Seismic retrofit of structures with supplemental damping (experimental and analytical evaluation)

The need for structures which function reliably without damage during severe earthquakes was reemphasized by the behavior of structures during recent earthquakes (Loma Prieta 1989, Northridge 1994, Kobe 1995, etc.). The existing structures and often new ones must rely on large inelastic deformations and hysteretic behavior to dissipate the motion's energy, while the capacity to sustain such deformations may be limited by previous non-ductile design or limitations of materials. An alternative method to reduce the demand of energy dissipation in the gravity load carrying elements of structures is the addition of damping devices. These devices dissipate most energy through heat transfer and reduce the deformation demands. In inelastic structures the supplemental damping mechanism reduces primarily deformations with small changes in the strength demand. The main benefit of added damping in the inelastic structures is the reduction of the demand for energy dissipation in the gravity load carrying structural members, thus reducing the deterioration of their low cycle fatigue capacity.; An experimental investigation of different damping devices was carried out individually to allow for physical and mathematical modeling of their behavior. A series of shaking table tests of a 1:3 scale reinforced concrete frame incorporating these devices were performed after the frame was damaged by prior severe (simulated) earthquakes.; Several different damping devices were used in this study: (a) fluid viscous, (b) friction (of two types) and (c) fluid viscous walls. An analytical platform for evaluation of structures integrating such devices was developed and incorporated in a computer program IDARC Version 3.2 (Kunnath and Reinhorn, 1994). The experimental and analytical study shows that the dampers can reduce inelastic deformation demands and, moreover, reduce the damage, quantified by an index monitoring permanent deformations. An evaluation procedure for the efficiency of dampers using a simplified pushover analysis method was investigated as an alternative method for prediction of structural behavior and design.; The experimental results and analytical predictions conclude that the structure benefits remarkably through retrofitting by supplemental damping devices tested. All of these damping devices reduce structural deformation significantly (viscous walls reduce the most). However, fluid viscous dampers and friction dampers may only minimally reduce or sometimes increase the structure's base shear force due to the combined effects of damping, stiffening and strengthening. Viscous walls may increase the structural base shear (with larger deformation reduction) due to significant stiffening.; This dissertation presents a comprehensive analytical and experimental evaluation of fluid viscous dampers, friction dampers and viscous damping walls used as supplemental dampers in the retrofit of reinforced concrete frame structures. The new techniques developed in this dissertation enable a more reliable and quicker evaluation of inelastic structures retrofitted with supplemental dampers. The new techniques were verified through the experimental and numerical studies.; It should be noted that all devices were originally designed to produce the same force under the design conditions. The actual dampers delivered significantly different forces such that the dampers cannot be compared directly. The comparison of the dampers in this research is based on the type of behavior instead of quantified contributions.