Seismic Performance of Rocking Frames with Flag-Shaped Hysteretic Behavior

This paper investigates, analytically and numerically, the seismic performance of a rocking frame which exhibits flag-shaped hysteretic behavior. The present study establishes the equation of motion for the hybrid rocking frame and examines its seismic behavior under both pulse-type and historic ground motions. Throughout this work, the deformation of the structural members and the sliding between the contacting bodies are ignored. The study introduces the dimensionless design parameters which control the flag-shaped hysteresis loop and reveals their influence on the seismic performance of the hybrid rocking frame. The analysis unveils that prestressing the tendons could be beneficial mostly for small rocking rotations. For large rocking rotations, however, the prestressing force becomes progressively detrimental as the size of the columns increases. The analysis compares hybrid rocking frames with negative, zero, or positive post-uplift lateral stiffness. The results reveal that increasing the stiffness of the frame does not necessarily lead to superior performance. Finally, the seismic performance of the examined rocking frames is sensitive to the characteristics of a ground motion; consequently, the hybrid rocking frame could outperform the freestanding or the opposite. (C) 2017 American Society of Civil Engineers.