Nonlinear Static Analysis of Structures with Rocking Columns

Abstract

In simple inelastic structures subjected to severe base motions, the maximum acceleration response is bound by the yield strength and is inversely proportional to its mass. It can be demonstrated that a similar effect is approximately produced in structures with multidegrees of freedom. In strong structures, the maximum acceleration response is dependent on the intensity of the earthquake. However, if the strength of the structure is reduced, the maximum acceleration response and associated forces in its structural and nonstructural components can be substantially reduced. If some of the structural columns (carrying gravity loads) are allowed to rock, providing very small resistance to lateral loads, it is possible to reduce the strength of the global structural system and limit the global accelerations in seismic events. However, before overturning such columns may have substantial resistance which may void the effectiveness of weakening. The objective of this study is to (1) develop a simplified analytical model for rocking columns from fixity to overturning; (2) build the computational tools to simulate the behavior of structures including such rocking columns; and (3) examine the global nonlinear static response of a weakened structure. An analytical model is developed using an equivalent flexibility approach, which considers rigid body rotations and flexural deformations. Physical experiments of rocking columns were performed, and the results are used for the calibration and validation of analytical models. An analytical model of a 1:3 scaled structure is developed using IDARC2D modified in this study to evaluate several alternatives of weakening using rocking columns.