PSI - Issue 31

F. Kheloui et al. / Procedia Structural Integrity 31 (2021) 140–146 F. Kheloui et al. / Structural Integrity Procedia 00 (2019) 000–000

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understanding of behavior. The type of confinement on cylinder performance is measured and analyzed to study the effectiveness of cylinder confinement. In addition, the numerical results in terms of overall response observed are

underlined and discussed. 2. Numerical simulation

A numerical simulation based on finite elements is carried out in a three-dimensional space on concrete cylinders with a height of 32cm and a diameter of 16cm, according to standard NFP18-406 (Association française de normalisation, 2001), confined by external bonding of a polypropylene fabric, using the calculation code (Help abaqus). The dimensions and all the mechanical properties of the different constituent materials were carefully introduced, in order to take into account all the study parameters and validate the proposed finite element model. The polypropylene fabric and the cylinder elements are modeled separately with their mechanical and geometric properties, the adhesion between these components is assumed to be perfect. The type of containment is as follows: • Partially confined concrete "Circular": hoops 5 cm wide and 16 cm in diameter with 4 cm spacing BPCC. • Partially confined concrete "Helical: a strip of 4-turn, 5 cm wide propeller BPCH. • Totally confined concrete: a shell with a diameter of 16 cm and a height of 32 cm BTC. Subsequently, the confined specimens are subjected to an axial load of monotonous compressive until failure on one side. 2.1. Material modeling The numerical analyzes carried out are of non-linear type, and make it possible to determine the failure mechanisms and the corresponding charge levels. Consequently, the Concrete damaged plasticity model allowing to taking into account the dissymmetry of the behavior of concrete in compression and in tension, is used. It thus allows to managing the problems of plasticity coupled with the damage. It assumes that the two main failure mechanisms are: cracking and crushing of concrete in compression. The stress-strain relationship is defined by: σ: Real stress tensor. The use of the principle of effective stress leads to a relation linking the real stress to the effective stress given by: ( ) 1 d σ σ = − which allows us to link the tensor of effective stress to the tensor of elastic stress by: (2) The degree of material degradation under external loading is represented by a single scalar variable of damage "d" affecting the Young's modulus. This model provides a general capacity for concrete modeling in all types of structures; the behavior and the mechanical parameters of this model are widely detailed in the literature. The composite materials are modeled according to an orthotropic elastic model in the hypothesis of plane stresses with the Hill-Tsai failure criterion. The stiffness and fracture parameters of this model are identified by characterization tests. 0 : ( e l ) p l D σ ε ε − = ( ) d D ( ) ( ) 0 1 = − : : e l p l e l p l D σ ε ε − ε ε − = (1) 0 e l D : Elastic stiffness matrix. ( ) 0 1 e l e l D d D = − : Stiffness matrix after damage.