Static pushover response of spring anchored unbonded post-tensioned rocking systems

Abstract

This paper describes the static pushover response of a proposed lateral force resisting system that uses spring anchored post tensioning (PT) tendon to create a rocking system. The spring at the PT tendon anchorage is aimed at facilitating manual post tensioning of the PT tendon which helps to implement rocking systems in developing communities subjected to high seismic hazards without the need for trained workers or specialized equipment. The reduction in the lateral stiffness of this system at high intensity loads causes rocking behavior that is initiated by a gap opening at the base of the system. The PT tendon is unbonded over the length of the system to prevent yielding and the loss of prestressing force. Because the prestress force in the unbonded PT tendon is maintained, the lateral force resisting system exhibits self centering behavior. This paper derives closed form expressions that describe the lateral force deformation behavior of the proposed system. A simple finite element analytical model is presented to verify the closed form expressions and to study the effects of the system parameters on the static pushover response. Results of this study show that the closed form expressions display an excellent agreement with the analytical model including the predictions of the gap opening, clamping of the spring element, yielding and fracture of the PT tendon.