Worldwide developments of precast frame structures and innovative methods in earthquake resistant design

Precast systems, have been started to be used extensively after Second World War especially in East European countries, Japan, USA and USSR. Precast systems were affected by the strong earthquakes in these seismically active countries. Lessons obtained from the earthquakes have indicated that the most critical points of these systems are the connections. In other words, the resistance to earthquake of a precast system mainly depends on the resistance to earthquakes of connections. Indeed, the recent disasters in Northridge and Kobe betrayed the requirement to a structural design providing structural integrity against seismic activity.This study addresses the historical development and current applications of precast frame systems which have wider applications than other precast structure types; and the enhancements in connections of these systems. Since early 1990s intensive experimental investigations have been performed to develop the innovative connections which will provide the integrity of the structure against seismic activity. The main aim of this research for precast frame structures is further to attain the seismic performance similar to reinforced concrete frame systems under moderate to strong earthquakes. Meanwhile in this new competitive system, to reduce damage and to easily repair after a strong earthquake are possible. In this scope the hybrid connections, whose main components are high strength post-tensioned steel and mild steel, were developed by combining both elastic and inelastic action at the connections for precast moment resistant frames to resist the dead, live and seismic loads. While post-tensioned steel provides high shear strength and self-centering capability to the connection to resist the dead, live and seismic loads mild steel would be utilized to serve as an seismic energy dissipater by yielding. This new technology was initially developed for beam-column connections, subsequently, it was extended and adapted to precast shear walls.The scope, importance, method and assumptions of this study are introduced in the First Section.The Second Section establishes the history of the precast systems, the development of precast frame systems in the seismically actives countries.Precast systems suffering damages during earthquakes are presented and shown in the Third Section.In the Fourth Section the connection details applied in precast frame systems up to the present, the positive and negative features of these details are emphasized.The Fifth Section covers the experimental studies on innovative precast hybrid connections to provide the integrity of the structure and their energy absorbing capacities under earthquake loading. This section includes two types of connection: beam-columns and shear walls. The nowadays applications of precast structures with hybrid connections under consideration are displayed as well.The past and present status of precast frame systems; experimental studies and results rising from the investigations on innovative post-tensioned precast moment resisting systems are presented in the Conclusion Section.Keywords: Precast, moment resisting frame, post-tensioned, hybrid connection, earthquake