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BAMBOO BAMBOO REINFORCEDREINFORCED CONCRETECONCRETE

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INTRODUCTIONINTRODUCTION Bamboo has been used as a Bamboo has been used as a

construction material in certain area construction material in certain area for centuries. A study of for centuries. A study of bamboo bamboo is used as a reinforcement in precast is used as a reinforcement in precast concrete elements was carried out in concrete elements was carried out in U.S Army Engineer Waterway U.S Army Engineer Waterway experiment station in 1964. Bamboo experiment station in 1964. Bamboo was given recent consideration for was given recent consideration for use as reinforcement in soil cement use as reinforcement in soil cement pavement slabs in which the slabs pavement slabs in which the slabs behave inelastically even under light behave inelastically even under light loads. loads.

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BAMBOO BAMBOO CHARACTERISTICSCHARACTERISTICS

Bamboo is giant grass not a tree.Bamboo is giant grass not a tree.The density of fibres in cross-section The density of fibres in cross-section

of a bamboo shell varies with of a bamboo shell varies with thickness as well as height.thickness as well as height.

The strength of bamboo is greater The strength of bamboo is greater than most of the timber products.than most of the timber products.

Bamboo is more prone to insect Bamboo is more prone to insect attack than other trees and grasses.attack than other trees and grasses.

Bamboo can prevent pollution.Bamboo can prevent pollution.

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SELECTION AND SELECTION AND PREPARATION OF BAMBOOPREPARATION OF BAMBOO

SELECTIONSELECTION Use only bamboo showing a pronounced Use only bamboo showing a pronounced

brown color. This will insure that the plant brown color. This will insure that the plant is at least three years old.is at least three years old.

Select the longest large diameter culms Select the longest large diameter culms available. available.

Do not use whole culms of green, Do not use whole culms of green, unseasoned bamboo. unseasoned bamboo.

Avoid bamboo cut in spring or early Avoid bamboo cut in spring or early summer. These culms are generally summer. These culms are generally weaker due to increased fiber moisture weaker due to increased fiber moisture content. content.

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VARIOUS SPECIES OF BAMBOOVARIOUS SPECIES OF BAMBOO

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PREPARATIONPREPARATIONSizingSizing

SplittingSplitting

SeasoningSeasoning

BendingBending

Waterproof CoatingWaterproof Coating

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CONSTRUCTION PRINCIPLESCONSTRUCTION PRINCIPLES

Concrete Mix ProportionsConcrete Mix Proportions The same mix designs can be The same mix designs can be

used as would normally be used with used as would normally be used with steel reinforced concrete. Concrete slump steel reinforced concrete. Concrete slump should be as low as workability will allow. should be as low as workability will allow. Excess water causes swelling of the Excess water causes swelling of the bamboo. High early-strength cement is bamboo. High early-strength cement is preferred to minimize cracks caused by preferred to minimize cracks caused by swelling of bamboo when seasoned swelling of bamboo when seasoned bamboo cannot be waterproofed. bamboo cannot be waterproofed.

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Placement of bambooPlacement of bamboo

• Bamboo reinforcement should not be Bamboo reinforcement should not be placed less than 1½ inches from the face placed less than 1½ inches from the face of the concrete surface. of the concrete surface.

• The clear spacing between bamboo rods The clear spacing between bamboo rods or splints should not be less than the or splints should not be less than the maximum size aggregate plus ¼ inch.maximum size aggregate plus ¼ inch.

• Reinforcement should be evenly spaced Reinforcement should be evenly spaced and lashed together on short sticks placed and lashed together on short sticks placed at right angles to the main reinforcement.at right angles to the main reinforcement.

• The ties can be maid with vegetation The ties can be maid with vegetation strips.strips.

• This embedded depth is approximately 10 This embedded depth is approximately 10 times the diameter of whole culms or 25 times the diameter of whole culms or 25 times the thickness of ¾ inch wide splints.times the thickness of ¾ inch wide splints.

• Spacing of the stirrups should not exceed 6 Spacing of the stirrups should not exceed 6 inches.inches.

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DESIGN PRINCIPLESDESIGN PRINCIPLES

Bamboo reinforced concrete Bamboo reinforced concrete design is similar to steel reinforcing design is similar to steel reinforcing design. Bamboo reinforcement can be design. Bamboo reinforcement can be assumed to have the following mechanical assumed to have the following mechanical properties.properties.

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Mechanical properties of bamboo reinforcement

Mechanical Property Symbol Value (psi)Value (psi)

Ultimate compressive strength --- 8,000

Allowable compressive stress s 4,000

Ultimate tensile strength --- 18,000

Allowable tensile stress s 4,000

Allowable bond stress u 50

Modulus of elasticity E 2.5x106

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When design handbooks are When design handbooks are available for steel reinforced available for steel reinforced concrete, the equations and design concrete, the equations and design procedures can be used to design procedures can be used to design bamboo reinforced concrete if the bamboo reinforced concrete if the above mechanical properties are above mechanical properties are substituted for the reinforcement.substituted for the reinforcement.

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BEAMS AND GIRDERSBEAMS AND GIRDERS Bamboo longitudinal reinforcement should Bamboo longitudinal reinforcement should

be between 3 and 4 percent of the concrete be between 3 and 4 percent of the concrete cross section.It have the same bending cross section.It have the same bending moment resistance coefficient as a balanced moment resistance coefficient as a balanced steel reinforced beam, singly reinforced. steel reinforced beam, singly reinforced. Economy of concrete increases going to the Economy of concrete increases going to the left on the curve; therefore, deeper, narrower left on the curve; therefore, deeper, narrower replacement beams are recommended. A replacement beams are recommended. A minimum number of rods should be used to minimum number of rods should be used to provide adequate spacing. The bamboo stirrup provide adequate spacing. The bamboo stirrup area should always be about 4 times the steel area should always be about 4 times the steel stirrup area.stirrup area.

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ExampleExample Design of Bamboo Reinforced Beam:Design of Bamboo Reinforced Beam: Design a bamboo reinforced concrete beam Design a bamboo reinforced concrete beam

to span 2.43m and to carry a uniform dead to span 2.43m and to carry a uniform dead load plus live load of 450 KN/m and two load plus live load of 450 KN/m and two concentrated loads of 108 KN each concentrated loads of 108 KN each symmetrically located 0.6m each side of the symmetrically located 0.6m each side of the center line of span. Assume the ultimate center line of span. Assume the ultimate strength of the concrete is 240KN/m2; the strength of the concrete is 240KN/m2; the allowable compression stress is 108 KN/m2 allowable compression stress is 108 KN/m2 Allowable unit diagonal tension stress,V , in Allowable unit diagonal tension stress,V , in the concrete is 72 KN/m2. Allowable tension the concrete is 72 KN/m2. Allowable tension stress, s, in the bamboo is 400 KN/m2; the stress, s, in the bamboo is 400 KN/m2; the allowable unit bond stress between bamboo allowable unit bond stress between bamboo and concrete is 40 KN/m2. and concrete is 40 KN/m2.

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SolutionSolution

1.1. At the intersection of the allowable stress curves for At the intersection of the allowable stress curves for concrete and bamboo, find R = 115 and p = 3.1 percent.concrete and bamboo, find R = 115 and p = 3.1 percent.

2. Maximum bending moment, M, is given by: 2. Maximum bending moment, M, is given by: M = [450(2.43)2(12)]/2.43 + 108(0.6)(12) =13899.6 KN m. M = [450(2.43)2(12)]/2.43 + 108(0.6)(12) =13899.6 KN m. R = M/bd2 R = M/bd2

3. From 3. From bd2 = 13899.6/115 = 120.86 m3bd2 = 13899.6/115 = 120.86 m3

4. If b = 2.43m. is chosen, then d = (120.86(10)/2.43)½ = 4. If b = 2.43m. is chosen, then d = (120.86(10)/2.43)½ = 7.05mm. 7.05mm.

5. Bamboo reinforcement = pbd = 0.031(2.43)(7.05) = 4.75 5. Bamboo reinforcement = pbd = 0.031(2.43)(7.05) = 4.75

6. Use ¾-inch-thick splints, area = 0.563 m2. 6. Use ¾-inch-thick splints, area = 0.563 m2. Number required = 4.75/0.563 = 8.4; round up to 9. Space Number required = 4.75/0.563 = 8.4; round up to 9. Space evenly in three rows. Bend up top row randomly in the evenly in three rows. Bend up top row randomly in the outer one-third ends of the beam. outer one-third ends of the beam.

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7. Check the bond stress. Maximum shear at the support, V, 7. Check the bond stress. Maximum shear at the support, V,

is determined as: is determined as: V = 450(2.43)/2 + 108 = 860 KN/m2.V = 450(2.43)/2 + 108 = 860 KN/m2.

The perimeter of one splint is 4(3/4) or 3 m.; the total The perimeter of one splint is 4(3/4) or 3 m.; the total perimeter of the longitudinal reinforcement, ∑0, is 9(3) = perimeter of the longitudinal reinforcement, ∑0, is 9(3) = 27 m. The value of j = 0.925 27 m. The value of j = 0.925 u = V ÷ ∑ojd = 654.7 ÷ 27(0.925)(7.06) = 13 KN/m2u = V ÷ ∑ojd = 654.7 ÷ 27(0.925)(7.06) = 13 KN/m2This is less than the allowable bond stress of 40 KN/m2.This is less than the allowable bond stress of 40 KN/m2.

8. Calculate the shear, V', taken by the concrete from8. Calculate the shear, V', taken by the concrete fromV' = νbjd = 72(2.4)(0.925)(4.75) = 759.2 KN/m2V' = νbjd = 72(2.4)(0.925)(4.75) = 759.2 KN/m2Where ν is the allowable diagonal tension stress of the Where ν is the allowable diagonal tension stress of the concrete.concrete.

9. Provide 0.4 mm thick splints for stirrups. The area 9. Provide 0.4 mm thick splints for stirrups. The area provided by one stirrup bent into a U-shape, A, is 4(0.4) provided by one stirrup bent into a U-shape, A, is 4(0.4) = 1.6 mm2 (Stirrup area 4 times the dia). Maximum = 1.6 mm2 (Stirrup area 4 times the dia). Maximum spacing, s, is given by:spacing, s, is given by:s = Aσjd ÷ (V - V') = 1.6(400)(0.925)(4.75) ÷ (860 – s = Aσjd ÷ (V - V') = 1.6(400)(0.925)(4.75) ÷ (860 – 759.2) = 10.1mm.759.2) = 10.1mm.

Common practice is to include two Common practice is to include two additional stirrups past the point where diagonal tension additional stirrups past the point where diagonal tension reinforcement is not needed.reinforcement is not needed.

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COLUMNSCOLUMNS Bamboo reinforcement in columns serves Bamboo reinforcement in columns serves

to resist a compression load equal to that taken to resist a compression load equal to that taken by the concrete it displaces; it also will resist by the concrete it displaces; it also will resist shear and tensile stresses. Of the full cross shear and tensile stresses. Of the full cross section of concrete, only 80 percent is section of concrete, only 80 percent is considered effective in rectangular tied, considered effective in rectangular tied, columns. Allowable concrete stress should not columns. Allowable concrete stress should not exceed 0.225 f'c where f'c is the ultimate exceed 0.225 f'c where f'c is the ultimate compressive strength of the concrete.compressive strength of the concrete.

Vertical reinforcement should be Vertical reinforcement should be approximately 4 percent of the column cross approximately 4 percent of the column cross section for rectangular columns. When bamboo section for rectangular columns. When bamboo is used as lateral tie reinforcement, the ties is used as lateral tie reinforcement, the ties should be spaced not over 16 times the least should be spaced not over 16 times the least dimension of the vertical reinforcement nor dimension of the vertical reinforcement nor farther apart than the least dimension of the farther apart than the least dimension of the column. column.

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ExampleExampleDesign of Bamboo Reinforced Design of Bamboo Reinforced

ConcreteColumn:ConcreteColumn: Determine the cross section and bamboo Determine the cross section and bamboo

reinforcement of a column required to carry reinforcement of a column required to carry an axial load of 700 KN. Ultimate an axial load of 700 KN. Ultimate compression strength of the concrete, compression strength of the concrete, 240.KN/m2240.KN/m2

Solution:Solution:1. 1. For an unreinforced rectangular column the For an unreinforced rectangular column the

safe axial load, P, is given by:safe axial load, P, is given by:P = 0.8Ac (0.225 f'c)P = 0.8Ac (0.225 f'c)Where Ac is the cross-sectional area of the Where Ac is the cross-sectional area of the concrete column and f'c is the ultimate concrete column and f'c is the ultimate compressive strength of concrete. compressive strength of concrete.

2. 2. The column should have a cross-sectional The column should have a cross-sectional area of:area of:Ac = 700 ÷ 0.8 (0.225) (240)(10) 3 = 16.20 Ac = 700 ÷ 0.8 (0.225) (240)(10) 3 = 16.20 m2. m2.

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3. 3. If a square column is chosen, it will have face If a square column is chosen, it will have face dimensions ofdimensions ofb = (16.20)½ = 4.0 m b = (16.20)½ = 4.0 m

4. 4. The amount of vertical reinforcement should be 4 The amount of vertical reinforcement should be 4 percent of the concrete area .These should be percent of the concrete area .These should be spaced evenly around the perimeter of 1 to 1½ spaced evenly around the perimeter of 1 to 1½ mm of cover. Provide each vertical splint with a mm of cover. Provide each vertical splint with a 90-degree corner. 90-degree corner.

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COMPARISON OF BAMBOO COMPARISON OF BAMBOO AND STEELAND STEEL

The strength of bamboo is greater The strength of bamboo is greater than steel.than steel.

Bamboo is easily accessible. Bamboo is easily accessible. Bamboo lowers the cost of Bamboo lowers the cost of

construction. construction. Increases the strength of the Increases the strength of the

buildings .buildings .Bamboo can crack and deflect more Bamboo can crack and deflect more

than steel reinforcement.than steel reinforcement.

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Other Applications Of Other Applications Of BambooBamboo

Bamboo bridge in the Amsterdam WoodsBamboo bridge in the Amsterdam Woods

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Bamboo theatre during the Festival of Vision, Berlin, 2000

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Bamboo scaffolding at the top of a new high-rise building in Hong kong

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CONCLUSIONCONCLUSION

The environmental and financial comparison demonstrates that bamboo can compete with building material. Bamboo is a natural product and will therefore always have some extent of irregularity. It is therefore suggested that the bamboo culm should be used in functions were the measurement requirements are not entirely precise or fixed, as in temporary buildings (e.g., pavilions and tents) or small civil projects. Furthermore, bamboo can play a role as a non-supporting or finishing material.

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