Structures designed in accordance with even the most modern buildings codes are expected to sustain damage during a severe earthquake; however; these structures are expected to protect the lives of the occupants. Damage to the structure can require expensive repairs; significant business downtime; and in some cases building demolition. If damage occurs to many structures within a city or region; the regional and national economy may be severely disrupted. To address these shortcomings with current seismic lateral force resisting systems and to work towards more resilient; sustainable cities; a new class of seismic lateral force resisting systems that sustains little or no damage under severe earthquakes has been developed. These new seismic lateral force resisting systems reduce or prevent structural damage to nonreplaceable structural elements by softening the structural response elastically through gap opening mechanisms. To dissipate seismic energy; friction elements or replaceable yielding energy dissipation elements are also included. Post-tensioning is often used as a part of these systems to return the structure to a plumb; upright position (self-center) after the earthquake has passed. This paper summarizes the state-of-the art for self-centering seismic lateral force resisting systems and outlines current research challenges for these systems.

There is increasing recognition that conventional ductility-based design of structures for collapse prevention may not be sufficient in a modern society that demands higher-performing alternatives. Such a reality has motivated research on structural systems that minimize the disruption and cost of repairs following major earthquakes. This paper presents the experimental investigation of an asymmetrical moment-resisting connection that concentrates damage in replaceable angles at the bottom flange, achieving a repairable connection in the presence of a concrete slab. A total of three full-scale subassemblies of beam-to-column composite connections were tested with two different types of angle configurations: reduced section angles and end-reinforced angles. The results demonstrated that the proposed asymmetrical connection exhibited a stable and full hysteretic behavior up to 0.036 rad story drift. The replaceability of the bottom angles was confirmed during the tests, and the replaced specimens showed a strength of 0.8 times the original strength at the initial stage, increasing to 0.95 after 0.015 rad. The angles were replaced after specimens experienced drifts up to 0.02 rad for this asymmetrical connection with similar subsequent performance. Although evident buckling of angles was observed, the strength degradation from one cycle to the next was 0.93 up to approximate 0.04 rad story drift. There was a negligible stiffness decrease in the asymmetrical connection compared with the same continuous composite beam when the moment capacity ratio was 0.5 or greater.

Post-tensioning (PT) strands have been employed in a number of self-centering seismic force-resisting systems as part of the restoring force mechanism that eliminates residual building drifts following seismic loading. Unbonded PT strand systems are particularly well-suited for providing elastic restoring force because they possess large elastic strain capacity. Although typically designed to stay elastic during design basis earthquake events, strands may experience inelastic cyclic loading during extreme earthquakes. Furthermore, the yielding and fracture behavior of PT strand systems is central to the collapse behavior of self-centering systems. A testing program was conducted to characterize the cyclic inelastic behavior of monostrand anchorage systems as they might be applied in self-centering seismic force–resisting systems. The experimental program included more than 50 tests with variations in testing protocol (both monotonic and cyclic tests to failure), strand manufacturer, anchorage manu...