This paper reveals the great potential of using combined superelastic shape memory alloy (SMA) bolts and steel angles for self-centering connections with variable performance targets. Eight full-scale specimens were tested, and the main parameters included SMA bolt prestrain, bolt length, angle thickness, and layout of bolts and angles. The specimens showed desired yielding sequences and deformation modes. The inelastic deformation was accommodated by the SMA bolts and angles with no damage to the column and beam. The specimens also exhibited very good self-centering abilities at 2% drift, beyond which the self-centering abilities were dependent on the considered parameters. A ductility capacity of at least 4% was provided by all the specimens. The maximum equivalent viscous damping ranged between 11 and 15%, indicating moderate energy dissipation. Following the test program, a design framework for such connections was proposed, and a calculation example was provided to further illustrate the proposed design procedures. The design framework was also validated through comparing the design predictions against the test results in terms of residual connection rotation.

This paper presents an innovative shape memory alloy (SMA) ring spring system used for high-performance steel beam-to-column connections. The ring spring system, which includes a series of SMA outer rings and high-strength alloy inner rings stacked in alternation with mating tapered faces, is used in conjunction with high-strength bolts in typical extended end-plate connections to achieve favorable self-centering and energy dissipation response while ensuring ease of construction. An experimental investigation on three proof-of-concept connection specimens with varying SMA ring thicknesses and bolt preload levels is conducted first, where the key properties, including strength, stiffness, ductility, self-centering capability, and energy dissipation, are discussed in detail. Following the experimental program, a three-dimensional (3D) numerical study is carried out that enables a more in-depth interpretation of the test results and supports the design of full-scale self-centering connections for a prototype steel moment frame. A system-level time-history analysis is then performed on the frame with various layouts of the SMA connections, and it is shown that, compared with a conventional steel frame, the structure with the SMA connections exhibits comparable maximum interstory drifts but significantly reduced residual drifts. The results also reveal that a reasonable balance between structural performance and cost may be achieved by an appropriate arrangement of the SMA connections within the structure.

A novel self-centering device that employs disc springs as its kernel components is developed and experimentally verified in this study. The device is suitable for use in self-centering braced frames and is expected to provide a large initial stiffness, reliable self-centering capability, and satisfactory energy dissipation. The fundamental mechanical behavior of the new device is described first. The component detailing, working principle, and fabrication process are discussed in detail. This is followed by a series of tests on individual disc springs and friction plates to gain an in-depth understanding of the performance of these basic components. Subsequently, a full-scale device designed based on a prototype building is physically tested, and the reliability of the specimen under multiple earthquakes is further understood by carrying out repeated rounds of cyclic loading. Among other findings, it is observed that the proposed device has excellent self-centering capability with equivalent viscous damping (EVD) of up to 36%. The device can provide sufficient deformability, corresponding to an available interstory drift of at least 4%. The device is capable of withstanding multiple rounds of loading with no degradation, highlighting its superiority for use against sequential strong earthquakes with no need to replace/repair. The analytical expressions are validated through comparisons against the test results, and a parametric study is then conducted to examine the effects of some key design factors on the device behavior. Based on the experimental and analytical studies, some practical design recommendations are finally given.