An error estimator, formulated earlier for h-adaptive strategies, is extended for use in the p-version finite element analysis. The estimation of error is based on solving a series of local problems, based on patches consisting of elements surrounding each node, with prescribed homogeneous essential boundary conditions. Unlike the original approach in which a patch was constructed based on one element, each patch in the present scheme is automatically formed based on a number of elements surrounding a corresponding node. The present scheme, based on enhancing the degree of interpolation, provides a better estimate than the original h-scheme while still preserving the original lower bound property. The capability of the new scheme is investigated in some numerical examples in terms of its global and local performance.
SUMMARYDiscontinuous failure is simulated via the introduction of a geometrical discontinuity. The cohesive zone is modelled via the use of the partition-of-unity property of the finite element interpolation. By this approach, a crack can pass through the elements without any restriction to the underlying mesh. Despite such a feature, it has been confirmed that a sufficiently fine mesh discretization still needs to be ensured in order to obtain a correct crack path and mechanical response. The p-adaptive scheme, driven by error in an energy norm measure or a goal-oriented measure, has been examined due to its implementational simplicity. The results have shown that, if considering only increasing the polynomial degree, the p-approach can greatly improve the results.
Formulations are presented to enforce constraint equations in the element-free Galerkin (EFG) method by means of Lagrange multipliers and by penalty functions. These formulations include prescribed values for degrees of freedom as well as relations between degrees of freedom. The formulations are tested on two benchmark problems. Due to the smooth character of the EFG shape functions, inaccuracies such as oscillations may appear near abrupt changes in the boundary conditions. It is argued and shown that the use of nodal integration, instead of Gauss integration, for the boundary integrals reduces these de每ciencies importantly.
This paper introduced a nonlinear finite element model using Msc.MARC to study behavior of concrete columns partially confined with metal sheet strips under uniaxial compression. The concrete and the metal sheet parts were modeled using the linear Mohr-Coulomb yield criterion and the Von-Mises yield criterion, respectively. Behaviors of the interface (bonding) material, both in the normal direction and the parallel direction to the interface, were modeled as a bilinear function based on the cohesive energy and the crack widths. The columns in this study had circular cross sections with the diameter of 15 cm and the height of 75 cm, wrapped around by 5 cm metal sheet strips. The results from 3D finite element modeling were analyzed for internally induced stresses and strains. The predicted column behavior was compatible with observed experimental data. The detailed mechanisms that were difficult to visualize during the laboratory experiments could be obtained from the analysis. It was revealed that the area of confinement and the number of applied metal sheet layers were important factors to the strength increase. The discrete confinement system was shown to be a promising alternative to the onepiece full-wrap system.
This paper investigated effect of concrete strength on axial strength improvement of the metal sheet confined concrete cylinders under axial compression. Totally, 27 concrete specimens were tested based on three different concrete strengths of approximately 13, 32 and 39 MPa. Epoxy was used as a bonding material along interface between concrete and metal sheet. Based on three different concrete strengths, different level of confinement was established by taking one layer and three layers of metal sheet confinement. The experimental results revealed that axial compressive strength of concrete cylinders could be improved by mean of metal sheet wrapping. It was shown that effectiveness of axial strength improvement of metal sheet confined concrete cylinders depended on original unconfined compressive strength of the core concrete. With lower concrete strength, it was found that use of metal sheet confinement could increase the original strength of the columns more effectively than the case of higher concrete strength. Based on existing results, it was observed that strength improvement prediction given by Richart et al. (1928) could be adopted conservatively with exception of very low concrete strength.
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