bamboo, hemp and jute composite

8/6/2019 Bamboo, Hemp and Jute Composite

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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.

bamboo, hemp and jute composite

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