Supplementary energy dissipators for maximum earthquake protection of tall building structures

Abstract

AbstractDuctility, or deformation energy, is by far the largest source of energy dissipation of structures, since normal levels of internal damping represent only a small portion of energy dissipation. However, large material deformations such as those required in building components to perform in a ductile manner, are often associated with cracking and degradation of its strength, particularly in concrete structures. The installation of some manufactured devices to critical regions of structural systems, specifically engineered to concentrate on them the largest part of the dissipated energy during an earthquake, increases the structure's overall thoroughness and improves its performance and reliability during major seismic events.Passive dissipation of energy is a promising trend in upgrading and retrofitting existing structures, since codes very seldom deal with detailed procedures to attain safe retrofits, as they strongly depend on the actual condition of the particular structure in each case. It is also sought as a very convenient method to reduce the impact of seismic forces on new structures, especially on tall and medium rise buildings in seismic regions.It is intended that the energy dissipative devices installed in the structure serve as a first defense line against seismic forces, leaving the structure itself and its inelastic reserve of strength, as a second defense line. If structures are designed in accordance to these criteria, the structures only receive part of the seismic forces calculated according to the Code, while the rest is being dissipated through the hysteric ductile behavior of the devices.Importantly, the hysteric cycles of steel plate devices, ADAS (Added Damping And Stiffness) provide substantial amounts of supplemental energy dissipation and internal damping to the structure, which can reduce the spectral acceleration and therefore, the earthquake forces.The 1987 Mexico Building Code1 contains no specific provisions regarding the use of energy dissipative devices of any type, and although it does not specifically admit their use, it does not forbid it either.In order to adopt this novel technique, the professional practitioner has to rely on analytical procedures not required by the Code to find what he believes to be the most appropriate procedure to a rational solution to the problem. It is necessary to identify the objective levels of system strength, stiffness and ductility, and be consistent with the selection of the input design earthquake.Being aware that system ductility is subjectively developed, and its basis comes largely from engineering judgment and intuition, the author encourages to look for a different seismic resistant approach in order not to depend only on ductility to resist earthquake peak demands