Seismic internal force in rocking shear frame with superelastic tendon restraint

A structure with rocking mechanism is able to prolong the period of vibration and reduce seismic internal force. Recent research demonstrated the effectiveness of a tendon made of superelastic material wire connected in series with steel wire in controlling the amount of rotation and providing a source of hysteretic energy dissipation, thereby lowering the risk of overturning to a rigid structure undergoing whole-body rotation. This article proposed to extend the use of superelastic tendon restraint on a (flexible) shear frame to strike a balance between the need to reduce the seismic force demand and the need to exercise control of the overturning risk. Initially, an analytical model for the rocking response of shear frame with the superelastic tendon restraint was developed. In addition, a physical model of the shear frame with tendon restraint was fabricated and tested under base excitations. Analysis results showed to match with experiment on both strain gauge and rotation sensor readings in the dynamic testing. Simulations and tests were also applied to an unrestrained shear frame for comparison. It was also found that the total deflection of the shear frame during the rocking phase could be described as horizontal vibration about a non-constant balancing deflection. The analytical models developed for flexible rocking systems were extended in the current study to deal with superelastic tendon restrained rocking shear frames. The validity and versatility were confirmed by shaker table test results.