8.1 Due to its fibrous texture, bamboo possesses high tensile strength. This can act as an alternate material for reinforcement in concrete within the limitations of design and construction. The ultimate strength of some of the species of bamboo in direct tension is nearly the same as that of steel at its yield point. On an average it varies from 1 400 to 2 000 kg/cm². The principles adopted for design of concrete structure with steel is also applicable for the concrete member with bamboo. Strength characteristics of steel, concrete and bamboo are indicated in Table 4 and the design data for balanced section in beams/slabs reinforcement is given in Table 5.
| Sl No. | Related Strength Characteristics | |||
| Stress(1) | Mild Steel(2) | Bamboo (Green)(3) | Mass Concrete(4) | |
| i) | Modulus of elasticity | 175 750 to 196 640(for all locations) | — | |
| ii) | Tensile stress | 1 265.5 to 1 400 | 158, Bending-tension(all locations) | — |
| iii) | Compressive stress | — | 105(D. strictus) | 50 |
| iv) | Bond stress | — | 3.5 (green) to 5.6(dry) reported(likely to increase up to 10) | 4 - 10 |
| v) | Shear stress | — | 115-180 | 5 |
PART 6 STRUCTURAL DESIGN — SECTION 3 TIMBER AND BAMBOO: 3B BAMBOO
| Sl No. | Design Data for Balanced Section M 15 (1:2:4) Bamboo and Mild Steel Reinforced Cement Concrete | ||
| Design Parameters | Mild Steel | Bamboo | |
| (1) | (2) | (3) | (4) |
| i) | Modular ratio | 18 | 1 to 1.4 |
| ii) | Position of neutral axis from the top | 0.4d | 0.25d to 0.254d |
| iii) | Lever arm of the resisting moment (MOR) | 0.87d | 0.917d to 0.915d |
| iv) | Constant for MOR (Q) where | 137 | 86 |
8.2 The whole bamboo culms are halved longitudinally and again splitted into four and strips of the size of 20 to 25 mm width and 9 mm thickness are prepared for use as reinforcement. Bamboo strips with triangular lugs (formed at nodes) due to conversion of bamboo into strips improve the bond strength because of the protruding lugs beings gripped firmly in concrete. Strength properties of split bamboo out of a few species are given in Table 6.
8.3 Bamboo has a tendency to absorb water from concrete which results in initial swelling and subsequent shrinkage leading to cracks in concrete. Following processes are thus recommended as mandatory:
a) Chemical treatment with preference for pressure impregnation (full cell treatment with warm coal tar creosote is likely to preserve and at the same time act as water repellent).
b) Treated strips be further given a water repellent treatment with a coating of very hot
bitumen 80/100 grade, followed by a liberal coating of coarse sand. Water inhibitor will also help maintain dimensional stability of strips.
8.4 Techniques in Placing the Reinforcement (see also Fig. 10)
Reinforcement shall be placed in the following manner:
a) Laid edge wise in sets of twin strips for main reinforcement.
b) Laid flatwise with smooth surface and rough surface alternating as distribution or subsidiary reinforcement (wedge effects increased bond).
c) For negative moments, bamboo strips of length equivalent to laid flatwise in alternate rows of slab reinforcement.
d) For beams and lintels, twin strips are arranged in tiers, placed one above the other depending upon requirement and held in position with the help of vertical strips.
e) Split bamboo strip or preferably steel rod be used for diagonal tension to resist shear in beams, etc.
f) Bind the reinforcement with the help of galvanized iron binding wire (or nylon thread/bamboo-cane string).
9 WALLING, FLOORING, ROOFING, AND IN-FILL PANELS FOR WALL, AND COMMON ROOF COVERING/CLADDING