9416516 Betereo The Northridge earthquake caused significant damage to a large number of multistory steel framed buildings. A number of different explanations for the damage have been proposed, including problems with welding, the material properties of the steel, and the general design philosophy and lack of redundancy and multiple lateral-resisting load paths in the structural systems. Coupled with these observations is the fact that several recent experimental investigations have highlighted the potential poor performance of large welded steel connections under inelastic cyclic loading. One approach for improving the seismic performance of the types of steel buildings is to increase the capability of the structural system to dissipate energy by introducing special devices for this purpose, and thus decreasing the energy demands on critical regions of the primary structural system. A combined analytical and experimental study focusing on the benefits of passive energy dissipation for steel frame structures is undertaken in this project. Four different passive energy dissipation systems are investigated. These devices are representative of the main classes of passive devices: friction, metallic, pure viscous, and viscoelastic. Two devices are studied experimentally (friction and pure viscous), and the results of the testing are used to develop numerical models of the two types of devices. These numerical models are then utilized in the analytical study. Two other types of passive dampers (shape memory alloy and viscoelastic) are also included in the study, but not investigated experimentally in the present project. Numerical models are developed for these dampers based on the results of other pervious and current research. An actual steel building, typical of those that suffered damage in the Northridge earthquake is identified and used as the basis of the analytical study. A set of earthquake ground motions are chosen, representing service-le vel, moderate and severe earthquake shaking. The selected building is first analyzed in its existing (non-upgraded) condition. Upgrade schemes based on each of the four types of damping devices are designed for the building and their benefits investigated by a careful comparison of response parameters. The performance benefits are assessed by considering ductility and energy demands on the primary structural system, and also by evaluating damage to nonstructural components and contents using appropriate response parameters. The impact of the upgrade schemes on the vulnerability of the building to economic loss due to earthquake shaking is finally assessed. Passive energy dissipation techniques represent a method for seismic upgrading of existing structures that offers performance and economic benefits over conventional approaches. This research project is designed to further develop and refine the methodologies for upgrading using these techniques. This is a Northridge earthquake project. ***
