PSI - Issue 17

B. Moussaoui et al. / Procedia Structural Integrity 17 (2019) 979–985 B.Moussaoui & Y.Bouamra & K.Ait tahar & al./ Structural Integrity Procedia 00 (2019) 000 – 000

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The external confinement of the tested specimens in comparison with the control one successfully enhanced the maximum capacity with the increase in ratio x/h. In other words, the improvement in the load carrying capacity increased as the aspect ratio increased. The improvements were 9, 12, 15.55 and 32% when ratios x/h were 0.25, 0.5 and 1 respectively, in comparison with the reference concrete cylinder UC. 3.Finite element models In order to allow for a better understanding of experimental observations, a finite element model has been performed with the FE software to simulate the behavior of partially and fully confined cylinders. The results of the simulation in terms of evolution of the stresses and evolution of the damage of the different specimens are plotted by stress-strain curves and cartography graphs. The gains in terms of bearing capacity are also quantified by the confrontation of the ultimate stress values, this allows us to highlight the influence of the partial confinement (parameter x / h) on the resistance and the mode of rupture of the confined cylinders. After preparing all the input data of material and geometrical properties, the specimen models were divided into small elements. The meshing results of all cylindrical specimens used for model validation are shown in Fig 3. The model is loaded with the same conditions as the experimental test. The model "Damaged plasticity for concrete is used for concrete. His mechanical characteristic is depicted in Table 2. The Composite GFRP is defined as an orthotropic elastic material. His orthotropic behavior under the assumption of plane stresses is described by introducing the stiffness constants in the principal directions given in Table 3. The interactive Hill-Tsai criterion (Eq 1) is used to evaluate the mechanical strength of composites. ( ) + ( ) − + ( ) = 1 ………………………………………………………………………… (1) Table 2 :Mechanical characteristics of the concrete material. ”‘’‡”–‹‡• š‹ƒŽ Ž‘ƒ† ‘…”‡–‡ ‘’”‡••‹˜‡ •–”‡•• fc ሺ ƒሻ ʹͷ ‘—‰ ‘†—Ž—• E ሺ ƒሻ ͵ʹͳ͸Ͷǡʹ Poisson’s ratio ‡•‹Ž‡ •–”‡••  ft ሺ ƒሻ Ͳ ʹ Ǥ ǡ ʹ ͳ Table 3:Mechanical characteristics of the composite (GFRP). ƒ”ƒ‡–‡” ƒŽ—‡ ‘–ƒ–‹‘• ͳሺ ƒሻ ͹ʹͲͲͲ ‘‰‹–—†‹ƒŽ ‘—‰̵• ‘†—Ž—• ʹሺ ƒሻ ͳ͵͸ͲͲ ”ƒ•˜‡”•‡ ‘—‰ ‘†—Ž—• υ12 ͲǤ͵ͳ ‘‹••‘̵• ”ƒ–‹‘ ǣ Ž‘‰‹–—†‹ƒŽ Ȁ –”ƒ•˜‡”•‡ ’Žƒ‡ υ13 ͲǤ͵͵ ‘‹••‘̵• ”ƒ–‹‘ǣ Ž‘‰‹–—†‹ƒŽȀ˜‡”–‹…ƒŽ ’Žƒ‡ ͳʹሺ ƒሻ Ͷ͹ͲͲ ”ƒ•˜‡”•‡ •Š‡ƒ” ‘†—Ž—• 3.1. Element meshing, loading and boundary condition A solid deformable cylinder was modeled according to the standard NFP18-406 [42] with a diameter of 16cm and a height of 32cm. In the same way, a 8, 16 and 32 cm wide variable width and two rigid discs with a diameter of 20 cm were modeled. Their corresponding materials subsequently assign the solid cylinder and the generated hoops namely: concrete and composite materials (GFRP), the two elements were assembled assuming a perfect connection for all the modeled elements. The confined cylinder, shown in Fig. 3 and 4, meshed with 3-dimensional elements (3D) that are 16 mm side hexagonal elements, having eight (08) nodes each having three (03) degrees of freedom. While the GFRP bands were meshed with quadrilateral surface elements of five (05) mm side, having four (04) nodes. The cylinder model was submitted to the loading simulating the current loading applied in the experimental tests. The same conditions of Loading and boundary conditions were respected in the experimental test.