A critical review of numerically predicted accelerations in nonlinear hysteretic systems

When evaluating the seismic behaviour of a structural system, peak floor accelerations must be considered because they determine the design forces for floor diaphragms and also affect the performance of nonstructural elements. Some studies of new self-centering systems, as well as of base isolation systems, have suggested that structures that include these systems may be subject to relatively large accelerations following abrupt stiffness changes. This paper examines a simplified two-degree-of-freedom system to gain insight into the accelerations that occur following abrupt stiffness changes in a dynamic system. These accelerations can be particularly large following a stiffness increase occurring at a high velocity, and they are exacerbated when an element has a very large initial stiffness. Both of these situations are common in analytical models of self-centering systems. Significantly smaller peak accelerations may be calculated for systems that are initially less rigid, even though these changes may have little effect on other seismic response parameters.