Experimental And Finite Element Analysisby Study Of Negative Bending Performance Of Glulam T Beam

With the continuous progress of material science,the emergence of glued wood has improved the shortcomings of traditional wood in the application of building structures.As a kind of renewable ecological building material,Glulam has been widely used in today’s society because of its material characteristics and unique aesthetic value.At present,the international research on Glulam mainly focuses on the material properties of Glulam,the stress analysis of beams with rectangular cross-section and various composite members,while the mechanical properties of other cross-section Glulam beams and their negative bending properties are rarely studied.Compared with the traditional rectangular section beam connected by bolts,T-section beam can improve the bearing capacity and rigidity of the component,avoid the slip and stress concentration phenomenon between the bridge deck and the beam,and effectively improve the overall mechanical performance of the component.Based on the national international science and technology cooperation project(2014dfa53120)"Research on manufacturing and application technology of large-span heavy-duty engineering wood structural materials" and the follow-up project of national forestry public welfare industry research project-research project on bending performance of T-section glued wood beam(201304504-3),this paper carried out the research on negative bending performance of glued wood T beam.Using Larix gmelinii as raw material and polyurethane structural adhesive as adhesive,two groups of T-section beams with different shear span ratio were designed and manufactured.The negative bending behavior of glued wood T-beam is studied by the method of field test,theoretical analysis and finite element simulation,and the failure mechanism is discussed.The research results can be used as reference for engineering application.The main research contents and achievements are as follows:(1)Taking the shear span ratio and span height ratio of glued wood T-beam as parameters,two groups of 6 parallel glued wood T-beam test pieces were designed and manufactured(The size of group A is 250cm × 25cm × 2 1cm,the height span ratio is 1/11,the shear span ratio is 5.24,in which the wing plate is glued by two 3cm thick wood plates,and the rib plate is glued by five 3cm thick wood plates;the size of group B is 250cm × 25cm× 18cm,the height span ratio is 1/14,and the shear span ratio is 6.11,in which the wing plate is glued by two 3cm thick wood plates,and the rib plate is glued by four 3cm thick wood plates).When the T-beam is reversed into an inverted T-beam,the positive moment will be generated in the middle of the span under the condition of simple support at both ends,so that the rib plate will be compressed and the wing plate will be tensioned,and the mechanical performance of the negative moment section of the supporting section of the continuous T-beam will be simulated.The two groups of members were tested in static bending destructive test.The strain,mid span deflection,ultimate bearing capacity,bending stiffness and ductility coefficient of the two groups of members under different loads were measured and analyzed.The failure mode and mechanism of the two groups of members were observed and analyzed.The results show that the ultimate failure modes of the two groups of specimens are all shear failure.When the shear span ratio is greater than 6,the phenomenon of shear failure occurs in the static bending of glued wood T-beam,which is basically in accordance with the conclusion of ASTM d198 on the relationship between the failure mode and shear span ratio of glued wood rectangular beam,but it is not completely consistent,indicating that the failure mode of T-beam is not completely consistent with that of rectangular beam;In group B,compared with group A,the yield load is reduced by 9.7%,the mid span yield displacement is increased by 27.5%,the ultimate bending capacity is reduced by 10.4%,the mid span ultimate displacement is increased by 42.7%the flexural rigidity is reduced by 36%,and the ductility coefficient is increased by 22.4%,which shows that with the increase of shear span ratio,the ultimate bearing capacity and flexural rigidity are decreased,but the ductility coefficient is increased;the load strain curve of two groups of specimens The shear lag effect exists in both groups of specimens,and the transverse distribution of the normal stress of the mid span section wing plate is uneven,showing a smaller relationship with the distance from the center of the rib plate.(2)Abaqus finite element software was used to establish a model of glulam inverted T beam and numerical simulation analysis was performed.The negative bending performance of glulam T beam was revealed by comparing the test results with the results of finite element simulation.The test beam and simulation were compared and analyzed.The beam mid-span deflection,ultimate tensile and compressive strain,flange plate normal strain,and ultimate shear stress are all shown.The results show that:the mid-span ultimate deflection difference is less than 15%;the cross-section ultimate tensile-compression strain difference is less than 10%;the ultimate shear stress is much greater than The ultimate strength of the along-stripe shear strength and the unfavorable area of shear stress coincide with the crack development position of the test beam.The load deflection curve and the transverse distribution curve of the wing plate strain in the mid-span agree well,indicating that the test results are accurate and reliable.(3)The Rammer shear strength formula is quoted to calculate the bending shear capacity of T beams.The theoretical and experimental results are in good agreement,indicating that this formula can be used to calculate the negative bending ultimate load capacity of T beam,Expanded the calculation range of Rammer shear strength formula.