PARAMETRIC ANALYSIS OF THE WHOLE LOADING PROCESS OF TRANSLATION-TORSION COUPLED VIBRATION CHARACTERISTICS OF THE MULTI-LAYER BI-DIRECTIONAL ECCENTRIC FRAME STRUCTURE1

Earthquake investigations confirm that irregular structures suffer more damage than their symmetric counterparts. The vibration mode of irregular structures is affected by the cou-pling of lateral and torsional vibration characteristics. The analysis of the lateral-torsional coupling effect is mainly limited to unidirectional eccentric structure or single-layer eccentric design. To fill this gap, this paper presents a parametric study of the whole loading pro-cess, exploring lateral-torsional coupling vibration characteristics of multi-layer bi-directional eccentric structures. The performed nonlinear static analysis revealed that the natural fre-quency of eccentric frames with different layers exhibited a general pattern with a three-stage evolution from elastic to elastic-plastic stages. Accordingly, three different elastic-plastic de-velopment stages of parametric analysis were defined. The effects of the uncoupled torsion -to--lateralfrequency ratios ,fl and stiffness eccentricities on the translation-torsion coupled vi-bration characteristics in the above three stages were simulated via self-compiled programs on the MATLAB platform. The results obtained show that the range of ,fl controlling the vibration characteristics was related to the eccentricities. Therefore, it was proposed to set different limit values of ,fl in designing and analyzing the structures with different bi-directional eccentric degrees. At ,fl = 1.1 similar to 1.2, the coupling effect between bi-directional eccentricities led to transformation between the first-and second-order vibration modes, while the direction with the lowest lateral stiffness could not be directly judged as the structure first-order principal vibration direction. In the third stage, when the bi-directional eccentricities reached or even exceeded 0.3, the second and third modes transformed into each other.