But
3(r + n)
3 A 15 + 2 X 15
=7 X ----------------- --
5.83"
3(15 + 15)
Therefore
V
=
933#
40 X 4 X 5.83
There is at the support a shear of
Then
1135 - 933 = 200#
1025#+ 110# = 1135#.
must be taken up by stirrups.
The proportion
1135 : 200
2' : x
=
will give the distance from support within which reinforcement by stirrups is necessary.
Solving the equa-
tion,
x = .35'
=
4.2"
In the actual beam, the stirrup reinforcement extends
as far as 20" from the ends of support to make it doubly sure failure will not occur at sections other than
that of maximum bending moment.
For stirrups 1/8"
rods are used.
The calculation for beams reinforced with
bamboo Strips are identical with that for steel in
*Brooks "Reinforced Concrete",
page 40.
however
7
every respect, with the difference that since bamboo
is approximately 2/3 of the tensile strength of steel
(from Ulrich's test), the sectional area of bamboo
should be 3/2 times as much as that of steel;
and
the beams reinforced with bamboo are so designed.
The author is aware of the unsoundness of this assumption;
but in the absence of better information on this
subject,
other.
this assumption is perhaps as good as any
The ratio of sectional areas for steel and
bamboo can be revised should the tests prove that the
assumption is incorrect.
The bamboo strips available are of the section
.3" X .7"
for one beam.
=
.21
.
Three strips are used
Hence
3 X .21
63
=
Steel with cross-sectional area of 2/3 of bamboo should
be as strong as the latter according to the assumption
2/3 X .63
=
42L
Two 1/2" rods are used.
Area
=
Actual ratio
=
2 X .19637
.3926
-----
-
=
.3926
.623
.63
The following figure shows the beam in its final form.
It
should be noted that two small steel rods of 1/8"
8
diameter are put near the top of every beam, the idea
being to prevent possible collapse due to making the
top side the tension side when handling.
Design of Form.
The accompanying blueprint shows the forms
The sides and
used for the making of these beams.
bottom are the same, but end pieces are different for
different beams,
as indicated,
to make provision for
the ends of the reinforcing rods to lodge in.
actually constructed,
As
every joint is a mortise and tenon
joint, and with numerous wood screws,
every joint is
made watertight.
We must note here that by keeping the lower
edges of both steel and bamboo pieces at an equal distance from bottom of beams,
the value of
d
for steel
in the preliminary calculation is not strictly correct
for bamboo;
neglected.
but the discrepancy is small and can be
Perhaps the assumption of ratio of cross
sectional areas for steel and for bamboo takes care of
this discrepancy.
Four beams, two of which reinforced with
bamboo, and the remainder with steel, have to be made.
Two extra bottoms are made to make possible the pourtwo
ing of concrete two weeks after the first/are finish-
ed, using the same sides and end pieces,
inasmuch as
it is unsafe to remove the bottom in such a short period of time.
43x~
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77
Estimate of Material Required.
1/2" dia.
4 steel rods:
6'-11" each.
Total 27'- 8"
"
Length of one stirrup
15.5"
=
Total 72.5"
4 beams each with 14 stirrups.
1 :2:4
concrete.
4x8
8"
------ X 6.66) X 4 + 6 X
Total volume =
55'- 4"
144
12
8"
X--x X-12
12
7.67 cu. ft.
Cement = 1/7
Sand
= 2/7
x
x
7.67
=
1.09 cu. ft.
7.67
=
2.2
cu.
ft.
It is customary to have as many cubic feet
of gravel as concrete, cement and sand filling up
voids in the gravel.
Gravel to pass through 1/2"
sieve.
Bending of Stirrups.
To secure uniform results, a form was made
of a thick pine plank
10" X 24" X 1-1/2"
into which
were driven from behind spike nails about 3" long at
carefully marked points where the stirrup stopped or
cornered.
This insured the greatest degree of ac-
curacy as well as uniformity.
As the rod for the
stirrup was only 1/8" diameter, bending with a pair
of pliers was not difficult.
The stirrups were fastened to the steel or
bamboo rods by means of small iron wires.
4 such
fastenings on one stirrup for the steel,.and five for
ba0boo.
Pouring of Concrete.
It
was on February 26, 1914, that the first
The outside temperature was
two beams were made.
in the neighborhood of 320 F.,
which was, of course,
objectionable as the concrete was liable to freeze before setting took place.
Fortunately the pouring
was executed in a shed adjoining the boiler room of
the Instit-ite, which kept the temperature inside the
shed always above 320 F.
The forms having been
previously oiled with cylinder oil to prevent concrete adhereing on to the form, the concrete was mixed
according to the directions given in Baker's "Masonry
Construction".
In
It
was,
of course,
all
hand mixing.
this pouring, gravel larger than 1/2"
grade was used by mistake;
when discovered it was
too late to correct the mistake.
This made it'very
difficult to pack well under and between the reinforc-
This difficulty was more pronounced in
ing rods.
the bamboo beam in which three strips were crowded into the space occupied by two steel rods in the steel
beam.
Three 8" cubes were first
course presented no difficulty.
poured which of
But when the beams
were poured, packing the portion underneath the rods
was a trying task.
A maximum and minimum thermometer was put
inside the shed to see if
the temperature would fall
sufficiently to freeze the concrete within a day or
two.
The temperature did not fall below 320 F. with-
in several days after the pouring of the concrete.
Water was occasionally sprinkled over the top of the
beams to prevent sudden drying.
Two weeks after the first
pouring, the con-
crete had set sufriciently to permit the removal of
the sides and ends of the wooden forms,
bottoms intact.
leaving the
Extra bottoms were screwed on to
the sides and ends to make ready for the second pouring of the other two beams.
The second pouring was performed on March
12, 1914.
The process was identically the same as
the previous;
but the difficulty of packing was much
less than before, inasmuch as 1/20 gravel was used in
place of the larger size.
Test of Beams.
60 days was the age chosen at which these
beams and cubes were to be tested.
first
The test on the
two beams and three cubes was performed on April
17, 1914, in the Beam Machine in the basement of the
Applied Mechanics Laboratory of the Institute.
The
cubes, previously faced with plaster of Paris to give
a good bearing,
were tested for compression in the
Emery Machine of 300,000# capacity in the same basement.
They gave the following results:
Compressive Strength of 8" Cubes.
Concrete 1:2:4;
age
60 days;
stored gravel l".
in air.
No. of Specimen.
Max. Load.
Comp.Stress,lbs./sq.in.
1
129,000#
2020
2
132,000#
2060
3
130,0 0 0#
2030
Average
2040
Beams were then tested in the Beam Machine.
The
beams were placed on jack screws 6' apart from center
to center with an overhang of 4" at each end.
Be-
tween the beam and jack screws were placed steel
plates to distribute pressure.
The load was a sin-
gle load concentrated at the middle,
and was applied
by raising the jack screws, first one end then the
other,
This load was balanced by a weight or
weights through a system of levers.
The deflec-
tion was measured by micrometers on both sides of the
beam, with reference to two piano wires, one on each
side, stretched taut by weights at each end at the middle height of the beam.
intervals.
Loads increased at 500 lbs.
The following pages show the result of
tests on the first two concrete beams.
- Transverse Test
April 17, 1914.
Specimen:
Concrete beam reinforced with steel rods.
Concrete 1:2:4;
l11 gravel;
age 60 days, storage
in air.
R
D
1
R1
Load
2
D2
-
D
2
Sum
Remarks.
2
.037
.066
500
2
1075
.077 .011 .048 .011
.011
.011
2000
.105 .028 .075 .027
.028
.039
2925
-141 .036
.036
.075
4000
.189 .048 .159 .048
e
Cra1Lc shown at
.048
.123
this load outside of stir-
.111 .036
nups.
R
=
R2=
reading by micrometer No. 1.
"f
-
"
"
No. 2.
difference of readings on micrometer No. 1
"
ifif
if
if
V
No. 2.
IG
Manner of Loading.
Single concentrated load at middle.
6'
Span
Dimens ions
Weight of yore
beam
220 lbs.
scale reading
4400 lbs.
*
Max.
25 lbs.
Sket ches:
-
Transverse Test
1
-
April 17, 1914.
Specimen:
concrete:
Concrete beam reinforced with bamboo.
1:2:4;
gravel 1";
age 60 days;
storage
in air.
D2
2
-
R
R2
600
.294
.211
875
.363
.069
.263
.052
1100
. 423
.060
.325
.062 .061
.122
1300
. 474
.051
.372
.047 .049
.171
1600
.585
.111
.482
.110 .111
.282
Load
3120
Sun
Remarks.
2
Small crack
.061
4 small cra cks
evenly spa ced.
Bad crack at a bad spot patched with neat
cement.
Manner of Loading:
18
Single concentrated load at middle.
Span
6'
Dimens ions
46I 8*
Weight of yore
*
beam
Max, scale a"4 reading
Sketch:
25 lbs.
220 lbs.
3120 lbs.
S5TRES53 3TRAIN
re-3T I
Mu4N
lOFOJ)N
DIAGRAM
The test for the second set of beams and
cubes was performed on May
7,
1914. at the same place.
The procedure and operation were practically the same
as in the former tests.
The manner of loading the
beams was two concentrated loads dividing the span in-
to three equal parts.
The three cubes gave the following results:
Compressive Strength of 8" Cubes.
Concrete 1:2:4;
No.of Specimen.
age 60 days;
Max. Load
storage
gravel 1/2"
in air;
Comp. stress in
in lbs.
Lbs./sq. in.
1
142,200
2220
2
141,500
2210
3
118,300
Average
2220
The following pages show the results of
tests on the two beams.
-
Transverse Test 2 -
May
Concrete beam reinforced with steel rods.
specimen:
Concrete:
Load
R
500
1000
1500
-015
DI
R2
D2
D 1+ D2
~~2--w Sum
storage
in air.
Remarks.
.063
.065 .014 .121 .016
-079 .014 .137 .016
.094 .015
- 110 .016
.124 .014
.139 .015
.165 .026
-185 .020
5000
5500
6100
6500
age 60 days;
gravel 1/2";
.005 .069 .006
.027 .007 -080 .029
.038 .011 .093 .013
-051 .013 .105 .012
2500
3000
3500
4000
4500
1:2:4;
.020
2000
7, 1914.
-151
.166
.185
.204
.231
.250
.014
.015
.019
.019
.027
.019
.005
.012
.012
.012
.024
.015
.039
*054
.015
.015
.069
.085
*016
-017
.017
.026
.020
-102
.119
2 cracks, one
.145
10
.165
to the
right and
other 4" to
the left of
C.L.
Manner of Loading:
2 concentrated loads dividing the
span into 3 parts.
6'
Span
Dimensions
Wt.
1"
of yoke,
I-beam, etc.
beam
Max. scale reading
Sketch:
220#
2 20#
6900#
Transverse Test2
-
May 7, 1914.
Specimen:
Concrete beam reinforced with bamboo.
Concrete: 1:2:4;
Load
500
1100
1500
2000
2500
3000
3500
4000
R1
D
R2
gravel 1/20;
2
2
2
2
age 60 days;
Sum
storage
in air.
Remarks.
.216
.285 *069 .009
.359 .074 .074 .065
.453 .094 .159 .085
.558 .105 .258 -099
.668 .110 .366 .108
-884 .216 .573 .207
.090
.160
.-102
.262
.214
.371
.585
.109
middle
.743
Manner of loading:
2 concentrated loads equally spaced.
Span
6'
Dimens ions
Wt.
Cracks at pts.
of application
of loads and at
.070
of yoke, I-Beam, etc
4H 18'
220#
beam
220#
Max. s cale reading
4600#
Sketc24:
-3TIR E5 M TIAIN DlAG C
TE T
MAN N E:40F LOfl N G
7.
4
pp
'8
N)
CA)
C)
Notes on the Tests.
Beams reinforced with steel did not show
cracks at low loads but at high loads, cracks began
At maximum load, deflection was con-
to develop.
siderable and beam failed to pick up load.
On the
other hand, the beam reinforced with bamboo began to
crack at very low loads;
crack continued to develop
as the load was added but the beam picked up load
readily in spite of the hideous outside appearance of
The explanation of this phenomenon will
the beam.
be attempted when we come to the "Analysis of Result"
on page
.
It
was feared thatencased in concrete,
bamboo would rot, from causes for being either too
wet or too dry.
Accordingly one of the failed
beams reinforced with bamboo was knocked open, and
strips were taken out and tested.
Care was taken
that the hammering did not strain these strips.
The result of test showed:
Strips of Bamboo Encased in Concrete 60 days.
Previously stressed by testing.
No.
Section
Breaking Load.
Tens. Lbs./sq.in,
1
0.293"X 0.260"
1600 lbs.
21,000
2
0.300"X 0.264"
1600 lbs.
20,200
3
0.273"X 0.225"
1400 lbs.
22,750
Average
21,320
Comment on this result will be found in "Analysis of
Results" on page 2r.
The strips showed perfect freshness when
taken out from the concrete.
The bonding between
concrete and bamboo seemed to be perfect in every way.
Stirrups did their share well as was shown by the
breaks which in every beam occurred outside of the
limit of the stirrup reinforcement.
In the test of the second two beams, it was
observed that beams failed at sections close or under
the roller which transmitted half of the total load.
If
there were any explanation at all, it could be at-
tributed to the excessive localized stress due to the
point of contact of the roller and beam.
this be the cause,
Should
it could be remedied by interposing
a narrow steel plate between the roller and the concrete beam.
Analysis of Results.
It is necessary that the results be analyzed,
and conclusion,
if
there can be any,
be drawn as to
the actual values of these investigations.
1. The compressive strength of the plain con-
crete cutes agrees in remarkable closeness with that
of others tested in the Institute Cement Laboratory.
Thus,
in 1905, a series of compression tests was made
on concrete blocks of same mixture, age and storage,
giving results of 2070 #/V".
On page
erage of three cubes was 2040#43",
202'0#/o"
average.
the av-
while on page
Smaller gravel, and therefore
better uniformity of mixture accounts for the increase
of strength of the last three cubes.
Since the working compressive stress was
taken at 650#In", we have a factor of safety of
2040
1st. set of tests
------
=
3.14
=
3.41
650
2nd. set of tests
2220
-----650
which are ample for the compression side under steady
load.
The character of cracks showed that the com-
pression side was never stressed to its limit.
It is
test.
The first
(a)
Load.
The Mayi.mim
2.
to be recalled that in the preliminary calcula-
tion the loading was of two concentrated loads equally
spaced,
while the actual load in the test was of a sin-
gle load concentrated at the middle of the span.
is,
It
therefore, necessary to make the correction in or-
der that the. theoretical load and actual load can be
On page 4
compared.
we have tie resisting mo-
ment of the material:
M
=
26,600 in.lbs.
and the bending moment for a load concentrated at middle
=
W
--2
X 3'
220 X 6'
+-------8
They should be equal
W
--2
220 X 6
X 3 +- ------8
W=
26,600
=--------=
2216
12
1365 lbos.
The actual maxinua load, however, was:
4400 lbs.
Steel bean
Bamboo
"
3120 lbs.
For steel team we have a factor of safety of
4400
------ =
1365
3.2
For bamboo beam we have a factor of safety of
3120
------
=
2.3
1365
The ratio of maximum loads,
steel to bamboo is:
4400
------
=
1.1
3120
That is,
the assumption in the preliminary calculation
that for the two beams to stand equal loads, the areas
of reinforcing rods should be inversely proportional
to their fibre stress.
For example,
if
the tensile
strength of bamboo is 2/3 that of steel, the reinforcing area of bamboo should be 3/2 that of steel.
Now
if we would increase the area of bamboo to the amount
of
3/2 X 1.41' =
2.12,
we should expect the bamboo beam to stand as much load
as did the steel beam.
The discrepancy appeared to arise from the
wrong value used of the tensile strength of bamboo.
When the beam was designed, the only available information on the strength of bamboo was from the results
of tests made by a German experimenter, Max Ulrich,
whose work is
reviewed elsewhere in this report, and
the tensile stress was shown to be very nearly 2/3
that of steel.
The subsequent investigation by the
author showed this stress excessively high.
The
author's value of tensile strength as shown by the average of eight tests was 18,400 #/t".
Taking the
tensile stress of structural steel to be 60,000#/"
we have the ratio of
60000
------18400
=326 *
If the bamboo area were proportioned with this ratio,
the bean would have stood as much,
as did steel.
if not more, load
The soundness of the assumption is
sustained.
(b )
The second test.
Expected load
...........
......
Actual load, steel
bamboo
6900#
..................
...........
4600#
Factor of safety, steel..............
"
"
"
tamboo
2050#
3.37
............
Max. Load of Steel
-------------------Max. Load of Bamboo
2.25
6900
4600
1.5
If the area of bamboo were increased to
3/2 X 1.5
=
2.25
we would expect the bamboo beam to stand as much load
as could steel.
The limit of this ratio as shown
30
above,
is 3 inasmuch as the tensile strength ratio
of steel to bamboo is 3.
The remarkable proximity of results of the
two tests can be appreciated in the following table.
Factor of safety for steel
"
"
Test 1.
Test 2.
3.2
3.37
2.3
2.3
1.4
1.5
2.12
2.25
............
bamboo
..........
Corrective ratio:
Max.
load of steel beam
-----------------------Max.
.
load of bamboo beam
Equal strength area ratio:
Area of bamboo
------------
...........
......
Area of steel
From plots of the two tests, it
can be seen
that each additional load produced considerably more
deflection on the bamboo beam than on the steel beam.
This can be attributed to the small modulus of elas-
ticity of bamboo.
It also explains why cracks in
bamboo beams developed at comparatively low loads.
There seemed no way to remedy this except by putting
in more reinforcing bamboo strips which is practicable
when we remember that the material can be procured in
superabundance and at low cost.
The author is
of
the opinion that if
the "equal-strength-area-ratio"
be made equal to the strength ratio between steel and
bamboo, the cracks will not develop at such low loads.
Conclusion.
It appears from the tests that bamboo does
contribute to the strength of the beam to which the
reinforcement has been applied, and such reinforcement
is
practicable both from considerations of durability
and strength.
The concordance of results of the
tests showed that the bamboo in concrete behaves very
much like steel and can be depended upon to act as we
expect it.
There can be no doubt that for small
structures bamboo reinforced concrete can be used to
advantage.
Much more experimental data is needed to
guide the designer.
information,
In the absence of any better
the author recommends the following method
of design:
Design the beam as if
with steel.
it
were reinforced
Multiply the reinforcing area of steel
thus obtained by the ratio of the tensile stress of
steel to that of bamboo, (usually less than 3) and the
product will be the reinforcing area for bamboo.
This gives a factor of safety of 5.
-
-
--
-
I,
-z
4~~
~
________________
1
0
1
4
4
~~1
A
i
aib
a
4
1
0
.
.
0
.
-
Tests on the Tensile Strength of Bamboo The difficulty of testing the tensile strength
of wood in general was so well known that the author
proceeded with every care.
The difficulty, of course,
lay in the clamping of ends of specimens such that the
specimen should fail by tension and not by shear.
Wood,
in general,
is strong in tension but very weak
in shear.
The fact that bamboo is a species of
wood put it
on the same ground of suspicion that ten-
sion specimens of bamboo would fail by shear and not
by tension.
A method of preparing the tension specimen such
that the full tension could be developed was proposed
by Mr. Gescher*, under the direction of Professor
Schramb.
His specimen consisted of a narrow and
thin strip of hard wood, necked down to about onehalf of the width in the middle for one-half of its
length,
to the ends of which were glued extra strips
of the same kind of wood cross-pieced with wooden dowels set in with glue.
as expected.
neck;
It did not, however, come out
Some of them broke by shear at the
others failed through tearing the holes into
#M.I*T. Thesis - M.E. Department,
1913,
.34
which the dowel pins were inserted.
The ease with which bamboo
could be bent
naturally suggested a way by which the ends of the
specimen could be secured in the testing machine and
tensile strength determined.
Accordingly specimens
about 8' long were prepared with loops at ends, strappei together by wires.
The loops were made by steam-
ing the ends of the bamboo strips in a steaming vessel
of the following construction:
After steaming for an hour, the strips were
talcen out and the ends were bent around the outside of
the vessel, using the latter as a form.
When one
end was finished, the other end was steamed and the
In this way bends or loops of 4"
process repeated.
The author attempt-
diameter could be easily made.
The
ed to bend the ends of strips cold and dry.
smallest diameter obtainable in
this way was about 8".
Moistened by immersion in water smaller diameters
could be obtained.
The specimen was then put into the Rope
Testing Machine of the Institute, the loop ends being
held by the pins in the Jaws.
The aurvatures of the
loop and pin were so different that extra wooden pieces
conforming to both curvatures had to be interposed between them.
Load was then applied.
To our sur-
prise, the extension bar clamped on the specimen for a
gauge length of 3' , did not register any elongation as
the load was increased.
Upon investigation it was
found that the wires that strapped the loop ends were
giving way under load, and there was considerable bending at the place where the curve of loop began.
Fur-
ther pulling failed the specimen at that place under
light load.
It
was clearly a case of bending in-
stead of direct tension.
It
was concluded that
this manner of testing should be abandoned.
Failing these,
a strip of bamboo was held in
the jaws of a Wire Testing Machine in the Institute.
It
met with considerable success.
The grip by the
rough cieckered faces of the jaws was so perfect that
the specimen broke in two by actual tension.
aged by this success,
made.
a large number of specimens were
They were about 4' long, 1/2" wide, necked
down to 1/4" for a length of 3',
leaving the gripping
A gauge length of 30" was
ends eaci about 6" long.
chosen,
Encour-
and elongations measured.
In every case the
The jaws of the machine were so
grip was perfect.
designed that the harder the pull the firmer the grip,
The ends of the specimen were actually compressed to
form a nick which contributed direct resistance to
pull.
As will be seen in the following pages, the in-
side fibres,
the sap wood,
cases gave way first,
of the specimens in most
followed by the inner fibres then
the outside, the green skin.
The tests made by ul-
rich showed that the strengths of the t1hree-eeen-, inside, 4AR44 and outside fibres, varied in the ratio of
1 'r-k4, : 2.25.
When the full thickness was tested
we naturally expected the inside fibres to give first;
and it
actually did.
The long gauge length chosen necessarily included one or two joints.
The specimens in almost
,
all cases failed at one of these joints.
The conWeak
clusion suggested itself that they were the spots in
the bamboo.
Tests 1 and 2 were made upon specimens badly
weathered.
The curves seemed to have comparatively
more curvature than the others.
Tests 3, 4, 5 were made upon specimens seasoned four months.
They showed better uniformity
of results.
Test 6 was made upon a specimen of short
gauge length such that no joint was included in the
This was done in order to ascertain wheth-
length.
er or not the joint was a weak spot and responsible
for the failures of the other specimens.
The spec-
imen, however, did not show any appreciable increase
in strength.
The seventh test was made upon a specimen
which had for a year been immersed in dirty water in
the pumping well under the floor of the Pierce Labora-
tory of the Institute.
The specimen was so soaked
with water that when strained under tension the water
was squeezed out and trickled down the specimen.
The curve presents the same general appearance as
others,
although the ultimate strength was lower
B8
which was in all probability due to a local weakness
near the joint rather than the general decay caused
by the immersion in dirty water.
From these tests it is justifiable in concluding that the weather quality of bamboo is good.
With the exception of one or two, the curves
are very flat, and for all practical purposes they can
be assumed to be straight.
The curvature would be
scarcely appreciable, had the scale for the elongation
been made half as large.
The assumption that the
curves are straight carries with it
the inevitable con-
clusion that the stress is proportional to strain, and
any point on the curve can be used for figuring the
modulus of elasticity.
In the following table the
Modulus of Elasticity is figured by using a point midway between the zero load and maximum load.
The caaracteristic points of steel curves,
namely,
the Elastic Limit,
the Yield Point,
the Apparent Elastic Limit,
are absent in bamboo curve,
since the
absence of such points is common to all woods, and bamboo is one kind of wood.
If
we should assume that
the Elastic Limit coincides with the breaking point,
then the former should be figured on the basis of the
latter.
The Elastic Limit in the following table is
figured in this way.
Table showing the results of tests on the modulus of elasticity and on
the tensile strength of bamboo made by different experimenters.
Prof. Johnson
Max Ulrich
-----------------------------
Captain Bond
Author
--------------------
f
2,420,000
Weathered
2,000,000
Seasoned , Ave.
2,300 ,000
one year in
dirty water
2,000,000
(a)
0
3,270,000
m
V
Average
3,560,000
Value.
(b)
4,270,000
1,565,000
,000
19
2,380,000
(c)
{
------
---------------
(a)
(a
-r4
Average
Value.
29,150
29,000
Green Ave.
Weathered
19,700
Seasoned
17,700
(b)
52,800
One year in
23,000
0
.
----
Seasoned Ave.
39,200
45,000
~----------------
dirty water.
27,400*
-
17,300t
-
17,300
22,350
of
(c)
u
.
*Modulus of Ruipture,
23,500
(a-------
ne
(a) whole thickness,
, (--------------------
(b)
outer half ,
tModulus of strength at the apparent elastic limit.
(c) inner half,
From the table it is
40
readily seen that the
author's results are lower than those obtained by the
other experimenters.
The discrepancy seems to arise
from the following possible causes:
(a)
Difference in the kind of bamboo each experi-
menter used, as there are no less than 200 varieties of bamboo.
(b) Difference in the way of preparing the speci-
mens.
Captain Bond's specimens "were cut to
shape similar to cement briquette
----
",
while
Max Ulrich's specimens, as seen from the photograph, had unusually small reduced sections,
and gauge lengths did not include one or two
joints.
Our knowledge of the results of
tests on steel shows us that a briquetted specimen always gives high values.
In Ulrich's
specimen, a slight inaccuracy in measuring the
cross-section will throw a large error upon
the final result.
The author's tension specimens
were about 40" long, having a gauge length of
30" which included one or two joints, and a
uniform reduced cross-section of about
1/4" X 1/4"
was maintained about 3/4 of the
length of the specimen.
A larger cross see-
tional area, a longer gauge length and there-fore less uniformity, accounts for the low
values the author obtained.
The author claims that his results are
more representative and approach more nearly
the actual working conditions than the rest.
Captain Bond must have been handicapped by
the lack of facility for testing in the field.
His results are subject to question.
The ab-
sence of joints within the guage length in
Max Ulrich's specimen is a serious defect
which can not be slighted.
47
Tension Test No. 1.
April 6,
Spe cimen:
R
L
100
D
.0320
.0545
.0763
.0965
1214
.1413
.1652
.1882
.2116
.2376
.2602
*0240
.0225
.0218
.0202
.0249
.0200
.0239
.0230
.0234
.0260
.0226
1200
.2902
.0307
1300
.3194
.0285
200
300
400
500
600
700
800
900
1000
1100
L = Load in
D = Diff.
lbs.
1914.
Bamboo weathered.
S
Remarks.
.0465
.0683
.0885
.1134
.1334
.1573
.1803
.2137
.2397
.2623
.2930
.3215
Grip perfect.
Broke near joint.
Inner fibres gave
way first.
R = Micro-meter Rdgs.
of Rdgs.
S = Sums.
Gauge length inches
30
Dimensions of cross section, inches
.247"X.296
Max.
1400
load on machine, lbs.
Area of cross-section, sq. ins.
Elastic Limit, Lbs./sq.in.
Modulus of Elasticity
.
..................
.073
.........
.
.
.
19,200
1,710,000
BAMo 50 1NTE- .)
I.- Ti5-T
iN
NA NP9I AGR \ M
6A MCTE- LE N RT H
S AD L-f
7400
0
20
0"40"
VE AT HE RE.D
:10,
44
Tension Test
To.
2.
April 6,
Sp ecimen:
R
100
200
.0250
300
.0607
.0792
.0983
.1142
400o
500
600
700
800
900
1000
1100
1200
1300
1400
.0435
.1380
.1578
.1784
*1990
.2200
.2398
.2600
.2838
L = Load in
Bamboo weathered.
Remarks.
S
L
.0185
.0172
.0185
.0191
.0159
.0238
.0198
.0206
.0206
*0210
.0198
.0202
.0238
lbs.
.0357
.0542
.0733
.0892
.1120
.1318
.1524
.1730
Grip perfect.
Broke near joint.
Inner fibres gave
.1940
.2138
*2340
.2578
way first.
R = Micrometer Rdgs.
D = Diff. of Rdgs.
Gauge length,
1914.
S = Sums.
inches
30
Dimensions of cross-section, inches
.......
Max. load on machine, pounds
Area of cross-section, sq.
inches
Elastic Limit, Lbs./sq.in.
Modulus of Elasticity
...................
.264X.281
1500
.........
.0742
20,200
2,190,000
13A M130 01NT ENi
0 N
60 GAU GEL E- N1T H
DA DLY NEA T H E
5004
400
6
00
koo
Loo
0"
ED
Tension Test No. 3.
April 9, 1914.
Specimen:
L
100
200
300
400
500
600
700
800
900
1000
1100
1200
1300
1400
1500
1600
1700
Bamboo,
R
-. 0015
.0095
.0213
.0328
.0453
.0556
.0701
.0824
.0941
.1052
.1200
.1317
.1430
.1556
-1692
.1807
.1949
seasoned 4 months.
Remarks.
S
.0110
.0118
.0228
-0343
.0468
.0571
.0716
.0839
.0956
.1067
.0115
.0125
.0103
.0145
.0123
.0117
.0111
.0148
.0117
.0113
.0126
.0136
.0115
.0142
.1215
.1332
Grip perfect.
Broke near joint.
Inner ribres gave
.1445
.1571
.1707
way first.
.1822
.1964
L = Load in lbs.
R = Micrometer Rdgs.
D = Diff. of Rdgs.
S
=Sms.
Gauge length, in inches
30
Dimensions of cross-sections,
Max. load on machine, lbs.
inches ....
..............
Area of cross-section, sq.in.
Elastic Limit, Lbs./sq.in.
Modulus of
Elasticity
...........
..............
.413*I. 303
1980
.1255
15,800
.................. 2,130,000
-~~~~~
-
-.
i
.. .
.
If
. . .
.... . . - ~~~~~~~~...
-1
.
-
-
.
.
-
---
.--
--
-
-
-- t
-*---* --
.. . ..-.-
. -. -
. .
-
48
Tension Test No. 4.
April 9, 1914.
Specimen:
Bamboo, seasoned 4 months.
Remarks.
L
R
D
S
100
200
.0000
.0111
.0229
.0111
.0118
.0229
.0353
.0478
.0601
.0736
.0858
-0124
.0125
.0123
.0135
.0122
.0353
.0478
.0601
.0736
.0858
.1360
.1478
.1608
.1741
.1874
.0118
.0118
.0130
.0133
.0133
.1360
.1478
.1608
.1741
.1874
300
4oo
500
600
700
800
900
1000
1100
1200
1300
1400
1500
1600
.0982
.1108
.1242
.0124
.0126
.0134
L = Load in lbs.
.0982
.1108
.1242
Grip perfect.
Broke between joints.
Inner fibres gave
way first.
R = Micrometer Rdgs.
D = Difference of Rdg's.
S = sums.
Gauge length, inches
30
Dimension of cross section, inches
Max.
..........
1950
sq.in. .........
.1135
load on machine, ts.
Area of cross-section,
Elastic Limit, lbs./sq.in.
Modulus of Elasticity
.376 X .302
...........
................
17,100
2,310,000
TIO 0
Albo
BAM W
TK E
71 0.0.
100
YU
GA u Gr F-LF- IqCtT-H
A '3 NE.D
m9
00
Z oo-':
N TE. 14 5 10 K
......
.
MAGMA
TVI
50
Tension Test No. 5.
April 9, 1914.
specimen:
L
R
100
200
300
.60000
.0118
.0240
400
500
600
700
800
900
1000
1100
.0361
.0486
.0621
1200
.0750
.0879
.1010
.1141
.1266
.1396
1300
1400
1500
1600
.1661
.1800
.1946
.1535
Bamboo seasoned 4 months.
D
S
.0118
.0122
.0121
.0125
.0135
.0129
.0129
.0131
.0131
.0125
.0130
.0139
.0126
.0139
.0146
.0230
.0351
.0476
.0611
.0740
.0869
.1000
.1131
.1256
.1386
.1525
.1651
.1790
.1930
Remarks.
Broke near the joint,
L = Load in lbs.
R = Micrometer Rdge.
D = Difft. of Rdgs.
S = Sums.
Gauge lengthinches
30
Dimensions of cross-sections,
Max.
inches..
load in lbs.
Area of cross-section,
1990
sq. in.
Elastic Limit, lbs./sq.in.
Modulus of Elasticity.........
.381"X.285
......
..........
.1086
18,350
2,375,000
IA
GOONT
NO
9 00
U(4E L,N THo
30 NEb
4'40,
4 MMTRS
Tension Test No. 6.
April 27,
Specimen:
L
Bamboo
Remarks.
D
S
.0035
.0041
.0040
.0046
.0043
.0036
.0046
.0034
.0044
.0070
.0056
.0076
.0116
.0162
-0205
.0241
.0287
.0321
.0365
.0435
.0491
R
1914.
100
200
300
400
500
600
700
800
900
1000
1200
14.00
L
=
Load in lbs.
D
=
Mean of diff. of Rdgs.
No joint within
gauge length.
R = Micrometer Rdgs.
S = Sums.
8
Gauge length, inches
Dimensions of cross-section, inches
.3168 X .2900
Max. load in lbs.
Area of cross-section, sq.
Elastic Limit, lbs./sq.in.
Modulus of Elasticity
i.
.......
.0917
19,600
2,380,000
loo
i0o
BAMB60 MTEMSION
1000
TRE53-, TMI NDAG RPM
Soo
G.4
44r E L ENC-4TH
110JOIJ-41- WITHIN THF- LE-N -TIA
70o
Soo
-100
Zoo
400
.01
0 -z
.04-
0
54
Tension Test No. 7.
Spe cinen:
L
R
100
.0265
.0685
.1150
.1690
.2150
.2640
.3150
300
500
700
900
1100
1300
May 14, 1914.
Bamboo,1 yr. in dirty water.
S
D
Remarks.
.0420
*0465
.0885
.1425
-1885
.2375
040
.0490
.0510
.2885
L
=
Load in lbs.
R
=
Micrometer Rdgs.
D
=
Diff.
S
=
Sums.
of Rdgs.
Gauge length, inches
30
Dimensions of cross-section, inches *
Max.
load on machine,
lbs.
Area of cross-section, sq.in.
1300
........
Elastic Limit, lbs./sq.in.
Modulus of Elasticity
.236 X .317
.0746
19,300
..
2........
2,o000,000
A
B
500 INTE 14 616 11
TRE-3
-5TRAI NDIA( WAM
A lJCjE LF-NCiTH
30"
ON E YEAR INDIRTY WATE R
__Solo
ro
OD
0
3c),
Tests on Shearing Strength of Bamboo.
Wood is as a rule very weak in longitudinal
shearing strength, and bamboo,
is no exception to the rule.
being a species of wood,
Many tension specimens
have failed by shear, and yet how surprising it is to
find so little attention has been paid to it.
None
of the experimenters who made tests on the strength of
bamboo has given the subject its due consideration.
It is the opinion of the author that in practice tension members on structures made of bamboo will never
fail by tension but will in all
shear.
probability fail
by
For this reason it is worth while to look
into the subject rather carefully.
A preliminary test was made upon a section
of bamboo so shaped that when placed between the heads
of the testing machine and compressed,
sections would slide by each other.
longitudinal
This method
works well for testing shears of timbers where large
blocks of wood can be easily gotten and good footing
obtained.
But it
failed in the case of bainboo for
the reason that good footing could not be obtained,
and compression was always accompanied by spreading
the footing,
thus introducing tension into Stress.
Various schemes were tried without good success.
Finally, a shearing block was designed by the author
as shown in the accompanying illustration.
It con-
sisted of two thick, rectangular steel plates bolted
together by four bolts passing through four short
pieces of piping which acted as distance pieces be-
tween the steel plates.
In the center of each
plate was cut a slot, into which a plunger or punch
fitfed accurately, taking care, however, that the
close fit
did not entail friction.
section of bamboo
2" X 1
When in use, a
was placed between the
plates across the bolts, and clamped in place by screwing down the four nuts.
Then the punch was put in-
to the slot of the upper plate over the specimen, and
the whole placed between the heads of the testing ma-
chine.
The scheme was attended with such success
that it was employed in the whole series of shear
tests.
It is hardly necessary to add that the
clamping of the specimen prevented the spreading of
the footing.
In the following table are shown the results
of two series of tests, one on specimen with joint,
SS
and the other without joint.
The column headed with
"Number" gives the distance in inches that each specimien was originally situated from the butt of the cane.
For example,
the "number 92" specimen was cut from a
section 92" from the butt of the pole.
This was
done primarily to study the shearing strength at different heights of a bamboo pole,
as it
is
to be remem-
bered that the thickness of the pole varies,diminish-
ingly. always,
from butt to tip.
Specimens marked with an asterisk had notches
at the shearing sections both at top and bottom.
The
idea was to study the influence of the specimen upon
the shearing strength of the material from which such
specimen was made.
41
/
- Shearing Strength of Bamboo Table I.
Specimens w-tht Joints.
Number
(Distance
from Butt)
Ins.
Sectional Area
of one Shearing Section.
Sq. in.
Load
In-lbs.
Shearing
Strength.
Lbs/sq.in.
5
.40
1900
2380
72
.34
1150
1690
92
.38
1570
2070
113
.35
1260
1800
138
.33
1330
2020
206
.37
1650
2230
255
.32
1150
1800
Av.value
2000
Shearing Strength of Bamboo.
Table II.
Specimens without Jo ints.
Number
(Dist.of
Sec.from
Dimensions of
one-Shearing
Section sq.in.
Load
Lbs.
Shearing Strength
Lbs./sq.in.
1670
3400
2740
butt ,in.)
25*
25
62*
57*
57
138*
138
160*
160
160
172*
172
210
232*
232
260*
260
282*
282
.39 1
. 4x
.3 X
.35 X
.78
1.45
1.0
1.10
.37 X 1.44
.31 X 1.14
.33 X 1.45
.32 X 1.10
.33 x 1.45
.31 X 1.42
.29 X 1.11
.30 X 1.45
.30 X 1.46
.26 X 1.11
.27 X 1.47
.25 X 1.00
.25 X 1.46
.23 X 1.10
.25 X 1.4-5
1630
1700
3130
1580
2930
1890
3010
1960
1360
2790
2400
1580
2170
915 (?)
1920
900 P)
2000
Ave.
*Specimens
with notches.
value
2930
2720
2670
2980
2230
3300
2690
3140
2230
2110
3200
2740
2740
2730
2630
2760
2740
It is evident that the joint is a weak spot in
the bamboo inasmuch as the everage for shear for specimens with Joint was 2000#/bW, while without joint
2740#/o.
It is also seen that the shearing strengths
of top and bottom pieces from the same cane of bamboo
do not differ in any material way.
Notched speci-
mens seem to give lower values than those from plain
specimens,
by which it
is
meant that the specimen is
to be out from a section of bamboo in a band saw and
left as it is without being subjected to further work-
The notches in author's specimens were obtain-
irig.
ed by cutting the specimen in the band saw, which cutting might have injured some of the fibres near the
shearing sections and might be responsible for the
lower shearing strengths.
In order to appreciate the value of these tests
on shear, a simple problem will be solved here.
it
Let
be required to design a joint in a bamboo structure
secured by round hollow iron pins passing through
holes drilled in the members connected,
such that a
load of 2000# can be transmitted by the joint.
bamboo Is
The
to be of 3-1/2" outside diameter and 1/2"
thick.
From Captain Bond's test, the compressive strength
(0 z
of bamboo is 8800#/a".
Using a factor of safety of
4 we have compressive strength = 2200#/fo0.
Hence the
outside diameter of the pin
2 (D I 1/2) X 2200
D = .91'
say
=
2000
1".
The inside diameter of the hollow pin may be 3/4.
How we mst determine the length from the pin to the
end of the member so as to have sufficient shearing
HLHI
areas to stand the pull or push as the case may be.
500
X 4 X LX
1/'2
2000
L2'
using a factor of safety of 5 for shear of bamboo.
If made shorter than what is required, the shaded por.
tion may be punched out.
300,000 POUNDS TESTING MACHINE
Column Tests on Bamboo.
The author at first
had an ambitious program for
the column tests on Bamboo, but the climate in Boston,
where these investigations were conducted delivered a
blow to the whole scheme,
for it
successfully cracked
80 per cent of twenty to thirty large canes that were
especially ordered from China for these tests.
It
was clear that the whole plan must be abandoned.
We
are glad that Captain Bond and Mr. ilrich made some
column tests, by which the designer can roughly be
guided in the absence of better information.
only criticism upon their test is
specimens used by them.
The
the small size of
Both of the experimenters
made column tests on specimens whose outside diameter
little exceeded one inch, while in actual practice
columns of 4 or 5 inches outside diameter are not uncommon.
We have reason to believe that results of
tests on small specimens can not apply to large columns.
There is need of tests on full size columns.
Some experiments along this line however, were
performed before the others cracked.
The column had
the following dimensions:
Length ..-----......
Average outside diameter .........
Average inside diameter ..........
Weight .
..----------.........
Number of joints ----------.......
'414
3.34"
2.76"
.
6.5
5
lbs.
The column failed under a load of 16,950 lbs. and
cracked radially into three pieces with a loud report.
The column did not show any permanent set, -Lut, instead,
sprang back taking up any back lash or clearance of
At high load the
the parts of the testing machine.
specimen began to buckle not by the whole column but by
one or two portions between joints.
It is to be particularly noted that the specimen
weigh ed only 6.5 lbs.
Area of ring
-----2
--
(3.34
Compressive stress
----2
2.76 )
-
16,950
2.65
=
2.65 sq. in.
=
6400 lbs/sq.in.
64
1
1.5
Another column test was made in which the deforma-
tion due to compression was measured with an extensometer set at 10 inches a pound.
The results of the
test are shown in the accompanying plot.
The com-
pressive strength per square inch was only 5500 for
1
16.
This is
to be explained by the initial
curvature which the specimen had.
The accompanying drawing shows the extensometer
used in Column Tests on Bamboo.
i
-J&
MA K B,Li _C0 L UMN T r-J4
6
'R
to "
Ila IqC',f,,
......... .
.............
dt
ASO N
AVE,
L r rillt T;R
-BREANJAGT
'51 R EL
00
Z
r
-q
0 1
------
6
tict
-
.5
-:
-- ---
Jcesfhrrs--
n
r
r
00~
-~
f
--
?-rkee/O
m0 m
frc
/
<JeCllO.,7 A 3
0
07e
m
EX TENJOM~ETEl Rfor M1E DEPT Mlz7
rk64
/'
11 O
ON ,
M
-
R
ri3
-U
I
-i7
Specific Gravity of Split Bamboo.
The specific gravity of bamboo was obtained by
the ordinary method of weighing the substance in water.
But since bamboo absorbs water, an absorption test must
first
be performed.
Wt. of specimen,
"
dry
"after
imme rs ion
...
...
9.0163 grams.
...
20 mins.
...
...
...
...
Wt. of water gained
...
...
9.2100
.0937
...
AS the error resulting from this 20 minutes ab-
sorption is less than one per cent, and as two or
three minutes time is all that is needed to weigh the
specimen in water, the correction is not worth while.
Wt. of specimen in air
"
...
...
copper sinker in air
(sp.gr. = 8.65)
--....
in water
Wt. of bamboo + sinker
8.8153 gr.
...
57.5988 gr.
and
in air
wire + special pan
...
...
159.7348 gr.+ pan
wt. of wire and special pan
in air
...
...
...
110.205
gr.+ pan
Wt. of bamboo + sinker
in water
Hence the equation:
...
...
49.529 gr.
57.5988
8.8153
(8.8153 + 57.5988)
-
8.65
-c667,
X
being sp. gr. of bamboo specimen.
It is interesting to compare the specific gravi-
ty of bamboo with that of other hard woods.
Thus:
Subs tafn ce
Gr.
Bamboo ........
Ash, white, red
Chestnut
Elm, white ....
Hemlock
Hickory .......
Sp.
0.862
..
.
..................
.. 3
.....
.. 3
Maple, hard.
.. 3
..................
.. 3
..............
white
Oak, Chestnut
i
live .....
if red, black
....
...
3
3...
..
..
..
"
white ....
Pine yellow, long-leaf
Walnut,, black
white
...
.. 3
Locust
I
3
..................
..
...............
...............
........
........
3........
Bamboo is only second to live oak in
0.62-0.65
0.66
0.72
0.42-0.52
0.74-0.84
0.73
0.68
0.53
0.86
0.95
0.65
0.74
0.70
0.61
0.41
this respect.
69
Coefficient of Friction.
A series of tests was made upon the Coefficient
of Friction of unpolished bamboo,
that is,
upon its
natural hard smooth surface, by the common inclined
plane experiment.
The cosine of angle of repose
was measured by suspending a plumb-bob thread from the
inclined plane,
ten inches from the tip of the angle,
which thread pointed out the reading on a ten-inch
scale on the side of the horizontal base.
In this
way cosines to three decimal places can be obtained.
T.
Bamboo on Bamboo.
Natural Surfaces.
Green skin to Green skin.
Cos4
el
With the
grain.
f = tan ,
Wt. of
.963
Specimen
only.
15 -40'
.280
.970
.960
.960
lO-10'
16*-20'
160-20'
.252
.293
.293
Average
2 lbs. wt.
4 lbs. wt.
8 lbs. wt.
.972
.978
.980
13*-40'
120- 0'
11*-30'
,279
.243
.213
.203
II.
Steel*on Bamboo.
Smooth steel on green skin of bamboo.
With grain.
tan"a
Cos at
Wt. of steel only
.941
19*-50'
2 lbs. wt.
.941
.950
.955
19*-50'
4 lCs. wt.
8 lbs, wt.
.361
.361
18*-10'
17*-20'
.328
.312
*Steel was thoroughly covered with grease which
was wiped as clean as possible, but it
is suspected
that sufficient grease still remained to render the
coefficient high.
It is to be noted that the coefficiencts responded readily to the increase in pressure, a slight increase of few pounds causing the coefficient to decrease appreciably.
It
is hoped that further study
will make it possible to use split bamboo to face launciing ways in the hope that the troublesome grease for
lubricating launching ways may be eliminated.
The
hard surface of bamboo,- perhaps harder than that of
any existing wood - will stand the pressure due to the
hull of the ship, and the low coefficient of friction
of bamboo due to increased pressure will make the ship
and cradle slide with ease.
Coefficient of Expansion of Bamboo.
Several attempts were mamde to determine the coefficient of expansion of bamboo.
The available ap-
paratus was crude and experiments were little short of
failure.
tion here.
The results obtained do not warrant quotaHowever, it is sufficient to say that
the coefficient of expansion of bamboo is practically
the same as that of concrete.
If bamboo is to be
used for reinforcing concrete, as has been used by the
author, there should be no fear of trouble arising from
the.equal expansion or contraction of the two materials.
The temperature of the specimen was raised by
passing a current of electricity througn a coil of
wire wrapped upon the specimen.
In one experiment,
the heat was so excessive that the specimen charred.
This led the author to study the charring point of
bamboo in order that temperature may be raised without
charring the specimen.
It
was found that bamboo
charred at a temperature of 1600 C. or 3200 F.
The charred- specimen showed that the fibres stood
fire better than pulp that gave adhesive force to fi-
bres - a property not possessed by common woods.
Relation of Number of Joints to Diameter.
In the accompanying plot, the abscissae represent
outside diameter of the larger end of a stalk of bamboo,
and the ordinate represents number of joints per foot
length.
It is seen that the latter varies with the
former in inverse ratio,
i.e., larger stalks have more
joints than do smaller ones.
drawn somewhat at random.
The curve has been
Perhaps a straight line
will accomplish the same purpose.
ut
0-
tz
-0
- - 0115-
d
.
F-PF
A
Mis cellaneous.
Veneering of Bamboo.
The varied use of split bamboo for ropes, baskets,
mats, etc., calls for a rapid process of splitting bamboo into thin slices.
The thing that suggests it-
self is the veneering machine for timbers.
But bam-
boo can neither be worked in plane veneering machine,
nor in that of a rotary kind.
A machine designed
upon distinctly different principles from the existing
veneering machines must be invented.
The machine
will be of great economical value.
Bamboo in Aeroplane Work.
There has been much speculation as to the possibility of employing bamboo canes for struts in aeroplanes.
It
seems that by having special caps fitted
to the ends of the canes,
there should be no difficulty
in attaching them wherever they are needed.
Its
strength coupled with its lightness are all in favor
of its introduction into the fascinating art of aeroplane construction.
Gluing quality of Bamboo.
Bamboo takes glue very well, perhaps not as good
as other wood whose structure is coarser than bamboo.
The author glued together pieces of bamboo with different surfaces (all
unworked) of contact.
They all
seemed to unite perfectly.
Carpenter's Tool on Bamboo.
A neat hole, neater than one in mahogany, can be
easily drilled with an ordinary brace and bit.
Bam-
boo seemed to take any carpenter's tool of good quality.
But pocket knife failed to make cuts on bamboo
as desired.
The auther had one occasion to trim a
piece of bamboo with a pocket knife, and the blade at
once became ragged.
According to Professor Johnson's
scale of hardness for wood, bamboo is
certainly the
hardest wood.
Bending of Bamboo Strips.
Loops can be easily formed by steaming the strips,
and bending the end around.
probably be sufficient.
An hour's steaming will
But the experiments of the
author demonstrated the fact that the temperature in
the steaming is not an essential factor in bending.
4
A
7.
7-
I,
G
By merely immersing the strips in cold water for a peI
riod of several days,
the same result can be accomplish-
ed.
Persons recommend the method of bending bamboo by
imparting a flame to the inside of curve of bending.
With experience as well as care, it
can be done very
But where both experience and care
expeditiously.
are absent, good results can be obtained by steaming
the bamboo or immersing it
in water.
The Cracks in Bamboo.
In a climate like that of Boston, where weather
changes abruptly,
cracks invariably develop in unsplit,
whole bamboo canes in air storage.
Once split, how-
ever, the individual strips will not crack.
It is
therefore, recommended that bamboo poles should be
split in places of like climatic condition as that of
Boston,
if
it
is to be used in split form.
storing bamboo in water, we can, of course,
By
obviate
this difficulty readily.
The cracks seem to occur anywhere,- at the joint
between joints - all having longitudinal directions.
A cracked section close to joint was sawed off and examined.
It was found that owing to the solidity of
'77
the partition, the cracks only penetrated skin deep;
that is, to the depth of the thickness between joints.
This shows that cracks must be a case of unequal conThe co-
traction of the inside and outside fibres.
hesion between adjacent fibres is weak, and will naturally give way under the force of contraction.
Cross Sectioning of Bamboo.
Mr. Romeyn Hough of Lowville, N.Y., the only per-
son in the world who makes a specialty of preparing
cross sections of wood so thin that they permit the
transmission of light through the specimen rendering
the latter transparent,
sectioning bamboo.
reported his failure of cross
Mr. Hough did not attempt to
explain the cause of failure and the author does not
seem competent to give any explanation.
It is be-
lieved, however, that the weak, and somewhat porous,
matter cementing the fibres together is responsible
for the failure since it breaks so easily under the
least pressure of handling.
- Review of Max Ulrich's Work In
"Zeitschrift fur Flugtechnik und
Motorluftschiffahrt",
september, 1913,
there appear-
ed an article by Max Ulrich on the strength of bamboo,
and other woods.
That part which treated the
strength of bamboo is herewith reviewed, and amplified at some places, by the author.
Transverse Test.
Experiments were made with test pieces whose
length was 25 times the outside diameter of the bamboo.
The specimen was supported at both ends and loaded at
the middle.
These tests showed the coefficient of elongation (---)
for bamboo between
--------2,410,000
and
--------3,140,000,
1
with pine, this value is ----------
,
i.e., twice as
1,130,000
great as bamboo.
In other words bamboo is twice
as stiff (or rigid) as ordinary wood.
The observed breaking loads as shown in
Fig. 1 vary with the size of the outside diameter,
and are proportional to it.
For many practical
purposes,
it
will be sufficient to assume that the
points obtained experimentally lie on a straight line,
i.e.,
=
P
where
240 d
P = breaking load in lbs., and
D = outside
diameter of bamboo in inches.
It is to be noted here that in each case the
span is
25 times the diameter,
1 = 25 D.
i.e.,
With
this manner of loading the Maximum Bending Moment is
P 1
4
Substituting
1 = 25 D
in this equation, we have
P 1
25 D P
4
X4
But
P
=
240 D
25 D X 240 D
Mb
-----------
D
4
D-/
1500
where
=
1500
D2
=
--
38.7
40
b = Bending Moment in in. lbs.
This expression gives the relation between
diameter and Bending Moment.
For example:
Find the size of bamboo that will stand a load of
2000 lbs.
Here
concentrated at middle of span 5'
long.
M
=
80
5 X 12 X 2000
---------
30,000 in. lbs.
b
=30,000
D
-
40
=
--
40
=
173
---40
=
4.3
The diameter should be increased with factor of safety.
From this it follows that the rule for calculating the size of canes loaded transversely is very
s imple, that is,
the diameter of bamboo cane must be
equal to 1/40 of the square root of the effective bending moment multiplied by the factor of safety.
8\
In order to make comparison with other ma-terials the fibre stress has been figured with the
usual formula for bending, i.e.,
fR
y
The results are plotted as shown in Pig. 2.
It
seen that the fibre stress varies inversely as the
is
8z
To prove the validity, the author pro-
diameter.
ceeds as follows:
D
My
f = --.
=-
K D 2 x ___
2
-
I
where
-(K
Mb = K D2
D !
(see foregoing paragraphs)
a constant.
K being
K' = ratio of inside and outside diameters.
*f
D3
1
cc --- 1- oc-D
D
ig.
3 shows a cross-section of a small cane
and Pig. 4, a large cane, both enlarged eight times.
An inspection of the figures shows the uneven distribution of fibres, being denser near the skin than the
The influence of such unevenness will be-
inside.
come evident when we come to the Tension Test.
F I93
Fig. 4
83
- Tension Test -
The tests were made upon strips cut f rom
the sides of bamboo.
Tensile
Series I.
1.18' Outside Diam. Strength
Lbs.
per
sq. In.
(a)
Whole thickness
Coefficient
of
Elongation,
1
39,200
3,270,000
(b) Outer half
52,800
( c) Inner half
23,500
4,270,000
---- 1--1,710,000
Series II. 3.15" Outside Diam.
(a) Whole thickness
29,150
(b) Outer half
45,000
(c) Inner half
It
22,350
21,420 ,000
3,560,000
-1-------
is seen from this Table that the outer
half , (The darker portions in Fig. 4 and 5)
than twice as strong as the inner half.
is
more
Reference
to this point has been made in the section of this re-
84
port which deals -with the tension tests by the author.
The breaks are usually of the character as shown in
Fig. 5.
- Compression Tests The test pieces were made with smooth and
parallel bearing surfaces at ends.
Coefficient of
Compression (-!-) for compression) was found to be
i'.a rl J 20 ,Io1
1
in the middle of a specimenA
The com-
2 ,650,000
pressive strength of the same specimen was found to be
9040 lbs. /sq.
in.
In further compression tests, the specimens,
3-4 cm diarfeter and 30 cm long, were wrapped between
joints with wire.
The compressive strength varied
between 10,450 lbs./sq.in. and 12,300 lbs./sq.in.
One of the specimens which before testing had cracks
did no better after being wrapped with wire and gave
7,800 lbs./sq.in.
The effect of wire wrapping upon
the strength was not apparent.
This is to be ex-
plained by the fact that the bamboo when breaking
split in the direction of length.
Compression Test
with Bamboo Poles
--
--------
Spec- Outer
imen
la
2b
3c
3 9.
-----
----
Thick-
4* (30 cm. ) long.
Length
Compres-
Load.
sive
Strength.
Lbs/sq.in
Diai.
ness of
Ins.
wall.
Ins.
Ins.
Lbs.
1.08
.146
36*2
2730
1.16
.126
37.4
.150
39.4
1.18
I------
--------
Max.
6370
Not
2210
5400
with
3960
8200
Average
6660
1.12
.170
36.2
3526
7080
2b
1.10
.122
37.4
1750
4650
3c
1.06
.138
39.4
2440
6120
Average
5950
la
wound
wire.
Wound
with
wi re.
4
1.14
.146
38.6
2970
6580
Not
5
1.23
.130
39.0
3650
8170
wound
6
1.20
.142
39.4
2860
6070
with
7
1.09
.134
39.4
2290
3950
wi re.
Average
6190
The average values are 6660, 5950 and 6190,
the average of which gives 6270 lbs./sq.in.
Those not wound with wires splintered completely upon breaking.
Those wound with 2 mm diam-
eter wires between joints did not present such full
81
length splinter, and failure came not very sudden.
Apart from this elimination of splintering,
the ad-
vantage of winding wire outside of bamboo is very
slight.
Strength does not seem to be affected by
the reinforcing.
The stress brought to bear upon the bamboo
is
always applied under ideal conditions,
i.e., the
ends are smooth and square, and there is no eccentriBut in practice such ideal condi-
city of loading.
tions can never be realized, and allowance must be
made for free side motion due to eccentric loading.
The allowance may be from 30 j to 50 16.
Suddenly Applied Load.
The test pieces were supported at ends
(Span = 25 Diameter ), and were struck at middle with
a swinging hammer, and were broken.
Work done by
the swinging hammer in breaking the specimen was measured.
The test on 1" or 1.18" poles gives,
with
small variation, the consumption of energy equal to
126 ft.lbs, per sq.
in.
of cross sectional area.
It
was found to be immaterial as far as the energy ,consumed was concerned,
tween joints.
whether the blow hit on or be-
Those which hit in between knots made
88
a break perpendicular to the longitudinal axis of the
specimen;
while those which struck on the knot split
the bamboo lengthwise as shown in Fig. 6.
89
-
Review of Captain Bond's Work In the 1913 September-October issue of the
"Professional Memoirs", a magazine published by the
corps of engineers, United States Army, there appeared
an article entitled "Some Experiments in the Use of
Bamboo for Hasty Bridge Construction" by Captain P. S.
Bond,
corps of engineers on duty in the Philippine
Islands.
He first made brief reference to the phy-
sical characteristics of bamboo, then enumerated the
advantages and disadvantages of its use;
then pro-
ceeded to relate the results of tests on bamboo trestles used in bridge work.
One large lithographic
sheet showed the constructional drawing of these trestles,
including connections,
bracing.
lashings,
flooring and
Two of the half-tone photographs illus-
trated the mode of testing these trestles, and the
other two showed the construction and disposition of
balks and flooring;
reproduced here.
all the illustrations have been
He concluded that while a tim-
ber bridge is superior to one constructed from bamboo
stalks, yet in the absence of the former,
the latter
can be used to advantage and when properly designed to
suit conditions,
kind of service.
can be depended upon to perform any
Fig. 12 (upper). Showing fooring sstem, using both urdinary banboo poles
and wattling made of bamboo. Bath to he covered with earth, straw, etc.
Fig. 38 (lower). Shows simple hamboo trestk and halk made of 4 bamboos
eah.
- Tests of Trestles and Balk "Two trestles of the type shown in Fig. 1
and 2 were tested up to 5000 pounds each.
One of
them endured the test without any signs of failure.
In the other, the cap, being made of a weak piece,
crushed and collapsed.
The failure of cap was so
gradual the men performing the test had time to leave
the bridge.
A trestle on the design shown in Fig.
6 was tested up to 6000 pounds, which was all that
could conveniently be put upon it.
it showed no signs of weakness.
trestle was 21 feet.
Under this load
The height of this
Two balk, consisting of three
stalks each, were tested on a span of 20 feet.
They
failed under a load of 1200 pounds (600 pounds each).
The average diameter of all
the stalks was 2.85 inches
and the average thickness of fibre 3/8 inch.
balk, consisting of four stalks each,
a span of 12 feet.
pounds.
Two
were tested in
They failed under a load of 5250
The average diameter of sticks was 3.375
inches and the average thickness of fibre 1/4 inch.
Of the test loads referred to, the first (1200 pounds)
was concentrated at the center of the two balk, whereas the other load (5250 pounds) was uniformly distrib-
uted.
The wattling was tested by being covered with
men placed as closely together as possible, which test
it endured without damage."
It
is
interesting to calculate the stresses
to which the individual stalks of the balk was subjected.
(a) First Two Balk.
20 X 600 X 12
M = -------------
4
f
--
Sy
in. lbs.
20 X 600 X 12 X 255
2
-------------------
I.(285)4
4 X 3 '
=
5300#c'"
-----64
(b) Second Two Balk.
12 X 2625 X 12
8
3.375
12 X 2625 X 12 X ----2
3140 #/
f = ----------------------
*
8 X 4 X 'T X (-----4
64
The stresses are considerably lower than those obtained in laboratory experiments.
It
seems that a factor
of safety of 5 should be allowed in practice.
It is also interesting to see how Ulrich's
formula on page -1.e
can be applied to these cases.
(a)
First Two Balks.
D = -----
=
Mb
in English Units.
(D X 40)2
W X 20 X 12
=
4
(2.85 X 40)
W =
220#
W
= 1320#
A ctual load
= 1200#
for one stalk
for six stalks.
(b) Second Two Balks.
W X 12 X 122
--
=
(3.375 X 4-0)
W
=
1010#
for one stalk
W
=
8080#
for eight stalks.
8
Actual loa d
It
is
=5250#
evident that Ulrich's formula gives good ap-
proximations.
In practice a factor of safety from
2 to 5 should be allowed.
- Strength Tests "Twenty small beams of bamboo were tested
for transverse strength.
The average fibre stress
at the instant of failure was:
Seasoned Bamboo,
17,060#/0"
Green Bamboo,
16,O00#/C3"
"TThe highest recorded test was 24,000 pounds
and the lowest 10,000 pounds.
Most of the speci-
mens were quite near the average.
Rupture was al-
ways preceded by a considerable deflection.
The
specimens were tested bark up and bark down, there
being no difference observable.
"A number of specimens were tested for tensile strength by direct pull.
The specimens were
cut to a shape similar to a cement briquette, having a
carefully measured minimum section.
An astonishing
strength was developed, as follows:
Seasoned Bamboo, average tests
Green
"
"
"
29,000#/0"
23,000#/|"
*It is evident that Captain Bond used split
bamboo for specimen.-
Author.
"The highest recorded test was 34,000#/t"
The fibre near the out-
and the lowest 21,000#/1".
side of the tree was found to be somewhat stronger
The minimum cross sec-
than that near the center.
Was
1/8" square.
tion of the pieces tested w4
"The test pieces for the compressive tests
were 1/4" to 3/16" square in cross section, and 1/2"
The average strength in compression between
high.
two iron platecs was as follows:
Seasoned Bamboo,
Av. Comp.
Green
"
"
Strength
8,800#/O w
"
7,000#/ "
"As has already been noted, failure resulted from splitting of the fibre as well as direct com-
It
pression.
is quite probable that specimens hav-
ing a greater cross-section would have developed a higher compressive strength.
It is to be noted that
the transverse fibre stress was computed by the formula for beams,
My
in
and
which
M
y
was assumed as half the depth of the beam
the bending moment of the known breaking load.
The average depth of beams tested was 11/32".
The
difference between the fibre stress resulting from the
application of the fornila, and the tensile stress as
determined by actual tension is accounted for by the
considerable variation between the tensile and compressive strengths of the material.
"The following is the result of tests of
small columns.
These had square ends and were test-
ed between two iron plates.
five were tested bare.
The first series of
The second series were wrap-
ped at each end with marline.
The first
failed by
crushing and splitting at ends, the last by buckling
near the center.
Dimension of Columns.
-----------------------Length DiaM.
Thickness
of Fibre.
Ins.
Ins.
1
12
17-1/l.4 1-5/16
18
1-1/2
12-1/2
13-1/8
18
13-1/2
1-1/32
1-1/32
1-1/2
1-1/8
15
15
17-1/4
1-1 4
1-1/4
1-7/16
Breaking
Load.
Ins.
Compressive
Stress.
Lbs. / sq. in.
1 *
(0
Founds.
3/16
3/16
Seasoned
3/16
Green
3440
2340
Half seasoned
2025
2220
1280
"
V
1/8
1/8
"
9
Seasoned
1-118
13-518
15
Kind of
Bamboo.
3/16
2430
3800
Green
3/ 16
Half seasoned
Seasoned
Half seasoned
30
31
28
28
4500
2780
3480
"
3/16
1/4
3/16
2750
5130
3560
5030
5500
5 50
4950 500
3000
3860
3110
2360
2900
29
26
27
30
30
30
30
28
-----------------------------------------
*Computed by anthor.
is taken equal to
r
+
2
where
r1 and r2
are outside and inside diameters respectively.
From the foregoing table it is seen that the average compressive stress
may be taken to be
5000#/"
for
---
=
30.
9~j
Johnson's Tests on Small Specimens of Bamboo
-
In that admirable work "The Materials of Construction",
its author, Professor J. B. Johnson, made
a brief reference to the strength of bamboo as tested
by him.
It seems expedient that the whole para-
graph be quoted here.
"The Strength of Bamboo is very great for its
weight as shown in the following table.
Thus,
taking
17,300 lbs. per square inch as the apparent elastic
limit strength per square inch of bamboo in cross-
breaking (using the formula
,
and computing
y
I for the actual annular section), we find, by compar-
M =
---
ing with results of tests on other strong timbers,
that the strongest timber, namely, pignut hickory, is
far below it
in strength, having a modulus at this
limit of only 12,600 lbs.
If we compare the bamboo
weight for weight with this, the strongest timber
found in the Forestry Division tests, to give a certain cross-breaking strength on a given span, as for
instance 28 inches,
and taking the timber in the formf
of a solid rectangular cross-section, we find that to
carry a load of 440 lbs. at the center, which was carried by the second specimen in the following table,
it would require a stick 1.14 inch square in crosssection.
This would weigh 1.4 lb., whereas the
bamboo specimen weighed only 0.58 lb.
That is to
say, BAIBOO IS JUST TWICE AS STRONG AS THE STRONGEST
WOOD IN CROSS-BENDING,
WEIGHT FOR WEIGHT,
WHEN THE
WOOD IS TAKEN IN SPECIMENS WITH A SQUARE AND SOLID
CROSS-SECTION.
crushing endwise#.
The same holds true also for
0
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Inches.
Inches.
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of Specimen beeen Supports in
Elastic Resilience
in Inch-rounds per
Pound Weight of
Specimen.
Deflection at the
Apparent Elastic
Limit in Inches.
Ult imate Deflection
of Specimen in Ins.
El astic Limit.
at the Apparent
Mod ulus of Strength 1
Mod ulus of Rupture
in Cross-Bending.
Square Inch.
Mod ulus of Elastici-f
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Out side Dia. between
to0
APPENDIX I.
BAMBOO:
ITS SOURCES AND USES.*
Bamboo canes are the stems of giant grasses belonging to the genus Bambusa and allied genera, whose
species are found in most tropical and sub-tropical
regions.
Arundo,
The allied genera include Arundinaria,
Dendrocalamus,
and some others;
Melocanna,
Gigantochloa,
and their species, numbering, alto-
gether two or three humdred, if not more, may be as
small and slender as pampas grass, or as large as the
Gigantocjloa aspera of Java, which in one instance
was found to be 170 ft. high, and whose stem may be
more than 20 ins,
thick.
Except only one or two species, bamboos are indigenous to some particular locality;
the principal
of these exceptions is Bambusa vulgaris,
which is
cul-
tivated extensively in sub-tropical Asia, the West Indies, and South America,
20 ft. to 120 ft.,
and which has a height of from
the stems of the larger kinds hav-
ing a diameter of from 4 ins, to 8 ins.
#From "Bamboo Works",
edited by
Paul N. Hasluck, 1911.
Page 9 to 18.
\ C!
All bamboo plants have stems that are very slender in proportion to their
height,
and these stems
grow to their full length without any branches forming;
when at their greatest possible heightthe plants throw
out straight, horizontal branches at the top, and these
form a dense thicket.
All bamboo plants shoot forth
jointed root-stocks or rhizomes beneath the surface of
the ground, and from one of these may grow fram ten to
one hIndred stems.
The stems of bamboo plants are very strong, but
hollow, with the exception of partitions at the nodes;
and to these two qualities is due the great popularity and usefulness of bamboo canes,
which to the Chi-
nese, Japanese, Indo-Chinese, and West Indians are essentials to everyday life, and have been so for many
centuries;
to the European they have been known popu-
larly for only a few years.
Bamboo stems resemble
the stems of all grasses in being jointed;
hard, light as regards weight,
they are
elastic, and, as has
been said, hollow, containing only a light, spongy
pith, and the partitions at the nodes,
these partitions
increasing the strength of the stems greatly.
Most
bamboos are of approximate circular section, but one
species is square;
this, when three years old, has a
sectional area of one square inch.
The species of Bambusa number about thirty;
all
those of similar height have much the same appearance,
the only iarked difference being the stem, which va-
ries in color through dozens of shades,
and in size
from a diameter of the human finger to a diameter of
twenty-two inches.
Perhaps the most beautiful and typical bamboo is
B. arundinacea, and it is this plant that is illustrated by Fig. 1.
There is little doubt but that this
is one of the most useful bamboos of which the Western
peoples have any knowledge.
Bamboo plants flower but rarely, but when flowering does occur, a large amount of seed results.
of the -Indian bamboos bear berries,
Some
the species noted
in this respect being Melocanna bambusoides,
on which
grows an edible and fleshy fruit, from 3 in.
to 5 in.
long, having the shape of a pear;
M. bambusoides
grows to a height of 70 ft. or 80 ft., and attains a
diameter of 12 ins.
is
Another berry-bearing bamboo
the Nandina domestica of China and Japan, which is
used chiefly for decorative purposes, and whose berries are red.
A silicious solution contained by the stems of
1o
some bamboos , amongst them Melocanna bambusoides,
This
already mentioned, is known as tabasheer.
Fig.
1.-The
Bamboo.
hardens to a white, opaque, or sometimes translucent,
variety of opal, which breaks up into what appears to
be dry starch of irregular size and shape.
A sug-
gestion has been made that the presence of tabasheer
in a bamboo plant denotes disease, or is
some previous injury.
caused by
Tabasheer will absorb its
(o+
own weight of water, being then quite transparent;
calcined and powdered, it
is of high esteem in India
as medicine.
It would not serve any useful purpose to tabulate
here all the species of bamboo that are known;
perhaps the names,
sources,
but
and the leading character-
istics of the principal bamboo plants may be found of
The table on the following pageigives an ar-
use.
bitrary selection of bamboos to the number of about
thirty;
the complete list would number two or three
hundred.
The use of bamboo in Great Britain and the westem part of Europe generally is increasing, but as yet
most of its applications are in furniture making.
Compared with China,, Japan,
ca,
India, and tropical Ameri-
its use in this country is
restricted, due,
of
course, to its being a new material, practically.
Europeans can have but little
idea as to the great
number of the exceedingly varied uses to which bamboo
is put in the countries of its source.
There is
hardly any purpose for which iron, stone, or wood is
used here but what is answered nearly, if not quite
as well,
in the Eastern countries named above by the
use of bamboo.
Species
Arundinaria
Souce
Species~~
Sources
Japan and South-
:ear7
Remarks.
Dwarf species;
hardy.
japonica
ern England.
Arundinaria
North America
10 ft. to 40 ft.
high.
North America
Small or switch
macrosperma.
Arundinaria
t e cta.
Anrndo
cane.
South Europe &
North Africa.
10'high; tough
Arundo
b engalens is.
China & India
Arundo
conspicua.
New Zealand &
10'high; variegated white & violet
leaves.
10high; decorative
plant.
Arundo donax.
Europe, North
Africa & Asia.
ampelodesmes
Arundo iarka.
Arundo
sellowiana.
Chatham Isls.
flower stems &
leaves.
9' or 10' high;
very slender reed.
Japan, China &
India.
Stem when split is
material for Durma
mats.
Lower South
Flowering reed; one
Ame rica.
kind of Pampas
South-east Asia.
grass.
Crooked and some-
India.
times creeping
stems.
Thorny; one of the
most useful bamboos.
Bambusa
bitung.
India.
Young shoots boiled
for food.
Bambusa
China.
Dwarf species; very
Bambu s a
agrestis.
Bambusa
arundinacea.
flexuosa.
3amnbus a
guada.
Bambusa
latifolia.
hardy.
South America.
Stem 16'in dian.
& contains water.
South America.
Stem contains water.
--e-
Species.*
--------o--rce-Sources.
- -ar---R --Remarks.
Bambusa
spinosa.
Bengal.
Bambusa
tabacaria
South-east Asia.
Bambusa
Asia & South
America.
20' to 120' high.
Malay ,Archipelago.
Very tall.
vulgaris.
Dendrocalamus
giganteus.
100'high; stem has
thick walls.
Exceedingly hard
stem.
Dendrocalamus
hamiltoni.
Himalayas,India. Tall; young shoots
Dendro calanus
Malay, Archipelago.
About 100' high;
Java.
Probably tallest
st ri ctu s,
Gigantochloa
aspera.
Gigantochloa
Rpus.
used as food.
stem nearly solid.
bamboo;
Indian Archipelago.
exceeds
150' high.
Very flexible and
strong;
ropes.
used for
GCiganto chloa
maxima,
Malay Archipelago.
Very tall & thick,
Gigantochloa
nigro ciliata.
India,
130'
Gigantochloa
robusta.
Java
120'to 1.30'high,
22" in diameter.
India.
Tall; young shoots
used as food.
India.
70' or 80' high;
Gigantochloa
verticillata.
Melocanna
bambusoides.
to 140' high.
berry-bearing.
c5
It is interesting to give here a few brief notes
descriptive of the many uses to which banboo canes are
applied,
chiefly, be it
said, in
the East.
In China, the tender, but tasteless, bamboo
shoots are used as food, being either boiled or pickled,
the seeds furnishing a farina suitable for cakes.
The gnarled roots are oat into fantastic carvings, or
into handles for the Chinese lanterns, or are turned
in a lathe to form oval sticks for the use of worshipThe tapering canes are used for all purposes
pers.
that poles can be applied to in carrying, supporting,
propelling, and measuring, and in all cases where
strength, lightness, and length are requisite.
The
joists of houses and the ribs of sails, the shafts of
spears and the wattles of hurdles,
ducts and the rafters of roofs,
brellas and the ribs of fans,
the tubes of aque-
the handles of um-
all are made of bamboo.
The leaves are sewn in layers upon cords to make
rain cloaks,
swept into heaps for manure, matted into
thatches, or used as cloths in which to cook rice dumplings.
Cut into splints and slivers of various
sizes, bamboo cane is worked into baskets and trays
of every form and fancy,
twisted into cables, plaited
into awnings for boats, houses,
and streets, and woven
into mats which find employment in theatre scenery,
house roofs, and casings for goods of all kinds.
The
chips are picked into a sort of oakum and mixed with
shavings to form a stuffing for mattresses.
The bam-
boo furnishes material for the bed and the lounge, chopsticks for use in eating, pipes for smoking, flutes and
other nusical instruments of a like nature,
for windows and doors, brooms,
screens,
curtains
stools,
coops,
stands, and almost every article of furniture that can
be thought of.
From bamboo is made a serviceable paper by a modern and Eastern process;
had bamboo paper;
but the Chinese long have
and antiquaries clain that as early
as 3000 B.C. the Chinese national records were written
on thin plates of bamboo.
Builders'
scaffolds can be made of bamboo canes,
and are found light and serviceable,
for the material
does not decay in water or in earth, and dryness makes
it
harder than ever;
is
very strong.
in proportion to its
Canes 4 in.
scaffolds 25 ft. hugh,
It
is
it
thick may be used for
and such scaffolds will bear
iron beams weighing 20 cwt.
for scaffolds,
weight,
Bamboo poles,
are obtainable 65 ft.
suitable
high.
the ease with which bamboo canes may be
transformed into serviceable articles that, perhaps,
is one of the chief reasons for its wide use.
Bam-
boo can be obtained nearly 2 ft. in diameter, and a
section of such a cane can be fitted very easily with
a bottom and handle to form a basket or pail, for instance.
Bamboo flower pots, from 3 in. to 1 ft. in
diameter, having wooden bottoms, can be constructed
at something under one penny each;
bamboo is very
durable in damp situations, and makes almost as good a
flower pot as earthenware, whilst it has not the fragile nature of this latter material.
In the Castle-
ton botanical gardens, Jamaica, are some thousands of
these bamboo flower pots, which, however, have not
come much,
if at all,
into use in Great Britain.
one curious use of bamboo is as a whetstone,
another being in the making of knives.
For both
these purposes is required the superior kinds of bamboo having surfaces as hard as flint.
has a stem so hard that it
B. tabacaria
strikes fire when cut with
a hatchet.
The Annamites of Indo-China use bamboo for the
making of domestic utensils, weapons of the chase and
of war, furniture, water pipes,
ropes, paper, and
1(0
buildings.
In
common with the inhabitants of China
and Japan, the Annamites are so skilled that they can
apply bamboo canes to many of the uses for which the
hardest wood or even iron or steel is considered necessary in this and in other parts of the Western hemisphere.
Thus, for hydraulic and mechanical work,
bamboo is made to serve,
tools for preparing it
though the only available
are of the roughest kind.
In the distilleries, where alcohol is made from rice,
bamboo pipes, having joints luted with clay, conduct
the spirit to and from bamboo receivers.
and rope-making frames are made from bamboo,
Weaving
and the
products of these frames probably will bear conparison with goods produced in any part of the Western
hanisphere.
Young and tender bamboo stalks provide
food for human beings, and the leaves are eaten by
horses and cattle.
Perhaps the most remarkable use of the bamboo
among the annamites is
these are wheels which,
in the constriction of norias;
during the dry season,
water from streams and distribute it
to the parched fields.
raise
through aqueducts
The spot on the bank for the
establishment of a noria having been selected, small
dams are constructed a little
higher up by planting
long and substantial bamboo rods in the bed of the
river so as to constitute a jetty.
A passage is
left free in the middle of the river so that navigation is not interrupted.
In putting together a
noria, two bamboo wheels, each 30 ft. in diameter, are
connected together at a distance of 3 ft. apart by
twenty-six paddles,
alternating with twenty-six bamboo
vessels arranged obliquely;
the vessels are mere
canes of large diameter, with one end closed.
The
paddles are struck by the current and cause the noria
to revolve around its bamboo axle, the bearings of
which are the sides of the canes in the structural
support;
the axle rests where certain of the canes
cross each other.
Each vessel in the water becomes
full and is carried to the top of the wheel, but on
the downward half-revolution its position, of course,
is inverted, and the water flows into a woven bamboo
conduit which communicates with a system of aqueducts.
The speed of the wheel varies with the current,
but
usually the wheel revolves once in about forty seconds;
and as each of the twenty-eight vessels contains about
2 qt. of water, the noria should raise about 21 gals.
per minute, or 1260 gals, per hour;
more than 18 gals,
or 19 gals,
in practice, not
would be raised per
minute under such conditions.
Sometimes, eight no-
rias will work together, raising between them about
150 gals. per minute,
VLen the current is weak the
noria is made narrower, and by substituting steps for
the paddles,
a tread-wheel is formed, which can be
worked by one coolie.
Sometimes the top of the no-
ria has a big wooden pinion which receives the motion
of a horizontal wheel turned by a bullock.
The Chinese house may be bamboo from "foundations"
to roof;
on plan, the house is a rectangle divided
into three, and the walls and two partitions are upright bamboos of large diameter, to which are lashed
horizontals of the same material but smaller in diameter, still
smaller canes or laths of riven cane being
interlaced and plastered over with mud or clay.
The
door has stiles and rails of bamboo, the panels being
interlaced bamboo strips.
The roof is constructed
by supporting bamboo purlins longitudinally on the
tops of the partitions,
rafters of smaller bamboos
being lashed to the purlins and then overlaid with
small cane, which supports a thatch of leaves obtained from the bamboo plant.
The floor is of earth
well rammed down.
Enough has been said to convince the reader that
the possibilities of bamboo as a constructional mateThough,
rial are practically unlimited.
of course,
its use in this country will never be so great as in
the countries of its source, yet as its properties desirable, and indeed unique - come to be better known
there can be no doubt but that it will be very generally used for many purposes for which the far more
costly woods are now employed.
.
The supply of bamboo cannot be exhausted, for, in
addition to the probable fact that its species ,grow
over a more extended area than do those of timber trees
in general, its growth is so much more rapid;
whereas,
timber trees are useless for constructional purposes
until they are several years old, many young bamboos
add from 10 ft. to 25 ft. to their height per month,
and their stems are strong enough for use in but a few
years.
The kinds of bamboo canes used in Great Britain
and in Europe generally are black, brown, yellow, mottled, mahogany, and spotted, these colors being approx-
imate only, and varying greatly in a bundle of canes,
traded as being all of one color.
The black and ma-
hogany canes which are colored artificially, are more
uniform than those sold in their natural state, the
94
yellow canes being excepted.
Besides the plain
stained canes, some resemble tortoise-shell with fancy
mottling artificially produced,
and this kind has be-
come very popular for furniture.
The sizes of bamboo canes in ordinary use vary
from 1/2 in. to 3 ins, in diameter, and from 18 ins.
to 12 ft. long;
for special purposes,
canes very much
thicker and very much longer can be obtained.
Deal-
ers in bamboo sell the canes as a rule by the dozen or
by the hundred, all of one size as nearly as possible
as regards both diameter and length, but generally an
assorted bundle can be obtained for a few shillings,
such a.bundle containing, perhaps,
from 18 ins.
150 canes ranging
to 7 ft. long, and from 1/2 in.
in diameter.
to 2 ins.
Canes with roots are slightly dearer
than the plain ones.
Generally, bamboo dealers sup-
ply also matting, Japanese leather paper, lacquer panels and trays;
from them also can be obtained the
small white solid canes sometimes used for filling in
open spaces in furniture instead of employing panels.
Matting, used very largely for covering the tops
of bamboo tables, may be either white or fancy-colored,
and is
sold by the square yard or by the roll, gener-
ally containing about 4-0 yards.
Japanese leather paper is
sold by the roll, and
may be had in many designs executed in gold,
gold, black and gold,
red and
etc.
Japanese lacquer panels are almost a necessity
in making up bamboo furniture.
kinds,
15 ins,
They are of many
qualities, and sizes, the latter ranging from
square to 24 ins. square,
obtainable for special purposes.
larger panels being
These remarks on
panels apply also to the shallow trays in
used for tea-tables and similar furniture.
lacquer work
II6
APPENDIXI II.
Properties of Fibres from Bamboo,
and Chemical
Treatment of Bamboo , in Paper-Making.
Bamboo,
like esparto,
was first introduced as a
fibre-yielding plant by the late Mr. Routledge, who
suggested it as an ally to esparto.
It is not so
easily reduced as esparto by either the soda or sulphite processes,
but yields a fibre strong and flexi-
ble, possessing good felting properties.
It bulks
well and can be treated in the beater with ease to
yield a close sheet of paper.
very abundant,
The plant itself
is
of rapid growth, and comparatively
cheap.
It belongs to the same botanical order as
straw.
Length of fibre is
eter = 0.00063 of an inch.
regular, and smooth;
nal small.
o.354 inches.
Dian-
The fibres are fine,
walls uniform, and central ca-
They are surrounded by much intercel-
lular matter, the bulk of which can be removed by washing.
The author has submitted various kinds of
bamboo cane to both the soda and sulphite treatment,
with th~e following results:*From "Paper Makers'
Pocket Book"
James Beveridge, 1911.
by
1'/
SODA PROCESS.-
The cane contained 1.62 per cent
51.25 per cent.
of ash, of the following composition:
It
Mg 003.
ter
and 6.07 per cent.
Ca 003,
Si 02P 9.25 per cent.
was crushed before placing in the diges-
-
Weight of bamboo per charge
...
.g
Volume of C. soda per charge
...
52 cwts.
...
1600 gals.
...
1741 lbs.
...
90 lbs.
...
331Fah.
Weight of 60 per cent. C.
soda per charge
...
Steam pressure (maximum)...
Maximum temperature
...
....
...
g
...
Number of hours under pressure
Proportion of 60 per cent.
...
ee.
15
C. soda
= 33.6 lbs.
to 1 cwt. of cane
The black lye, after blowing off
pressure = 16-1/2
Twaddell at 600 Fah.
The pulp obtained was well boiled but dark in
appearance,
resembling soda wood pulp.
It bleached
readily at a temperature of 1200 Fah. to a pale yellow
color, with 25 per cent.
powder (35 per cent.
of its weight of bleaching
avail.
did not exceed 40 per cent.
dry cane.
chlorine).
The yield
of air-dry fibre on air-
BISULPHITE PROCESS.-
A similar cane to the above
was crushed between rollers and boiled in bisulphite
of lime solution having a sp. gr. of 1.040 = 80 Twaddell, and of the usual composition prevailing in
sul-
phite pulp works, precisely as in the case of wood
boiling.
The pulp obtained was sort, a pale yellow
color, and was readily washed with water.
The
boiled fibre was lighter in color than the corresponding pulp obtained by the soda process, but turned a
deep red on addition of bleaching powder solution.
With 23 per cent.
of its weight of bleaching powder it
remained a pale yellow tint, which could only be removed with permangarates.
The actual yield of
bleached air-dry pulp (10 per cent.
water)
was 42.7 parts per 100 parts operated upon.
obtained
References.
Snow,
Charles Henry:
"Principal Species of Wood"
Page 190.
Their Characteristic Properties.
1 Page of illustrations.
2 Pages.
Hubbard, Henry G.: "U.S. Forestry Bulletin No. 11".
Page 29,
4 pp.
A Brief Description of Scanty
Growth of Bamboo in Florida.
Gamble, J. S. :
"A Manual of Indian Timbers"
14 Pages.
Page 742.
A Brief Botanical Dee
"BambuseaE of British
e
scription of Bambuseat.
India".
Annals of the Royal Botanical Garden
of Calcutta."
Krz:
Vol. VII.
"Bamboo and Its Uses".
Vol.
I.
Freeman, Mitford, A.B.:
Riviere, Messrs A. and C.:
Hasluck,
"Indian Forester",
Paul N.:
"Bamboo Garden".
"Les Bambous".
comprising the
"Bamboo Works"
construction of Furniture, Household Fitments,
and other articles in Bamboo.
Beveridge,
James:
"Paper Makers'
160 pages.
Pocket Book".
Properties of Fibre from Bamboo,
cal Treatment.
Page 82,
and its Chemi-
1 page.
Articles appeared in current Engineering
Magazines on the Strength of Bamboo.
Ulrich, Max:
et c.
Stuttgart
Zeitschrift fur Flugtecnik und Motor-
luftschiffahrt.
Bond,
"Investigations on Bamboo,
Captain P.S.,
Jahrgang IV, Heft 18.
Corps of Engineers,
U.S.A.
"Some Experiments in the Use of Bamroo for Hasty
Bridge Construction".
Professional Memoirs
Vol. V, September -October issue, 1913.
JohLnson, Professor J.B.:
"Materials of Construction".
1ambxi (rve, China.
5f inche, diameter.