Energy Dissipating Connector for Precast Shear Walls in High-Seismic Areas

Abstract

ABSTRACT ENERGY DISSIPATING CONNECTOR FOR PRECAST SHEAR WALLS IN HIGH-SEISMIC AREAS By Mohammed Aljuboori The University of Wisconsin – Milwaukee, 2019 Under the Supervision of Dr. Habib Tabatabai Precast concrete systems are widely used in a variety of structures such as parking garages, residential units, shopping centers, and transportation stations. In some cases, precast structures are preferred over conventional cast-in-place (CIP) concrete conventional structures because of ease of construction, rapid implementation, and lower levels of energy consumption. One area where precast systems have traditionally been at a disadvantage is high seismic applications. In seismic regions, precast concrete structures must have enhanced connection systems to address the inherent discontinuity between various components. The lateral load resisting systems may consist of shear wall systems, moment frames, or a combination of the two. The objective of this research was to develop a new seismic connector device for precast shear walls that could significantly enhance energy dissipation and improve the performance of the building under seismic load by reducing drift and base shear forces. Several devices were previously developed and tested by the PRESSS program. The U-bar system that was studied in the PRESSS program is currently the most commonly-used connector device for precast shear wall applications. This study was aimed at developing a device that could offer improved seismic performance with compared to the U-bar system. Several geometries and shapes were considered as potential new devices based on trials and optimization studies. Subsequently, two shapes were chosen for scaled laboratory testing. Based on the analytical and experimental results, one shape (designated NS-5) is proposed because of its improved performance in relation to the U-bar system. The response of a shear wall building system utilizing either the new NS-5 connector or the current U-bar system was then evaluated using a frame model proposed in the PRESSS study. This simplified frame model was used to simulate the response of the building under a seismic excitation used in the PRESSS study. In addition to the two connector systems, the structure response was also examined under free (no connection between walls) and rigid (rigid point connections) conditions to understand the limiting structural response values. The proposed NS-5 connector performed better than the U-bar system both in terms of energy dissipation in the device and with respect to improved structure response (30% lower drift and 70% higher dissipated energy). The NS-5 connector offers resistance and energy dissipations when relative movement occurs in both horizontal and vertical directions, whereas the U-bar system only offers substantial resistance under vertical deformation. Therefore, the proposed connector is a feasible alternative to the U-bar system in seismic precast wall applications. The NS-5 can also be an alternative in other energy dissipation applications in building and bridge structures.