Experimental Study On Bending Performance Of Orthogonal Rib Beams With Different Height-span Ratios In Poplar LVL Box Floor

Poplar LVL box floor is a hollow box floor constructed by Poplar LVL orthogonal rib beams and OSB cladding.This new type of combined floor has the advantages of light weight and convenient construction of traditional wooden floor,and the structure of the hollow box is beneficial to sound insulation and heat insulation,reducing the vibration frequency of the floor and improving the comfort of the floor.In order to obtain the force mechanism of Poplar LVL box floor and provide theoretical support for the application of this new floor,the project team conducted a series of studies.In this paper,the stress performance of orthogonal rib beams with different high-span ratios in Poplar LVL box floor is mainly studied,and the finite element simulation and theoretical analysis are carried out on the basis of the experiment.The main research work and results are as follows:Firstly,the physical mechanical performance test of Poplar LVL material was carried out,and the physical and mechanical parameters such as water content,bending strength,anti-pull strength and bending elastic module of Poplar LVL were obtained,and the relationship of the structure of Poplar LVL wood was determined.The experimental results show that under the same conditions,the density of Poplar LVL is higher than that of Poplar logs,and there is no significant difference between the bending strength of Poplar LVL in the direction of parallel adhesive layer and the direction of vertical glue layer,while the pressure strength is 5.9 times that of the vertical glue layer.Secondly,the design and production of 3 groups of U-type nested,T-base beam support and L-type connection structure of the plane size of 1200mm×1200mm orthogonal rib beam node test,The load distribution variation law of the rib member node test parts,stiffness and two directions was studied by bending test.The results show that the three groups of rib beam node test pieces have good carrying capacity,and when the damage has obvious signs of destruction,belong to the ductility of destruction;After comparative analysis,it is concluded that the L-type connection is better in performance,and the construction is simple,the connection is convenient,can be used in the subsequent Poplar LVL orthogonal rib beam node.Subsequently,the design and production of 4 flat size 3600mm×4800mm Poplar building cover rib beam test piece,of which,3 for different high-span ratio of orthogonal rib beam test pieces,1 for traditional form of building cover rib beam test piece.Through the bending performance test,the load-displacement curve,load-strain curve and the evolution law of bending stiffness of each test piece are obtained,the influence of the high span ratio change on the force performance of the orthogonal rib beam of Poplar LVL is analyzed,and the comparison and analysis of the traditional floor cover rib beam test piece is obtained.The results show that the change of rib beam height ratio has an important effect on the overall stiffness of the orthogonal rib member test piece,and for every 50mm increase in the cross-sectional height,its bending stiffness can be increased by about 70%,and when the load is applied to 2.5kN/m2(equivalent to the general floor load in the load specification),the deflection allowed value of the wood structure design standard is met except the D1 test piece,and the load load is increased by 7.5kN/m2,orthogonal rib member test piece is still showing good integrity,deflection deformation in the midpoint of each test piece is the largest,and along the midpoint to the four-fold decline,the whole floor rib beam test piece deformation is "bowl-like";Under the same conditions as the high span ratio and load size of the rib beam,compared with the traditional floor rib beam test piece,the stiffness of the orthogonal rib member test piece is improved,the deflection deformation decreases and the cross-sectional strain decreases.Then,through ABAQUS finite element software,the model of Poplar LVL orthogonal rib beam finite element is established,the force process is analyzed by non-linear numerical simulation,the influence of the high cross ratio of rib beam against Poplar LVL orthogonal rib beam is further studied,and the test results are compared and analyzed.The results show that the typical destruction phenomenon of the test piece obtained by the finite element simulation,the load displacement curve and the test match well,and through the whole process simulation analysis of the orthogonal rib member test,it is found that the D2 and D3 test pieces still have a large strength reserve when the load reaches about 7.5kN/m2.Finally,three calculation methods,two-way plate method,plate method and cross-beam system method,are used to examine the deflection of the Poplar LVL orthogonal rib beams with different high-span ratios,and to explore the more suitable theoretical calculation methods.The results show that the two-way plate method is the closest to the experimental value,with an average relative error of only 8.63%,while the average relative error of cross beam system and plate method is 25.76 percent and 27.25 percent,respectively.Therefore,the two-way plate method is more in line with the deflection deformation calculation of the ethnol LVL orthogonal rib beam structure system,and the theoretical analysis method is simple and the conclusion is reliable.The research shows that Poplar LVL orthogonal rib beam structure system has good bending performance,the increase of the high span ratio of rib beam has an important influence on the stiffness and carrying capacity of the orthogonal rib member test piece,and the cross-setting of the rib beam improves the stiffness and integrity of the test piece,and the bending performance of the orthogonal rib beam system is better than that of the traditional building cover rib beam.Orthogonal rib member test sits with a cross-section dimension of 40 x 285mm have a greater safety reserve when the scratch allowable value is met with the load specification.The research results can provide reference basis for the experimental research and theoretical analysis of Poplar LVL box cover,and can expand the application of Poplar LVL material in the construction structure.