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Research on nonlinear constitutive relationship of permanent deformation in asphalt pavements

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Science China(Physics,Mechanics & Astronomy) 2006年第6期49卷 671-682页

作者： PENG Miaojuan1 & XU Zhihong2.1. Department of civil engineering,{2. university,{2. 2.0072.China 2. School of Transportation engineering,tongji university,shanghai 200092,China 1. Department of civil engineering Shanghai University Shanghai 200072 China 2. School of Transportation engineering Tongji University Shanghai 200092 China

To predict correctly the rut depths in asphalt pavements,a new nonlinear viscoelastic-elastoplastic constitutive model of permanent deformation in asphalt pave-ments is presented. The model combines a generalized Maxwell model with an elasto-plastic one. Then from the creep theory,the linear and nonlinear constitutive equations of the generalized Maxwell model are obtained. From the nonlinear finite element method for the rutting of the asphalt pavement,the rut depths of 4 asphalt-aggregate mixtures are obtained. And the results are compared with the ones from the finite element method by SHRP and the experiments by SWK/UN. The results in this paper are better than the ones by SHRP,and agree with the ones of the experiment by SWK/UN. This shows that the nonlinear viscoelastic-elastoplastic constitutive model,which is presented in this paper for the rutting of the asphalt pavement,is effective. The properties,such as nonlinear elastic-ity,plasticity,viscoelasticity and nonlinear viscoelasticity,which affect the rutting of an asphalt pavement,can be shown in the model. And the characteristics of the permanent deformation of the asphalt pavement can be presented entirely in the model.

关键词： asphalt pavement,permanent deformation,nonlinear viscoelastic-elastoplastic constitutive relationship,generalized Maxwell model,creep compliance.

Homogenization-based multi-scale damage theory

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Science China(Physics,Mechanics & Astronomy) 2010年第4期53卷 690-698页

作者： LI Jie 1,2.& REN XiaoDan 1 1 School of civil engineering, {2., shanghai 200092, China 2.State Key Laboratory of Disaster Reduction in civil engineering, shanghai 200092, China 1. School of civil engineering Tongji University Shanghai 200092 China2. State Key Laboratory of Disaster Reduction in Civil Engineering Shanghai 200092 China

The research of modern mechanics reveals that the damage and failure of structures should be considered on different scales. The present paper is dedicated to establishing the multi-scale damage theory for the nonlinear structural analysis. Starting from the asymptotic expansion based homogenization theory, the multi-scale energy integration is proposed to bridge the gap between the micro and macro scales. By recalling the Helmholtz free energy based damage definition, the damage variable is represented by the multi-scale energy integration. Hence the damage evolution could be numerically simulated on the basis of the unit cell analysis rather than the experimental data identification. Finally the framework of the multi-scale damage theory is established by transforming the multi-scale damage evolution into the conventional continuum damage mechanics. The agree- ment between the simulated results and the benchmark results indicates the validity and effectiveness of the proposed theory.

关键词： Multi-scale damage representation asymptotic method constitutive model numerical simulation

Fracture analysis of a functionally graded interfacial zone between two dissimilar homogeneous materials

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Science China(Physics,Mechanics & Astronomy) 2006年第5期49卷 540-552页

作者： CHENG Zhanqi1,2.& ZHONG Zheng1 1. School of Aerospace engineering and Applied mechanics, tongji university, {2., China 2. college of civil engineering, Zhengzhou university, Zhengzhou 450002. China 1. School of Aerospace engineering and Applied mechanics Tongji University Shanghai 200092 China 2. college of civil {2. Zhengzhou University Zhengzhou 450002 China

In this paper the plane elasticity problem for a functionally graded interfacial zone containing a crack between two dissimilar homogeneous materials has been considered. It is assumed that in the interfacial zone the reciprocal of the shear modulus is a linear function of the coordinate, while Possion’s ratio keeps constant. By utilizing the Fourier transformation technique and the transfer matrix method, the mixed boundary problem is reduced to a system of singular integral equations that are solved numerically. The influences of the geometric parameters and the graded parameter on the stress intensity factors are investigated. The numerical results show that the graded parameters, the thickness of interfacial zone, the crack size and location have significant effects on the stress intensity factors.

关键词： functionally graded material interfacial zone fracture stress intensity factor

Macro-micromechanical approaches for non-coaxiality of coarse grained soils

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中国科学：技术科学英文版 2011年第S1期54卷 147-153页

作者： QIAN JianGu 1,2.HUANG MaoSong 1,2.& SUN HaiZhong 1,2.1 Key Laboratory of Geotechnical and Underground engineering of Ministry of Education,tongji university,{2.,China 2.Department of Geotechnical engineering,tongji university,{2.,China 1. Key Laboratory of Geotechnical and Underground engineering of Ministry of Education Tongji University Shanghai 200092 China2. Department of Geotechnical Engineering Tongji University Shanghai 200092 China

For coarse grained soils,their principal stress directions may change when the water level of embankment dam varies *** this loading case,the principal directions of stress and strain rate will become *** an effort to model non-coaxial behavior,a modified three-dimensional non-coaxial model is developed in the context of vertex yield(tangent plasticity) *** Element Method(PFC) incorporating user-defined interparticle contact models is also employed to gain an insight into microscopic mechanism of *** analysis focuses on non-coaxial behaviors under simple shear *** has been shown that the proposed non-coaxial model gives good predictions for non-coaxiality with reference to microscopic observations while the classical coaxial model fails to simulate the non-coaxial *** general,non-coaxiality as a result of the rotation of principal stress,is large at a small shear strain,and inclined to become negligible with increasing shear *** coarse grained soils,their non-coaxiality tends to largely depend on the initial normal pressure,where a larger degree of non-coaxiality can be observed at a higher pressure.

关键词： coarse grained soils non-coaxiality particle flow code simple shear

Two-dimensional thermoelasticity solution for functionally graded thick beams

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Science China(Physics,Mechanics & Astronomy) 2006年第4期49卷 451-460页

作者： Lü Chaofeng1, CHEN Weiqiu1 & ZHONG Zheng2.1. Department of civil engineering, Zhejiang {2., Hangzhou 31002., China 2. Key Laboratory of Solid Mechanics of Ministry of Education, School of Aerospace engineering and Ap- plied Mechanics, tongji university, shanghai 200092, China Department of civil engineering Zhejiang University Hangzhou 310027 China Key Laboratory of Solid Mechanics of Ministry of Education School of Aerospace Engineering Applied Mechanics Tongji University Shanghai 200092 China

Two-dimensional thermoelasticity analysis of functionally graded thick beams is presented using the state space method coupled with the technique of differential quadrature. Material properties vary continuously and smoothly through the beam thickness, leading to variable coefficients in the state equation derived from the elasticity equations. Approximate laminate model is employed to translate the state equation into the one with constant coefficients in each layer. To avoid numerical instability, joint coupling matrices are introduced according to the continuity conditions at interfaces in the approximate model. The differential quadrature procedure is applied to discretizing the beam in the axial direction to make easy the treatment of arbitrary end conditions. A simply-supported beam with exponentially varying material properties is considered to validate the present method. Numerical examples are performed to investigate the influences of relative parameters.

关键词： state equation differential quadrature approximate laminate model joint coupling matrices thermal stresses.

Wind-resistant studies on tall buildings and structures

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Science China(Technological Sciences) 2010年第10期53卷 2630-2646页

作者： GU Ming State Key Laboratory of Disaster Reduction in civil engineering, {2., shanghai 200092, China 1. State Key Laboratory of Disaster Reduction in civil engineering Tongji University Shanghai 200092 China

This paper introduces some aspects of wind-resistant studies of our research team on tall buildings and structures. Wind tunnel tests were carried out on 2. typical tall building models by using wind pressure scanning and HFFB techniques. The characteristics of wind pressures and forces acting on these buildings were analyzed. Some results have been adopted in a shanghai code for structural design of steel tall buildings. Interference effects on wind forces and wind pressures among two and three tall buildings were experimentally investigated with about 10000 testing conditions. Regression analyses of the interference factors under different parameter conditions were made and the main regression formulas are presented. Theoretical study on equivalent static wind loads of tall buildings and structures are then introduced. Especially,a new concept of "mode coupling factor" and a modified SRSS method for wind response and equivalent static wind load of complicated tall buildings and structures with consideration of multi mode contributions and their coupling effects are presented. Finally,practical applications of wind-resistant studies on tall building and structures,taking the Guangzhou New TV Tower as an example,are presented.

关键词： tall building and structure wind pressure and force interference effect equivalent static wind load application

Influence of Additives on the Formation of Electrodeposits in the Concrete Cracks

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Journal of Wuhan university of Technology(Materials Science) 2011年第2期26卷 367-371页

作者：储洪强 Key Laboratory of Advanced civil engineering Materials Ministry of EducationTongji University college of Mechanics and Materials Hohai University

The electrodeposition method for rehabilitation of the cracked reinforced concrete,based on the electrochemical technique,was presented *** aim of this study was to evaluate the influence of additive on the formation of electrodeposits in the concrete *** mortar specimens of size 40 mm×40 mm×160 mm were immersed in electrolyte solutions（ZnSO4,MgSO4）,and a constant current was applied between the reinforced steel and the external electrode for 15 *** of surface coating,rate of crack closure and rate of crack filling depth were measured and the appearance of electrodeposits in the cracks was *** experimental results demonstrate that,under the experimental conditions,rate of surface coating and crack filling depth increase,while rate of crack closure decreases as the percengtage of additive *** addition,the electrodeposits become more denser and the microstructure varies with additive content,while the compositions of electrodeposits do not change.

关键词： repair of cracks additive formation microstructure

Recent research and applications of GPS based technology for bridge health monitoring

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Science China(Technological Sciences) 2010年第10期53卷 2597-2610页

作者： YI TingHua1,2. LI HongNan1 & GU Ming2.1 Faculty of Infrastructure engineering, Dalian university of Technology, Dalian 11602., China 2.State Key Laboratory for Disaster Reduction in {2. engineering, tongji university, shanghai 200092, China 1. Faculty of Infrastructure engineering Dalian University of Technology Dalian 116023 China2. State Key Laboratory for Disaster Reduction in Civil Engineering Tongji University Shanghai 200092 China

Today,long-span bridges are being designed to be more flexible and to resist extensive impacts from changes in temperature,severe wind gusts and earthquake tremors. Structural responses (especially displacement) of bridge structures are becoming increasingly important for the finite element (FE) modal updating,structural response prediction and safety evaluation. Methods of global displacement sensing were developed for these needs. This paper presents an overview of current research and development activities in the field of bridge health monitoring using the global positioning system (GPS). The GPS monitoring technology and its accuracy assessment method are also briefly described. Finally,existing problems and promising research efforts in the GPS based bridge health monitoring are discussed.

关键词： global positioning system (GPS) structural health monitoring (SHM) bridge measurement

Boundary element-free method for elastodynamics

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Science China(Physics,Mechanics & Astronomy) 2005年第6期48卷 641-657页

作者： CHENG Yumin1 & PENG Miaojuan2.1. shanghai Institute of Applied Mathematics and Mechanics, shanghai {2., shanghai 2.0072. China 2. Department of civil engineering, shanghai {2., shanghai 2.0072. China 1. shanghai Institute of Applied Mathematics and Mechanics Shanghai University 200072 Shanghai China 2. Department of civil engineering Shanghai University 200072 Shanghai China

The moving least-square approximation is discussed first. Sometimes the method can form an ill-conditioned equation system, and thus the solution cannot be obtained correctly. A Hilbert space is presented on which an orthogonal function system mixed a weight function is defined. Next the improved moving least-square approximation is discussed in detail. The improved method has higher computational efficiency and precision than the old method, and cannot form an ill-conditioned equation system. A boundary element-free method (BEFM) for elastodynamics problems is presented by combining the boundary integral equation method for elastodynamics and the improved moving least-square approximation. The boundary element-free method is a meshless method of boundary integral equation and is a direct numerical method compared with others, in which the basic unknowns are the real solutions of the nodal variables and the boundary conditions can be applied easily. The boundary element-free method has a higher computational efficiency and precision. In addition, the numerical procedure of the boundary element-free method for elastodynamics problems is presented in this paper. Finally, some numerical examples are given.

关键词： moving least-square approximation, improved moving least-square approximation, elastodynamics, boundary integral equation, meshless method, boundary element-free method, Fourier eigen transform.