This paper proposes a new metallic damper based on the plastic deformation of mild steel. It is intended to function as an energy dissipation device in structures subjected to severe or extreme earthquakes. The damper possesses a gap mechanism that prevents high-cycle fatigue damage under wind loads. Furthermore, subjected to large deformations, the damper presents a reserve of strength and energy dissipation capacity that can be mobilized in the event of extreme ground motions. An extensive experimental investigation was conducted, including static cyclic tests of the damper isolated from the structure, and dynamic shake-table tests of the dampers installed in a reinforced concrete structure. Four phases are distinguished in the response. Based on the results of the tests, a hysteretic model for predicting the force-displacement curve of the damper under arbitrary cyclic loadings is presented. The model accurately captures the increment of stiffness and strength under very large deformations. The ultimate energy dissipation capacity of the damper is found to differ depending on the phase in which it fails, and new equations are proposed for its prediction. It is concluded that the damper has a stable hysteretic response, and that the cyclic behavior, the ultimate energy dissipation capacity and failure are highly predictable with a relatively simple numerical model.

This paper presents a new hybrid energy dissipation device and investigates experimentally its capability to improve the seismic response of an inherently very flexible structural system: a reinforced concrete waffle-flat plate structure. The new device combines in parallel within a single device a low-cost viscoelastic (VE) component and a metallic yielding (MY) component. The device has a gap that prevents deformations on the MY component in the range of displacements caused by wind or low intensity earthquakes, to avoid high-cycle fatigue damage. The MY component is expected to activate under the design or the maximum credible earthquake, providing the main structure with lateral stiffness, and a reliable and large source of energy dissipation capacity. Six new hybrid energy dissipation devices (energy dissipation system) were installed in a scaled two-story portion of a prototype RC waffle-flat plate structure (main structure) designed only for gravity loads, without considering special ductility detailing or capacity design rules for the columns. The VE component of the hybrid energy dissipation devices reduced the translational periods with largest effective modal mass along the horizontal directions X and Y to 60%, and increased the fraction of damping to about 12%. The main structure with the energy dissipation system was subjected to bidirectional shake table tests that represented frequent, design and maximum credible earthquakes. In the tests, the main structure remained basically undamaged under the frequent and the design earthquakes, whereas it suffered minor (reparable) damage under the maximum credible earthquake. The MY component remained undeformed under low intensity earthquakes.