Research On Innovative Column Base Joints And Seismic Performance Of Steel Frames With Rocking Truss

As a kind of self-centering structures,steel frames with a rocking truss have characteristics that the hinge or semi-rigid connection is usually adopted at the column base of the rocking truss,while the rigid connection is still adopted at the column base of the main steel frame.However,its have been shown by the existing research that the damage evolution pattern of steel frames with a rocking truss structure is generally as follows: the main frame column base first forms plastic hinge,then the energydissipating member enters into plasticity,and finally the frame beam end and other members yield.It can be seen that the failure mode of plastic yielding at the base of the main frame does not conform to the design concept of self-centering structures,and it is also difficult to ensure the collapse resistance of the structure under rare or even extremely rare earthquakes.For this reason,this thesis proposes a new type of steel frame with a rocking truss,in which the buckling restrained steel(BRS)plate is used as the energy dissipation member,and the semi-rigid connection of the column base is realized through reasonable design.The prestressed reinforcement and the spring are used as the self-centering members to realize the self-centering of the structures.It is hoped that the structures can reduce the probability of plastic failure,reduce the residual deformation and improve the post-earthquake recoverability of the structures.The main research contents of this thesis are as follows:(1)Design and analysis of self-centering behavior of truss column base joints.A new type of column base joint with prestressing tendon and spring is proposed,and 20 3D refined finite element models for this innovative joint are established in ABAQUS.The initial stiffness,ultimate bearing capacity and self-centering behavior of the new column base and the traditional column base are compared and analyzed.For the parameters including the initial value of the prestressing tendon,the number of prestressing tendons,the spring only,the prestressing tendon only,the combination of prestressing tendon and spring,the full height and half height of the prestressing tendon,the self-centering behavior of the base joint of truss column is analyzed.Based on the analysis results,the design suggestions of the prestressed reinforcement and the spring are given.The feasibility of applying the new type of base joint to the rocking truss is demonstrated.(2)Analysis of energy dissipation mechanism of frame base joints.10 finite element models of base joints with buckling constrained steel plates are established.For the parameters including the thickness ratio,the width ratio,and the axial stiffness ratio,the initial stiffness,the energy dissipation capacity and the ultimate bearing capacity of the joints are analyzed,and the rationality of the joint design is also demonstrated.(3)Seismic collapse resistance analysis of structures.The pushover method is used to analyze the ductility and the collapse resistance of an 8-story-3-span steel frame structure and the steel frame with a rocking truss structure and the new column base joints.Based on collapse margin ratio,the collapse resistances of the two structures are compared and evaluated by the IDA method.(4)Seismic damage analysis of structures.According to the results of incremental dynamic analysis,and based on the four damage states given by HAZUS,the structural damage index is adopted to conduct quantitatively comparative analysis of seismic damage of the two structures.22 ground motions are selected to conduct elastic-plastic time-history analysis of the two structures under moderate and major earthquakes,and the seismic performance of the two structures was evaluated based on parameters including damage concentration factor,peak story drift angle,and the residual story drift angle.Through the investigations of this thesis,it has been found that steel frames with a rocking truss adopting new column base joints can be used as the further improvement and perfection of rocking structures,which can significantly reduce seismic damage,and improve structural ductility,collapse resistance capacity and functional recoverability of steel frame structures.