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This paper mainly discusses the derivation and usage of simplified analysis model of circular concrete-filled steel tube specimen under lateral impact. At first, the robust software, LS-DYNA, is employed in this paper to simulate a test of circular concrete-filled steel tube (CFT) specimen under drop impact carried out by Li (2007). The numerical simulations results agree well with the experiment results and it shows good prediction of dynamic response of the CFT specimen under lateral impact could be achieved. Further analysis based on LS-DYNA model is then made to investigate the stain rate effect of the CFT column with fixed-simple supported ends. At last, a simplified analytic model is derived based on the combination of the tests results, the numerical simulation and theoretical analysis. The comparison between the maximum deflections at the mid-span obtained from the proposed simple analytical model and the numerical simulation shows that the proposed method gives good predictions of the maximum deflection of the CFT specimen under lateral impact.

For nonconforming finite elements, it has been proved that the models whose convergence is controlled only by the weak form of patch tests will exhibit much better performance in complicated stress states than those which can pass the strict patch tests. However, just because the former cannot provide the exact solutions for the patch tests of constant stress states with a very coarse mesh (strict patch test), their usability is doubted by many researchers. In this paper, the non-conforming plane 4-node membrane element AGQ6-I, which was formulated by the quadrilateral area coordinate method and cannot pass the strict patch tests, was modified by three different techniques, including the special numerical integration scheme, the constant stress multiplier method, and the orthogonal condition of energy. Three resulting new elements, denoted by AGQ6M-I, AGQ6M-II, and AGQ6M, can pass the strict patch test. And among them, element AGQ6M is the best one. The original model AGQ6-I and the new model AGQ6M can be treated as the replacements of the well-known models Q6 and QM6, respectively.

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