Control of Inelastic Structures by Weakening and Damping

Many simple structures yield and develop inelastic deformations, while the accelerations are limited by the yield strength. These structures develop permanent deformations (and possible damage). Some structures, which employ special materials or innovative structural systems, may yield and recover without damage. These are known as nonlinear-elastic structures. Often the post yielding excursions are very large and may exceed the deformability capacity of the structure. Introducing damping in form of supplemental devices, it is possible to control such deformations and keep them within acceptable limits. The modified systems can be designed using control theory and implemented approximately while minimizing the difference between the required control forces to the supply provided by protective devices and damping. While the above design method may require special skills in control of structures, a spectral analysis method can be applied instead, with good approximations. The paper presents the approach, the model for the design of the control system and the design spectra needed for approximate computations. The procedure is exemplified using a three stories moment resisting frame model that shows the efficiency of negative stiffness devices added to "emulate" nonlinear-elastic behavior and contribution of dampers to control deformations during "yield excursions".