Mechanism and Prevention of Dynamic Failure of Concrete Structures Due to Destructive Earthquakes

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The Great Hansthn-Awaji Earthquake which occurred on January 17, 1995 caused destructive failures in many buildings and architectural structures. In such failures, several specific destructive patterns emerged, that have not been observed in usual earthquakes which occurred in the past.The characteristic patterns of failures due to this earthquake are, for example, the crack initiation and development in horizontal direction in many buildings, and compressive fractures in concrete structures with reinforced bars. Such phenomena are not explained by static loading and/or the vibration mechanics, therefore an analysis in the term of the dynamic mechanics and dynamic fracture mechanics may be necessary to clarify the mechanism of those failures and to find out the method to prevent them.In the present research deformation and failure of reinforced concrete structures subjected to dynamic loading were both numerically and experimentally investigated, and based on the analytical results we … More tried to c1arify the mechanism of dynamic failure of concrete structures due to destructive earthquakes such that prevention measures can be taken.Numerical analyses for T-type column models and Gate-type column models were performed by using the bi-characteristics^<(2)(4)(6)> method and dynamic finite element method, DYNA-2D and 3D^<(9)(12)> In the bi-characteristic method analyses, we introduced a new algorism to treat the stress pmpagation in an anisotropic medium^<(1)(5)(11)> and also to treat partial impact^<(3)(7)(8)> or eccentric impact problems^<(10)>, and the obtained numerical results were then compared with the corresponding experimental results. It was found that the rate of applied force against the time in the initial and final stage of impact and the boundary conditions of the target medium deeply influence the magnitude of the stress concentration in anisotropic bodies. As for the partial impact problem of long bars with rectangular cross sections, a new numerical algorithm was found to work reasonably and the calculated magnitudes and positions of stress concentration showed fairly good agreement with the experimental results.In the analyses by DYNA 2D and DYNA 3D, it was found that the values of the dynamic stress induced in the structures are affected not only by the magnitude of the oscillation of the ground motion but also by the time derivatives of the ground velocity, the boundary conditions between the column and its upper structure^<(9)>. Less