Nonlinear fracture mechanics investigation on the ductility of reinforced concrete beams

Abstract

In the present paper, a numerical algorithm based on the finite element method is proposed for the prediction of the mechanical response of reinforced concrete (RC) beams under bending loading. The main novelty of such an approach is the introduction of the Overlapping Crack Model, based on nonlinear fracture mechanics concepts, to describe concrete crushing. According to this model, the concrete dam- age in compression is represented by means of a fictitious interpenetration. The larger is the interpenetration, the lower are the transferred forces across the damaged zone. The well-known Cohesive Crack Model in tension and an elastic-perfectly plastic stress versus crack opening displacement relationship describing the steel reinforcement behavior are also integrated into the numerical algorithm. The application of the proposed Cohesive-Overlapping Crack Model to the assessment of the minimum reinforcement amount neces- sary to prevent unstable tensile crack propagation and to the evaluation of the rotational capacity of plastic hinges, permits to predict the size-scale effects evidenced by several experimental programs available in the literature. According to the obtained numerical results, new practical design formulae and diagrams are proposed for the improvement of the current code provisions which usually disregard the size effects.

Numerical analysis on displacements of steel-fiber-reinforced concrete beams

“…Regarding the investigation of the applicability of constitutive models for cracked concrete, there are several numerical tools which stand out, including the following: (a) Continuum Damage Mechanics (CDM) Models [3], [24]- [30]; (b) Concentrated Damage Model [31]- [36]; (c) Cracking distributed [37]- [40]; (c) Multi-scale models [41]; (d) Models based on failure or rupture criteria [28], [42]; and (e) Fracture models [28], [43]. On the other hand, the models can be called phenomenological models, which are intended to model the mechanical behaviour of materials based on dissipative processes which occur in the microscale.…”