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The at table jig used here to make identical trusses would be quite different if
bamboo were connected using a wrapping method commonly seen for connection
points on wicker furniture or bamboo scaffolding. This sort of connection would be
better where binding materials and skills are available. Supporting jigs with space
under the joint would better allow for wrapping the joints than the at table in the
photo. A cement soaked ber wrapping would be quick and easy if the bamboo isclamped in a jig and the joint wrapped like applying a bandage to a wrist or knee.
The previous smooth plane roof on the small structure used wood which was cut to
2 x 4 centimeters so it would approximate the bamboo used in the trusses. Keep in
mind that the wood was covered with cement and acrylic soaked ber, the same idea
that the wood is merely a mold for the ber carries through here with the bamboo,
that is why these designs are thought of as a method for utilizing the lowest quality
of bamboo.
Fiber reinforced composite membranes Garrett Connelly
Fiber reinforced composite membranes Garrett Connelly
Chapter Eight : Bamboo, Hemp and Jute Composite
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The truss to be constructed is for a roof which is 3 x 4 meters (9.8 x 13.1). Eves
will be 25 centimeters (10) and the outside dimension of the building will be 2.5 x3.5 meters (8.2 x 11.5). Five trusses with a spacing of 62.5 centimeters are required
(24.5). Purlins will be attached under the slope chord to connect trusses and extend
25 centimeters beyound end walls to create end eves. This roof design will have
added strength of surface deection equal to bamboo thickness to purlins and the
slight sag between them.
Trigonometry is the relationship between the lengths of the different sides of triangles
and the angles of triangles. There are books of tables which print the ratios of different
sides and angles. One can also type the term describing the ratio into the google
y
x
h
62.5
27.5
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search box and hit enter/return and google will give the answer. 27.5 degrees is the
selected angle because it is easy to set on my power saw. Its an angle Ive grownaccustomed to using, if you dont care about setting the angle on your saw, measure
out what looks good to your eye.
The full width of the truss is four meters, thus, the distance to the center is 2 meters.To compute the height of the truss we need to know the length of the side opposite
the roof angle of 27.5. The ratio of the opposite side divided by the adjacent side of
an angle is known as the tangent. h in the drawing refers to the hypotenuse of the
triangle which is half of the roof.
We are referring to the distance to the center as x (two meters) and we are solvingfor the height of the roof peak which is labeled y. Without trigonometry tables we
resort to the computer and type tangent 27.5 degrees in the google search box, hit
return and the solution is rendered = 0.520567051. Two meters multiplied by 0.5206
is 1.04 meters, which is the height of the top of the truss.
The overall height of the truss is measured from the bottom of the horizontal length
of bamboo to the top of the hypotenuse lengths which dene the slope, note that the
hypotenuse is also referred to as a chord. Thus, because the bamboo is of various
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thicknesses, the center piece will vary in length (height).
The joint method of wrapping with fabric around the bamboo, with a ller of cementsoaked hemp in the joint proved to be excessively strong. A simple wrap without the
ll would be sufcient, keeping in mind that the bamboo itself will be covered as the
rafters were in the previous chapter.
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Plywood girders are positioned with exterior dimension at 3.5 meters to simulateexterior walls for example assembly. The actual roof material will not be placed until
someone wants a 2.5 x 3.5 meter structure. The size is large enough to require extra
permits for transport to a nal site, also extra trusses could be made and the size
might become three or four meters in length by 3.5 meter width.
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Purlins and the additional near end-wall eve are placed on one side only to illustrate
construction order. Brief examination of the photo will reveal there are two Xbraces extending along the center, from end-to-end. Purlins are below the truss roof
line. A tension controlled sag in each square created by the truss line and purlins will
provide three dimensional strength which is not present in a two dimensional at
plain like that in the previous structure. Additional dimensional or geometric shape
will provide strength to the roof plane since the bamboo would be covered by strips
of soaked fabric and additional layers applied as in the previous photo series.
The next step is to build these roofs for actual use, perhaps in an emergency area
like that still being dealt with after the earthquake in Pakistan or the Hurricane in
Bangladesh. The joints for bamboo shelters being built to protect the tents in Pakistan
are no more advanced than what is presented here. I am studying high tech materials
to replace cement so that you will be sure to need me there, if only for the synergy.
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Economic cost analysis:
Imagine a 400 square foot house = 37.2 m2
That house will have about 1200 ft2 of surface 111.5 m2, (roof edges can be built to
collect drinking water, save on gutters).
Acrylic...... $ .90/ft2 6.68/m2
cement..... .10 .74
ber.......... .06 .44
bamboo... .24 1.78
_______ ______
Total........ $ 1.30 9.65
$1.30 per ft2 of surface area x 1200 ft2 = $1560
9.69/m2 of surface area x 111.5 m2 = 1080
This is for a shell (no windows doors, foundation or oor), add a little artful nish for
pride of place = material cost for a decent shelter, (amenities equal to a tent).
Finished shell material cost:
$1800 $4.50 per ft2 of oor space
1250 11.2 per m2 of oor space
Thus, a nice looking and permanent home can be built for about one third the cost of
an emergency ten, per area unit measure.
Caution, these are rough gures from a controlled environment and something may
be overlooked.
Note: Further signicant savings are possible if bulk dry
acrylic is procured from the renery. There are serious
health risks associated with this that require a mixing
facility where the dry acrylic can be safely mixed with
water. (Research term: fungal lung disease).
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Chapter nine illustrates use of a new material to bind the joints of a truss. Antoon
Versteegde, an extraordinary bamboo maestro who I am honored to be in consortium
with at self-sheltering.org, and future projects unlimited, sent me a link to a very sadpresentation of collapsed tents under snow load, in Pakistan, following earthquake
disaster. I tried to salute the awesome efforts of those who still struggle there by
building this to match their conditions. I failed at rst because sliding on the ice gave
me a stiff back. The next chapter was put together with hope for those in Pakistan
who are still working to overcome a devestating earthquake and chilling winters.