Experimental Study On Flexural Performance Of Poplar Laminated Veneer Lumber Box Beam

In 2016,the State Council advocated the development of modern wood structure in relevant documents,which laid a new policy support for the development of modern wood structure in China,and brought new opportunities.As the main architectural form of ancient China,Wooden structure has an ancient history and brilliant achievements in our country.The ancient wood structure is mainly made of logs,but in modern China,forest resources are scarce,and large diameter logs are no longer suitable for building materials.Under the condition of shortage of timber,the research and development of engineered wood provide a good solution for the development of wood structures.LVL is a kind of engineering wood which is made of small diameter logs.It has the advantages of high strength,small variability,high utilization rate of material and green environmental protection.Box girder section is a section with good mechanicalperformance:It can not only provide high-strength but also.reduce deadweight of components.In this paper,eight group of box beam and a group of Solid beam are designed to study the physical and flexural performance of the poplar LVL box beam.First of all,the physical and mechanical properties of LVL material were tested.The study is reference to the domestic and foreign norms and the moisture content,density,parallel grain tensile strength,flexural modulus,flexural strength and compressive strength of the batch specimens are determined in this study.The results show that the failure mode of test in tensile strength parallel to grain of LVL is brittle failure,and the failure mode of test in tensile strength parallel to grain of LVL is somewhat ductile.There are three main types failure pattern in the layer horizontal specimen:the single board fiber breakage,crack between layers,slip between layers;one main type failure pattern in the layer vertical specimen:fiber breakage.Secondly,the flexural properties of LVL box beam were tested.The failure mode,ultimate bearing capacity,ultimate deflection and bending stiffness of LVL box beam are obtained.The load displacement curves of each specimen,the load displacement curve of different parameters and the load strain curve contrast diagram of different parameters are drawn,and the influence of different parameter changes on the bending performance of the LVL box beam are analyzed in this chapter.The results show that the failure model of the flexural LVL box beam is brittle failure,there are three main forms:the box beam bottom flange tensile failure,slip failure at joint,the box beam bottom flange and web tensile failure.In terms of the failure form,the thickness of the flange leads to the connection problem of the joint surface,and the thinness of the flange leads to the failure of the web.Then the bending performance of box beam are analyzed by means of mechanical analysis.The influence of various factors on the bearing capacity of box girder is discussed.The calculate formula of flexural elasticity modulus,flexural strength,deflection and ultimate load capacity of box girder is deduced,and the design theory of box girder is established.In the last,the three-dimensional model of LVL box girder is built by ABAQUS finite element simulation software,and the load and deformation of the LVL box girder are analyzed.Compared with the test results,the validity of the simulation is verified.The research shows that the Poplar LVL box beam has good mechanical performance and can be applied to the wood building construction in the new era and become a force member.The research results provide theoretical support for the popularization and application of Poplar LVL Box Beam.