| Timber-steel composite beam is a new type of composite component shape,the reasonable combination of timber plate and steel beam can give full play to the material properties of timber and steel.Since the high tensile and compressive strength of timber and the low shear strength of timber,and the high strength of steel,the timber-steel composite I-beam is formed by using the steel I-beam as a skeleton and covering the upper and lower surfaces with a timber plate,and the composite beam is bolted together for the convenience of construction and to ensure sufficient connection rigidity.By controlling the cross-sectional height of the composite beam,and changing the ratio of the thickness of the timber plate to the height of the I-beam(referred to as the timber-to-steel height ratio),a total of 3 groups of 6 timber-steel composite I-beam specimens are designed and fabricated,and the bending bearing capacity test was carried out on the 3 groups of specimens to investigate the effect of the timber-steel height ratio on the flexural performance of timber-steel composite I-beam.The equations for calculating the elastic ultimate load capacity of the composite beam were proposed based on the composite coefficient method,and theoretical calculations of the elastic ultimate load capacity and mid-span deflection of the composite beam were carried out.The numerical simulation analysis of three groups of specimens was carried out using the finite element software ABAQUS,and the finite element calculation results were compared and analysed with the test results.The main research contents and achievements are as follows:(1)The failure process of timber-steel composite I-beams was observed and analysed by the three-equinox loading method,and the failure mode and failure mechanism of timber-steel composite I-beams were revealed.The three groups of specimens are all typical bending tensile failure mode,after reaching the ultimate load,the lower surface of the bottom timber plate is pulled off and fails.With the change in the timber-to-steel height ratio,the splitting damage on the upper surface of the timber plate to different degrees and the local buckling of the upper flange of the I-beam appeared in some specimens during the loading process.(2)Through the load-capacity test and analysis,the load-capacity and deformation law of timber-steel composite beams were discovered.Compared with the specimens with a timber-to-steel height ratio of 0.33,the two groups of specimens with a timber-to-steel height ratio of 0.25 and 0.44 have different degrees of improvement in flexural load-capacity and ductility,indicating that a better timber-to-steel height ratio can fully utilize the mechanical properties of timber and steel,and observed from the point of view of the mechanical properties of 3 sets of composite beam specimens.,the optimum timber-to-steel height ratio is 0.44.(3)The overall deformation of the timber-steel composite beam no longer satisfies the flat-section assumption,but because the bolt provides sufficient joint stifness,the slip generated at the timber-steel interface is small,and the addition of longitudinal stiffening ribs to the upper flange of the I-beam can effectively reduce the relative slip of the timber-to-steel interface.The composite beam as a whole belongs to a strong composite joint,and its overall performance is better,however,the degree of combination of the composite beams weakens to some extent as the timber-to-steel height ratio increases.In addition,due to the use of a wide flange I-beam,the lateral distribution of normal strain of the upper and lower timber plates is relatively uniform,and the shear lag effect is not obvious,and changes in the timber-to-steel height ratio do not affect the shear hysteresis effect..(4)Referring to the composite coefficient method,the calculation formula of the elastic ultimate load-capacity of timber-steel composite beam is proposed,and the elastic ultimate load-capacity and mid-span deflection of the composite beam are calculated theoretically,and compared with the test results,the accuracy of the calculation formula is verified by analysis.The calculation formula proposed in this paper can be used to calculate the elastic ultimate bearing capacity of timber-steel composite beams.(5)The numerical simulation analysis of three groups of timber-steel I-beams was carried out by ABAQUS finite element software,and the main mechanical properties such as stress,deformation,and relative slip of timber-to-steel composite I-beams under the same load and boundary conditions as the test were compared.The results show that the error of the finite element calculation and the test results are small,which indicates that the results of the finite element simulation calculation are close to the actual situation,which further verifies the reliability of the experimental analysis results. |
