Numerical simulation of shear tests on RC, FRC, prestressed HPFRC beams without shear reinforcement

Nowadays, the development of modern buildings and infrastructures demands best performing material in terms of high strength, high toughness, and energy absorption ability. For these reasons the mechanical and structural behavior of Fiber Reinforced Concrete (FRC) and High Performance Fiber Reinforced Concrete (HPFRC) is investigated in this work. In particular, the thesis is focused on the shear behaviour of beams without conventional shear reinforcement. FRC shear failure domain is related both to its tension and compression properties, characterized by a high level of non-linearity of the problem due to the ductility fibers resource. Consequently, in order to assess the shear structural behaviour of fiber reinforced elements a nonlinear finite element analysis (NFEA) was conducted. The aim of the thesis is to provide practical recommendations for the numerical modelling of fiber reinforced elements in order to develop reasonable and reliable predictions. The nonlinear material characterization requires several modelling options and input parameters. Furthermore, an accurate prediction of the failure mechanism of the FRC or HPFRC beam can be detected when a careful modelling of the stress-strain relationship in tension and compression or numerical instabilities such as convergence difficulties and mesh sensitivity are taken into account. In this research work a modelling in STKO OpenSees © of two sets of beams is presented. The first set considered the passive reinforced beams, which is composed of three different rectangular shaped sections. The beams are made of three different materials: normal concrete, fiber reinforced concrete with a different fiber volume. The second set consists of four prestressed HPFRC beams with different IPE sections. The results of the numerical analysis are compared with the experimental one in order to evaluate the reliability of numerical predictions, discussing how the parameters considered into the analysis affect the solution. Hence, some of the investigated beams are modelled in another FEA software, called JCONC, able to predict the failure conditions in terms of load, displacement and crack formations, considering a concrete rigid plastic stress-strain relationship. The results obtained have been compared with the STKO Opensees© ones, which take into account a more complex stress-strain law for concrete. Finally, the modelling strategy is applied for HPFRC prestressed I-beams designed by the Structural Laboratory Team of Universidad Politécnica de Madrid, partnered with Acciona S.A, with the aim to predict element failure in the future experimentation steps. The work remarks that nonlinear finite element analysis are only numerical predictions and not the reality of physical behaviour. This assumption must guide practitioners in a preliminary design phase to avoid rough mistakes in the final project.