Análise da fluência em vigas de concreto armado simplesmente apoiadas usando o método dos elementos finitos

Reinforced concrete creep is a phenomenon of great importance. Despite being appointed as the main cause of several pathologies, its effects are yet considered in a simplified way by the structural designers. In addition to studying the phenomenon in reinforced concrete structures and its current account used in the structural analysis, this paper compares creep strains at simply supported reinforced concrete beams in analytical and in experimental forms with the finite element method (FEM) simulation results. The strains and deflections obtained through the analytical form were calculated with the Brazilian code NBR 6118 (2014) recommendations and the simplified method from CEB-FIP 90 and the experimental results were extracted from tests available in the literature. Finite element simulations are performed using ANSYS Workbench software, using its 3D SOLID 186 elements and the structure symmetry. Analyzes of convergence using 2D PLANE 183 elements are held as well. At the end, it is concluded that FEM analyses are quantitative and qualitative efficient for the estimation of this non-linearity and that the method utilized to obtain the creep coefficients values is sufficiently accurate.

Análise e modelagem do escoamento transitório de fluidos de perfuração

Drilling fluids present a thixotropic behavior and they usually gel when at rest. The sol-gel transition is fundamental to prevent the deposit of rock fragments, generated by drilling the well, over the drill bit during eventual stops. Under those conditions, high pressures are then required in order to break-up the gel when circulation is resumed. Moreover, very high pressures can damage the rock formation at the bottom of the well. Thus, a better understanding of thixotropy and the behavior of thixotropic materials becomes increasingly important for process control. The mechanisms that control thixotropy are not yet well defined and modeling is still a challenge. The objective of this work is to develop a mathematical model to study the pressure transmission in drilling fluids. This work presents a review of thixotropy and of different mathematical models found in the literature that are used to predict such characteristic. It also shows a review of transient flows of compressible fluids. The problem is modeled as the flow between the drillpipe and the annular region (space between the wall and the external part of the drillpipe). The equations that describe the problem (mass conservation, momentum balance, constitutive and state) are then discretized and numerically solved by using a computational algorithm in Fortran. The model is validated with experimental and numerical data obtained from the literature. Comparisons between experimental data obtained from Petrobras and calculated by three viscoplastic and one pseudoplastic models are conducted. The viscoplastic fluids, due to the yield stress, do not fully transmit the pressure to the outlet of the annular space. Sensibility analyses are then conducted in order to evaluate the thixotropic effect in pressure transmission.