| With the vigorous promotion and development of steel structures and assembly buildings in our country,the steel structures and the assembly buildings have become an important direction of the domestic building structure development.In steel frame structures,the design of connections is indispensable.Whether the structure is safe or not is closely related to the performance of the connections.Especially the beam-column connections which transfer the force of the structure and ensure the safety of the structure are the most important parts of the design.This paper mainly introduces the “upper flange welded-lower flange bolted”(UWLB)beam-column connection and the connection is the beam-to-column connection with cantilever beam.The upper flange of the cantilever beam and upper flange of the frame beam are connected by butt weld,while lower flanges are connected by a splice plate.The splice plate is connected to the cantilever beam by fillet welds and connected to the frame beam by bolts.Four specimens were designed to carry out quasi-static loading tests.The hysteretic behavior,skeleton curves,stiffness degradation,ductility and energy dissipation capacity of the connection are analyzed.In order to improve the energy dissipation of the splicing area,the connection was improved to be the UWLB connection with slotted holes.And the finite element analysis software ABAQUS was used to simulate the UWLB connection with slotted holes.The seismic performance including hysteresis curves,skeleton curves and energy dissipation capacity was studied.The main research contents are as follows:(1)Four specimens were designed to carry out quasi-static loading tests with the following parameters: the cross-section area of the lower flange splice plate and the number of bolts at the lower flange.The failure modes,hysteretic behavior,ductility and energy dissipation capacity of the connection are analyzed.The results show that the failure modes of four specimens are buckling of the lower flange splice plate and tearing of weld at the beam-column connection.The hysteretic curves are asymmetric due to the different splicing methods of the upper and lower flanges at the splicing area.Compared with the traditional beam-to-column welded connections,the hysteretic curve of the connection presents a significant pinch phenomenon.The ductility coefficient is ?=3.48?5.71,the ductility is good.When the lower flange splice bolts number is 2/3 of the equal strength design bolts number,the ductility increases by 5.85% on average in the positive and negative loading directions.The total energy dissipation and splicing area energy dissipation of the connections are obtained by calculating the envelope area of hysteretic curves of the connection and the envelope area of hysteretic curves of the splicing area.The sliding energy dissipation ratio of the splicing area is 10.7%?13.7%,the connection can utilize the slipping and plastic deformation to dissipate energy.(2)On the basis of the UWLB beam-to-column connections,the bolt holes of splicing plates are designed as slotted holes,thus a new type of rotational friction energy dissipation connection,i.e.the UWLB beam-to-column connection with slotted holes is studied.Six specimens are designed and analyzed by the finite element software ABAQUS.The hysteretic behavior and energy dissipation capacity of the connections with different sizes of slotted holes are analyzed.The analysis results show that all the six specimens exhibit good hysteretic curves with a stable and saturated shape,presenting a obvious slip platform segments,and the energy dissipation performance is excellent.The UWLB beam-column connections with slotted holes have stronger rotational capacity,achieving more than 5% rotation,meets the rotation requirements of semi-rigid connections.The slip of the connections and the energy dissipation of the connections increase with the increase of the dimension of the slotted holes.The proportion of the energy dissipation in the splicing area of the UWLB connections with slotted holes to the total energy dissipation is 37.7%?42.4%,and it increases with the increase of the dimension of the slotted holes.With the increase of loading displacement,the shear force of connections exceeds the maximum static friction force so that the splice plate begins to slip,exceeding the ultimate state of friction-type connections.With the gradual extrusion of bolts with the hole wall,the high-strength bolts become compressive connections,and the bearing capacity increases after the sliding section on the hysteretic curve.The UWLB beam-column connection with slotted holes can dissipate energy by plastic deformation and slip of splice plates. |
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