tesi A. Caggiano.pdf - EleA@UniSA - Università degli Studi di Salerno

Chapter 5. Model performance and numerical predictions30 o , respectively. As it can be observed, the combined action of normal and sheardisplacements causes a more pronounced softening branch in post-peak regime. Thetensile strength tends to zero more rapidly and, moreover, changes its sign becoming acompressive stress, due to the fact that the normal dilatancy, produced by the appliedshear displacements, exceeds the fixed normal opening rate.The inclusion of steel fibers leads to an increment in the tensile strength, as well asof the ductility in post-peak regime. Simultaneously, the compression branch of thenormal stress continuously reduces and then disappears. In other word, the steel fibersreduce the material dilatancy.σ [MPa]4.03.0θ = 30 n f = 30n f = 202.01.0n f = 100.0plain joint-1.0-2.0-3.0Hassanzadeh's test-4.00.0 0.1 0.2 0.3 0.4 0.5u [mm]τ [MPa]12.0θ = 3010.08.0n f = 306.0n f = 204.0n f = 102.0Hassanzadeh's testplain joint0.00.0 0.2 0.4 0.6 0.8 1.0v [mm]Figure 5.9: Hassanzadeh [1990] tests with different number of fibers and θ = 30 o : a) normalstress vs. relative normal displacement and b) shear stress vs. relative tangential displacement.Figures 5.7b, 5.8b and 5.9b report the shear stresses against the relative transversedisplacements. The significant influence of fiber content on both peak stress andpost-peak toughness can be (again) easily recognized.The simulation of the interface model in this section demonstrates the capability ofthe proposed formulation to capture the variation of stiffness, strength, ductility andthe overall behavior of concrete due to the presence of steel fibers both in pure tensilefailure mode and under mode II type of fracture with different levels of confinementpressure, originated by constraining the dilatancy of both plain and fiber concretes.5.1.3 Parametric studyThe parametric analyses presented in this section are performed by means of the twolinear elastic four node FEs connected by one interface element. The considered FEset-up and boundary conditions are discussed in Figure 5.5. Therefore, the inelas-100