NONLINEAER NUMERICAL SIMULATION STUDY AND REGIONAL-SCALE SEISMIC RESILIENCE ASSESSMENT OF DEFICIENT WOOD-FRAME STRUCTURES RETROFITTED WITH SELF-CENTERING VISCOELASTIC DAMPERS

Abstract

Timber structures are among the most favorite types for constructing low- to mid-rise buildings. Many older wood-frame buildings were not designed to meet the current seismic provisions, and are considered as wood-frame buildings with soft story deficiency. Such residential buildings with three- and four-story are particularly common in the United States. Recent advancements in seismic design have led to the development of various innovative seismic protection strategies. Notably, the concept of damage-free self-centering systems has garnered significant interest. This approach incorporates a recentering element to restore the structure to its original position and employs fuse devices for energy dissipation, ensuring that the primary structural system remains undamaged during design basis earthquakes. In this study, new types of retrofitting systems have been developed to overcome the soft-story issue in code-deficient light-frame wood structures. The existing timber soft-story building has been retrofitted using three different systems. In the first phase, the nonlinear seismic behavior of the original unretrofitted building was studied. Then, the existing building has been retrofitted with wood structural panel (WSP) system. In the third phase, the retrofitted building in the previous step was retrofitted on its ground story only with the proposed novel self-centering viscoelastic damper (SCVD) system. Finally, in the next phase, the original unretrofitted wood building has been seismically retrofitted with the state-of-the-art Y-type braced self-centering viscous damper eccentrically braced frame (Y-SCVD-EBF) system providing high lateral stiffness to the deficient wood framed building. The energy dissipation of the developed systems is mainly provided by fluid viscous damper (VD), and TPAD (Trapezoid Plate Added Damping) acts as the backup fuse device. While the system recentering capability is enabled by utilizing preloaded disc springs. The load-displacement behavior of the proposed self-centering viscoelastic damper (SCVD) systems was analytically derived, and their seismic performance was assessed through nonlinear numerical static and dynamic analyses of the prototype buildings exposed to far-field (FF) ground motions (GMs). A Python-based framework was used to conduct an intensity-based regional seismic resilience assessment of wood framed soft-story buildings retrofitted with Y-SCVD-EBF systems. The seismic damage and loss assessment follows the FEMA P-58 methodology, with the resilience metrics visualized using a digital twin model in Geographical Information System (GIS) software. As a case study, the regional seismic resilience of over 2,000 wood-frame residential buildings retrofitted with Y-SCVD-EBF systems was studied in San Francisco.