1306 1 Southern Methodist University, Dallas, TX, at the National Institute of Standards and Technology, Gaithersburg, MD 2 Southern Methodist University, Dallas, TX 3 National Institute of Standards and Technology, Gaithersburg, MD IMPROVED LINEAR PROCEDURES FOR ANALYSIS OF STRUCTURES WITH PASSIVE ENERGY DISSIPATION DEVICES Fahim SADEK 1 , Bijan MOHRAZ 2 And Michael A RILEY 3 SUMMARY Passive energy dissipation devices are used to reduce the damaging effects of earthquakes. These devices can absorb a portion of the earthquake-induced energy in structures and thus reduce the energy demand on structural members. Wide acceptance of these devices in structures will depend on the availability of simplified methods for their analysis and design. The objectives of this study are to: 1) investigate the effect of increased viscous damping on the seismic response of structures; 2) assess the accuracy of the linear static and linear dynamic procedures recommended in the NEHRP Guidelines for the Seismic Rehabilitation of Buildings (FEMA 273) for the design of structures with velocity-dependent passive energy dissipation devices; and 3) propose modifications to the current design procedures to improve their accuracy and reliability. Based on the analysis of single-degree-of-freedom structures under an ensemble of earthquake records, it is shown that the effect of increased damping on the displacement response is more pronounced in structures with intermediate periods. For long-period structures, however, an increase in damping decreases displacements, but increases the absolute accelerations and, consequently, the seismic forces. The study also identifies the following limitations of the FEMA 273 procedures: 1) the use of a constant reduction factor for the displacement response of short-period structures; 2) the assumption of a harmonic response to compute the peak velocity; and 3) the computation of design forces based on the assumption that the structure undergoes a harmonic motion with an amplitude equal to the peak displacement and a frequency equal to that of the fundamental mode. In most cases, these assumptions result in non-conservative estimates of the peak response and design force. Comparisons of the methods proposed in this study and in FEMA 273 indicate that the former produces more reliable results. INTRODUCTION Supplemental dampers, also known as passive energy dissipation devices, can absorb a portion of earthquake- induced energy in the structure and reduce the energy demand on the primary structural members such as beams, columns, beam-column joints, and walls. These devices can substantially reduce the inter-story drifts and consequently, non-structural damage. The NEHRP Guidelines for the Seismic Rehabilitation of Buildings (FEMA 273) categorize these devices according to their mechanical behavior as: 1) displacement-dependent devices where the force-displacement response characteristics are primarily a function of the relative displacement rather than the relative velocity between the ends of the device; 2) velocity-dependent devices where the force-displacement response characteristics are primarily a function of the relative velocity between the ends of the device or the frequency of motion; and 3) other devices that cannot be classified as either displacement- or velocity-dependent. Wide acceptance of passive energy dissipation devices in structures will depend on the availability of simplified methods for their analysis and design. FEMA 273 guidelines present linear static and dynamic procedures, as well as the more sophisticated nonlinear static and dynamic procedures, for the analysis of rehabilitated structures incorporating these devices. This paper is concerned with investigating the influence of velocity- dependent supplemental dampers on the seismic response of structures, evaluating the accuracy of the linear