Evolutionary Optimization of Compensators to Improve Earthquake Resistance

Abstract eng:
Earthquakes are one of the most dangerous and hurting fatalities people are facing. Shock waves impose displacements on the base of buildings which are excited to dynamic response [1]. The following vibration of the building may cause severe damage up to the total collapse of the structure. For high buildings the dynamic impact is multiplied by the deformability of the long free vibrating height. In many designs, the classical method to improve the load carrying capacity by increasing the static strength is not sufficient. In consequence dynamic approaches have to be used. Isolation and compensation of the excitation are realised by the introduction of efficient isolators in the base of the construction or by dynamic compensators along the height of the building. Compensation is done by introducing springs, masses and dampers, which are designed to absorb much or most of the earthquake energy. As the impact of an earthquake is not uniquely defined, the compensating system has to respond for a certain variety of excitations. On the other hand, the total of mass and space of the compensating system has to be limited, as it reduces the space in the building. Designing an efficient compensating system includes a proposal of the number and dimension of compensators which reduce the loading of the structure. For very high buildings this may include up to 10 or more compensators, each defined by mass, stiffness and damping in two directions resulting in a total of 60 degrees of freedom to be taken into account for the compensating system. Finding an optimal set of parameters may be a tricky task, as the response surface of the building’s damage vs. the parameters may exhibit a large number of local maxima. Gradient search strategies tend to converge to the next local maximum, so they are not very well suited to deal with this optimisation problem. Evolutionary strategies [2, 3], reproducing the course of the history of biological development may be able to cover larger regions of the parameter space, avoiding to get stuck to local maxima. The application of dynamic loads to simplified models of high buildings, studying the response for given compensator designs and performing an evolutionary improvement shows significant reduction of the destructive impact structures have to carry during earthquake events. A short review of the theory and some examples demonstrate the potential of the method proposed. As it is relatively easy to implement and to apply, many variants may be checked, yielding proposals for more detailed studies. References [1] H.P. Hong, H.P., K. Goda, K.: Characteristics of horizontal ground motion measures along principal directions, Earthq Eng & Eng Vib (2010) 9: 9-22 [2] Ghanea-Hercock R.: Applied Evolutionary Algorithms in Java, Springer, New York, 2003.

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