Computational Methods in Engineering

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Bridges are potentially one of the most seismically vulnerable structures in the highway system during earthquake events. It is known that the seismic performance of transportation systems plays a key role in the post-earthquake emergency management. Hence, it is necessary to evaluate both physical and functional aspects of bridge structures. The physical aspects of the seismic performance of bridges are evaluated by seismic fragility functions or damage probability matrices of transportation facilities. The fragility curves represent the probability of structural damage due to various levels of ground shaking. The fragility curve describes a relationship between a ground motion and a level of damage. In this paper, the fragility curves (F.C) are developed. The vulnerability of a railway prestreed concrete bridge is assessed using fragility curves derived from dynamic nonlinear finite element analysis. A software package is developed in MATLAB to study the results obtained. Modeling of the bridge using 3D nonlinear models and modeling of abutments, bearings, effect of falling of girder on its bearings, and nonlinear interaction of soil-structure are some of the advantages of this research compared to previous ones. Reliability curves developed in this study are unique in their own kind. The proposed method as well as the results are presented in the form of vulnerability and structural reliability relations based on two damage functions.

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The assessment of seismic performance of existing structures is becoming an important problem in earthquake engineering. Some important ructures are considerably old and, therefore, their strengths and ductilities are less than strength and ductility demands because of changes in codes and design methodologies. Such structures must be strengthened to resist future earthquakes. First, a structural model must be developed and then, based on seismic hazard and seismic risk analysis or code quantities, the design (or control) parameters can be determined. The next step is defining the damage indices in order to quantify the structural damage. Then the nonlinear dynamic analysis is carried out and damage indices are calculated. In the present paper, a power plant stack (located in Mashhad) is investigated for some levels of peak ground acceleration (PGA) considering return periods of 75, 500, 1000, and 2500 year. The height of stack is 100 m and the external diameter of the structure is 10 m. Several records are used for nonlinear dynamic analysis. It has been used from Park-Ang damage index that is a suitable model for concrete structures and has been considered in IDARC. It is clear that nonlinear dynamic analysis is necessary for the seismic vulnerability of existing structures. Special structures such stacks can be modeled with some 2-D or 3-D elements. However, the beam-column element is a proper model for special structures such as chimneys, considering calculation cost.

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The continuum mechanic simulation of micro-structural damage process is important in the study of ductile fracture mechanics. In this paper, the continuum damage mechanics model formulation proposed by Lematire has been validated against ductile damage evolution experimentally measured in A533B-C1 steel under stress triaxiality conditions. First, a procedure to identify the model parameters from test was defined. Then, the finite element model was used to simulate the experiment carried out on a notched flat rectangular bar. Good agreement was observed between the experimental results and finite element predictions. Next, the identified parameters on A533B-C1 steel were used to simulate the results from a conventional tensile test by finite element method. The specimen was prepared according to ASTM E08 standard. The stresses at necking stage and ultimate load calculated by the damage based method were compared with those obtained from the test. The comparisons indicate a good agreement between the simulated and the experimental results.

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In this research, nonlinear dynamic analysis of concrete shear wall using a new nonlinear model based on damage mechanics approach and considering bond slip effects is presented. Nonlinear behavior of concrete is modeled by a rotational smeared crack model using damage mechanics approach. The proposed model considers major characteristics of the concrete subjected to two and three dimensional loading conditions. These characteristics are pre-softening behavior, softening initiation criteria and fracture energy conservation. The model was used in current research analysis after verification by some available numerical tests. Reinforcements are modeled by a bilinear relationship using two models: Discrete truss steel element and Smeared model. In Discrete model the effects of bond-slide between concrete and rebar is mentioned using the bond-link element model concept. Based on the presented algorithms and methodology, an FEM code is developed in FORTRAN. The validity of the proposed models and numerical algorithms has been checked using the available experimental results. Finally, numerical simulation of CAMUS I and CAMUS III reinforced concrete shear walls is carried out. Comparisons of deduced results confirm the validity of proposed models. The obtained results, both in the expected displacements and crack profiles for the walls, show a good accuracy with respect to the experimental results. Also, using discrete truss element model with respect to the smeared steel model leads to increasing the accuracy of maximum displacement response to 7% in analysis.

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In this paper, a new vibration-based damage detection method for damage localization in shear frames is presented. For this purpose, a new damage index is proposed by means of static displacements estimated using only the first several mode data and Grey Relation Theory. The efficiency of the presented method has been demonstrated through studying several damage scenarios on three examples of shear frames with a different number of stories. The effects of various situations such as the existence random noises in the recorded data, number of available modes, different damage scenarios and irregularity in the structural characteristics have been studied on the applicability of the presented method. The obtained results show the robustness and good performance of the presented method in the damage diagnosis of shear frames. Some of the most important advantages of the suggested method can be summarized as its ability in damage localization by means of only the first mode data, low sensitivity to the random noises, and high speed and accuracy in estimating damage locations.

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This article predicts lifetime of high cycle fatigue loading using Chaboche-Lemaitre damage model. The Chaboche-Lemaitre damage model takes into account mean stress effect as well as compressive stresses effect, making crack to close. In the this paper, a numerical algorithm is offered to integrate this model implicitly and the obtained algorithm is implemented as a user material subroutine of the ABAQUS finite element software. To reduce computation time, Jump-in-Cycles procedure is used based on fatigue loading simulation. To verify the proposed algorithm, a V-notched specimen is chosen under a fatigue loading with different stress ratios, and its lifetime is compared with experiments. Next, an aviation industry part, main rotor spindle of an aircraft blades, subjected to a variable fatigue loading is analysed.

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In this paper, wave propagation method was applied to detect damage of structures. Spectral Finite Element Method
(SFEM) was used to analyze wave propagation in structures. Two types of structures i.e. rod and Euler-Bernoulli beam were
modelled using spectral elements. The advantage of spectral finite element over conventional Finite Element Method (FEM), in
wave propagation problems, is its accuracy and lower computational time. Two examples of rod and Euler-Bernoulli beam with
embeded concentrated mass were presented to illustrate the superiority of SFEM to FEM. Finally, a cracked beam was modeled
and analyzed using spectral finite elements and the location of the crack was determined using time history response of beam
structure.

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In this paper A progressive damage model based on multi-scale modeling has been developed to predict the initiation and propagation of damage in plain weave fabrics. For this purpose, microscopic damage in yarns and resin is calculated by an RVE (Representative Volume Element) FE simulation. By applying suitable boundary conditions of RVE, macro-scale average stresses were derived to extract the components of the equivalent stiffness matrix. Finally, by developing UMAT and USDFLD subroutines in the ABAQUS commercial software, the strength of the woven composite rings is predicted numerically. In order to confirm the numerical predictions, composite rings using the woven glass tapes of 5 cm width and epoxy resin are fabricated according to ASTM D2290 and tested. A good correlation between experimental and numerical results could confirm the accuracy of the finite element simulation.

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In this paper, a finite element model is presented for the transient analysis of low velocity impact, and the impact induced damage in the composite plate subjected to low velocity impact is studied. The failure criteria suggested by Choi and Chang and the Tsai-Hill failure criteria are used for the prediction of the damage in the composite plate; then the effect of various parameters on the impact induced damage is investigated. The first order shear deformation plate theory and the Ritz finite element method are employed for modeling the behavior of plate, and the modified Hertz contact low is used for the prediction of the contact force through the impact. In the numerical results, the time history of indentation, contact force and stress during the impact and the impact induced damage is investigated. The matrix cracking and delamination in the plies of the laminated composite plate subjected to low velocity impact are studied and the effects of various parameters are investigated.

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Peridynamics is a nonlocal version of the continuum mechanics, in which partial differential equations are replaced by integro-differential ones. Due to not using spatial derivatives of the field variables, it can be applied to problems with discontinuities. In the primary studies, peridynamics has been used to simulate crack propagation in brittle materials. With proving the capabilities of peridynamics, the idea of using this theory to simulate crack propagation in quasi-brittle materials and plastic behavior has been proposed. To this end, formulations and models based on peridynamics have been developed. Meanwhile, the high computational cost of peridynamic methods is the main disadvantage of this theory. With the development of peridynamic methods and introduction of hybrid methods based on peridynamics and local theories, the computational cost of peridynamic methods has been reduced to a large extent. This paper introduces peridynamics and the models based on it. To this end, we first review peridynamics, its formulations, and the methods based on it. Then we discuss the modeling of quasi-brittle materials, simulation of plastic behavior and employing the differential operators in this theory.