Study On Seismic Performance Of H-shaped Beam To Square Tube Column Assembled Joint With Outer Sleeve

Assembled buildings with steel-structure have many advantages,such as light weight,high strength,excellent seismic behavior,fast construction speed and high degree of industrialization.In steel frame structure,the beam-column joint has an important influence on the bearing capacity and seismic behavior of the structure.A new type of assembled H-shaped beam to square tube column joint with outer sleeve was proposed.The seismic performance of the new joint were studied in depth by theoretical analysis,experimental research and finite element analysis.(1)3 cross type joint specimens with outer sleeve were designed and tested under low-frequency cyclic loading.The experimental results show that the outer sleeve joints connecting steel beams by welding have good seismic energy dissipation capacity.With the increase of the thickness of the sleeve,the seismic energy dissipation capacity of the joint increases.The thicker outer sleeve is beneficial to meet the seismic design principles of "strong joints and weak components",forming plastic hinge at the end of the beam.The equivalent viscous damping coefficient and equivalent energy dissipation coefficient of the outer sleeve joint connecting steel beams by welding are greater than those of by bolting.Compared with the outer sleeve joints connecting steel beams by welding,anti-seismic energy dissipation capacity of the joints connecting steel beams with bolts is reduced because of the slip of high strength bolts and the premature yield of the extended end plate.The ductility factor of all specimens is greater than 3.0,indicating that this joint has strong late deformation capacity,and meets seismic code.The ductility of the joints decreases with the increase of outer sleeve thickness.The initial rotational stiffness of the specimens increases with the increase of the sleeve thickness.The initial rotational stiffness of ST-1W is about 19% more than that of ST-2W.Before the ultimate bearing capacity dropped to 85%,the angle of the joint is more than 0.035 rad required by the US seismic code,which shows that this joint has a large rotational capacity which can meet the seismic requirements of “strong joints” and“no collapse in the great earthquake”.Using high strength pull bolt connect beam to column produce “pull effect”,which makes the joint have greater rotational ability.However obvious “pull effect” makes the joint slip and the hysteresis loop pinch,and the energy dissipation capacity of the joints is reduced.(2)A nonlinear finite element numerical analysis was carried out for the test specimens.The results were compared with the results of experiment from failure phenomenon,hysteretic curve,skeleton curve,moment rotation curve,stiffness degradation curve and anti-seismic index.The former is in good agreement with the latter in all aspects,which proves that the nonlinear finite element analysis is feasibleand effective for studying the mechanical properties of the joints with outer sleeve.(3)Through nonlinear finite element numerical analysis,parametric modeling was established to study the static performance of joints under monotonic loading.According to the analysis results,the influences of the outer sleeve thickness,the diameter of the high strength pull bolt and the thickness of the extended end plate on the failure mode,the yield bearing capacity,the ultimate bearing capacity and the initial rotational stiffness were studied.The study shows that the bending capacity of the joints increases with the thickness of outer sleeve in a certain range.When the sleeve thickness increases by 2mm,the bending capacity increases by about 14%.With the sleeve thickness increasing,while the ductility of the joint decreases,the initial rotational stiffness of it increases.When the yield of the joint is controlled by the outer sleeve and column,the ultimate bearing capacity,ductility and initial rotational stiffness of the joints are basically unchanged with the increase of the diameter of the pull bolts.When the thickness of the extended end plate is small,the yield of the joint is controlled by the extended end plate,and the bending capacity of the joint increases with the increase of the thickness of the extended end plate.When the thickness of the extended end plate exceeds a certain value,the yield of the joint is controlled by the outer sleeve and column.At this time,the thickness of the extended end plate has no effect on the bending capacity and rotational stiffness of the joints.(4)Through experimental strain analysis and finite element stress path analysis,yielding mechanism of the joint was studied.The yield mechanism of the outer sleeve joints connecting steel beams by welding is as follows: first the flange of the steel beam yields,second the outer sleeve and the column yield under pressure,third the joint(the whole specimen)yields,then the end plate is subjected to the longitudinal compression yield,at last the high strength pull bolts yields.Using the joints connecting steel beams with bolts will cause the extended end plate to yield earlier than the outer sleeve.(5)Based on the yield line theory,through the analysis of the force transmission mechanism of the assembled H-shaped beam to square tube column joint with outer sleeve,the formulas of the tensile bearing capacity of the outer sleeve,the column and the extended end plate are established,and the calculation model and theoretical formula of the bending capacity of the joint are established.The theoretical calculation value of the bending capacity of the joint is in good agreement with the test value and the finite element simulation value.It is proved that the theoretical calculation formula of the bending capacity of the joint is reasonable and can be applied to the design of this joint.