This proposal requests funding for conceptual development, analysis, and physical testing of a novel new passive energy dissipation device called a Viscoplastic Damper (VPD). The name of the device is derived from its behavior: under small deformations the device acts as a viscoelastic damper, and under large deformations the device dissipates additional energy through plastic behavior in structural steel. The device is constructed from readily available materials and may be assembled in most steel fabrication plants. In this sense the VPD is similar to the buckling restrained steel brace. However, the VPD has the advantage that it dissipates energy at all levels of excitation, and that the added lateral stiffness that results from the addition of VPD assemblies is relatively low, thereby minimizing damaging floor accelerations at lower levels of response.
There are three basic approaches to reduce damage in non-sesmically isolated structures. These are (a) to increase the damping, (b) to increase stiffness, and (c) to isolate those elements that are expected to dissipate energy through inelastic deformation. The visco-plastic device proposed herein is the only such device that incorporates each of these concepts, allows for independent control of each concept, and is constructed from ordinary materials. Structural analysis already performed at Virginia Tech has shown that the visco-plastic device is conceptually viable. On this basis, the idea of the visco-plastic device has considerable intellectual merit. However, true proof of concept requires experimental validation. History has shown that good engineering ideas, once proven, find rapid implementation in the field. This is particularly true if technical barriers, such as high tolerance manufacturing, do not exist. A recent case in point is the buckling restrained brace, which was rapidly implemented in Japan and in the U.S. once it was proven in the laboratory. It is expected that the visco-plastic device, when proven viable, will also be rapidly implemented. Furthermore, the visco-plastic device will be useful in all seismic hazard areas (not just the Western U.S.), in wind engineering, and in a myriad of other vibration suppression applications. In addition to providing a new device for mitigation of damaging vibrations, it is expected that the research performed herein will broaden the analytical and experimental knowledge and experience base for applications in viscoelastic solids (e.g., high damping rubber) and for analysis of highly nonlinear structural systems and components.
This project will add the VPD as a viable member of the collection of passive energy dissipation devices that are useful for reducing damage and enhancing behavior of structures during all levels of seismic excitation. Because of the reduced damage to the main structure at all levels of excitation, the predictability of the response of structures incorporating VPDs will be improved. Increased response predictability is a critical issue for performance-based engineering. The broader impact of the research is multi-faceted. If the VPD is successful in seismic applications, modified versions of the device may also be successful in mitigating discomforting wind and floor vibrations. Considerable effort will be put forth to establish appropriate mathematical models for the viscoelastic filler materials and to develop a hierarchy of mathematical models of the device. The knowledge gained will be useful in developing other applications for high damping viscoelastic materials, including seismic isolation and bridge bearings.
