Research On Mechanical Properties Of Structural Bamboo Scrimber And Its Composite Beams

Bamboo scrimber is one of the most typical engineering bamboo material,and has wide application prospects in building structures due to its high production efficiency and excellent mechanic properties.However,bamboo scrimber is still mainly used in non-structural field,such as floor,furniture,decoration and so on,because of lacking a series of studies about how to be used in building structures.Researching on mechanical properties of bamboo scrimber and its structural members,it can provide a theoretical basis of developing a reliability evaluation system of mechanical properties for bamboo scrimber and engineering design for bamboo scrimber used as structural members.This study has a great role in the promotion for the expansion of bamboo scrimber applications,and also has a significant improve for added value.In this paper,as to the bamboo scrimber material,the influence factor,sampling technique,evaluation technique of characteristic value and determination method of design value of mechanical properties were investigated by experimental research combined with numerical simulation,theoretical analysis.While,as to the structural beam manufactured by bamboo scrimber,a new designed reinforced bamboo scrimber composite（RBSC）beam was developed for the improvement of loading capacity.For RBSC beam,mechanical properties of adhesive interface between bamboo scrimber and steel bar,and the whole bending capacity of beam were studied.The main results were summarized as follows:（1）The influencing factors of mechanical properties of bamboo scrimber were investigated by tensile,compression,bending,shearing,and hardness mechanical tests.The effects of forming density,bamboo bundle,loading direction on the tension strength parallel to the grain,compression strength parallel to the grain,modulus of rupture,modulus of elasticity,shearing strength parallel to the grain and hardness,and the relationships between the hardness and other mechanical properties were revealed.（2）Through a self-developing calculation program and multi-parameter numerical simulation,the influencing factors of sampling errors of mechanical properties for bamboo scrimber were analyzed.The influence laws of probability distribution,coefficient of variance,and number of specimen contained in sample on sampling errors of mechanical properties were obtained.The calculation formulas for different sampling errors were established.（3）Through a self-developing calculation program and multi-parameter numerical simulation,the calculation principles of confidence level of sampling errors were given.At a error precision of 0.05,the influence laws of probability distribution,coefficient of variance,and confidence level of sampling error on the minimum sampling number of specimens(n_min)were obtained.The calculation formulas of n_min were developed.Then,the n_min of each mechanical property of bamboo scrimber was determined based on the mechanical test data.（4）Through a self-developing calculation program and multi-parameter numerical simulation,the calculation principles of confidence level of characteristic value for strength and modulus of elasticity were clarified based on the parameter and non-parameter method.The influence laws of probability distribution,coefficient of variance,number of specimen contained in sample,and confidence level of characteristic value on the characteristic value were gotten.The determination methods for characteristic value of strength and modulus of elasticity were proposed.Finallly,the characteristic values of strength and modulus of elasticity for bamboo scrimber were calculated based on the mechanical test data.（5）Through a self-developing calculation program and multi-parameter numerical simulation,the relationships between the reliability index and partial factor under different probability distribution models,fitting data points,load combinations,and load ratios were obtained by reliability analysis.The determination method for strength design value of bamboo scrimber was suggested.And the differences in relative design value of mechanical properties between bamboo scrimber and Chinese larch dimension lumber,Q235 steel were analyzed.（6）The influence laws of forming density of bamboo scrimber,heat treatment of bamboo bundle,diameter of reinforcement,and reinforcement thread on the pull-out properties of RSBC specimens were obtained by pull-out test.A mechanical model of adhesive interface between bamboo scrimber and reinforcement was proposed.The variations of normal stress of bamboo scrimber,shear stress of adhesive layer along the embedded depth of reinforcement were deduced.（7）The influence laws of heat treatment of bamboo bundle and diameter of reinforcement on the bending properties of RBSC beams were revealed by full-size bending test.The theoretical calculation models of ultimate load capacities and bending stiffness of RBSC beams were established.For the whole cross-section of RBSC beams,the ratios of bending stiffness,ultimate load capacity contributed by the reinforcement element and bamboo scrimber element were investigated.Based on the research results of this comprehensive study,it is concluded that it is a systematic project,involving scientific research,mathematical statistics,numerical simulation and reliability design,etc.,for scientifically and reasonably determining the characteristic value and design value of mechanical properties of bamboo scrimber.The sampling technique,evaluation technique of characteristic value and determination method of design value of mechanical properties established in this study,can be theoretical support for the systematic project.Through the pull-out and full-size bending test of RBSC specimens in this study,it is verified that a cold-press molding process for the new type RBSC beam is feasible and can significantly improve the ultimate bearing capacity and stiffness of traditional bamboo scrimber beam.