Experimental Research On The Mechanical Properties Of Wood-like Materials And Calculation Theory Of Column Bearing Capacity

Wood is a traditional building material.However,log is characterized by structural heterogeneity and stress anisotropy.There is many natural defects such as knots and cracks,and its moisture resistance is weak,its anticorrosive performance is poor,and it is prone to be damaged by moth.Therefore,a large number of researches on glued timber structures have been carried out at home and abroad in recent years.“Technical Standards for Multi-story Wood Structures”(GB/T51226)compiled by China has played a great role in promoting the development of modern wood structure.However,the shortage of available forest resources is the key factor restricting the development of modern wood structure.It is very necessary to look for alternative logs for the development of green and low-carbon buildings.China’s straw and other plant resources are very rich but the overall utilization rate is not high so that it is necessary to find a new way to use plant fibers in building structures.In this paper,dry plant fiber or sawdust particles are used as reinforcement and magnesium cementitious material as matrix.After mixing and stirring,it is injected into the mold and compacted on 800t press.After static curing,it is demoulded to obtain a new type of inorganic cementitious artificial integrated material similar to wood.Or add defoamer on the basis of the original ingredients and then pour to form to prepare materials.In this paper,the two materials mentioned above are respectively pressing similar wood material and cast-in-place similar wood,and the mechanical properties and the columns’bearing capacity of the two materials are mainly studied.The scanning electron microscope shows that the matrix can completely infiltrate the reinforcement,but the uneven mixing of the raw materials causes the fiber to have the phenomenon of agglomerating and in-line arrangement,which will affect the mechanical properties of the material.The average density of the pressing similar wood material is 1258 kg/m~3,and the coefficient of variation isδρ=0.085.The average density of the cast-in-place similar wood material is 1296 kg/m~3,and the coefficient of variation isδρ=0.045.The density of the cold-pressing similar wood material and cast-in-place similar wood material is close to that of common wood.The research on the properties of pressing similar wood material based on the measurement of cubic and prismatic specimens shows that:the failure mode of cubic specimen mainly has cone failure,splitting failure and local failure,while the prismatic specimen mainly has splitting failure.The average compressive strength of cube is 12.3MPa,the coefficient of variation is 0.094,and the average compressive strength of prism is about 0.878 times of cube.The two-stage constitutive equation of similar wood materials is proposed.the elasticity modulus is 3400 MPa and poisson’s ratio is 0.23.The shear strength of the material which is based on the short-beam test shows that:the failure of short-beam is relatively sudden,the vertical cracks appear in middle of specimen but development is slow,while crack on shear surface quickly penetrates specimen.The test value of shear strength is 3.86 MPa,and the coefficient of variation is 0.101.The tensile strength of the material which is based on the cube test shows that:when cubic specimens are damaged by splitting tensile,transverse crack is generated on side parallel to mat,and vertical crack rapidly penetrates split surface when broken.The test value of tensile strength is 3.17 MPa,and the coefficient of variation is 0.078.Repeat the above study for the cast-in-place similar wood material to show that:the cubic specimen mainly has cone failure and sheer failure,while The prismatic specimens are mainly splitting failure and shear failure,and the location of shear plane is random.The average compressive strength of cube is 10.2 MPa,the coefficient of variation is 0.006,and the average compressive strength of prism is about 0.990 times of cube.The material constitutive relation only obtains the ascending section.The elasticity modulus of cast-in-place similar wood materials is 3000 MPa and poisson’s ratio is 0.24.In this paper,the slenderness ratio is taken as the control factor,and three groups of specimens with the same section size were designed for the columns’axial compression test.The load lateral displacement relationship and load strain relationship of each control measuring point of the similar wood column are studied,and the axial compression stability coefficient is obtained.Combined with the compressive strength test,the material partial coefficient is proposed.The results show that with the increase of slenderness ratio,the lateral deflection of the middle part of pressing and cast-in-place similar wood columns is increasing.Because of the influence of the initial eccentricity and the initial defect,the ultimate bearing capacity of the measured similar wood columns is less than the theoretical analysis value.The standard value of the pressing similar wood material’s compressive strength is about 73.1%times of that of the cubic specimen.The standard value of the cast-in-place similar wood material’s compressive strength is about 83.3%times of that of the cubic specimen.The partial factor of the pressing and cast-in-place similar wood material can be taken as 1.6.In this paper,the eccentrically compressed test of pressing similar wood columns is studied.With the slenderness ratio as the main control factor,the failure mechanism of eccentric column under different slenderness ratio and the calculation method of bearing capacity were studied.The test results show that the eccentrically loaded capacity of similar wood columns decreases with the increase of slenderness ratio.According to the test results,the relationship between slenderness ratio and mechanical property parameters is proposed,which provides a reference for the formulation of general standard formula.Through the structural test design of wood like materials,the cross-section dimensions of wood like beams and columns are calculated.Finally,this experiment provides reference for the research and analysis of similar wood materials.