Study On The Flexural Behavior Of Different Spacing Poplar LVL Orthogonal Rib Beams In Box Floor

Poplar laminated veneer lumber(LVL)is a kind of engineering wood,which is made of small diameter logs with high strength and small variability.The project team proposed a new type of wood floor system,i.e.poplar LVL orthogonal rib beam floor,using poplar LVL as the raw material,and carried out a series of Mechanical Properties Research on the floor.The research work in this paper is one of a series of studies.The main purpose of this paper is to study the influence of the joint form of rib beam and the different rib beam spacing on the flexural performance of poplar LVL orthogonal rib beam in the floor.The research work and achievements are as follows:(1)The material parameters such as density,moisture content,tensile strength,bending strength and compressive strength of poplar LVL were measured.The constitutive relationship of the material under tension and compression was established to provide theoretical basis for ABAQUS finite element analysis.(2)Three groups of orthogonal rib beam joint specimens,each of which has three specimens,are designed and fabricated.The dimensions of the test pieces are 1200 mm x 1200 mm,and the interior is composed of a continuous beam and two short beams which are connected by the above-mentioned connectors to form an orthogonal rib beam joint.The bearing capacity,stiffness and load distribution in two directions of each rib beam joint are studied.The results show that:the three kinds of joint specimens are all ductile failure,the main failure phenomenon is the separation of the joint and the wood beam at the middle joint,some self tapping screws are pulled out;the end of the rib beam appears different degrees of collapse;the load transferred in two directions at the joint conforms to the load distribution law of the orthogonal rib beam.Among them,the U-shaped nested type has the smallest overall stiffness and larger node deformation;the T-shaped base beam drag type and L-shaped connector have similar stiffness and smaller deformation.Through comparative analysis,L-type connectors are selected as the rib beam joint connectors in the subsequent bending performance tests of poplar LVL orthogonal rib beams with different spacing in the box floor.(3)Four poplar LVL rib beams with the size of 4800mm × 3600mm were designed and fabricated,among which one was traditional one-way rib beam,three were orthogonal rib beams with the spacing of 600mm in the short side direction,900mm and 1200mm and 600mm in the long side direction respectively.Through the uniform load test,the joint damage,load-strain curve and load displacement curve of popular LVL orthogonal rib beam with different rib spacing are studied.The results show that when the load is up to 7.5kN/m2,the four groups of rib beams are not damaged significantly,and the overall mechanical performance is still good.The main failure phenomenon is that the self tapping screw at the joint is slightly pulled out;the lower part of the connector is slightly separated from the poplar LVL wood beam;the end position of the rib beam and the edge beam is slightly separated;the deflection of the four groups of rib beam specimens under the test load of 2.5kN/m2 meets the deflection limit of flexural members specified in the design standard for wood structures(GB50005-2017);the change of the rib beam spacing affects the floor rib beam The results show that the stiffness of the box type floor is higher than that of the traditional one-way floor.It is found that the provisions of the floor rib beam spacing in the code are relatively conservative.(4)The cross beam system method,the two-way slab method and the quasi slab method are used to analyze the bending performance of the orthogonal rib beam,and the results are compared with the experimental data.The results show that compared with the experimental results,the error of the cross beam method is larger;the calculation of the quasi plate method is more complex and the error is larger;the calculation of the two-way plate method is simple and the error is the smallest.(5)Based on ABAQUS finite element software,a finite element model is established for the joint specimen and the poplar LVL orthogonal rib beam specimen.The deformation,strain development,bearing capacity and load displacement curve under the vertical load are analyzed.Compared with the test results,the failure phenomenon of the model is consistent with the test results,and the load displacement curve calculated by the model is also consistent with the test results.Based on the experimental research,theoretical analysis and numerical simulation in this paper,it is concluded that the three kinds of floor rib beam specimens with different rib beam spacing have good mechanical properties;with the increase of rib beam spacing,the stiffness of the rib beam decreases;the stiffness of the orthogonal rib beam specimens is better than that of the traditional one-way floor rib beam;the two-way plate method is more suitable for the deflection calculation of the orthogonal rib beam;the finite element model established can be used for the calculation of the orthogonal rib beam analysis and calculation of beams.The research results of this paper provide theoretical support for the following research on the mechanical properties of poplar LVL box floor.