Experimental Study On Bending Performance Of Poplar LVL Orthogonal Rib Beams Floor

Poplar LVL orthogonal ribbed beam floor is a new type of wooden structure floor system composed of Poplar LVL bidirectional orthogonal ribbed beams and OSB cover panel.This paper mainly studies the influence of different rib height/span ratio,spacing and OSB plate thickness on the flexural performance of Poplar LVL orthogonal ribbed floor.The main research work and achievements are as follows:(1)The physical and mechanical properties of poplar LVL were tested,and the physical and mechanical parameters of poplar LVL,such as water content,density,bending strength,compressive strength,tensile strength,? type and ? type fracture toughness,were obtained.(2)Tensile tests were carried out on Poplar LVL and OSB panel nail joints to study the influence of different adhesive layer directions and different OSB thickness on the tensile properties of nail joints.Through the test,it can be found that the bearing capacity and ductility of the joint made by the combination of poplar LVL and OSB are consistent in both directions.When the thickness of OSB reaches 15mm or above,the failure mode of the panel nail joints is mainly that the nails are pulled out and bent,and there is no damage to the OSB plates.With the decrease of the thickness of the plates,the insertion depth of nails increases,and the tensile strength of nails increases.Finally,the load-slip relationship of the nail joints was established,and the failure strength of the 18.3mm thick OSB panel nail joints was calculated to be 253MPa,and the failure strength of the 15.1mm thick OSB panel nail joints to be 317MPa.(3)On the foundation of the trial of ribbed beam joints by the research group,four Poplar LVL orthogonal ribbed beam floor specimens with plane size of 3600mm×4800mm were designed and manufactured.Through experimental research,the influence of different rib spacing,height span ratio and OSB plate thickness on the bending performance of Poplar LVL orthogonal ribbed beam floor was analyzed,and the failure mechanism of Poplar LVL orthogonal ribbed beam floor was explored.The test results show that the floor specimens do not have any obvious damage phenomenon under local loading.Under the overall loading,when the test load is 2.5kN/m2,the deflection of the four floors is all less than the allowable deflection value stipulated in the "Wood Structure Design Standard"(GB50005-2017).The flexural stiffness of the floor with orthogonal ribbed beams decreases with the increase of the space between ribbed beams,increases with the increase of the height-span ratio of ribbed beams,and increases slightly with the increase of OSB.Among them,the variation of the span of the ribs has the greatest effect on the overall bending stiffness of the floor,followed by the spacing of the ribs,and the OSB plate thickness has the least effect.When all the specimens were loaded up to 12kN/m2,the overall mechanical performance of the orthogonal ribbed floor specimens was still good,and the deflection deformation showed a decreasing trend from the center of the floor to the periphery,like a "bowl" shape.(4)Finite-element simulation was carried out on the floor of Poplar LVL orthogonal ribbed beams by ABAQUS software,and the deformation,internal force distribution,and the influence of different ribbed beam spacing,high-span ratio and OSB plate thickness on the bearing capacity of the floor under uniform load were analyzed.The results show that the failure mode,deformation and stress distribution of rib and roof of the finite element model are basically consistent with the test results.Through the simulation of the whole loading process of the four specimens,it is found that the four specimens enter the failure stage when they are loaded to about 18.2kN/m2,15.4kN/m2,26.3kN/m2 and 17.8kN/m2,respectively.The bearing capacity of LVL orthogonal ribbed floor increases with the increase of ribbed height,decreases with the increase of ribbed spacing,and increases slightly with the increase of OSB plate thickness.(5)Three different calculation theories,such as cross beam system method,two-way plate method and quasi-plate method,were used to check the deflection of Poplar LVL orthogonal ribbed beam floor to explore the design calculation method suitable for the deflection calculation of orthogonal ribbed beam floor.The results demonstrate that the mean error between the theoretical and experimental values is 6.61%.The mean error of cross beam system method is 10.99%.The mean error of bidirectional plate method is 22.77%.Based on the above research,it can be seen that the orthogonal ribbed floor structure system of Poplar LVL has good mechanical performance,and the bidirectional and orthogonal ribbed beam arrangement is beneficial to reduce the stiffness difference in the vertical and horizontal direction of the floor and improve its integrity.The change of the height to span ratio of the ribbed beams has the greatest influence on the bearing capacity and stiffness of the floor of the orthogonal ribbed beams,followed by the change of the spacing of the ribbed beams,and the change of the thickness of the OSB plates has the least influence.The research results can contribute to the development of new timber structure system.