Initial Stress Method Research Articles

The Wetting Deformation Model of Rockfill and Its Two Methods for Simulating Rockfill Dam Collapse Settlement.

The wetting deformation of the upstream dam shell material during the impoundment of the core wall rockfill dam seriously affects the safety of the dam. Based on the proposed Ew - νw wetting model, this paper proposes its corresponding two methods to simulate the collapse settlement of the rockfill dam: the initial strain method and the initial stress method. By simulating the collapse settlement of the Guanyinyan core wall rockfill dam, it is found that the simulated result using the initial stress method is in good agreement with the field monitoring data, while the displacement simulated using the initial strain method is larger. The distribution of displacement contours simulated using the initial strain method is obviously inconsistent in the area where the wetting deformation occurs, and the simulation results of the initial stress method are more reasonable. With the rise in the water level, the wetting deformation of the upstream dam shell material causes the tensile stress zone at the top of the dam. Therefore, the wetting deformation is the direct cause of the crack at the top of the dam, and the initial stress method should be preferred in the simulation of the wetting deformation of rockfill materials.

Effect of the Location of Broken Wires on Prestressed Concrete Cylinder Pipes under Working Pressure

The precise analysis of the overall mechanical performance of prestressed concrete cylinder pipes (PCCPs) with broken wires is a complicated problem. In this article, powerful finite element numerical means are applied to solve this problem. Firstly, the advantages and shortcomings of the current prestress simulation methods in the finite element analysis (FEA) literature are discussed, and the initial stress method based on a novel single-spring joint element method to model the pre-stress of wires is proposed. Then, different distributions of broken zones, including random broken distributions, are developed for two typical PCCP pipes with different wire-wrapped layers. The established nonlinear FEA model considers actual service processes such as manufacturing, installation and operation to investigate the mechanical behavior of two typical PCCP pipes with different breakage distribution regions and breakage ratios, and in particular, the overall mechanical behavior of a pipe with random breakage is determined first. To verify the accuracy of the proposed pre-stress simulation method and the established nonlinear finite element model, the overall mechanical response of a pipe before wires broke is compared with the results obtained via the specifications. The computed results under the corresponding breakage assumptions are consistent with the conclusions in the existing literature, providing important guidance for pipeline management and operation.

On the theory of constitutive equations for composites with different resistance in compression and tension

The paper proposes a new approach to the construction of nonlinear constitutive equations for the description of elastic deformation of fibrous composites with different resistance in compression and tension. The framework of the approach is the generalized rheological method of constructing constitutive equations of the uniaxial stress–strain state. Transition to the tensor equations uses the hypothesis of existence of a special cone of all possible compression states in the space of strains. The cone structure is governed by the reinforcement pattern of a composite. When imposed with strains in the cone, the composite behaves as a linearly elastic medium, while beyond the cone, the composite is nonlinear, with higher stiffness conditioned by tension of high-modulus reinforcement fibers. It is highly critical that the constitutive equations obtained using this approach belong to the theory of hyperelasticity. The elastic potentials of stresses and strains are obtained for these equations, which guarantees implementation of fundamental principles of equilibrium thermodynamics. Application of the developed general theory is exemplified by construction of the constitutive equations for the plane stress state of a thin unidirectional fiber reinforced composite plate and for a multilayer plate with different-direction reinforcement of layers. Using the finite element method in combination with the initial stress method, the stress and strain patterns are analyzed in rectangular one-, two- and three-layer carbon fiber reinforcement polymer plates with a circular cut under the action of external stresses at the boundary.

A quantitative display index that considers tensile failure to predict the full sliding surface of a landslide

In slope stability evaluation, it is common that a potential tensile sliding surface is not accurately positioned. In this paper, the strength reduction method considering shear and tensile failure with a strain-softening model is adopted to simulate the deterioration of the strength parameters of geomaterials during failure. Based on the initial stress method, a new quantitative display index of the full sliding surface is proposed. This method was applied to the stability analysis of a heterogeneous slope and a homogeneous slope. The results show that the plastic zone determined with the strain-softening model is much smaller than that determined with the Mohr-Coulomb model, and the difference is 34–40%. The safety factor obtained without considering tensile failure is 3.1% larger than that obtained considering tensile failure. The index can be used to quantitatively display the shear failure zone and tensile failure zone of a sliding surface.

Algorithms for Solving Boundary Value Problems of Deformable Solid Mechanics in View of Creep Strain

Further development of power and, primarily, engine engineering is associated with significantly increasing specific indicators. For example, the main trend in development of gas turbine engines is to increase gas parameters before the turbine. At the same time, there is an intensive growth of thermal and mechanical tension, and first of all this applies to the parts and components of the flow range. The destruction of these structural elements may have grave consequences. Increasing reliability and durability of responsible components of engines under operating conditions of complex cyclic thermo-mechanical loading is one of the priority tasks of modern engine engineering.One of the factors to determine a design performance is high-temperature creep. When solving the problems of deformable solid mechanics (DSM) in terms of creep, various options of the theory of hereditary creep and three main technical theories of aging, flow and hardening are widely used. There are also theories known that use an apparatus of the structural models and mechanical analogues to describe the creep. Most theories satisfactorily describe the creep strain under constant or slowly changing loads. Analysis of stress-strain states under variable loads is better described by the theories of flow and hardening, and the theory of hardening has some advantages over the theories of flow, as it gives more exact approximation for experiment results. From the point of view of the computing cycle arrangement, the technical theories have well-known advantages over the hereditary ones.When using the finite element method (FEM) to solve the boundary value problems of DSM considering the creep strain, an explicit or implicit Euler scheme is very often used. Depending on the features of the problem under consideration, a solution algorithm is constructed either in accordance with the method of initial stress, or by the method of initial strains. The method of initial strains when solving the problems in terms of creep is used more often, because the application of an initial stress method for this class of problems is technically much more complicated. The paper examines the explicit and implicit Euler schemes in combination with FEM. Both schemes are formulated in accordance with the method of initial strains. A constitutive relation was chosen in the form of the theory of flows.

ПОДХОДЫ К ОЦЕНКЕ ДЕФОРМАТИВНОСТИ ИЗГИБАЕМЫХ ЖЕЛЕЗОБЕТОННЫХ ЭЛЕМЕНТОВ НА ОСНОВЕ ИТЕРАЦИОННЫХ МЕТОДОВ РАСЧЕТА

The article deals with existing methods for evaluating the load bearing capacity and deformability of bent reinforced-concrete elements, including the composite section. The analysis of idealized nonlinear dependencies and compressed concrete deformation diagrams. Iterative methods for structural analysis: the method of successive refinement of stiffness, the method of successive loadings, initial stress method. Results of their algorithms and shows the advantage of using the method of the dual stiffness are considered.

A harmonic one-dimensional element for non-linear thermo-mechanical analysis of axisymmetric structures under asymmetric loads: The case of hot strip rolling

This work presents a one-dimensional harmonic finite element for the transient elasto-plastic analysis of axisymmetric structures loaded by non-axisymmetric thermal and mechanical loads. The one-dimensional element exploits a semi-analytical approach, based on Fourier series decomposition of the applied loads. The initial stress method is used for the non-linear solution of elasto-plastic analysis. As a case study, the proposed one-dimensional harmonic element is applied for modelling a two-dimensional circle under thermal and mechanical loadings rotating over its surface, which is used as an approximation of a work roll in hot strip rolling. With the one-dimensional harmonic element, the cyclic thermo-mechanical behaviour of the work roll can be simulated by considering localized plasticity caused by thermo-mechanical loads representative of strip and back-up roll. Compared to two-dimensional models already used in the literature, the one-dimensional element allows a significant reduction in the computational time to be achieved; it follows that the whole transient thermo-mechanical response can be simulated, thus permitting a more complete evaluation of the stress–strain response that is necessary for fatigue life assessment.

Numerical and experimental analyses for bearing capacity of rigid strip footing subjected to eccentric load

A footing may get an eccentric load caused by earthquake or wind, thus the bearing capacity of footing subjected to eccentric load become a fundamental geotechnical problem. The conventional limit equilibrium method used for this problem usually evaluates the material properties only by its final strength. But the classical finite element method (FEM) does not necessarily provide a clear collapse mechanism associated with the yield condition of elements. To overcome these defects, a numerical procedure is proposed to create an explicit collapse mode combining a modified smeared shear band approach with a modified initial stress method. To understand the practical performance of sand foundation and verify the performance of the proposed procedure applied to the practical problems, the computing results were compared with the laboratory model tests results and some conventional solutions. Furthermore, because the proposed numerical procedure employs a simple elasto-plastic model which requires a small number of soil parameters, it may be applied directly to practical design works.

Analysis of Long-Term Deformation of Reinforced Retaining Wall Using Optical Fiber Sensor Geotextile

Geotextile have been widely used in the reinforced retaining wall, but it is not easy to measure the deformation of the wall during and after construction. To assess the deformation stability of the reinforced retaining wall, an optical fiber sensor was used in geotextile. Based on the measurement accuracy of strain for the sensor geotextile, an actual geotextile-reinforced retaining wall was studied using the fiber sensor geotextile. The experimental results were compared with the results from a numerical procedure, which employs the Mohr-Coulomb yield criterion and an initial stress method and determines the plastic displacement at collapse represented by the distribution of yield elements. The comparison shows that the numerical results have a good agreement with the corresponding measurement values. The result shows the possibility that the procedure gives the realistic evaluation of long-term deformation of reinforced retaining wall.

Failure Mechanism of Strip Footing on Geotextile-Reinforced Soil

Several laboratory model tests were carried out on the bearing capacity of strip footings on reinforced soil foundation and reinforced slope. Compared with unreinforced cases, the deformation and failure of reinforced earth in different foundation conditions were monitored and analyzed. In order to visualize a failure mechanism when the ground reaches the state of limit equilibrium, a new numerical procedure was proposed. Assuming an elastic-perfectly plastic model, a smeared shear band approach and a modified initial stress method enable the proposed procedure to create an explicit collapse mode by the stress yield condition. On the basis of the development of failure mode and deformation of foundation, the bearing capacity of strip footings can be significantly increased by the inclusion of geotextile. And because the procedure considers the stiffness and deformation of the material, it may be applied to complex stability problems.

Limiting Plastic Load in a Pressure Vessel with a Branch Pipe under Combined Internal Pressure and Bending Moments

An applied procedure for elastoplastic analysis, and results of determination of limiting plastic loads for a pressure vessel with a branch pipe under a combined loading are presented. The analysis is performed with the use of the finite-element method, shell theory, plastic-flow theory, and initial-stress method. A new method based on the criterion of maximum rate of increase in relative plastic work is employed to determine limiting plastic loads.

Research on Space Frame Structure in Regard of Member Initial Stress

To reveal the harm of member initial stress on space frame structure, several models which are different in initial imperfection methods, material computational models and upper optimized stress ratios are employed to do nonlinear finited element analysis. It finds that the initial stress method and Marshall model are more accurate to simulate. When design the space frame structure, it must be avoided to optimize the cross section excessively in pursuit of economic factors.

Nonlinear dynamic analysis on rigid-flexible coupling system of an elastic beam

Previous work examined the effect of the attached stiffness matrix terms on stability of an elastic beam undergoing prescribed large overall motion. The aim of the present work is to extend the nonlinear formulations to an elastic beam with free large overall motion. Based on initial stress method, the nonlinear coupling equations of elastic beams are obtained with free large overall motion and the attached stiffness matrix is derived by solving sub-static formulation. The angular velocity and the tip deformation of the elastic pendulum are calculated. The analytical results show that the simulation results of the present model are tabled and coincide with the one-order approximate model. It is shown that the simulation results accord with energy conservation principle.

Analysis of Pore Pressure and Stress Distribution around a Wellbore Drilled in Chemically Active Elastoplastic Formations

Drilling in low-permeable reactive shale formations with water-based drilling mud presents significant challenges, particularly in high-pressure and high-temperature environments. In previous studies, several models were proposed to describe the thermodynamic behaviour of shale. Most shale formations under high pressure are expected to undergo plastic deformation. An innovative algorithm including work hardening is proposed in the framework of thermo-chemo-poroelasticity to investigate the effect of plasticity on stresses around the wellbore. For this purpose a finite-element model of coupled thermo-chemo-poro-elastoplasticity is developed. The governing equations are based on the concept of thermodynamics of irreversible processes in discontinuous systems. In order to solve the plastic problem, a single-step backward Euler algorithm containing a yield surface-correction scheme is used to integrate the plastic stress–strain relation. An initial stress method is employed to solve the non-linearity of the plastic equation. In addition, super convergent patch recovery is used to accurately evaluate the time-dependent stress tensor from nodal displacement. The results of this study reveal that thermal and chemical osmosis can significantly affect the fluid flow in low-permeable shale formations. When the salinity of drilling mud is higher than that of pore fluid, fluid is pulled out of the formation by chemical osmotic back flow. Similar results are observed when the temperature of drilling mud is lower than that of the formation fluid. It is found that linear elastic approaches to wellbore stability analysis appear to overestimate the tangential stress around the wellbore and produce more conservative stresses compared to the results of field observation. Therefore, the drilling mud properties obtained from the elastoplastic wellbore stability in shales provide a safer mud weight window and reduce drilling cost.

The inclusion of rheological properties of rocks to calculation of stress-strain state of an undermined rock mass

The procedure proposed for calculation of deformation and collapse of underworked strata is based on using the stiffness calculation matrix, representing the pre-mining state of rocks. The initial stress method is employed to account for variations in elastic constants in the deformation area in terms of the linear viscosity-elasticity. Potentialities of the described approach are considered. A number of solutions to the research problems are presented.

Calculation of stress-strain state for an over-goaf rock mass

The stress state of a rock mass over a goaf is analyzed by using the mathematical modeling. The initial stress method is used to consider caving and failure zones within overlying rocks and makes it possible to derive an effective estimation algorithm for the undermined rock state.

유한요소 교호법을 이용한 삼차원 균열의 탄소성 J 적분 해석

SGBEM(Symmetric Galerkin Boundary Element Method)-FEM alternating method has been proposed by Nikishkov, Park and Atluri. In the proposed method, arbitrarily shaped three-dimensional crack problems can be solved by alternating between the crack solution in an infinite body and the finite element solution without a crack. In the previous study, the SGBEM-FEM alternating method was extended further in order to solve elastic-plastic crack problems and to obtain elastic-plastic stress fields. For the elastic-plastic analysis the algorithm developed by Nikishkov et al. is used after modification. In the algorithm, the initial stress method is used to obtain elasticplastic stress and strain fields. In this paper, elastic-plastic J integrals for three-dimensional cracks are obtained using the method. For that purpose, accurate values of displacement gradients and stresses are necessary on an integration path. In order to improve the accuracy of stress near crack surfaces, coordinate transformation and partitioning of integration domain are used. The coordinate transformation produces a transformation Jacobian, which cancels the singularity of the integrand. Using the developed program, simple three-dimensional crack problems are solved and elastic and elastic-plastic J integrals are obtained. The obtained J integrals are compared with the values obtained using a handbook solution. It is noted that J integrals obtained from the alternating method are close to the values from the handbook.

Elasto-Plastic Analysis of 3-D Inner Cracks Using the Finite Element Alternating Method

The finite element alternating method (FEAM) was extended to obtain fracture mechanics parameters and elasto-plastic stress fields for 3-D inner cracks. For solving a problem of a 3-D finite body with cracks, the FEAM alternates independently the finite element method (FEM) solution for the uncracked body and the solution for the crack in an infinite body. As the required solution for a crack in an infinite body, the symmetric Galerkin boundary element method formulated by Li and Mear was used. For elasto-plastic numerical analysis, the initial stress method proposed by Zienkiewicz and co-workers and the iteration procedure proposed by Nikishkov and Atluri were used after modification. The extended FEAM was examined through comparing with the results of commercial FEM program for several example 3-D crack problems.

ブロック積み擁壁土圧の模型実験と数値解析

This paper discusses active earth pressure acting on concrete block retaining wall considering deformation and stiffness of wall and backfill material. Many laboratory model tests are performed, subjected to block retaining walls which have reinforced or unreinforced backfill, and which have different inclination. Earth pressure distribution and active thrust, etc. are monitored according to the displacement of retaining wall. The monitored results are simulated fairly well by proposed FE analysis which employs Mohr-Coulomb yield criterion, a simple non-associated flow rule, and initial stress method for nonlinear analysis. By applying the proposed procedure to the result of full-scale model test, it is shown that the procedure duplicates fairly well the results observed in the test.

경계요소법의 탄소성문제에 대한 초기응력법의 적용

The BEM, known as solving boundary value problems, could have some advantages In solving domain problems which are mostly solved by FEM and FDM. Lately, in the elastic-plastic nonlinear problems, BEM could provide the subdomain approach for the region where the plastic deformation could occur and the unknown nodal displacement of this region are added as the unknown of the boundary integral equation for this approach. In this paper, initial stress method was used to establish the formulation of such BEM approach. And a simple rectangular plate having a circular hole was analyzed to verify the suggested method and the result is compared with that from FEM. It is shown that the result of two methods are showing similar stress-strain curves at the root of perforated plate and furthermore the plastic deformation obtained by BEM shows more reasonable behavior than that of FEM.