SELF-CENTERING PENDULUM SHEAR WALLS VIA NONLINEARELASTIC KINEMATICS

One of the main challenges in structural engineering is nowadays the development of structural design concepts that can be used in the built infrastructure towards achieving immediate occupancy and minimum economic losses following an extreme seismic event. Research on unbonded post-tensioned shear walls (UPSW) has clearly demonstrated that these systems fit well within this grand challenge because of their self-centering response under earthquakes. Research has clearly substantiated the superior self-centering performance of UPSWs when compared to monolithic cast-in-place concrete walls, that they are nowadays accepted as viable lateral force resisting elements. Yet, these UPSWs have not been adopted extensively in the built infrastructure and the following critical issues need to be further resolved: concrete crushing at the wall toes, yielding of tendons, wall walking, and energy dissipation from ductile connectors that must be replaced and can lead to permanent deformations after an extreme hazard. Notably, combination of these issues requires setting strict drift limits to preserve the self-centering capabilities of UPSWs. Building on the assets of UPSWs, this research proposes a new method of designing UPSWs that can improve, or eliminate, many of the above noted technical issues. This is achieved by incorporating the following synergistic concepts: (1) At the footing interface the wall geometry consists of circular profile, and (2) use multistable elastic devices as vertical shear connectors. In the concept investigated in this research the superior performance of being damage-free and self-centering under lateral loads are maintained; but in addition, system kinematics are optimized to increase the system’s energy dissipation capacity. This new system is designated as a pendulum UPSW system because, instead of rocking about the wall toes, it rotates about a fixed point on the wall. The proposed pendulum UPSW concept harnesses geometric system kinematics in a novel and synergistic manner as a means of achieving damage-free and self-centering systems, while providing progressive amounts of energy dissipation capacity. This paper presents experimental and analytical results in support of characterizing the in-plane load-deformation response of uncoupled pendulum UPSWs. Experimental results are presented to substantiate findings from a computational investigation which shows that for coefficients of friction higher than 25% there is loss of contact at the interface between the wall and the footing. This suggests that an engineered material with a lower coefficient of friction will have to be used in future research in order to ensure no/minimum contact separation at the footing interface. Although separation at the footing interface was observed, the system was able of reducing stress concentrations at the wall toes because the contact region was spread of a larger region, and due to the geometry of the interface wall walking was eliminated.