Quantification of higher mode effects of steel frame and control method using dual self-centering variable friction damper brace

Abstract

Self-centering energy dissipation braced frames (SCEDFs) have been developed to satisfy the requirements of resilience. However, low post-yield stiffness in such systems often leads to a higher mode effect, resulting in a significant deformation concentration that may exceed the design objectives. A novel dual self-centering variable friction damper (DSC-VFD) brace with high post-yield stiffness and enhanced energy dissipation capability was proposed. Its hysteretic behavior, characterized by a loading stiffness that is larger than the unloading stiffness, was developed by incorporating the C++ language into the OpenSees platform. To evaluate the higher mode effect in different types of frames, a quantification measure based on the higher mode results of the steel frames, considering the seismic responses around the peak value, was therefore established. Then, the seismic responses of the DSC-VFD frames (DSC-VFDFs) using the proposed uniaxial material were calculated and compared with those of the traditional moment resisting frame (MRF) and SCEDF with the same design process. Finally, the four parameters, including the first stiffness modification coefficient α1, second stiffness ratio α2, strength ratio β, and fourth stiffness ratio α4, were considered to evaluate their influences on nonlinear seismic responses and the higher mode effect of the DSC-VFDF by the above-mentioned quantification measures. The results indicate that the influence of higher modes should not be ignored in the design of self-centering braced frames, and the higher mode quantification results of base shear are more sensitive than those of effective displacement. The DSC-VFD brace can more effectively improve the seismic responses and control the higher mode effect than the traditional SCEDF.