Experimental Study And Theoretical Analysis Of Bamboo Bending Member

Parallel strand bamboo (PSB), fabricated through industrial process by using raw bamboo, isa high strength bamboo-based composite. It has extensively potential prospective application as astructural material for building constructions. The mechanical properties and flame retardance aresuperior to those of lumber. The emission of carboxaldehyde is less than the requirement of E1grade of EU standard. It has extensively potential prospective application as a structural materialfor building constructions.The structure and mechanical properties of PSB have a distinct oriented. As a matter of fact,raw bamboo is a natural oriented fiber reinforced composite. The approach of strength theory andmechanical model proposed by classical theories to analyze the behaviors of the component madeof homogeneous or isotropic materials cannot be suitable to conduct the inelastic analysis forPSB structural members. Therefore, to well understand engineering behaviors of PSB composite,such as constitutive relations, inelastic analysis, failure mechanisms, and failure criterion, is avital work to analysis and design of PSB structure. Based on the theories of mechanics ofcomposite, PSB was treated as a transversely isotropic composite, this paper aimed at studying onthe relationships between bamboo microscopic structure and macro mechanical properties,constitutive law, failure mechanism, the nonlinear flexural and shearing performances of PSBbeams through the experiments and theoretical analysis. The main contents and results can beconcluded as follows.(1) Through the analysis of bamboo microscopic structure and the test of macro mechanics,the relationship between the ratio of vascular bundles and mechanical properties was investigated.A hybrid method to determine the mechanical parameters of vascular bundles and the matrix wasdeveloped. The relationships of the mechanical parameters between transverse-to-andparallel-to-grain directions were proposed.(2) The uniaxial tensile and compressive properties in each main material axis and the pureshearing properties in each main material plane were studied by experiments. Failuremechanisms and the stress-strain relationship of each stress state were investigated. It was foundthat the strength and stress-strain relationships in each stress state depend on the way the fibersinvolved in the damage process. If the expending of cracks were restricted by fibers, the failurepresents progressive process and higher strength and the stress-strain relationship exhibits linearbehavior. Otherwise, if the damages took place in matrix or in fiber-matrix interface withoutfibers involved in, the material shows lower strength and brittle behavior and then thestress-strain relationship exhibits nonlinear characteristics. (3)4-point bending tests for PSB beams were carried out to investigate the flexural behaviorsand the damage mechanism of them.3stages of bending failure of PSB beams under purebending loading can be observed. The first is perfect elastic bending stage, the beams was in theelastic state when the loading less than the proportional limit. The second is nonlinear hardeningstage, i.e. when the loading exceeded the proportional limit, part of fibers in compressive zone incritical section came into nonlinear state, the inelastic compressive zone was gradually expandingtowards the neutral axis, and the stiffness of PSB beams was continuously degraded with theaugment of loading. The last one is failure stage, i.e. when the depth of inelastic compressivezone was reached the ultimate value, the fibers in the out surface of compressive zone werebulking and those in out surface tensile zone were broken. Hence the PSB beam was failed.(4) Considering the differences between compressive and tensile properties, a theoreticalmodel to evaluate the loading capacity and the deflection of PSB beams was proposed based onexperimental studies and theoretical analysis. Well agreements were achieved between the resultsobtained by using the proposed model and those obtained by experiments.(5) The mode and the mechanism of shearing failure of PSB beams were studied. The resultswere shown the shearing damage cannot be took place in transverse to grain direction, instead itwas took place along the parallel to grain direction in the shearing span. Therefore, the shearingstrength in parallel to grain should be adapted to evaluate the shearing strength of PSB beams.Analytical results obtained by using the constitutive law and the calculate model developedin this paper are well agreement with the results obtained by tests. Hence it can be stated that themethodology proposed by this paper is appreciate.