Bamboo can be used as reinforcement in concrete. It has strength greater than most timber and can be prepared through splitting, sizing, and seasoning. Bamboo reinforced concrete design is similar to steel reinforced design but uses different mechanical properties for bamboo. Beams, girders, and columns can all be designed using bamboo as longitudinal and shear reinforcement. While bamboo cracks and deflects more than steel, it is cheaper and more accessible in some areas.

1. BAMBOO REINFORCED CONCRETE www.civilengineerstalent.in

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

3. BAMBOO CHARACTERISTICS Bamboo is giant grass not a tree. The density of fibres in cross-section of a bamboo shell varies with thickness as well as height. The strength of bamboo is greater than most of the timber products. Bamboo is more prone to insect attack than other trees and grasses. Bamboo can prevent pollution.

4. SELECTION AND PREPARATION OF BAMBOO SELECTION Use only bamboo showing a pronounced brown color. This will insure that the plant is at least three years old. Select the longest large diameter culms available. Do not use whole culms of green, unseasoned bamboo. Avoid bamboo cut in spring or early summer. These culms are generally weaker due to increased fiber moisture content.

5. VARIOUS SPECIES OF BAMBOO

6. PREPARATION Sizing Splitting Seasoning Bending Waterproof Coating

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

8. Placement of bamboo Bamboo reinforcement should not be placed less than 1½ inches from the face of the concrete surface. The clear spacing between bamboo rods or splints should not be less than the maximum size aggregate plus ¼ inch. Reinforcement should be evenly spaced and lashed together on short sticks placed at right angles to the main reinforcement. The ties can be maid with vegetation strips. This embedded depth is approximately 10 times the diameter of whole culms or 25 times the thickness of ¾ inch wide splints. Spacing of the stirrups should not exceed 6 inches.

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

10. 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 2.5x10 6

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

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

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

14. Solution At the intersection of the allowable stress curves for concrete and bamboo, find R = 115 and p = 3.1 percent. 2. Maximum bending moment, M, is given by: M = [450(2.43)2(12)]/2.43 + 108(0.6)(12) =13899.6 KN m. R = M/bd2 3. From bd2 = 13899.6/115 = 120.86 m3 4. If b = 2.43m. is chosen, then d = (120.86(10)/2.43)½ = 7.05mm. 5. Bamboo reinforcement = pbd = 0.031(2.43)(7.05) = 4.75 6. Use ¾-inch-thick splints, area = 0.563 m2. Number required = 4.75/0.563 = 8.4; round up to 9. Space evenly in three rows. Bend up top row randomly in the outer one-third ends of the beam.

15. 7. Check the bond stress. Maximum shear at the support, V, is determined as: V = 450(2.43)/2 + 108 = 860 KN/m2. The perimeter of one splint is 4(3/4) or 3 m.; the total perimeter of the longitudinal reinforcement, ∑0, is 9(3) = 27 m. The value of j = 0.925 u = V ÷ ∑ojd = 654.7 ÷ 27(0.925)(7.06) = 13 KN/m2 This is less than the allowable bond stress of 40 KN/m2. 8. Calculate the shear, V', taken by the concrete from V' = νbjd = 72(2.4)(0.925)(4.75) = 759.2 KN/m2 Where ν is the allowable diagonal tension stress of the concrete. 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) = 1.6 mm2 (Stirrup area 4 times the dia). Maximum spacing, s, is given by: s = Aσjd ÷ (V - V') = 1.6(400)(0.925)(4.75) ÷ (860 – 759.2) = 10.1mm. Common practice is to include two additional stirrups past the point where diagonal tension reinforcement is not needed.

16. COLUMNS Bamboo reinforcement in columns serves to resist a compression load equal to that taken by the concrete it displaces; it also will resist shear and tensile stresses. Of the full cross section of concrete, only 80 percent is considered effective in rectangular tied, columns. Allowable concrete stress should not exceed 0.225 f'c where f'c is the ultimate compressive strength of the concrete. Vertical reinforcement should be approximately 4 percent of the column cross section for rectangular columns. When bamboo is used as lateral tie reinforcement, the ties should be spaced not over 16 times the least dimension of the vertical reinforcement nor farther apart than the least dimension of the column.

17. Example Design of Bamboo Reinforced ConcreteColumn: Determine the cross section and bamboo reinforcement of a column required to carry an axial load of 700 KN. Ultimate compression strength of the concrete, 240.KN/m2 Solution: 1. For an unreinforced rectangular column the safe axial load, P, is given by: P = 0.8Ac (0.225 f'c) Where Ac is the cross-sectional area of the concrete column and f'c is the ultimate compressive strength of concrete. 2. The column should have a cross-sectional area of: Ac = 700 ÷ 0.8 (0.225) (240)(10) 3 = 16.20 m2.

18. 3. If a square column is chosen, it will have face dimensions of b = (16.20)½ = 4.0 m 4. The amount of vertical reinforcement should be 4 percent of the concrete area .These should be spaced evenly around the perimeter of 1 to 1½ mm of cover. Provide each vertical splint with a 90-degree corner.

19. COMPARISON OF BAMBOO AND STEEL The strength of bamboo is greater than steel. Bamboo is easily accessible. Bamboo lowers the cost of construction. Increases the strength of the buildings . Bamboo can crack and deflect more than steel reinforcement.

20. Other Applications Of Bamboo Bamboo bridge in the Amsterdam Woods

21. Bamboo theatre during the Festival of Vision, Berlin, 2000

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

23. CONCLUSION 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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