Developing mechanical properties for flexure and capacity-based grading using measurable indicating properties (IPs) for selected local bamboo species

Bamboos have always been a part of the lives of the Filipino people, culturally and economically. Bamboos have always been known to be a sturdy and flexible material, however, in construction, it is still perceived as a “poor man’s material” because its highest share of its users belong to low-income groups who experience shortcomings tapping into more commercial options. The lack of local codes and grading procedure also contributed to its underutilization. This study conducted 70 and 32 four-point bending tests for Bambusa blumeana and Bambusa vulgaris, respectively. From the results of the test, characteristic values for bending strength (fm,0,k), mean modulus of elasticity (Emean), and the 5th percentile modulus of elasticity (E0.05) were computed. The allowable stress was computed using a factor of safety of 2.5 and compared with the high strength group of unseasoned structural timber of Philippine woods. The allowable bending strengths of the bamboo species were 22.36 MPa for B. blumeana and 15.58 MPa for B. vulgaris; the modulus of elasticity values were 5.16 GPa for B. blumeana and 3.77 GPa for B. vulgaris. The high strength group of unseasoned structural timber have bending strength values ranging from 13.6 MPa to 19.6 MPa, and modulus of elasticity ranging from 3.11 GPa to 6.08 GPa. The results show that the bamboo species tested have comparable values for the timber in this group. This study also develops the structural grading for the bamboo species. Several parameters for Indicating Properties (IP) were analyzed as well as its relationship to Grade Determining Properties (GDP). The IPs show a good correlation with GDPs such as flexural capacity (Mult) and flexural stiffness (EI) which suggests that a capacity-based grading would be better in grading bamboo. The linear mass (q) provides the strongest correlation with the flexural capacity (Mult) and flexural stiffness (EI). However, the combination of the external diameter (D) and the linear mass (q) provides a stronger correlation with Mult and EI. Therefore, D and q were chosen as the IP for capacity grading. The confident band method was used in developing the structural grading which utilizes the intervals of the IPs as the structural grade and each grade has its own GDP which include the mean flexural capacity (Mult) or flexural stiffness (EI), five percent exclusion limit (R0.05), and characteristic structural property (Rk)