Study On Dynamic Characteristics Of Steel Frames With Reduced Beam Sections

During the 1994 Northridge earthquake and 1995 Kobe earthquake,the typical beam-column moment connection (bolted-web-welded-flange) in steel moment -resisting frame suffered unexpected brittle failures.After 1994 Northridge earthquake and 1995 Kobe earthquake many studies on the behavior of beam-column connections used in steel moment resisting frame and their effect on seismic behavior of steel frames have been carried out.This paper presents a Contrastive analysis between the behavior of single normal steel beam-column connection and that of single dog-bone connection. Furthermore,a comparison between the seismic behaviors of steel frames with these two different kinds of connections is also given.This paper derives stiffness matrix of steel frame beam with dog-bone connection by using principle of virtual work.The equivalent stiffness of steel frame beam with dog-bone connection is showed.This paper designs 6 series (altogether 24) of finite element analytic models.On the basis of the finite element analytic models of steel frames with single normal steel beam-column connection and single dog-bone connection established in this paper,the mode of structure is analyzed.The results show that the basis dynamic characteristics of steel frames with these two different kinds of connections are consistent.Under seismic loading based on the time course of context,dynamic performance analysis of steel frames with normal steel beam-column connections and dog-bone connections are carried out respectively.It is found that time-curve of vertex displacement and shear force at the end of column persent a similar nature in the case of EL-Centro and Tianjin Ninghe seismic waves excitation.Time-curve between steel frames with normal steel beam-column connections and dog-bone connection show a relatively stable state.It is found that dog-bone connections can effectively reduce the peak shear in the bottom layer.Fourthermore,it will not increase the displacement peak of top layer in steel frames obviously.Appropriate design of steel frames with dog-bone connections is done,which is to meet the needs of displacement at the same time reduce the seismic force.More importantly,the steel frames with dog-bone connections can avoid premature destruction of the structure as a result of the destruction of rigid welded node in the earthquake. Based on the distribution of plastic hinge,it is obtained that steel frames with dog-bone connections can make it easier for yielding joints to be formed in beams instead of columns than steel frames with normal connections.Therefore steel frames with dog-bone connections can meet the design requirement Strong Column Weak Beam and improve seismic behaviors of structures greatly.It is much easier to form plastic hinge between beam and column end in the bottom layers in steel frames.Therefore it is economical and reasonable to employ dog-bone beam-column connections in the bottom layers in steel frames.