With the development of modern high speed and heavy haul transportation, new challenges are confronted by railway bridges and highway bridges. Highstrength concrete and steel fiber reinforced concrete, which have ex...With the development of modern high speed and heavy haul transportation, new challenges are confronted by railway bridges and highway bridges. Highstrength concrete and steel fiber reinforced concrete, which have excellent mechanical properties, have called more concern, and have wideranging application in railroad and highway bridge. The dissertation focuses on numerical simulation of the nonlinear structural behavior of prestressed highstrength concrete boxsection continuous beam. It consists of: (1) The constitutive model of concrete based on microplane theory is studied. Microplane theory, a theory based on the micromechanics, has been developed in the last ten years. On the basis of the author′s research fruit, some modifications about the effect of the principal stress combination on the shear stiffness of the microplane and loading/unloading criterion of the microplane are proposed. In Prof. Bazant′ paper, the confining stress is used to reflect the effect of the principal stress combination on the shear stiffness of the microplane. In this dissertation, the author adopts the direction cosine between vector and vector to describe the effect of the principal stress combination on the shear stiffness of the microplane. New loading/unloading criterion of the microplane is developed. The new criterion includes all cases that may happen in loading or unloading, and effectively overcomes the drawbacks that the unloading stress may exceed the limit stress of microplane. On the basis of those researches, the constitutive model of concrete is established. To verify the accuracy and efficiency of the model, several classical tests are studied and excellent agreements are obtained. (2) The basic mechanical behaviors of highstrength concrete and steel fiber reinforced concrete are studied. The compressive strength, tensional strength, elastic module, axial stress and strain relationship, the failure criterion under multiple axial stress, section ductility and the creepage of highstrength concrete, along with the compressive strength, tensional strength, elastic module, axial compressive stress and strain relationship, axial tensile stress and strain relationship and the failure criterion under biaxial stresses of steel fiber reinforced concrete are reviewed. The failure criterion of highstrength concrete is established with Ottosen′s criterion. On the basis of those researches, the triaxial stressstrain relationship including strain softening and the failure criterion of highstrength concrete and steel fiber reinforced under biaxial stresses are depicted with the microplane theory. (3) The fournode sixDOF degeneration shell element is developed. The establishment process of the fournode sixDOF degeneration shell element is introduced in detail, and the penalty stiffness matrix to deal with the tensionalrotation degreeoffreedom is derived. The elastic linear analysis program is completed on this base, and lots of examples are analyzed. (4) The fundamental idea and realization means of arclength method are introduced in detail. Several problems including the dealing of the tangential stiffness matrix near the limit point and the choice of the first incremental load factor of every iteration step are pointed out, and some suggestions are proposed. To overcome the solution difficulty caused by the illposedness of the tangential stiffness matrix near the limit point, the tangential stiffness matrix is modified. The first incremental load factor of every iteration step is chosen according to the positive definition or negative definition of the tangential stiffness matrix. The geometrically nonlinear analysis formula of shell structure is derived. Then, the arclength method is applied to the geometrically nonlinear stability analysis of shell structure, and good agreement with the results of other scholars is obtained. (5) The arclength method is applied to the material nonlinear analysis of concrete structure. The展开更多
文摘With the development of modern high speed and heavy haul transportation, new challenges are confronted by railway bridges and highway bridges. Highstrength concrete and steel fiber reinforced concrete, which have excellent mechanical properties, have called more concern, and have wideranging application in railroad and highway bridge. The dissertation focuses on numerical simulation of the nonlinear structural behavior of prestressed highstrength concrete boxsection continuous beam. It consists of: (1) The constitutive model of concrete based on microplane theory is studied. Microplane theory, a theory based on the micromechanics, has been developed in the last ten years. On the basis of the author′s research fruit, some modifications about the effect of the principal stress combination on the shear stiffness of the microplane and loading/unloading criterion of the microplane are proposed. In Prof. Bazant′ paper, the confining stress is used to reflect the effect of the principal stress combination on the shear stiffness of the microplane. In this dissertation, the author adopts the direction cosine between vector and vector to describe the effect of the principal stress combination on the shear stiffness of the microplane. New loading/unloading criterion of the microplane is developed. The new criterion includes all cases that may happen in loading or unloading, and effectively overcomes the drawbacks that the unloading stress may exceed the limit stress of microplane. On the basis of those researches, the constitutive model of concrete is established. To verify the accuracy and efficiency of the model, several classical tests are studied and excellent agreements are obtained. (2) The basic mechanical behaviors of highstrength concrete and steel fiber reinforced concrete are studied. The compressive strength, tensional strength, elastic module, axial stress and strain relationship, the failure criterion under multiple axial stress, section ductility and the creepage of highstrength concrete, along with the compressive strength, tensional strength, elastic module, axial compressive stress and strain relationship, axial tensile stress and strain relationship and the failure criterion under biaxial stresses of steel fiber reinforced concrete are reviewed. The failure criterion of highstrength concrete is established with Ottosen′s criterion. On the basis of those researches, the triaxial stressstrain relationship including strain softening and the failure criterion of highstrength concrete and steel fiber reinforced under biaxial stresses are depicted with the microplane theory. (3) The fournode sixDOF degeneration shell element is developed. The establishment process of the fournode sixDOF degeneration shell element is introduced in detail, and the penalty stiffness matrix to deal with the tensionalrotation degreeoffreedom is derived. The elastic linear analysis program is completed on this base, and lots of examples are analyzed. (4) The fundamental idea and realization means of arclength method are introduced in detail. Several problems including the dealing of the tangential stiffness matrix near the limit point and the choice of the first incremental load factor of every iteration step are pointed out, and some suggestions are proposed. To overcome the solution difficulty caused by the illposedness of the tangential stiffness matrix near the limit point, the tangential stiffness matrix is modified. The first incremental load factor of every iteration step is chosen according to the positive definition or negative definition of the tangential stiffness matrix. The geometrically nonlinear analysis formula of shell structure is derived. Then, the arclength method is applied to the geometrically nonlinear stability analysis of shell structure, and good agreement with the results of other scholars is obtained. (5) The arclength method is applied to the material nonlinear analysis of concrete structure. The
