Study On The Compression Performance And Load Carrying Capacity Of Bamboo/Wood Columns

Modern bamboo/wood structure is gradually developing to multi-storey and high-rise buildings,which poses unprecedented challenges to the analysis and design of bamboo/wood structure.The non-linear analysis of Engineered Bamboo/Wood columns under ultimate states is an urgent theoretical problem to be solved.In this paper,the compressive performance of Bamboo/Wood columns was investigated.Numbers of axial and eccentric compression tests of solid and hollow columns were carried out.The failure mode and failure mechanism of the columns were analyzed.A nonlinear calculation method of the ultimate bearing capacity of columns under eccentric load was proposed.The following conclusions can be obtained:(1)The compression failure modes of solid and hollow columns under axial loads are basically the same,which depends on the slenderness ratio of the column.The failure mode of long columns is overall instability failure,and of the intermediate slender columns is plastic buckling.The maximum compressive strain in the column decreases with the increase of slenderness ratio.(2)The ultimate bearing capacity of columns under axial compression decreases significantly with the increase of slenderness ratio.By using the differential calculation of material stress-strain curve,the practical application methods of tangent modulus theory and reduced modulus theory were put forward.The analysis showed that the bearing capacity of Euler theory is only applicable to slender columns,and the bearing capacity of intermediate slender columns is between the tangent modulus theory and the reduced modulus theory.The difference of the calculation formula of the bearing capacity of the axial compression member in the current wooden structure design codes of various countries is compared.(3)The eccentric compression failure modes can be divided into compression failure and tension failure,depending on the load eccentricity.The compression failure mode is small eccentric failure mode,which shows that the compression strain at the edge of the compression zone reaches the ultimate compressive strain of the material.The longitudinal fiber bends and bulges out.The tension failure mode is large eccentric failure mode,which shows that the tensile strain rate at the edge of the tension zone reaches first.(4)The deformation of the midspan section of the member basically conforms to the assumption of plane section.Along the height direction of the section,the section can be divided into three parts: tension area,elastic compression area and plastic compression area.Because of the different eccentricity angle,the tension area of the biaxial eccentric compression member may be triangular or trapezoid distribution.(5)Considering the geometrical nonlinearity and material nonlinearity of the columns,the calculation method of the ultimate bearing capacity of the columns with solid and hollow sections under eccentric compression is proposed: the deflection curve equation of the members with rigid region at the end is derived;the internal force response expression of the section is solved by the strip integral method;the ultimate bearing capacity of the members is obtained by the iterative approach method.The calculation results are basically consistent with the test results.(6)The bearing capacity difference of hollow and solid section members with the same consumables is calculated: the ultimate bearing capacity of hollow members is much higher than that of solid members,and the maximum bearing capacity can be increased by 60%;the bearing capacity of different hollow ratio members is compared: when the hollow ratio of members is large,the ultimate bearing capacity increases significantly with the decrease of hollow ratio,when the hollow ratio of members is small.(7)The ideal elastic-plastic model is used as the general simplified material model of bamboo and wood materials.Six typical materials are selected.Based on the principle of equal area of cut and fill,the equivalent elastic proportional ultimate stress of each material is calculated.On this basis,the bearing capacity checking formulas of flexural members,unidirectional eccentric compression members and bidirectional eccentric compression members are proposed.