Seismic behavior of structures using rocking columns and viscous dampers
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In inelastic structures, the maximum acceleration response is proportional to the structural yielding strength. Current retrofit methods, such as those employing supplemental bracing, lead to an increase in the global strength of the structure. In such cases, although the displacements and the ductility demands decrease, there is an increase in the floor accelerations. Therefore, in order to protect structural elements and acceleration-sensitive nonstructural components in inelastic structures, the overall strength of the structure needs to be decreased. The use of "rocking columns" is suggested to reduce the structural strength for controlling the story acceleration. In this study, an analytical model, a flexibility model, and a stiffness matrix formulation for the lateral behavior of rocking columns are developed. A simplified model is also suggested and implemented in IDARC2D computer program for the pushover, quasi-static cyclic, and nonlinear dynamic analysis of structures weakened with rocking columns. The modeling technique for the stiffness during post-rocking is introduced as well. Experimental tests of scaled rocking columns were performed, and the experimental data obtained is compared to the analytical results evaluated from IDARC2D. In addition, an analytical 1/3 scaled model structure, which was tested at the University at Buffalo in 1992 and modeled in IDARC2D, is used to verify and evaluate the behavior of several weakening and damping alternatives. The typical strategy employed rocking columns for weakening and supplemental viscous dampers for added damping to reduce story displacements. Nonlinear static analysis (pushover), nonlinear dynamic analyses, and incremental dynamic analyses (IDA) are conducted to demonstrate that both story acceleration and displacement responses can be reduced compared to conventional structures. This work shows that rocking columns have both non-negligible stiffness and strength prior to rocking which in turn affects both the local and global behavior of the structure. Proper consideration and implementation of such behavior makes the use of rocking columns a valid technique for weakening structures.