| The externally strengthened square steel tubular joint studied in this paper is an improved steel frame beam column joint.The joint area is strengthened by adding T-shaped parts between the upper and lower flanges of adjacent H-steel beams.At present,the research on the mechanical properties of joints and frame structures is mostly concentrated in the plane,and the spatial mechanical properties of joints and structures are rarely considered,However,due to the uncertainty of the direction of seismic,the beam column joints of steel frames are characterized by spatial force,which has not been widely studied.Therefore,this paper analyzes the static behavior of externally strengthened square steel tubular joints under plane and spatial loads.By changing the thickness of square steel tubular column plate,the ratio of beam to column linear stiffness,the length of T-shaped part web,the height of T-shaped part flange,the thickness of T-shaped part web,the thickness of T-shaped part flange,and the length of T-shaped part corner,the static performance of T-shaped part external strengthened square steel tubular column spatial joints under plane symmetric load is explored.It is found that the plastic hinge displacement can be realized in most of the T-shaped strengthened joints.First,the stress appears in the welding position between the T-shaped part and the square steel tubular column.With the increase of displacement,the stress expands along the T-shaped part.The stress at the connection between the flange of the T-shaped part and the beam flange develops rapidly.The flange of the beam yields first,the stress transfers to the web,and the displacement continues to increase,The yield hinge line through the whole beam section is formed.The European Code EC3 is used to define the rigidity of the joints.Most of the space joints strengthened by T-shaped part are rigid under plane symmetrical loads.According to the results of initial stiffness and bearing capacity obtained from the whole process analysis,seven parameters are considered,and the expressions of initial stiffness and bearing capacity of externally strengthened square steel tubular spatial joints are proposed.The whole process analysis of the finite element model of externally strengthened square steel tubular spatial joints under four-way beam end loading is carried out.The stress development nephogram,moment rotation curve and ultimate load of the joints under monotonic load are obtained.The initial stiffness,plastic ultimate bending moment and relative rotation angle of beams and columns are compared and analyzed.It is found that compared with the plane loading,the stress development trend of the joint is the same as that of the plane loading,the plastic ultimate moment of the joint basically remains unchanged,and the initial stiffness of the joint is improved.The spatial joints of square steel tubular column strengthened by T-shaped part are all rigid joints under four-way beam end load,and the expression of initial stiffness of the joints under spatial load is proposed.The difference between the calculation results of the expression and the finite element simulation results is small,which can be used to estimate the initial stiffness and bearing capacity of the joints.The improved method is proposed for some joints that fail to realize the plastic hinge outward movement.The improved failure mode of spatial joint has obvious plastic hinge displacement.The full section yield of the joint end of the outer beam flange and T-shape part of the joint domain is yield,which effectively improves the stress set phenomenon at the root of the joint domain,and makes the stress distribution in the joint region more reasonable.Based on the static performance of the improved spatial joints,the calculation expressions of initial stiffness and bearing capacity of the outer reinforced square steel tubular spatial joints under the action of space load are proposed,and the structural requirements of T-shaped reinforced square steel tubular column joints are determined.It is suggested that when the width of column plate is 300 mm,the wall thickness of square steel tube column should not be less than 12 mm,other specifications of square steel tubular column should be used,the width thickness ratio of column section should not be greater than 25,and the linear stiffness ratio of beam to column should not be greater than 2.30.The length of T-shaped part web is greater than half of the width of column web,the flange height of T-shaped part is not less than 1/6 of the width of column web,the thickness of T-shaped part web is equal to that of H-shaped steel beam,the flange thickness of T-shaped part is not less than that of T-shaped part web,and the corner length of T-shaped part shall not be less than 1/8 of the width of column web... |
