Length effect on bending properties and evaluation of shear modulus of parallel bamboo strand lumber

One hundred sixty-two parallel bamboo strand lumber (PBSL) beams were tested for the bending properties under three-point bending with variable span. Two typical failure types were classified, type I was tension failure of the bamboo fiber located below the neutral axis at mid-span, while type II was shear failure which was mainly found in specimens with large depth-span ratio. The shear modulus \({\text{G}}_{{{\text{LR}}}}\) of PBSL was also calculated according to Timoshenko’s bending theory. To evaluate the shear modulus, 45° off-axis compression tests had been done. The results showed that the mean values of shear modulus for \({\text{G}}_{{{\text{LT}}}}\), \({\text{G}}_{{{\text{TR}}}}\), and \({\text{G}}_{{{\text{LR}}}}\) are 1254.5 MPa, 408.1 MPa, and 716.4 MPa, respectively. The bending test result was compared with the shear modulus measured by 45° off-axis compression test. It was found that the shear modulus measured by three-point bending test with variable span was significantly less than the shear modulus obtained by 45° off-axis compression test. The empirical equation of shear factor s corresponding to depth-span ratio h/l was proposed. The calculation results gained from the proposed formula are in good agreement with the 45° off-axis compression test results.