Adaptive Force-Based Frame Element for Regularized Response

Abstract eng:
Distributed inelasticity force-based elements, widely used in earthquake engineering modeling, lose objectivity at local and global level of response in the softening range of sectional behaviour. This motivated many researchers in the past to propose various regularization techniques to trace a physically meaningful post-peak curve. However, elements that give regularized response under softening behaviour are too flexible to be used for the hardening branch. The present work presents a new adaptive force-based plane element that overcomes the aforementioned limitations. As the name suggests, the element is capable of providing solutions for both hardening and softening response by automatically adjusting the element integration weights when a section undergoes into softening. The latter are computed with theoretically derived closed-form expressions from interpolatory quadrature. The ‘adaptive’ nature of the integration scheme renders it numerically very efficient. Furthermore, the proposed element can directly account for the value of axial force installed on the element in the estimation of the corresponding length of plastification, thus creating a physically sound regularization scheme. The performance of the proposed adaptive element is first evaluated by comparing its results with those obtained by the standard numerical integration scheme under otherwise similar conditions. It is found that for both monotonic and cyclic response the adaptive model gives good matching at a little computational effort. Moreover, the results from the current model compare well against experimental data, both in the hardening and softening ranges of behaviour.

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