Experimental Study On Mechanical Properties Of Cold-formed Thin-walled Steel Tube Fast-growing Poplar Glued Laminated Timber Column

Timber structure building is mainly composed of natural wood,which has a long history in China.Compared with steel-concrete structures,timber structures have the advantages of good degradability,easy processing and transportation,and are widely used in buildings.However,the wood resources are relatively scarce in China,and the wood growth cycle is long,which makes the fast-growing artificial tree species-fast-growing poplar considered to be applied to modern wood structure buildings.Through the modification and strengthening of the timber structure,the timber structure components made of fast-growing poplar exert higher mechanical properties such as strength and stiffness,making the poplar structure more suitable for the practical application of building structures.In this study,the cold-formed thin-walled square steel tube was combined on the previous glued fast-growing poplar columns,and the mechanical properties of the steel tube glued timber columns were analyzed.Considering the three influencing factors of the thickness of the steel tube thickness,wood plate thickness and the length of the specimen,the failure mode,load-displacement relationship,load-strain relationship,bearing capacity,stiffness and ductility of the steel tube glulam columns were studied,and the advantages were summarized.The main conclusions are as follows:(1)Through the comparative analysis of the mechanical properties of steel tube column,glulam column and steel tube glulam column,the results show that the steel tube glulam column is significantly improved in terms of bearing capacity,stiffness and ductility compared with steel tube column and glulam column.After the combination of steel tube and glued laminated timber column,the external steel tube provides effective restraint for the internal glued laminated timber,and the overall deformation capacity and stability of the steel tube glued laminated timber column are significantly improved.(2)The mechanical properties of steel tube glulam columns under the influence of steel tube thickness,wood laminate thickness and specimen length were investigated.The results showed that under axial compression load,the steel tube glulam specimens were subjected to compressive damage.With the increase of steel tube thickness,the bearing capacity,stiffness and ductility of the specimens are significantly improved.With the increase of wood laminates,the bearing capacity,stiffness and ductility of the specimens showed a downward trend.As the length of the specimen increases,the bearing capacity,stiffness and ductility of the specimen also decrease to a certain extent.Among them,the influence of tube thickness on bearing capacity,stiffness and ductility is greater than that of wood laminate thickness and specimen length.(3)The mechanical properties of steel tube glulam specimens under the influence of steel tube thickness,wood laminate thickness and specimen length were analyzed by grey correlation statistics.The results show that the factors have a high correlation with the bearing capacity and ductility of the specimens,and have a significant influence on the bearing capacity and ductility of the specimens.The stiffness of the specimen is more related to the steel tube thickness and the wood laminate thickness,and less related to the specimen length.(4)Based on the domestic and foreign codes,the calculation formula of the bearing capacity of the steel tube glulam column is derived,and the reinforcement coefficient of the steel tube glulam is proposed.The parameters that affect the reinforcement coefficient are the diameter-thickness ratio of the steel tube and the strength ratio of the steel to the glulam.The functional relationship between parameters and enhancement coefficient is analyzed,and the calculation formula of axial compression bearing capacity of steel tube glulam column is established.(5)The load ratio of steel tube and glulam in steel tube glulam structure is analyzed.The load ratio of glulam is significantly greater than that of steel tube.With the increase of steel tube thickness and wood laminate thickness,the load ratio of steel increases.The bearing capacity of the specimens under the influence of steel tube thickness,section width,member length and glulam strength was analyzed.The three-dimensional surface model under the influence of two factors was established,and the bearing capacity of the specimens under the influence of two factors was compared and analyzed.(6)The bearing capacity of steel tube glulam columns was predicted by machine learning.The results show that the random forest model is optimal and has higher performance.The random forest model has high prediction accuracy,and the predicted bearing capacity is slightly lower than the experimental bearing capacity,which is conservative for engineering design.