Showing papers in "Engineering mechanics in 2007"

3d consistent viscous-spring artificial boundary and viscous-spring boundary element

Abstract: The stiffness and damping matrixes of 3D consistent artificial boundary are deduced through viscous-spring artificial boundary theory. 3D equivalent viscous-spring artificial boundary element is developed by comparing the matrixes of general finite element and consistent viscous-spring artificial boundary. This boundary element is applied to uniform and layered half space problems, respectively. The results show that 3D equivalent viscous-spring boundary element has the same precision as viscous-spring artificial boundary, and the former is more applicable and simple.

Study on the deformation failure and energy properties of marble specimen under triaxial compression

Abstract: In the paper,experiments were carried out to investigate marble specimens under conventional triaxial compression by the RMT-150B servo-controlling testing machine.Based on the experimental results,the deformation failure and energy properties of marble specimens under conventional triaxial compression were studied.The results show that marble will manifest the property of strain inteneration when the material in the rock does not turn uniform under the lower confining pressure.However,marble will show the property of plastic flowage when the material deformation becomes uniform under higher confining pressure.There is a a positive linear relation between the peak strain of rock material and the confining pressure.The sensitivity of residual strength on the confining pressure is higher than that of peak strength.The failure strain energy of rock increases linearly as the confining pressure increases.The total fracture energy of rock specimens also increases linearly as confining pressure increases.

Numerical simulation for the hysteresis behavior of rc columns under cyclic loads

Abstract: Precise prediction for the hysteresis behavior of reinforced concrete (RC) columns under seismic loads is important to assess the safety of RC frames and bridges during sever earthquake. Due to the complicated material behavior and complex external force during the earthquake, an accurate simulation of the behaviors under seismic loads currently mainly depends on numerical method, and more precisions are demanded for the hysteresis constitutive laws of concrete and steel reinforcement. In this paper, a fiber model program is developed with more precise hysteresis constitutive laws of concrete and steel reinforcement. Two columns, which are under cyclic compressive-bending loads, with different axial load ratios and reinforcement ratios, are analyzed and the simulation results are found agreed well with test results.

Elasticity solution of simple beams with different modulus under uniformly distributed load

Abstract: A semi-inverse method from stress functions is used to obtain elasticity solutions of a simply supported beam with different modulus under uniformly distributed load and its approximate solutions derived from mechanics of material are also checked The results show that because the materials with different modulus are employed, the stress redistributes across section in a large extent and the maximum normal stress obtained from mechanics of materials is underestimated to a certain degree These errors fluctuate according to different modulus of materials and enlarge especially in the case of deep beams

A one-dimensional optimization algorithm for non-probabilistic reliability index

Abstract: The following points are proved in this paper: (1) Non-probabilistic reliability index of an arbitrary structure merely exists at one of the crossing points at which standard failure surface of the structure intersects the straight lines passing through both origin of a standard infinite space and vertices of holohedric convex polyhedron centered at the origin, and (2) The non-probabilistic reliability index equals to the absolute value of the coordinate of one of the crossing points Based on the reduction of feasible region from the standard infinite space to finite crossing points within the standard infinite space, a one-dimensional optimization algorithm for non-probabilistic reliability index is developed to replace the interval algorithm and multi-variable optimization approach The algorithm is reliable and efficient in arithmetic operations

Extended finite element method based on abaqus

Abstract: A virtual node method for coupling the eXtended Finite Element Method (XFEM) with commercial finite element software ABAQUS is presented. The relationship between the subdomain integration and the Heaviside function is formulated, and a subtriangle integration algorithm is improved. The brittle fracture process of a 3-point bending beam was simulated. The computational results demonstrate the capacity of the presented method to simulate the moving discontinuities. Crack path is not necessary to coincide with element boundaries in XFEM and re-meshing can be avoided. The coupling with commercial finite element software proposes an efficient way for solving practical complex problem using XFEM.

Stress analysis on steel box girders of super-long-span suspension bridges with submodel method

Abstract: A 3-dimensional, Finite Element, full model for the Runyang Suspension Bridge, the longest bridge in China was established and analyzed. The submodel of the steel box girder was then particularly established based on the analyzed results considering the connection of the two models. The local stresses of the steel box girder under various load conditions were calculated with the submodel. The calculation stress values were found to be reliable by comparing with the field measurements and the submodel method was proved to be effective on analyzing the stress levels and distributions of steel box girders of super-long-span suspension bridges. Finally the working behaviors and mechanical characteristics of the steel box girder of the Runyang Suspension Bridge were analyzed. The analysis results could provide theoretical references for analyzing the steel box girders of super-long-span suspension bridges.

Simulation of mixed-mode fracture of concrete using extended finite element method

Abstract: The eXtended Finite Element Method (XFEM) is employed to simulate the fracture process of a concrete beam under mixed-mode loading. The cohesive crack model is used to describe the mechanical behavior between the crack surfaces. Tangential retention stiffness is introduced to consider the effects of the shear component. The cracking direction is determined by a simplified maximum tangential stress criterion. The experiments by Arrea and Ingraffea are simulated. The relationship between load and crack mouth sliding displacement (CMSD) predicted numerically agrees well with the experiment results. The results demonstrate that XFEM is an efficient method to simulate the mixed-mode fracture process of quasi-brittle materials because the expression of displacement discontinuities on both sides of cracks is independent of element meshes.

Simulation of damage for bridge pier subjected to ship impact

Abstract: A review is made for HJC concrete model which includes strain rate effects and material damage. Sensitivity of damage parameters in HJC model are discussed through a collision of a rigid ball with a concrete plate, and the parameters used in HJC concrete model are determined. A scenario of a 12000 DWT bulk cargo collision with a bridge pier is simulated by the software of LS-DYNA, and the time history of ship collision force and the damage of the bridge pier are presented. The results show that the peak value of ship collision force decreases remarkably due to the failure of concrete. Damage characteristic of concrete should be taken into account to achieve objective result in the simulation of ship collision with thin-wall bridge pier.

Shell-spring-contact model for shield tunnel segmental lining analysis and its application

Abstract: Considering the stress release around excavation, the shell-spring-contact calculation model of stratum-structure mode is presented so as to analyze the 3D member forces of the segmental linings of shield tunnel. With the application of FEM, the model employs several types of elements, such as thick shell, shear spring, rotational spring, compression spring, contact and solid elements, and concerns with the extrusion between segments in the joints, the stiffness contribution of joints, the cooperation between segments and surrounding rock, and the approximate insertion angle of Key Segment. Consequently, the complex mechanical behavior of the segmental linings can be effectively simulated by applying the model.

Experiments on saturated concrete under different splitting tensile rate and mechanism on strength change

Abstract: The tensile strengths of saturated and dry concrete under different loading rates were studied by splitting tensile tests. The experimental results show that the tensile strength of saturated concrete was lower than that of the dry concrete under low loading rate but was larger under high loading rate. The comparison between dry and saturated concretes indicates that the free water in the pores and cracks affects the mechanical properties of concrete. The mechanisms of these changes are analyzed in terms of the acting modes of pore water on the saturated concrete under different loading rates. The free water in the cracks acts as a wedge, which decreases the strength of saturated concrete under quasi-static loading, but it acts as opposite force, which increases the strength of saturated concrete under high loading rate according to the Stefan effect in physics. The fracture mechanics based on these mechanisms are used to discuss these changes and the results show that these mechanisms can explain the mechanical properties of saturated concrete well.

First order reliability method based on linearized nataf transformation

Abstract: The principle of iso-probability marginal transformation was firstly introduced, and then, it was proven that the usual Rackwitz-Fiessler transformation is the first order approximation of the iso-probability mar- ginal transformation The extended Rackwitz-Fiessler transformation was developed through the combination of the equivalent normalization principle and linearized transformation, and its defects were also pointed out Noting that Nataf transformation is nonlinear for non-normal variables in nature, so a linearized Nataf transformation has been put forward Furthermore, a new FORM method based on the proposed linearized Nataf transformation and iHLRF algorithm is proposed Finally, the computing results of a numerical example are analyzed and compared between Nataf transformation’s and linearized Nataf transformation’s and extended Rackwitz-Fiessler transfor- mation’s, respectively The example shows that the results of structural reliability analysis based on linearized Nataf transformation convergence the ones resusting from Nataf transformation, while there are errors in the re- sults of extended Rackwitz-Fiessler transformation by comparing with the exact ones

A 1d time-domain method for in-plane wave motion of free field in layered media

Abstract: A 1D finite element method in time domain is developed, which is used to calculate the in-plane wave motion of free field in elastic layered semispace by oblique seismic incidence First, the layered semispace is discretized virtually according to the propagation characteristic of elastic wave Then, the finite element method with lumped mass and the central difference method are combined together to establish the 2D wave motion equations On the basis of the discretization principle and by the advantage of the explicit finite element method, the 2D wave motion equations can be transformed into 1D equations By solving the 1D equations, the displacement of nodes in one vertical line can be obtained Finally, the wave motions of the whole free field are determined on the basis of the characteristic of traveling wave As an example, P-wave is assumed as the incident wave Theoretical analysis and numerical results demonstrate that the proposed method possesses high accuracy and good stability

Non-stationary random seismic analysis of long-span spatial structures under multi-support and multi-dimensional earthquake excitations

Abstract: The non-stationary random seismic analysis of long-span spatial structures under multi-support excitations of three-dimensional orthogonal earthquake motion was performed A method for seismic analysis of the multi-support excitations under the three-dimensional non-stationary random earthquake motion was established, and a simplified calculation for the long-span spatial structures was carried out with the wave-front method The seismic responses of the roof structure of the Tianjin Olympic Center Stadium subject to the uniform excitation, the traveling-wave excitation, and the multi-support excitation considering the partial coherence effect and the seismic nonstationarity, under one-dimensional and three-dimensional random earthquake motions were numerically simulated The results show that the axial forces of the control bars may be increased by about 30% when considering the three-dimensional effect of earthquake motion, or changed by about 10% when considering the partial coherence, or increased by about 15% when considering the three-dimensional earthquake excitation, or decreased by about 35% when considering the nonstationarity of earthquake motion A conclusion was given that the multi-support and multi-dimensional earthquake excitations must be considered in the seismic analysis of the long-span spatial structures, and the seismic design is secure when the nonstationarity of earthquake motion isnot considered

Design of double-axis elliptical flexure hinges

Abstract: The compliance equations for double-axis elliptical flexure hinges are presented utilizing matrix theory, energy method, Castigliano’s displacement theorem and calculus knowledge, the analytical model predictions were confirmed by finite element analysis. The practical application and the analysis result of FE software ANSYS show that the compliance equations for double-axis elliptical flexure hinges are correct and can be used in practical design.

Calculation of the thermal stresses in concrete pavements at early ages

Abstract: An analytical solution of thermal stress in concrete pavement subjected to a nonlinear temperature distribution is presented.In the analytical model,the temperature distribution along the slab depth is divided into three components,an average temperature component,a linear temperature component and a nonlinear temperature component.The thermal stresses resulted by each temperature component are calculated separately.The total thermal stress is obtained by superimposing the three stress components together.In addition,the effect of concrete creep on the thermal stresses is taking into account in the calculation.The computing results of the model show that as a result of the nonlinear characteristic of the temperature distribution,the thermal stress is nonlinearly distributed along the slab depth.The maximum stress may occur at any location along the slab depth,which is governed by the sum of three stress components.Concrete creep significantly reduces the thermal stress.

An approach to numerical simulation for external source wave motion

Abstract: The wave field of artificial boundary is separated into free field without local topography effect and scattering field induced by local topography effect. In infinite ground, the influence of wave propagation on artificial boundary is realized by transforming displacement field as well as velocity field to stress field which are imposed on the boundary nodes, and scattering wave field is modeled as a far field approximately solution introduced by Du Xiuli. On this basis, the time domain numerical simulation of local topography effect under obliquely incident transient plane wave can be performed in virtue of general FEM software. Thusly, an efficient method to calculate external source wave motion such as local topography effect in two or three dimension irregular, uneven field and soil structure dynamic interaction is developed. The advantage of the proposed method will simplify the analysis of nearfield wave with strong solver and pre-post process of general finite element software. In fact, due to the strong calculation function of general FEM software, the method can easily applied to the analysis of uneven and nonlinear problems.

Study on influence of hollow ratio to bearing capacity of h-cfst

Abstract: The influence of sectional parameters to ultimate bearing capacity of hollow-concrete-filled steel tube (H-CFST) under axial loading is investigated through 55 test specimens,and the influence of hollow ratio to stress-strain relations is analyzed. The experimental results show that ultimate bearing capacity of circular section specimens is higher than that of other section specimens, the results also show that the higher the hollow ratio is, the more flat the descending segments of stress-strain curves is, and the shorter the elastic-plastic stage is, the lower the ultimate bearing capacity is. This implies that the continuity of H-CFST is sound with the change of sectional parameters. Contrasting with the experimental results, formula used to calculate composite standard compressive strength is proved to be correct.

Research in form-finding of suspension structures based on newton-raphson iteration and zero order optimization arithmetic

Abstract: To find the form of suspension cables precisely, the Newton-Raphson iteration is used and the zero order optimization arithmetic is also dedicated to control the procedure. Meanwhile, the factors that influence the precision of solution are analyzed. Based on this, the form-finding of Runyang suspension bridge under dead load is taken as an example, and the results are compared with those of membrane theory and data from field test. The results show that through the control of the coordinate of the predefined points, the more precise solution can be achieved. This method can be used in form-finding and construction control on main cables of suspension bridge and other long-span cable structures.

Analysis of time-dependent reliability of rc highway bridges considering chloride attack and concrete carbonation

Abstract: Based on the results of other researchers on the corrosion rate of tensile reinforcement steel, moment resistance deterioration models of reinforced concrete girder bridges due to steel corrosion induced by chloride attack or concrete carbonation are developed with pitting corrosion being considered for chloride attack and average corrosion being considered for concrete carbonation. A computer program for time- dependent reliability assessment of highway concrete bridges based on Monte Carlo method and statistic regression is also developed. A concrete girder bridge in Beijing area is taken as an example. The results show that the ultimate limit state reliability of the bridge due to chloride attack reduces to the design target reliability at the 30th year or so and the reliability due to concrete carbonation to the value at the 50th year or so. Therefore, the bridge can not work through the presumed working life of 100 years without major repair. The results also show that cracking time of concrete cover induced by corrosion of tensile reinforcement is much earlier than the time when the ultimate limit state reliability reduces to the target value. This is important for bridge inspection/repair schedule.

A damage plastic constitutive model for reinforced concrete and its engineering application

Abstract: A damage-plastic constitutive model for reinforced concrete is proposed by applying a Representative Volume Element (RVE). Assumptions of strain harmony and equivalent strength are adopted. The property of reinforcement within the RVE is modeled by defining hardening-softening law of the stress-strain curve of the Representative Volume Element. And the Representative Volume Element is taken as a uniform continuum. The model proposed here has enriched the library of models for concrete under tension in ABAQUS software. For the purpose of validation, numerical examples of uniaxial tension and simple-supported beam under bending were presented. Application of the model to the elastoplastic damage analysis of an engineering structure of reinforced concrete under soil pressure and underground water pressure was carried out.

Constitutive model and numerical analysis for the coupled problem of water, temperature and stress fields in the process of soil freeze-thaw

Abstract: According to heat transfer, filtration theory and mechanics of frozen soil, a mathematics model and its control equation were put forward, which is of the coupling problem of temperature field, water field and stress fields By utilizing the program developed by ourselves and the constitutive relation and mathematics mechanics model which we built up, numerical analysis was carried out to obation moisture, temperature and stress fields of frozen roadbed The result agreed with actual temperature field coupled with stress field, moisture field and strain field, and is consistent with the result of predecessors and the test result

Analytical model for rain-wind-induced vibration of three-dimensional continuous stay cable with quasi-moving rivulet

Abstract: Using three-dimensional continuous stay cables as objects, the partial differential equations for stay cables with rain-wind-induced vibration are derived and an analytical model for rain-wind-induced vibration of three-dimensional continuous stay cable is developed. In order to simplify the complex problem, the moving of rivulets is assumed to be sinusoidal by experiences, and rivulet balance position and rivulet moving amplitude are also presumed on the basis of wind tunnel test results. With fixed rivulets on the surface of stay cables, classical galloping is firstly studied. The results show that classical galloping occurs at certain conditions. The influences of velocity, rivulet frequency, rivulet position, wind speed profile and cable damping to rain-wind-induced vibration are particularly investigated. It is found that rain-wind-induced vibration depends deeply on wind velocity, rivulet frequency, rivulet position and cable damping.

Nonlinear helical buckling of drillstring in inclined wellbore

Abstract: Based on the principle of minimum potential energy, the helical buckling of a drillstring is studied, with its top end free circumferentially and lower end hinged. To simplify the problem from contact nonlinear to geometric nonlinear, cylindrical coordinate system is used in the derivations. Using Rayleigh-Ritz method, the non-dimensional nonlinear integral equations are developed for determining the helical buckling loads corresponding to a certain lateral load. Practical examples are analyzed with the help of symbolic computational software Maple 10. It is found that the numerical results agree with existing experimental data. It implies that the helical buckling of a drillstring is a nonlinear problem and the established nonlinear analytical method may be used for analysis of drillstrings in inclined wellbores.

Creep analysis of long span concrete-filled steel tubular arch bridges

Abstract: Based on some reasonable hypotheses and the stress-strain relationship of concrete obtained by the “adjusting valid modulus depending on age” method, a compact formula to calculate the conversion elastic modulus of the core concrete is presented, which can consider both the influences of creep and the interaction between steel and concrete. The application of the formula to creep analysis for the concrete-filled steel tubular (CFST) arch bridge can simplify the analysis process. At the same time, the method is implemented for creep analysis of a 308-meter-span CFST arch bridge by the FEM software ANSYS. By comparison, the proposed method is proved to be feasible and relatively precise. At the same time, the creep effect on structures is compared regarding the two different creep coefficient models recommended by the new and old bridge design codes.

Seismic wave passage effect's influences on longitudinal seismic pounding response for continuous girder bridges

Abstract: In multiple continuous girders with piers of the same height,although natural periods of adjacent segments at expansion joints are the same,pounding between adjacent segments at expansion joints can be induced by seismic wave passage effect.In this paper,the seismic pounding responses between adjacent girder decks at expansion joints of continuous girder bridges due to seismic wave passage effect were investigated by the nonlinear time history analysis method.In analysis,contact element is used to model pounding and damper is used to describe the energy dissipation during collision.The results show that seismic wave propagation effect can cause relative displacements between adjacent bridge decks enough large to induce impact at expansion joints.The magnitude of pounding force depends on apparent velocity of seismic wave.Pounding can amplify relative displacements between adjacent bridge decks or piers and decks,which may even cause bridge decks to drop from piers and collapse.Therefore,influences of seismic wave passage effect on longitudinal seismic pounding response should be emphasized in seismic design and assessment for continuous girder bridges.

Response of multi-layered structure due to impact load using material point method

Abstract: The multi-layered structure with porous materials is often applied in the blast/impact-resistant structures The compound structure that porous aluminum is added to the middle of two steel plates can absorbs impact energy and relieves deformation of materials To explore theory on the analysis of blast/impact-resistant structures, the material point method and nonlinear constitutive model are adopted to simulate large deformation and fracture of materials under impact load MPM takes advantage of both Eurlerian and Lagrangian methods, and the material points is independent of mesh Therefore, remeshing of FEM can be avoided, and coupling condition is automatically satisfied on interface of multiple materials In this paper, a robust MPM simulation tool is developed and used to solve the response of compound blast/impact-resistant structure under explosion and impact load

Simulation study of stochastic fluctuating wind field on large span elatricity transmission tower-line system

Abstract: To perform a wind-induced response analysis for large span electricity transmission tower-line systems in time domain, considering various influences such as tower-line distribution, variation of mean velocity profile, power spectral energy and cross-spectral coherence in relation with structural style and power spectral characteristics of stochastic fluctuating wind field, a simplified scheme which can transform a multivariable 3D fluctuating wind field ( n ? V ? 3D) acting on large span transmission tower-line systems into a multivariable 1D stochastic wind field ( n ? V ? 1D) has been presented Based on harmonic wave superimposing method and appropriate modified spectral decomposition, time marching generating method of fluctuating wind has been developed, which is suitable to analyze the wind-induced response of transmission tower-line system in combination with the finite element method Finally, taking a real case as example, the time-marching curves were simulated The results from statistical analysis of simulated data and comparison with target spectrum demonstrated the validity of the presented method and the applicability of simulated wind time-marching for wind-induced response analysis

Springback of sheet metal after plane strain stretch-bending

Abstract: For the springback problem of sheet metal stretch-bending, a mathematical model was proposed based on Hill’s yielding criterion, exponential hardening and plane strain assumption. The model was validated by a stretch-bending example. The effects of stretching force per unit width, die profile radius, friction and anisotropy on the springback were studied. The results from the proposed model indicate that only if the shift distance of neutral surface exceeds one-fourth of sheet thickness, the increase of stretching force can control the springback effectively. Furthermore, the larger the bending radius, the more effective the increase of binder force in controling the sheet springback. However, the stretching force cannot increase without limit. Its calculation criterion is that the effective strain at the outer sheet layer is not greater than the material limit strain. It also shows that with the increase of stretching force, the friction has much larger influence on the sheet springback. Besides, the anisotropy also has effect on the sheet springback of stretch-bending. Comparison with FE simulation results shows that the predicted results by the mathematical model consist well with those by FEM.

Unstable criterion of rock specimen subjected to shear failure in uniaxial compression based on energy principle

Abstract: Stability of the system(rock specimen in uniaxial compression)composed of inclined shear band and elastic rock outside the band was analyzed in terms of energy principle.Axial deformation of the specimen is decomposed into two parts.One is due to the compression of elastic rock;the other is induced by the shear slip along shear band.The latter is related to the relative shear deformation between the top and base of shear band through a simple geometrical relation.Total potential energy is composed of elastic and dissipated potential energies in shear band as well as work done by external force.Potential energies in the band depend on the volume of shear band.The thickness of the band is determined by gradient-dependent plasticity.The first-order derivative equal to zero of total potential energy with respect to the relative shear deformation of shear band leads to the equilibrium condition of elastic rock.The second-order derivative less than zero of total potential energy with respect to the relative shear deformation of shear band results in the unstable criterion of the system.The present unstable criterion can reflect the influences of the constitutive parameters of rock in elastic and strain-softening stages,the volumes of elastic rock and shear band as well as the structural form on the stability of the system.The present analytical unstable criterion is strict and accurate,which is a generalization from existing analytical unstable criterion by Wang et al.