Lanterna Rally

Author: Omar Alrayes

Publisher:

Published: 2023

Total Pages: 0

ISBN-13:

Many concrete structures, such as bridges and wind turbine towers, fail mostly due to fatigue following cyclic loading where the cracks are initiated and propagate under cyclic loading. Therefore, a detailed analysis of the fatigue behaviour and the associated crack propagation is required for the economical and reliable design of concrete structures. Damage due to fatigue can be divided into different categories dependent on the loading conditions as well as other environmental conditions. These types of fatigue are high cyclic fatigue loading with more than 1000 load cycles. The type of low cyclic fatigue has less than 1000 cycles. The very low cyclic loading for a specific number of cycles (i.e. 10 cycles). The application of the vehicles load vibration is classified under high cyclic fatigue caused by small elastic strains under high number of load cycles. The earthquake loading is classified under the low cycle fatigue type. Also, the corrosion fatigue failure in reinforcement concrete structure occurs under moisture cyclic loading. Different combinations of the above fatigue types can occur. The deterioration process is related to the type of load frequency which results in loss of material stiffness. This work's focus is developing a new approach that predicts crack growth and damage accumulation within the cohesive response of very low cyclic crack propagation in concrete members. The advanced studies on cyclic crack propagation for concrete are primarily empirical, where a large number of data samples from experiments are used for fitting the numerical simulation. Many approaches as Paris law used to predict fatigue life and crack growth rate. However, it has been shown that such phenomenological law loses much of its prediction ability for numerical implementation since the crack grow very slowly and cyclic damage zone is not detected for large part of concrete life. In the numerical approximation framework in literature, the Cohesive Zone Model (CZM) has been implemented to simulate the material damage and crack propagation under monotonic loading. Concerning cyclic loading scenarios, however, the prediction of crack propagation is still limited mainly by the analysis method mentioned. For concrete material, the damage models whose localization is governed numerically by finite element simulation, are aimed to simulate the propagation of fracture in cohesive process zone under monotonic loading. However, these types of models are used to determine the damage only along the loading/unloading paths. Several modelling approaches in finite element (FEM) for crack propagation under cyclic and fatigue loading are well documented in the literature. The CZM has been implemented in classical fracture mechanics to reduce the mesh quality required for crack simulation. Many models in the literature are dedicated to simulating the quasi-brittle behaviour, including a set of constitutive equations for monotonic, fatigue and hysterical material response. Furthermore, several calculation schemes are also done to predict tensile, flexural monotonic, and fatigue material behaviour. However, a damage accumulation process for concrete energy dissipation under random cycles is required. One of the most important implementations of the SBFEM approach is to model crack nucleation, and propagation under general loading conditions. The cohesive fracture and stress field can be determined using interface elements with zero-thickness, which were inserted directly into the SBFEM for only monotonic loading. Furthermore, the cohesive traction forces close to the crack tip are accurately computed as it is defined analytically. This enables to predict the crack path and to obtain the correct load-deflection response for different load scenarios. In the present work, a novel crack cyclic damage model has been developed within the SBFEM framework. The model considers the cumulative crack opening/sliding measure to dominate the damage mechanism at the subcritical loading levels. The aim of this approach is to establish a link between cyclic damage rate and the efficiency of the SBFEM in modelling crack propagation. Comparing the thermodynamic softening law of the constitutive model for fracture, several aspects have been provided, which incorporate the loading-unloading path, the damage evolution during the load cycle, and the crack traction displacement behaviour. This model is developed to simulate the discrete crack propagation in SBFEM for both single and mixed crack modes. It introduces a model for efficient simulation of cyclic behaviour. In the process of this work, a general derivation of the SBFEM method is given to simulate the crack propagation of the studied domain. The constitutive law is inserted into the SBFEM framework as interface element at crack tip. The nonlinear consistent interface model is solved using displacement control algorithm to obtain the load displacement for both monotonic and cyclic loading scenarios. The cyclic damage accumulation during loading and unloading is formulated within the constitutive concrete model. Two common problems of the three-point bending of a single-edge-notched concrete beam have been studied to validate the developed method. Also, two mixed-mode crack propagation examples are modelled for monotonic and cyclic loading, with results discussed and compared with available data in publications. The simulation results showed good agreement compared to experimental test measurements from the literature. The study provides a numerical procedure of fatigue crack growth in concrete which can help to identify the primary governing mechanism of fatigue crack propagation in concrete. The numerical investigations focused on the effect of the loading sequence on the fatigue material life. The developed method is validated using experimental results of several examples subjected to different loading conditions. The method also applies to offshore foundations, dams and slabs of airport taxiway calculations. This work can be used as a tool for fatigue material assessment within a non-linear finite element framework. The complexity of the calculation makes the application of the method quite expensive. However, further improvement in computer science will overcome this disadvantage.