Studies On Axial Loading Capacity Of CHS T-joints Reinforced With External Stiffening Rings And External Stiffeners

Circular hollow steel?CHS?joints have excellent mechanical properties in compressive,tensile,bending,torsion and fluid dynamics.Although the cost of unit material is slightly higher than that of ordinary H section steel,the corresponding cost can be reduced by less steel and less anti-corrosion paint on the outer surface.As compression,tension,bending and bidirectional bending members,circular hollow steel joints have higher bearing capacity,while the flatness and section size accuracy of cold-formed pipes are better than that of hot-rolled open sections.The connection of circular hollow steel joints is suitable for direct welding.There is no need to be connected by joint plates or other connections.There are no redundant connecting members,which makes the shape of the circular hollow steel building beautiful,smooth and modern.But at present,most of the research on circular hollow steel is focused on the research of bearing capacity without pre-loading.Only a small number of scholars are involved in the study of axial tension of joints,and the research on bearing capacity under load is blank at present.Therefore,it is necessary to explore the tensile performance of the reinforced joints and the bearing capacity of the joints under pre-loading,so as to optimize the circular hollow steel section,make full use of materials and save costs.The research contents of this paper are as follows:the bearing performance of the T-shaped circular hollow steel joints under axial tension under the reinforcement of the external stiffener rings without pre-loading,and the bearing performance of the T-shaped circular hollow steel joints under the reinforcement of the external stiffeners under pre-loading.The size,loading device,loading system and final data of three groups of six T-shaped without pre-loading circular steel pipe joints were introduced in detail.Based on the test data,the finite element model of T-shaped steel joints without pre-loading was analyzed with ANSYS software,and the selection of finite element tool,the yield criterion of the model,the setting of dimension and thickness,the setting of weld,the finite element meshing,the boundary condition and the loading solution were introduced.The finite element analysis model of the stiffening ring outside the T-shaped steel joints under tension state was obtained by comparing the finite element simulation data with the experiment.On this basis,three groups of six load bearing capacity of the joints were tested.The dimension design before the experiment,the loading process of prestress,the loading system,the welding work during the load holding process and the failure form were introduced in detail.Finally,the load-displacement curves of three sets of joints under different initial loads were obtained.The influence of reinforced circular hollow steel joints on the bearing capacity of axial compression was investigated.This paper draws the following main conclusions:?1?The test results show that the bearing capacity of T-shaped joints with stiffening rings is significantly higher than that of T-shaped joints without stiffening rings.The values of the joints are 0.25,0.50 and 0.73,and the relative strength of the displacement at 6%d₀ increases by 20.5%,23.1%and 14.8%,respectively.The initial stiffness of the T-joint was increased by47.0%,22.2%and 33.8%,respectively.?2?The size of the external stiffening rings and the?value of the bearing capacity of the joint have an important impact.However,when the?value is between 0.25 and 0.50,the influence of the value on the bearing capacity of the joints is more significant.With the further increase of the?value,when the?value reached 0.50 to 0.73,the ultimate strength of the specimen increased correspondingly,but the strength did not increase significantly.?3?Both the outer stiffeners and the outer stiffening ring can improve the tensile performance of the joints,and the improvement of the initial stiffness of the joints is close to each other.The improvement of the initial stiffness of the joint of the stiffeners is slightly better than that of the reinforcement of the outer stiffening rings.When the value of?is 0.73,the axial tensile performance of the outer stiffener joints were obviously better than that of the outer stiffener rings.The chord of the stiffening joint of the outer stiffening ring joints produces obvious bending deformation,while the outer stiffeners provides support to restrain the deformation of the chord along the direction of the length of the chord under the strengthening effect of the outer stiffeners.?4?The influence of initial loading on the bearing capacity of the joints varied with different values.When the load was 0.25,the greater the initial load came,the later the ultimate bearing capacity would arrive,and the total displacement of the structure would increase,but there was no obvious change in the bearing capacity.When the value was 0.50,the greater the initial load came,the smaller the ultimate bearing capacity and the smaller the joint stiffness arrived.When the value was 0.75,the experiment was stopped in advance due to the excessive out-of-plane tilt of T3-60.However,it can be seen that the greater initial load suffered,the greater the ultimate bearing capacity arrived and no significant changed in the joint stiffness.