An adaptive enriched beam–column element for mesh-nonconforming finite-band plastic hinges in reinforced concrete frames

Abstract

A conforming displacement-based plastic-hinge analysis of reinforced-concrete (RC) frames requires the hinge locations to be anticipated in the mesh, and the softening response can become strongly mesh dependent. This paper presents a displacement-based beam–column element that carries a fixed-band regularized fiber hinge model independently of host-mesh alignment. The standard crack-band regularization sets the full-softening energy for a prescribed band length. The enriched element uses node-vanishing functions to place one or more bands anywhere within a host element, without aligning their boundaries with mesh nodes. The mesh may remain as coarse as one element per member where it adequately resolves the smooth response. The condensed amplitudes directly provide the localized hinge rotation and localized axial shortening, while static condensation keeps them out of the global system. An equilibrium recovery detects and inserts bands at in-span positions during the analysis. Mesh objectivity is conditional on post-peak localization remaining within the activated bands. The element is verified against analytical solutions and conforming models of the same regularized hinge, then demonstrated on frames whose gravity-dominant beams hinge within the span. In these examples, the demand peak migrates by several band lengths as the frame yields, so a band placed at a pre-estimated position misses the hinge. The adaptive element finds all in-span hinge locations and activates the complete hinge pattern in a single fixed-mesh analysis. With modest host refinement, it matches the aggregate local accuracy of the standard two-pass workflow while avoiding a separate search analysis and remeshing.

The authors' abstract, as published at the source. Computer-Aided Civil and Infrastructure Engineering, 2026 · DOI ↗