Seismic response control of rigid block systems by using Tendon System: the case of Greek column

The paramount objective of Seismic Engineering is to contribute in deep for the policies of prevention, formation or development leading to the mitigation of the seismic risk concerning the structural damage or collapse. The safety verification of a seismic action involves several concepts: necessary conditions, performance criteria, probabilistic reliability, hazard scenarios and quality guarantee. In spite of several scientific areas being under constant development, it is still nowadays very common to get important knowledge following the occurrence of each new catastrophic earthquake in a developed zone of the globe. In fact, there is no better seismic testing “laboratory” than the real place where an earthquake takes place, because it is absolutely impossible to reproduce artificially, and simultaneously, all the concerned phenomena. Anyway, and despite the wide numerical methods and computer capability developments, the tests will be always indispensable because they are the only way to reproduce seismic actions allowing its systematic repetition and the necessary scientific observation of their effects. Consequently, the main objective of the Seismic Engineering experimentation is, basically, to allow the observation and analysis of the damage and behaviour of different types of structures, under different conditions, while submitted to a seismic action. In fact, the response of a structure to a seismic action is influenced by innumerable parameters whose implications must be widely analyzed. For instance, not only the characteristics of the seismic action itself, but also the foundation and bordering structures interaction, the structural and material characteristics or the already existent damage induced by previous events. Seismic Engineering experimentation is also indispensable for the validation of analytical models and for the verification of new design methodologies or new strengthening or reinforcement structural techniques. The study of new materials behaviour and the analysis of the new methodologies still in a pre-normative phase need also the use of experimental tests. It should be noticed too that, apart the multiple aspects already referred, experimentation with earthquake simulators provides the certification of several types of equipment in order to ensure their proper way of functioning during the occurrence of a major earthquake. In fact, shaking table tests of important equipment are quite common; mechanical, electrical and electronic equipment of various types are main-stations and sub-stations material, nuclear power plants control units or hospital vital devices, just to quote a few of the more relevant examples. Moreover the already referred activities, of seismic engineering itself or equipment certification, civil protection authorities can also use earthquake simulators for didactic campaigns. This utility is a role very disseminated in countries, like Japan, where the occurrence of earthquakes felt by all the population is part of their common life. Without the purpose of exhausting, there is however another aspect of the seismic engineering experimentation that should be mentioned; that is its use in order to evaluate the seismic vulnerability of different types of the building stock, with obvious applications in the aim of the insurance companies activities. Consequently, it is of paramount importance the improvement of the seismic engineering experimental conditions in order to raise new techniques to pay a better and clearly more important role in the seismic risk mitigation. Testing of complete structures is normally used to enable the understanding of the global behaviour of a construction and to capture the interplay of the response of its different components. It corresponds to quite expensive tests but, in principle, provides quite realistic information on the expected response of the specific structure under testing. By the nature of these tests and the usually high degree of redundancy of complete structures, the comparison of the experimental results with analytical simulations can only be made in terms of global variables as for instance storey displacements or accelerations and external forces or base reactions. Measurements of internal forces are normally quite difficult, among other reasons, because normally the corresponding load cells would disrupt or significantly modify the structural behaviour and also due to the large number of those load cells that would be required to enable the complete identification of the internal action effects pattern. On the contrary, tests on single structural elements or sub-assemblages are much less expensive but can only provide information of what could be called local nature. They are mostly suitable for the calibration and validation of analytical models of the elements that can be incorporated into a computer code with which the simulation of the response of a complete structure may be achieved. Hence, tests on elements or sub-assemblages are normally conducted on a large series of specimens so that the effect of different variables (for instance, geometrical proportions, mechanical properties or sequence of loading) can be checked and considered in the above referred validation of analytical models.