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May 2007, June 2007, July 2007, August 2007, September 2007, October 2007,
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Issue 5, Volume 2, May 2007
Print ISSN: 1991-8747
E-ISSN: 2224-3429







Title of the Paper: Lumbar Spine: Parameter Estimation for Realistic Modeling


Authors: Ayman Kassem, Ahmed Sameh

Abstract: We have developed a parameter estimation routine that uses genetic algorithms to systematically identify stiffness and damping properties that can accurately predict spine segment motions associated with forces applied during chiropractic manipulation. Enhancements to the current computer simulation and visualization capabilities established are made. The ensuing computer simulation and modeling program is tested with experimental displacement-time and acceleration-time spine motion data. Experimentally-optimized stiffness and damping properties derived from the model are used to characterize the normal and pathologic spine. This study provides a tool for diagnosis of spinal disorders and will assist chiropractic clinicians and researchers in understanding the mechanical response of the human spine to mechanical forces.

Keywords: Lumbar spine, Optimization, Genetic Algorithms, simulation, parameter estimation

Title of the Paper: A Simple Equilibrated Homogenization Model for the Limit Analysis of Masonry Structures


Authors: Gabriele Milani

Abstract: In this paper, an equilibrated homogenization model for the limit analysis of running bond masonry walls is revised. Assuming brickwork under plane stress condition and adopting a polynomial expansion for the 2D stress field, a linear optimization problem is derived on the elementary cell in order to recover the homogenized failure surfaces of the brickwork. Different models of higher accuracy can be obtained by increasing ad libitum the degree of the polynomial approximation. The homogenized failure surfaces so obtained are then implemented in a FE limit analysis code for the evaluation of collapse loads and failure mechanisms of entire masonry structures. Both upper and lower bound homogenized limit analysis approaches are used for treating a meaningful structural case consisting of a two storey panel seismically loaded. A comparison with a pushover analysis conducted with a standard commercial code shows the efficiency of the technique presented with respect to: 1) accuracy of the results; 2) reduced number of finite elements required; 3) reduced time required for the simulations.

Keywords: Masonry, Homogenization, Limit analysis, FEM

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