The conventional earthquake resistant design approach, as it is specified in most seismic codes, is based on the concept of ductility. Ductility is the ability of the structural elements to exceed their elastic limits and develop inelastic deformations in a controlled ductile mode, in order to dissipate the energy, induced by the earthquake action. Thus, a structure, subjected to an earthquake excitation, will develop significant damages, which may be not repairable in case of a severe magnitude earthquake. Contrarily, seismic isolation is a novel design method, based on the decoupling of a structure from the horizontal components of a ground motion, by the insertion of flexibility at the isolation level, and the avoidance of resonance, as the fundamental frequencies of the structure are shifted away from the predominant frequencies range of common earthquakes. The application of seismic isolators attenuates drastically the earthquake response of the structure, while structural and non-structural damage can be avoided. Besides the period alteration, seismic bearings due to their inelastic deformations provide considerable supplemental damping to the structure, decreasing its displacement response.
Our office offers feasibility studies, assessing comparatively, technically and financially, the conventional earthquake resistant design and seismic isolation methods for each considered structures. Both elastomeric bearing and friction-sliding systems can be elaborated as well as more recently launched hybrid systems, combining the utilitarian advantages of the two aforementioned categories of isolators.
Energy dissipation devices
Energy dissipation devices are installed in the superstructure of the buildings, usually distributed along the height of the building and supply it with the so called “in-structure damping”. Τhe structural philosophy of these systems does not rely on the prevention of the transmission of the earthquake actions to the structure, but in the dissipation of a portion of the transmitted energy through their inherent damping capacity, activated by their cycling deformation due to the interstory deflections. Passive energy dissipating systems are less effective than the isolation systems in the reduction of the structural response; however they are implemented in many cases, due to their lower cost and their less disruptive installation process. Our structural engineers are adequately qualified to assess the purposefulness of the potential utilization of damping devices and to determine the most appropriate type of dampers for each individual building, among a variety of choices, such as viscous fluid, viscoelastic, metallic yielding, friction and other systems.