SUMMARYShaking table tests were conducted to investigate the response of rectangular wooden blocks and block assemblies of various sizes and slenderness to harmonic and earthquake base excitation. The shaking tests were followed by an analytical and a numerical study of response of single blocks and block assemblies. The analytical study was aimed at establishing criteria for the initiation of rocking and of overturning in response to harmonic base motion and consisted of solving numerically the differential equations of motion of a rigid block on a rigid foundation. The numerical study, in the course of which the response of both single blocks and block assemblies was examined, was implemented by means of the Distinct Element Method (DEM). Prior to the DE simulation of actual shaking tests, preliminary analyses were conducted to confirm numerical stability and to evaluate material and damping parameters. Comparing the recorded time histories with those given by the analytical study and the DE simulation, good agreement was found. The distinct element model in use appeared to follow the highly non-linear motion of rigid body assemblies faithfully to reality. On the basis of the results, provided that the necessary parameters are carefully estimated, the employed DE model can be regarded as an appropriate tool to simulate response of rigid body assemblies to dynamic base excitation.
A new method, Applied Element Method (AEM) for analysis of structures is introduced. The structure is modeled as an assembly of distinct elements made by dividing the structural elements virtually. These elements are connected by distributed springs in both normal and tangential directions. We introduce a new method by which the total behavior of structures can be accurately simulated with reasonable CPU time. This paper deals with the formulations used for linear elastic structures in small deformation range and for consideration of the effects of Poisson's ratio. Comparing with theoretical results, it is proved that the new method is an efficient tool to follow mechanical behavior of structures in elastic conditions.
A new extension of the Applied Element Method (AEM) for structural analysis is introduced. This paper deals with the large deformation of structures under dynamic loading condition. As no geometric stiffness matrix is adopted, the formulation used for large deformation is simple and it can be applied for any structural configuration or material type. A new technique based on determining the residual forces due to geometrical changes is proposed. The accuracy of this technique is verified in small deformation range by eigen value analysis. In large deformation range, the collapse behavior of structures and the rigid body motion of the failed structural elements can be followed accurately.
A new method for analyzing the fracture of concrete structures is proposed in which concrete is considered a granular assembly. Because concrete is a complex, extremely heterogeneous material, it is difficult to analyze it's failure properties by the Finite Element Method (FEM) in which concrete is considered a homogeneous, continuous medium. We have developed a Modified Distinct Element Method (MDEM) that can be applied to the problems of fracture of concrete structures. In the MDEM the respective major constituents of concrete, gravel and mortar, are represented as circular particle elements and nonlinear springs, called pore-springs. We have used the MDEM to simulate the dynamic fracture behavior of concrete structures. The numerical results obtained are in good agreement with the seismic damage recorded during past earthquakes.
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