Cyclic behavior of an adaptive seismic isolation system combining a double friction pendulum bearing and shape memory alloy cables

A new composite isolator named shape memory alloy cable-double friction pendulum bearing (SCDFPB), which combines a double friction pendulum bearing (DFPB) with superelastic shape memory alloy (SMA) cables, is proposed. Based on the SMA cables, the proposed isolation bearing named as SCDFPB had capability to adapt to multi-level earthquake intensities in horizontal directions, which was superior to the conventional DFPB. A series of research was performed to investigate hysteretic behavior of the SCDFPB, and a numerical simulation method for this isolation device was also developed. First, the configuration design and operation principle of the SCDFPB were described and explained in detail. Then, an analytical model of SCDFPBs was presented to understand their control and energy dissipation properties. Next, a SCDFPB specimen was designed and fabricated, and the quasi-static tests on the isolator specimen under different loading conditions were conducted to examine the isolator’s real cyclic response. The influence of displacement amplitude, vertical load and loading frequency on the hysteretic performance of SCDFPB specimen was investigated, and the behaviors of SCDFPB were compared with those of DFPB. Theoretical analyses were also performed to trace the vertical and horizontal components of the force provided by the SMA cables and their influence on the overall response of the entire isolation system during the cyclic loading process of the SCDFPB specimen. Finally, a numerical model of the SCDFPB implemented in the OpenSees program was established and validated by comparison to the experimental results.