Seismic Response Of Structures With Coreless Self-Centering Braces And Metallic Dampers

In recent years,disaster control after the earthquake has been paid more and more attention by earthquake engineers.Traditional seismic structures resisted the earthquakes by increasing stiffness and strength,which were not economically advanced.Even so,the post-earthquake structure were often disfunctioned,due to severe residual deformation.Self-centering braces reduce or even eliminate residual deformation of the structures,in light of the special configuration,thus ensuring the structure to be functional after the earthquakes.Therefore,this paper first studies the mechanical properties of a coreless self-centering brace?CLSCB?.Then,the seismic response of SDOF steel frames equipped with coreless self-centering braces and metallic dampers?CLSCB+MEDF?are studied.The CLSCB+MEDFs are characterized by trilinear self-centering hysteresis.The following conclusions are drawn:?1?The basic configuration and mechanical properties of CLSCB are introduced.Based on the parametric analysis of CLSCBs using by ABAQUS with python scripts,the effects of different geometric parameters on the mechanical properties of CLSCB are analyzed,and the differences in tensile and compression properties of CLSCB are emphasized.It is found that the initial stiffness ratio of tension and compression basically maintained at about 1.0,while the second stiffness ratio of tensile and compressive is basically greater than 1.1,indicating that the difference in tensile and compression performance of CLSCB is mainly reflected in the second stiffness.The changes of T_in,B_in,LT₂,T_out,B_out basically do not affect the second stiffness of the tension,but their increase makes the second stiffness of the compression increase.The increase of L and Ab reduces the second stiffness of the tension and compression significantly,respectively.Based on the results of finite element analysis of 64 sets of parameter combinations and the theoretical formula of the initial stiffness of CLSCB,the regression formula of the initial stiffness is proposed.It is suggested that the regression formula can be used to calculate the first stiffness of CLSCB,and the theoretical formula is used to calculate the second stiffness of CLSCB.?2?The trilinear hysteresis model of self-centering braced steel frames considering P-? effect is proposed.The time history analysis program of single-degree-of-freedom?SDOF?CLSCB+MEDF was written by MATLAB based on Newmark method.Through the statistical regression of large amount of data,the nonlinear displacement ratio spectrum?C_R-R-T relationship?of CLSCB+MEDF considering P-? effect under far-field earthquake was obtained.The influence of different hysteresis parameters on C_R is analyzed showing that the negative stiffness causes a significant decrease in the energy dissipation capacity of self-centering braced steel frames,which in true leads to an increase of C_R.Recommendations are made for the design of CLSCB+MEDF: with sufficient self-centering capability,smaller R,greater ? and ?_c.?3?The CR-R-T relationship of CLSCB+MEDF considering P-? effect,under nearfield records are also investigated.The near-field ground motion records with pulse characteristics were discriminated and selected as external excitations.The influence of different parameters on C_R spectrum under near-field ground motions was analyzed.The displacement response of CLSCB+MEDF is significantly increased by near-field ground records,compared with far-field ones.With negative third stiffness,greater absolute value of T₂,greater yield strength ratio ? and smaller initial stiffness ratio ?c,the displacement rises around the fundamental period half of the pulse period TP.?4?The C_R-R-T equations considering the P-? effect are respectively proposed for the far-field and near-field records.The corresponding range of T₀ in engineering applications is given.