This paper presents the development of the finite element method in the field of fluids and an overview of the adjoint equation method applied to the backward analysis in the continuum mechanics. Generally, the behavior of the continuum can be determined solving the state equation specifying the initial and boundary conditions. Contrary to this, there are some cases that a behavior of the continuum at some points or some parts can be measured and known, however, the initial and boundary conditions are not known. Sometimes, the coefficient in the state equation or the boundary configuration is not known. To solve those problems, it is referred to as the backward analysis, which consists of the main part of the synthesis. Roughly, the backward analysis can be classified into two categories, one is the sensitivity method and the other is the adjoint method. In this paper, overall concept of the adjoint method is developed and applied to Data Assimilation, Boundary Control, Parameter Identification and Shape Optimization. The optimal shape determination of the boby located in the transient viscous flow is discussed for the application of the present formulation.
An analytical study and the application of the rectangular plates with two adjacent sides fixed and other two sides free under triangularly distributed regional loads are shown in this paper. The Type-3 Fourier series analytical method proposed by Higashi, Y. and Komori, K. was developed here. A comparison study for the bending moments of the fixed sides of the rectangular plates was carried out with Finite Element Method (FEM). The rationality and the applicability of analytical results were estimated and discussed. The figures of the coefficients of the bending moments and the shearing forces on the fixed sides of the rectangular plates were presented for the designer.
Many high-order theories for plate bending have been presented, in which the transverse shear deformation is included. Although those refined plate theories retain high accuracy for plate analyses, their governing equations are usually quite complicated and arenot suitable for practical use. In addition, few researchers carefully discuss influence of estimation of lateral loads. In this paper, we pay attention to constitution of lateral loads of plates. Especially we formulate the new theory for plate bending, in which the effect of a body force is distinguished from that of surface tractions. As a result, we can establish a quite simple plate theory including not only transverse shear deformation but also transverse normal stress effect. It follows form the present numerical examples that the new theory presented here is as accurate as Lo-Christensen-Wu's theory for thick plate bending.
Effects of fluctuations of an acoustic wave field on far field patterns were analyzed in this paper. The multiscale decomposition of the volume integral equation was employed for the analyses. The additive decomposition of the far field patterns was carried out according to the scale decomposition for the fluctuation of the medium as well as solution of the integral equation. Numerical results were presented to clarify the relationship between the size of the localized low velocity area and the wavelength.
This paper presents an investigation on the design procedure of steel check dam in the gorge point using the interactive optimal design method. The design of check dam at the gorge point is a new design situation for Sabo engineers, so the optimal shape structure has to be found without so much detail constraints or conventional knowledge. In order to discover an optimal shape of steel frame structure under new design back ground, the interactive optimal design can be utilized as a supporting device for giving a human designer a hint of design direction. The design example treated in this study shows very clearly that the supporting potential of proposed interactive optimal design method is high and useful.
The variation of engineering properties (i. e., Attedoerg limits, grain size distribution, undrained shear strength and elastic shear modulus) of Pleistocene clay (Ma 12) was examined by using a 85cm long sample retrieved at the construction site of Kobe Airport. In this experimental study, a direct shear box apparatus equipped with bender elements was newly developed so as to examine both strength and elastic stiffness of the clay sample. It was found that physical and mechanical properties were highly uniform, implying little variations of the soil mineralogy with ageing effects over 1m depth.
This paper presents the way to control of water level using optimal control theory and finite element method. The shallow water equation is employed for the analysis of the flow behavior. The optimal control theory is utilized to obtain the control value for the objective state value. The Sakawa-Shindo Method is employed as a minimization technique. The Crank-Nicolson method is applied to the temporal discretization. A method for the optimal control of water level has been presented.
The occurrence of damage in a structure produces changes in its global dynamic characteristics such as its natural frequencies, mode shapes, modal dampings, modal participation factors, impulse response and frequency response functions. In this paper, a newly derived algorithm based on changes in power spectral density (PSD) is presented. The algorithm is used to detect damage, predict its location and assess the extent of damage in structures. The proposed method is based on only the measured data without the need for any modal identification. The method is described theoretically and applied to the experimental data, from a steel bridge model and bookshelf structure. Several damage scenarios were introduced to the members of the test structures. The method detected the damage, determined the exact location and monitored the increase in damage.
A method for structural matrix identification is presented that uses microtremor measurements based on the canonical variate analysis (CVA), one of the subspace methods that enable the simultaneous identification of parameters under the multi-input-multi-output (MIMO) system. In the case where the structural responses at all nodes can be measured as well as the vibration at the basement, the damping and stiffness matrices can be obtained using the proposed method. Compared to the methods that tries to identify directly the element stiffness and element damping based on least squares method and prediction error method, the proposed method does not need to assume any distribution of stiffness and damping matrices, and identifies directly the total stiffness and damping matrices. The method is validated with the numerical simulation using a four-story structure.
The shape and location of reinforcing bars in the structural material are reconstructed from ultrasonic scattered waveforms in the low frequency. Two linearized inverse scattering methods are investigated for the imaging of reinforcing bars. The Born and Kirchhoff inversions reconstruct domains and boundaries of the bars, respectively. Although the dynamic interaction effect exists in the adjacent part of multiple bars, we can reconstruct the whole shape of bars with the Born inversion. On the other hand, the Kirchhoff inversion leads to the classification of the damaged area around a reinforcing bar. These performances of proposed imaging methods are demonstrated by numerical simulations using the boundary element method.
To avoid mechanical resonance and fatigue damage in engineering designs, it is crucial to predict and understand the responses of structure due to high frequency vibration and noise. This paper presents high frequency vibration analysis of Mindlin plates using spline Ritz method. To demonstrate an accuracy and convergence of the present method, some numerical examples are solved and the results are compared with those obtained by analytical method and other numerical methods. We also demonstrate the present method for high frequency vibration analysis by providing accurate frequencies for Mindlin plates vibrating in the first 5000 modes.
It is found that the sum of response design sensitivity coefficients multiplied by sensitivity variables over the whole structure equals the product of a constant and response value. Sensitivity coefficients are required in engineering problems such as structural design, optimum design and back analysis. Exact sensitivity coefficients can be computed by sensitivity analysis, but its computational cost is considerably high especially when many iterations are needed. For that reason, practically, sensitivity coefficients are computed approximately by finite difference. This paper proposes a very simple method of improvement of accuracy of approximate sensitivity coefficients computed by finite difference, using properties of sensitivity coefficients. And also the validity of this method is stated from the computational examples.
The most major procedure for fatigue design is to use the S-N curve as of now. According to the curve, it is expected that steel structures have a long life with the low stress amplitude. In this paper, we propose the formulation of the optimization problem considering the fatigue damage, which is based on minimization of an evaluation stress like a hot spot stress or a 1st principal stress. Then it is necessary to transform the discontinuous objective function written as a min-max problem into a continuous function using the temporary objective function, β. Additionally we describe the shape optimization technique effective to control a local shape.
A cable element has been developed in our papers for flexible cable structures with pulley. This element is formulated by modified functional of variational principle and has the same features as usual finite element based on the displacement method in which displacements are unknown variables. In this paper some functions are appended for shape finding of many cable structures such as cable net, suspension bridge and cable stayed bridge. Some numerical examples are to show the accuracy and efficiency of the proposed numerical method.
This paper presents an application of hybrid parallelization to the fast multipole accelerated boundary integral equation method. Expensive parts in the FMM (fast multipole method) algorithm are parallelized with MPI and OpenMP. The effectiveness of parallelization is examined with numerical examples, which include a two-dimensional potential problem with one hundred million DOFs.
The partial analysis method is developed to solve the scattering problem of Lambwaves by a finite crack in a plate. First, the scattering coefficients of Lamb waves due to a semi-infinite crack are obtained by using the mode-exciting method. Then we consider the equivalence between scattering coefficients of Lamb waves by a finite crack and those by a semi-infinite crack to obtain a system of equations depending on the crack length explicitly. The partial analysis method has an advantage in computational time when several plates with single cracks of various lengths are to be analyzed. Comparison between the results of the partial analysis method and the direct mode-exciting method shows a good agreement. The application of the partial analysis method to an inverse analysis is also demonstrated.
This paper presents an FMM formulation for periodic boundary value problems for two dimensional rigid-inclusion problems. This formulation uses a potential representation for periodic boundary value problems which includes no divergent series. Also an application to homogenisation problems is cosidered in order to obtain a macroscopic elastic constant based on a microscopic structure.
A recently developed semi-analytical method, called scaled boundary finite element method, is applied to evaluate the coefficients of stress field at a crack-tip for two-dimensional linear-elastic cracked structures. The method has ability to analytically compute stress and displacement field of singularities region at the crack tip more accurately without any apriori assumptions. A simple and independent formulations for evaluating the coefficients, not only of the inverse square root singular term but also of the constant and higher order non-singular terms, of the stress fields near crack-tip is presented by comparing the stress along the radial points ahead of the crack-tip with that of standard Williams' eigenfunction solution for the crack-tip. The accuracy and efficiency of the formulations are examined by numerical examples for a range of crack sizes. The results are in agreement with available solutions in literatures
Free vibration problem of rectangular plates with multiple point supports is analyzed by a discrete method. The concentrated loads with Dirac's delta functions are used to simulate the point supports which limit the displacements of the plate but don't offer constraint on the slopes. The fundamental differential equations are established for the bending problem of the plate with point supports. The solution of these equations is obtained by transforming these differential equations into integral equations and using numerical integration. Green function which is the solution of deflection is used to obtain the characteristic equation of the free vibration. The effects of the number and positions of point supports, the boundary condition and the aspect ratio on the frequencies are considered. By comparing the numerical results obtained by the present method with those previously published, the efficiency and accuracy of the present method are investigated.
High-speed transport infrastructure such as the Shinkansen mil line in Japan or superhighways involve the construction of very long elevated bridges, and seismic analyses of such semi-infinite structures are typically performed by considering a unit of the structure with free boundary at each end. However, the end of the unit is not free in practice, and interaction with adjoining structures is inevitable. Furthermore, a simple wave solution that can be applied to the soil structure is not applicable to the structure of a discrete system such as an elevated bridge, which consists of columns, beams and joints. The present authors have formulated the energy transmitting boundary as an infinite continuous system using the mass-spring model or a beam element model. However, the energy transmitting boundary is for analysis in frequency domain, and then it is not applicable to nonlinear analysis. In this research, for applying to the analysis in time domain, a viscous boundary is introduced using the mass-spring model for a discrete system with an infinite medium. And an equivalent viscous boundary is proposed for frame structure using a two-dimensional beam element.
This paper presents bending and vibration analyses of annular sector Mindlin plates using a semi-analytical method combined spline collocation method with Levy method. No numerical integration is required in the formulation and the resulting matrix has the advantage of being narrow bandwidth. To demonstrate an accuracy and convergence of the present numerical method, some numerical examples are solved and the results are compared with those obtained by analytical method and other numerical methods. It is seen that good accuracy and stable convergence are obtained.
The dynamic properties of composite plates are analyzed by the boundary element method in this study. The composite plate is defined in this analysis by combining an infinite thin plate and a finite thin plate, that is casted into the infmite plate, and whose material properties are different from the infmite plate. To investigate the dynamic response of the composite thin plate, numerical analyses for some models are carried out The results show the dynamic response of the composite plates well, and also confirm the usefulness of the proposed method for the composite plate problems. Furthermore, the proposed method was applied to numerical experiment of evaluation for a defect in thin plate. Results of numerical experiment on these models show that this nondestructive evaluation method has high appropriateness and usefulness to inspect defect in thin plate.
We develop an analysis method by the finite cover method (FCM) incorporated with the discontinuous Galerkin approximation for imposing displacement and traction compatibility conditions at material interfaces in heterogeneous solids. Treatment of the interface compatibility is a key ingredient for the FCM, which is regarded as one of the generalized versions of finite element method (FEM) since the FCM often employs a fixed regular mesh independetly of physical domain. First, the FCM is formulated and then the discontinuous Galerkin approximaiton is intoduced for imposing interface compatibility conditions. Secondly, after carrying out several numerical experiments to examine the approximation properties of the FCM at material interfaces in comparison with the stadard FEM or the penalty-based FCM, we discuss the characteristics of the discontinuous Galerkin FCM in the analyses of multi-phase materials.
The paper presents numerical solution of the three dimensional Navier-Stokes equations for complex flow domains consisting of fluid and porous regions with free surface boundary. Flow in both regions is described by single set of conservation equations, extending the momentum equation for porous regions by additional viscous drag term according Darcy law. Free surface kinematics is “tracked” by Volume of Fluid method. Firstly the model is verified by comparision with numerical solution of Laplace equation for simple free surface flow through vertical dam. Good result agreements are observed. Application on realistic problems is presented on two cases. First case considers problem of pressure redistribution process around a deep tunnel excavation in low-conductivity porous media and second considers flow under and through porous, partially submerged bridge.
In this paper, a relationship between the stabilized.finite element method and the bubble function element stabilization method with orthogonal basis is shown for the unsteady and steady Navier-Stokes equations. A two-level three-level formulation with bubble function, a bubble function element stabilization method, is proposed for incompressible viscous flow. The special bubble function with two-level partition is extended as an orthogonal basis bubble function element. The three-level bubble function is applied to derive a stabilized operator control term. The two-level three-level formulation with the bubble function formulation possesses better stability than the Bubnov-Galerkin formulation with the bubble function.
This paper presents a conservative CIVA method for advection equation on unstructured mesh, and its application to lattice Boltzmann method. The CIVA method is highly accurate interpolation scheme for advection equation based on CIP method. The parameter of the CIVA interpolation function is determined to guarantee the mass conservation. The present method was applied to the lattice Boltzmann method based on unstructured mesh. Some numerical examples are carried out to test the validity of the method.
We combined Overset Grid with Soroban Grid to calculating free surface flow around objects. We proposed Overset-Soroban grid system as one of adaptive moving grid, which is more feasible and effective than conventional lattice methods to solve a flow field with a complicated boundary shape. We used CIP-CSL2 method that is conservative Semi-Lagrangian scheme and M-type CIP method to calculate the advection term with Ovserset-Sroban grid system. We examined adaptive grid movement and local mesh refinement to computations of an interaction between solid and free surface flow.
The simulation intended for the real social systems has been performed on each domain. However, it is necessary to deal with as one system including natural environmento understand the entire intertwined object complexly. In this paper, interaction of a traffic system and natural environment is inquired by integrating a traffic simulation system and a local area wind energy prediction system. In that case, several issues will occur owing to a difference of the scale to be governed in the events. Therefore, we may separate scale-dependent effects in each event, and assume model on each scale. And then, a method of verification or validation of the models is considered At this point, we need model validation method linking between each scale. This paper describes a micro-level validation method in a traffic simulation including interaction of natural environment Clustering spatio-temporal datasets is proposed as the validation method. It is shown that a spatio-temporal data obtained from the movement of each vehicle can be clustered in a space constructed from the summation of absolute values of the accelerations and the average of OV function proposed by Bando et al., or the average of the velocities.
In a high-speed impact, both projectile and target experience an extreme distortion. A simulation in Eulerian formulation is therefore favorized. Contact-impact with Lagragian meshes are also presented. Focused topics here are Lagrangian and Eulerian formulation of a continuum media, plasticity flow, material separation due to failure or penetration, contact algorithm, 1-point integrated elements for computational time performance.
We propose a new procedure for approximately solving two-scale boundary value problems (BVPs) that can be derived in the framework of mathematical homogenization method for nonlinear heterogeneous solids. Although the micro- and the macroscopic BVPs are strongly coupled in the original algorithm for nonlinear two-scale BVPs, the proposed method enables us to decouple them without losing the distinct features of the two-scale BVP. That is, in this method, the solution for the macroscopic problem still reflects the mechanical behavior characterized for the microscopic one, and vise versa. We carry out representative numerical analyses for the structure with hyperelastic heterogeneous material and that with polycrystalline metal to demonstrate the capability and availability of the proposed method.
This paper concerns the evaluation method for normal contact force in the Distinct Element Method (DEM) in terms of the energy conservation. The contact force in DEM is usually obtained from the relative displacement and velocity of the particles, using analogy of springdashpot system. In the usual evaluation, the kinetic energy of the system is not taken account for the contact force because the model of the contact force is a mere imitation of the springdashpot system. In this paper, an evaluation method for normal contact force, that conserves the kinetic energy is newly proposed. A basic validation is carried out to confirm the validity of the proposed model. It is shown that the proposed model evaluates the normal contact force properly compared to the existing models.
This paper presents an ALE (Arbitrary Lagrangian-Eulerian) finite element methodfor fluidstructure interaction (FSI) problems with free surface. The mesh re-generation method based on background mesh is introduced to improve the applicability to the complicated FSI problems. The incompressible Navier-Stokes equation based on ALE description is used as the governing equation of fluid. The SUPG/PSPG formulation is employed for the finite element discretization. The structure is assumed to be a rigid body. As numerical examples, the present method is applied to the floating problem of a circular object, the water entry problem ofa wedge object and the falling problem of a circular object. The efficiency of the present method is shown by numerical results.
In the multi-dimensional fluid computations for actual hydraulic problems, it is necessary to take account of the complicated boundary shapes to obtain suitable computational results. One of the effective methods is to employ the elliptic-type grid generation to transform the physical computational domain to the regular one. In this paper, a locally pseudo-unsteady model is proposed to make the grid generation much faster than the usual methods in the distributed-memory system. The non-linear equations for the grid generation are discretized by introducing psedo-time and the numerical process is divided into a time-marching outer-loop and an inner-loop in which numerical solutions for linearized elliptic equations are derived. This model allows us to decrease message passings included in the inner-loop, which largely reduces the computational load in the parallel computations using distributed memory systems. The validity of the proposed model is demonstrated in some numerical experiments.
This paper presents an Eulerian solution for large deformation solid analysis. The present approach is based on the SUPG (Streamline-Upwind/Petrov-Galerkin) finite element method, which is employed to solve the advection equations in Eulerian solution. The present method is applied to the impact-bar and necking problems. The computational results are compared with the results obtained by the Lagrangian solution with finite element method and MUSCL (Monotonic Upwind Schemes for Conservation Laws) method based on finite difference method.
A novel approach of the Eulerian finite element method for large deformation problems of solid is proposed in this paper. The proposed method uses Lagrangian marker particles to evaluate the motion of materials including the free surfaces and advection of internal variables. The equation of motion is approximated by the characteristic Galerkin finite element method with a fixed spatial mesh. In this approximation, the material derivatives are evaluated by the special numerical integration along the characteristics in which the locations of the integration points are set at those of the marker particle. The internal variables at the marker are updated from the spatial derivatives of velocity field calculated on the fixed finite element mesh. It is remarked that no advection equation appears in the proposed method and the proposed method exhibits less diffusive properties than the conventional Eulerian method.
We develop an computational method by the finite cover method (FCM) incorporated with the discontinuous Galerkin approximation for simulating fracture behavior in heterogeneous solids. The FCM is formulated and then the discontinuous Galerkin approximaiton is intoduced for imposing interface compatibility conditions. On the ohter hand, the fracture behavior on cracking surfaces is represented by the cohesive crack model, which realizes smooth transition from continuity to discontinuity in the fracuture process zone near the crack-tip. Representative numerical examples demonstrate the performance of the proposed method.
In this paper, finite element analyses were applied to find the exact limit load of a rough rigid strip footing on a sand layer overlying clay. In addition to the information of ultimate bearing capacity, the normal and shear stress distributions below the footing and on the clay surface were obtained. The results were compared with those calculated using the limit equilibrium and the upper bound methods. A comparison with existing methods indicated that the finite element analyses can provide more reasonable results than the existing ones can. As the depth of the sand layer (H/B) or the undrained shear strength (cu) of the clay was increased, the failure zone was confined to the upper sand layer. Then, the contact normal and shear stress distributions were similar to those observed below the footing on homogeneous sand. Also, as H/B was increased or; was reduced, the width over which normal and shear stresses were applied to the clay surface tended to increase. The ultimate bearing capacities obtained from the finite element analyses were presented in the form of dimensionless charts that may be used in design, for different internal friction angles of sand. Finally, the “critical depth”(the failure mechanism is totally contained within the upper sand layer and the ultimate bearing capacity becomes independent of the undrained shear strength of the lower clay) was proposed.
Deformation of soil skeleton and flow of pore water must be coupled for deformation analyses of saturated soil structures. On the other hand, a rational treatment for contact boundaries connecting each body is needed for analyses of engineering problems since friction and/or sliding are included in almost all technical applications. In this article, in order to strictly consider not only the deformation phenomenon but also the frictional sliding phenomenon, the soil-water coupled finite element program incorporating both the subloading surface and the subloading friction models is developed. Subsequently, simulations of consolidation test by a constant strain rate control are performed. It is revealed by the present program that the frictional sliding phenomenon of the contact boundary influences the deformation behavior as well as flow of pore water phenomenon in the specimen.
This article examines the localized and diffuse bifurcations of deformation in an incompressible circular cylinder subjected to axisymmetric loading consisting of the tangential-subloading surface model. The analysis considers the conditions for shear band formation, diffuse buckling formation, and the long and short wavelength limits of diffuse buckling modes in relation to material properties and stress. The effects of the normal-yield ratio describing the degree of approach to the normal-yield state and the tangential-plastic strain rate due to the tangential-stress rate effect on the diffuse bifurcations are discussed in details. It is revealed that the normal-yield ratio and the tangential strain rate influence the onset of diffuse bifurcation.
Damages in composite materials are mostly governed by interfacial debonding. In order to take this into account, we employ an analytical model considering partial debonding along interface, and formulate a finite element. The model utilizes a concept where a moduli of an inclusion is replaced by an equivalent one of debonded inclusions. By several examples, eligibility of the model is shown. As an application, excavation analysis of a tunnel in jointed rock mass is carried out, and the results are compared with other observations.
When materials deform plastically, damages accumulate. A theory called 'void damage theory', where damages are replaced by voids, can express degradation of stiffness. However most models by this theory neglect stiffness of particles which in reality exist in materials and are one cause of further damage. Since debonding along such particles creates new damage, it is important to take into account the characteristics of such particles. In this study, the stiffness of particles or inclusions are included by an analytical averaging method, and the results are compared with experimental data to show eligibility of the method.
In nonproportional loading process, the traditional elastoplasticonstitutive model predicts the unrealistically stiff mechanical response leading to an excessively high critical load. The new concept of the tangential stress rate relaxation, called the tangential relaxation, is proposed by Hashiguchi, in which the direction of the tangential strain rate induced by the tangential stress rate has the components not only tangential but also outward-normal to the subloading surface. In this paper, the validity of the concept for the prediction of the deformation behavior of sand is evaluated by simulating the directional dependency of the inelastic strain increment on the stress increment directions, i.e. vertex effect, and also the inelastic deformation during the rotation of the principal stress axes direction under the constant mean stress and deviatoric stress, i. e. non-coaxiality.
A new constitutive model for compacted bentonite material is proposed in this paper in order to evaluate mechanical characteristics of buffer material. According to the results for a series of consolidation tests for the compacted bentonite material, it is found that nonlinear stress-strain behavior at the unloading process gets dominant comparing to the ordinary clay material. These peculiar characteristics of bentonite material cannot be described by conventional elasto-plasticonstitutive models such as an original Cam-clay model. Therefore, in this paper, a new function to describe the nonlinear behavior at unloading process is proposed and it is introduced into the original Cam-clay model. The simulationresults of the triaxial compression test show that the modified model proposed in this paper isreasonably applicable to the bentonite material.
Geomaterials such as soils may be sujected to complicated wetting and drying histories. Shearing tests of specimens which experienced wetting and drying process have been conducted by Shemsu. In this paper, we verify the Kohgo's elastoplastic model by simulating the experiment of soils subjected to such a suction history. Through the investigation, we show to need two types of subloading surface.
The application of integral type non-local constitutive model to 2D RC members was investigated. The investigation is to aim at the nonlocal variable, the treatment of nonlocal variable as well as the integral region which are available to apply to the general stress field by computing the uniaxial compressive concrete member and the compression flexure failure RC beam. As the results, the nonlocal variable was suitable using the strain with the local coordinate direction to evaluate uniaxial stress. Moreover, the conventional circle integral region was not appropriate. The concept of ellipse integral region which is varied the shape and size with the state of stresses was proposed. It showed that the proposed method could evaluate the behavior of RC members approximately.
Studied herein is the structural performance of hybrid box girders using high-performance steels under both bending and shear force by FEM analysis. Remarkable performance of hybrid girders observed through the study are as follows:(1) Under pure bending, the bending moment can reach to almost the fully plastic moment depending on the width thickness ratio of web.(2) Under both bending and shear force, the box girder can keep the load level even after the buckling occurs and may be superior depending on the ratio of the area of the flange to the area of the web.
The behavior of piled raft foundations on natural deposited soils subjected to ground subsidence due to dewatering is analyzed in this paper. A three-dimensional finite element model considering the soil-water coupled problem has been developed. In this analysis the piled raft and the soil are modeled as an elastic material and a two-phase elasto-plastic material, respectively. It can be deduced from the calculations that changes in axial forces and bending moments acting on the piles of piled raft foundations are lower than these corresponding to bearing pile foundations. This suggests that piled raft foundations are more effective for the reduction of negative skin frictions on piles. Piled rafts with longer piles can reduce the settlement due to dewatering in case that delayed consolidation does not occur. If the toes of piles locate in the layer which causes delayed consolidation, the settlement of piled rafts would be larger than that corresponding to raft foundations
For the design of a rock bolt in a tunnel construction, the standard patterns of the installation of a rock bolt are mostly employed. The standard patterns are determined by engineering experiences or geological categories. Therefore, there is a possibility of the overabundant design of a rock bolt. In order to improve the design of a rock bolt, many experiences were conducted and gave us a valuable knowledge. Most of them used the rock specimen having a cut-through joint so as to seize the performance of the installation of a rock bolt, but this kind of situation is considered to be rare in a rock mass during the construction of a tunnel. Most of rock joints are included in a rock mass and their deformation is constrained by the rock mass. Therefore, there are some questions about the knowledge from room tests to seize the performance of the installation of a rock bolt. Thus, in this article, several analyses with various size of joint included in a rock mass are carried out, and the installation effects of a rock bolt are discussed from an analytical point of view.
Highly structured naturally deposited clay exhibits the softening with plastic compression due to the decay of soil structure. The softening behavior can be expressed by Super/subloading Yield Surface Cam-clay model, SYS Cam-clay model (Asaoka et al., 2002), in which the concepts of “structure”, overconsolidation, anisotropy, and their evolution laws, are introduced into the modified Cam-clay model. Inthe present study, in order to examine the effects on the softening behavior, the consolidation test with some constant stress ratios controlled by the strain rate was carried out using Joban clay, highly structured clay, and calculated by SYS Cam-clay model. The new findings are as follows.(1) The large compression due to the softeningwith plastic compression occurs when the stress ratio of consolidation was large, initial degree of structure was large and degradation speed of structure is rapid through the calculation.(2) The experimental results showed the same tendency as the calculation results.(3) The axial strain proceeded by 4% keeping the deviator stress q and mean effective stress p constant axial strain in the consolidation test with stress ratio of 1.3.
Using a simple X-FEM, in which only the four-node quadrilateral isoperimetric elements in the fractured element are employed without the enrichment by the near-tip asymptotic solution, we analyze the stress distributions near a crack tip for an elastic-plastic material in a rectangular plate with a centered crack under two axial compressive loads. The friction forces assumed to follow the Coulomb law with a slip criterion is analyzed in the context of an implicit return mapping algorithm. The elastic-plastic material is also analyzed by the implicit return mapping algorithm. Thus the contact problem and the elastic-plastic material become a simultaneous combining incremental and iterative method of the same implicit scheme of the Newton-Raphson method. This makes the algorithm very simple. The stress distributions near the crack tip obtained by the simple X-FEM agree well with the exact solution in the elastic material and with the classical FEM solution in the elastic-plastic material.