Cyclic testing and assessment of shape memory alloy recentering systems.

摘要

In an effort to mitigate damage caused by earthquakes to the built environment, civil engineers have been commissioned to research, design, and build increasingly robust and resilient structural systems. Innovative means to accomplish this task have emerged, such as integrating Shape Memory Alloys (SMAs) into structural systems. SMAs are a unique class of materials that have the ability to spontaneously recover strain of up to 8%. With proper placement in a structural system, SMAs can act as superelastic "structural fuses", absorbing large deformations, dissipating energy, and recentering the structure after a loading event. Though few applications have made it into practice, the potential for widespread use has never been better due to improvements in material behavior and reductions in cost.;In this research, a single degree-of-freedom study was first conducted in order to investigate the benefits of recentering compared to energy dissipation. Through this study the following fundamental observation was made: enhanced performance, in terms of maximum displacements, can be obtained from a recentering system by maximizing the hysteretic loop, thus increasing the energy dissipation. This observation, coupled with previous work that has shown that recentering systems are capable of meeting or exceeding the performance level obtained from other advanced systems, has further motivated the experimental work conducted herein.;For the experimental portion of this research, three different structural applications were developed and tested. The first was a tension/compression damper that utilized either nickel titanium (NiTi) helical springs or Belleville washers. These new forms of NiTi were previously untested; therefore the properties were largely unknown. Nonetheless, the results indicated that unique applications may be possible with both forms. For the second part of the experimental work, a SMA-based partially-restrained interior beam-column connection utilizing NiTi tendons was investigated. The connection was designed to concentrate all of the inelastic deformation into the SMA tendons and then recenter due to the superelasticity of these tendons. The connection proved to have good recentering and ductility even after it was cycled to 5% drift. Finally, for the last part of the experimental work, a special bracing system was developed using an articulated quadrilateral (AQ) arrangement. The AQ arrangement allowed SMA wire bundles to be put in parallel with c-shaped dampers, thus enabling the designer to tailor the amount of damping in the flag-shaped hysteresis. The braced frame experimental results demonstrated that a maximized hysteresis can indeed be obtained while the analytical results demonstrated that one can obtain more evenly distributed deformation demands for an SMA-based system than compared traditional system. This exploratory experimental work highlights the potential for SMA-based structural applications to enhance seismic structural performance and community resilience.