Seismic-resisting self-centering structures with superelastic shape memory alloy damping devices

Abstract

The pursuit of post-earthquake resilience challenges the design of seismic-resisting structures in earthquake prone regions. The objectives of minimizing repair cost and downtime after earthquakes have motivated the development of high-performance self-centering (SC) structures that are associated with minimal post-earthquake permanent deformation. This thesis systematically investigates an emerging type of seismic-resisting SC structures that take advantage of superelastic shape memory alloys (SMAs). Although previous studies have revealed the prospects of such innovative SMA-based SC structures, the relevant research is still in its infant stage, with many questions with regard to seismic performance, practical implementation, and design methodology remaining unanswered. This thesis aims to fill in the existing knowledge gaps through a combination of numerical and experimental studies. Seismic performance of two novel structures, namely, steel braced frames with SMA-based damping braces (SMADB) and highway bridges with SMA-based isolators, is particularly investigated in this thesis and the corresponding design methodology is developed. The major outcomes of this thesis are summarized as follows: (1) Two types of superelastic SMA wires, namely, the monocrystalline Cu-Al-Be and Ni-Ti wires, are cyclically characterized and their major mechanical properties relevant to seismic applications are systematically discussed. Particularly, monocrystalline Cu-Al-Be is identified as an emerging and promising SMA material for seismic applications, because of its substantial superelastic strain and superior low-temperature behavior. Subsequently, SMA wire- and spring-based dampers are also experimentally characterized. (2) Seismic performance of steel frames with SMADB and highway bridges with SMA-based isolators at different seismicity levels is numerically evaluated via incremental dynamic analysis (IDA). The potential high-mode contribution in multi-story steel frames with SMADB is particularly highlighted and the corresponding mitigation measure is discussed. (3) The superior seismic performance of steel braced frames with SMADB, such as limited damage and residual deformation, and the ability to sustain several significant earthquakes without repair and replacement, is successfully validated by a series of shaking table test on a 1/4-scale frame model with SMADB. (4) An ad hoc performance-based seismic design (PBSD) method is developed for steel braced frames with SMADB, and the designed structures can effectively meet the prescribed seismic performance objectives. The presented work and corresponding new findings in this thesis offers more in-depth understanding of SC structures with SMA-based damping devices, and the demonstrated superior performance, together with the developed design methodology, will facilitate the practical implementation of SMA-based seismic-resisting structures in future. Although this thesis is focused on two particular forms of structures with SMA-based damping devices, its outcome will also shed light on the seismic assessment and design of other types of seismic-resisting SC structures.