2003 Vol. 20 No. 3
2003, 20(3): 1-5.
Abstract：
A submerged body, which interacts with the surrounding water, is essentially one of the Fluid-Structure Interaction (FSI) problems. The displacement-pressure pattern, in which the structure and the fluid are described by the displacement and the pressure respectively, is used to model the submerged body. A large un-symmetric equation is introduced as a result of this pattern and the finite element method (FEM). To get the dynamic characteristics of the submerged body, the Arnoldi method is adopted to solve for the eigenvalues of such a large unsymmetric equation. In addition, the shift-frequency technique with a special iteration pattern is contrived to overcome the zero frequency problem resulting from the rigid body抯 motion. Finally, a numerical example, in which there is a long cylinder with two cones at both ends, is given out to validate the methods in this paper.
A submerged body, which interacts with the surrounding water, is essentially one of the Fluid-Structure Interaction (FSI) problems. The displacement-pressure pattern, in which the structure and the fluid are described by the displacement and the pressure respectively, is used to model the submerged body. A large un-symmetric equation is introduced as a result of this pattern and the finite element method (FEM). To get the dynamic characteristics of the submerged body, the Arnoldi method is adopted to solve for the eigenvalues of such a large unsymmetric equation. In addition, the shift-frequency technique with a special iteration pattern is contrived to overcome the zero frequency problem resulting from the rigid body抯 motion. Finally, a numerical example, in which there is a long cylinder with two cones at both ends, is given out to validate the methods in this paper.
Abstract：
Based on the wave propagation theory of the free field in soil under the conventional weapon burst circumstances, the analysis of the punching failure mechanism of slab-column connection is performed using the structure medium interaction theory and the twin shear strength theory. The resistance model of structure and the eqution of motion for the structure are established. The calculated results are in good agreement with the experimental ones.
Based on the wave propagation theory of the free field in soil under the conventional weapon burst circumstances, the analysis of the punching failure mechanism of slab-column connection is performed using the structure medium interaction theory and the twin shear strength theory. The resistance model of structure and the eqution of motion for the structure are established. The calculated results are in good agreement with the experimental ones.
2003, 20(3): 13-18,2.
Abstract：
Based on the lower bound theorem of shakedown analysis, a solution procedure for shakedown analysis of three-dimensional elastoplastic structures has been established using conventional boundary element method (BEM). The elastic stress field for lower bound shakedown analysis is computed directly by 3-D BEM. The self-equilibrium stress field is constructed by the linear combination of several self-equilibrium stress field is constructed by the linear combination of several self-equilibrium“basis vectors”which can be computed by elastic-plastic incremental iteration of 3-D BEM analysis. The lower bound shakedown analysis problem is finally reduced to a series of nonlinear programming sub-problems with relatively few optimal variables. The complex method is used to solve effectively the nonlinear programming sub-problems. Numerical results show the effectiveness of the present solution algorithm.
Based on the lower bound theorem of shakedown analysis, a solution procedure for shakedown analysis of three-dimensional elastoplastic structures has been established using conventional boundary element method (BEM). The elastic stress field for lower bound shakedown analysis is computed directly by 3-D BEM. The self-equilibrium stress field is constructed by the linear combination of several self-equilibrium stress field is constructed by the linear combination of several self-equilibrium“basis vectors”which can be computed by elastic-plastic incremental iteration of 3-D BEM analysis. The lower bound shakedown analysis problem is finally reduced to a series of nonlinear programming sub-problems with relatively few optimal variables. The complex method is used to solve effectively the nonlinear programming sub-problems. Numerical results show the effectiveness of the present solution algorithm.
2003, 20(3): 19-25.
Abstract：
In this paper, the lattice model and statistical distributions are used to represent the initial heterogeneous distribution of material properties. Equations of the reduplicate multi-sub-region (RMSR) boundary element method are established for the lattice model of 2-D heterogeneous materials. Each row of sub-regions in the lattice are integrated into a super-sub-region and the transfer matrix of sub-region method (TMSRM) is employed to solve the super-sub-region placed in chain. Since the memory demand of the TMSRM is only a little more than that of solving one super-sub-region and the coefficient matrices are only generated just once in RMSR, the capacity and efficiency can be increased significantly. As an example of application of the above-proposed methods, the failure process of 2-D heterogeneous materials is numerically simulated. With the RMSR and TMSRM, the continuous distribution of stress with high accuracy is expected, which provides a good foundation for further research on the initiation, propagation of crack and failure process in heterogeneous materials.
In this paper, the lattice model and statistical distributions are used to represent the initial heterogeneous distribution of material properties. Equations of the reduplicate multi-sub-region (RMSR) boundary element method are established for the lattice model of 2-D heterogeneous materials. Each row of sub-regions in the lattice are integrated into a super-sub-region and the transfer matrix of sub-region method (TMSRM) is employed to solve the super-sub-region placed in chain. Since the memory demand of the TMSRM is only a little more than that of solving one super-sub-region and the coefficient matrices are only generated just once in RMSR, the capacity and efficiency can be increased significantly. As an example of application of the above-proposed methods, the failure process of 2-D heterogeneous materials is numerically simulated. With the RMSR and TMSRM, the continuous distribution of stress with high accuracy is expected, which provides a good foundation for further research on the initiation, propagation of crack and failure process in heterogeneous materials.
Abstract：
Taking cable-stayed Kap Shui Mun Bridge as an example, this paper presents a new damage locating method for cable-stayed bridges based on the combination of cable tension index and neural network technique. By using BP network, damage localization for 12 potential damage cases are simulated based on a high-precision FE model. Taking cable tension indices as inputs of neural network for both training and testing, damage locations are indicated by the outputs of the network. The outstanding feature of the method is that a good result can be obtained by using only fundamental natural frequencies of a few stayed cables. Because measurement of fundamental natural frequencies of a few stayed cables is much easier than some other damage-oriented measurement, the method has great practical value. The method can be easily used for damage locating of cable suspension bridges.
Taking cable-stayed Kap Shui Mun Bridge as an example, this paper presents a new damage locating method for cable-stayed bridges based on the combination of cable tension index and neural network technique. By using BP network, damage localization for 12 potential damage cases are simulated based on a high-precision FE model. Taking cable tension indices as inputs of neural network for both training and testing, damage locations are indicated by the outputs of the network. The outstanding feature of the method is that a good result can be obtained by using only fundamental natural frequencies of a few stayed cables. Because measurement of fundamental natural frequencies of a few stayed cables is much easier than some other damage-oriented measurement, the method has great practical value. The method can be easily used for damage locating of cable suspension bridges.
2003, 20(3): 31-37.
Abstract：
Structural aseismic characteristics can be explained more clearly by dynamic analysis based on energy concept. The concept of structural aseismic design and research information is introduced firstly. From seismic elastic and inelastic time history analysis of lumped mass MDOF structure systems, the storey energy distributions are analyzed in this paper. Energy concentration and its causes are pointed out. Based on the analysis of results, this paper gives the rule of ECS and suggests a method for calculating inelastic displacement of ECS relying on equal cyclic energy criteria of vibration.
Structural aseismic characteristics can be explained more clearly by dynamic analysis based on energy concept. The concept of structural aseismic design and research information is introduced firstly. From seismic elastic and inelastic time history analysis of lumped mass MDOF structure systems, the storey energy distributions are analyzed in this paper. Energy concentration and its causes are pointed out. Based on the analysis of results, this paper gives the rule of ECS and suggests a method for calculating inelastic displacement of ECS relying on equal cyclic energy criteria of vibration.
Abstract：
Based on the softened truss model for reinforced concrete, a simplified calculation method is proposed to simulate the whole loading process of high strength reinforced concrete panels in this paper. The calculated results of eight panels using the method are in good agreement with available test data. The new method is simpler than other methods, since it is accomplished from stress evaluation to strain evaluation. The new method can be used in designing the reinforced high strength concrete panels and in checking the resistant capacity of high strength reinforced concrete panels.
Based on the softened truss model for reinforced concrete, a simplified calculation method is proposed to simulate the whole loading process of high strength reinforced concrete panels in this paper. The calculated results of eight panels using the method are in good agreement with available test data. The new method is simpler than other methods, since it is accomplished from stress evaluation to strain evaluation. The new method can be used in designing the reinforced high strength concrete panels and in checking the resistant capacity of high strength reinforced concrete panels.
2003, 20(3): 42-46.
Abstract：
On the basis of the reset integrator model, a stochastic friction model is established. A quantitative mean ratio v for the effect of friction on the motion of rigid body system is introduced. With the manipulator, which consists of three joints and three links and operates in a horizontal plane, the mean ratio v is verified and used for the evaluation of the friction effect in several different parameters by simulation. The relationship between the friction effect on the motion and the parameters, including driving velocity, the kinetic friction coefficient, the friction drop ratio between the static and kinetic friction coefficients, and the joint equivalent spring stiffness, is investigated quantitatively.
On the basis of the reset integrator model, a stochastic friction model is established. A quantitative mean ratio v for the effect of friction on the motion of rigid body system is introduced. With the manipulator, which consists of three joints and three links and operates in a horizontal plane, the mean ratio v is verified and used for the evaluation of the friction effect in several different parameters by simulation. The relationship between the friction effect on the motion and the parameters, including driving velocity, the kinetic friction coefficient, the friction drop ratio between the static and kinetic friction coefficients, and the joint equivalent spring stiffness, is investigated quantitatively.
Abstract：
Recent terrorist activities have rekindled an interest in studying the local damage of reinforced concrete (RC) structures subjected to explosion or impact loads. Scabbing is one of three types of local damage of RC structures. It is also the major factor that influences the resistance of RC structures to the local damage. In this paper, the presently widely-used formulae of the scabbing thickness of RC structures are compared with the test data and analyzed. The application range and the predicting error of each empirical formula is obtained. It is concluded that, the predictions of Bechtel formula and modified BRL formula fit best with the test results. The Bechtel formula can be used to predict critical scabbing thickness, and the modified BRL formula can be used to predict the critical penetration thickness.
Recent terrorist activities have rekindled an interest in studying the local damage of reinforced concrete (RC) structures subjected to explosion or impact loads. Scabbing is one of three types of local damage of RC structures. It is also the major factor that influences the resistance of RC structures to the local damage. In this paper, the presently widely-used formulae of the scabbing thickness of RC structures are compared with the test data and analyzed. The application range and the predicting error of each empirical formula is obtained. It is concluded that, the predictions of Bechtel formula and modified BRL formula fit best with the test results. The Bechtel formula can be used to predict critical scabbing thickness, and the modified BRL formula can be used to predict the critical penetration thickness.
Abstract：
Using the standard three-point bending beam specimens, the precritical crack propagation length caD was evaluated from the maximum load maxP and the corresponding critical crack mouth opening displacement (CMODc) was measured in experiments. A practical analytical method is proposed for determining the stress intensity factor cKI caused by the cohesive force )(xs along the fictitious crack zone, thereby, the double-K fracture parameters iniKIC and unKIC are determined. With this method the double-K fracture parameters iniKIC and unKIC can be easily determined using the measured maxP, CMODc, elastic module E, and tensile strength tf of a concrete material, and the numerical integration can be avoided for the calculation of cKI. Many calculations and analyses show that the newly proposed method is of high accuracy and of significance to draw up the standard testing method for the double-K fracture parameters of concrete.
Using the standard three-point bending beam specimens, the precritical crack propagation length caD was evaluated from the maximum load maxP and the corresponding critical crack mouth opening displacement (CMODc) was measured in experiments. A practical analytical method is proposed for determining the stress intensity factor cKI caused by the cohesive force )(xs along the fictitious crack zone, thereby, the double-K fracture parameters iniKIC and unKIC are determined. With this method the double-K fracture parameters iniKIC and unKIC can be easily determined using the measured maxP, CMODc, elastic module E, and tensile strength tf of a concrete material, and the numerical integration can be avoided for the calculation of cKI. Many calculations and analyses show that the newly proposed method is of high accuracy and of significance to draw up the standard testing method for the double-K fracture parameters of concrete.
2003, 20(3): 62-66.
Abstract：
Although green sand squeeze molding is very popular in casting production, from the point of view of mechanics it is a complicated process which includes material nonlinearity, geometrical nonlinearity, and contact nonlinearity problems. All these cause difficuties in simulating the squeeze moulding process numerically. Nonlinear Finite Element Method is an effective numerical tool to solve these problems. In this paper a commercial software has been used to simulate the stress field of green sand moulding. Results show that the present approach is promissing.
Although green sand squeeze molding is very popular in casting production, from the point of view of mechanics it is a complicated process which includes material nonlinearity, geometrical nonlinearity, and contact nonlinearity problems. All these cause difficuties in simulating the squeeze moulding process numerically. Nonlinear Finite Element Method is an effective numerical tool to solve these problems. In this paper a commercial software has been used to simulate the stress field of green sand moulding. Results show that the present approach is promissing.
Abstract：
The use of prestressing in curved large span bridges results in new problems to analysis and construction. Especially, some problems in construction have to be solved, for example, friction coefficients and curvature change, which would affect significantly the distributing of prestressing in tendons. The available mechanics models are helpless to solve these problems. It is necessary to establish a new model that is applicable to the tension of tendons in curved prestressed large span concrete bridge girders. The model of tension under control given in this paper can deal with the above problems, and has been validated in practical engineering. The results are satisfactory. The model can not only solve the problems of friction coefficients and curvature change in practice but also deal with some uncertainties. Constructions with reference to the model have improved the distributing of prestressing in tendons.
The use of prestressing in curved large span bridges results in new problems to analysis and construction. Especially, some problems in construction have to be solved, for example, friction coefficients and curvature change, which would affect significantly the distributing of prestressing in tendons. The available mechanics models are helpless to solve these problems. It is necessary to establish a new model that is applicable to the tension of tendons in curved prestressed large span concrete bridge girders. The model of tension under control given in this paper can deal with the above problems, and has been validated in practical engineering. The results are satisfactory. The model can not only solve the problems of friction coefficients and curvature change in practice but also deal with some uncertainties. Constructions with reference to the model have improved the distributing of prestressing in tendons.
2003, 20(3): 72-77.
Abstract：
This paper addresses the linear Mohr-Coulomb yield criterion and Drucker-Prager yield criterion, and the relation among the linear Mohr-Coulomb criteria in material mechanics and rock mechanics. The geometrical characteristics of the linear Mohr-Coulomb yield surface and the Drucker-Prager yield surface are described. The linear Mohr-Coulomb criterion is approximated using the Drucker-Prager criterion in three ways and the resultant differences are highlighted. An example is given in which the Drucker-Prager criterion is used to fit the linear Mohr-Coulomb criterion.
This paper addresses the linear Mohr-Coulomb yield criterion and Drucker-Prager yield criterion, and the relation among the linear Mohr-Coulomb criteria in material mechanics and rock mechanics. The geometrical characteristics of the linear Mohr-Coulomb yield surface and the Drucker-Prager yield surface are described. The linear Mohr-Coulomb criterion is approximated using the Drucker-Prager criterion in three ways and the resultant differences are highlighted. An example is given in which the Drucker-Prager criterion is used to fit the linear Mohr-Coulomb criterion.
2003, 20(3): 78-88.
Abstract：
In this paper, single-mode and multi-mode control of the seismic response of multistory structures with MTMD is investigated. The multistory structures are predigested as MDOF systems in series. Response is obtained using the absolute value of transfer function of harmonic response of structure in the frequency domain, which is deduced by means of three different methods. In the first method, the differential equation of structure system with MTMD is given and transformed from time domain into frequency domain. The transfer function in frequency domain is obtained. In the second method, the reaction of MTMD to structure and the earthquake load are taken as input of structure. The transfer function is deduced considering structural mode coupling. In the third method, the transfer function is obtained considering structural mode uncoupling. Inertia mass participation coefficient is presented which elucidates the action mechanism between MTMD and structure. They are illustrated, and compared with the dynamic time history analysis result. For control of multistory structures with MTMD, multi-mode control is superior to single-mode control. For analysis precision, considering modes coupling is superior to doing mode uncoupling. For shearing model, the result with uncoupling meets the engineering demand.
In this paper, single-mode and multi-mode control of the seismic response of multistory structures with MTMD is investigated. The multistory structures are predigested as MDOF systems in series. Response is obtained using the absolute value of transfer function of harmonic response of structure in the frequency domain, which is deduced by means of three different methods. In the first method, the differential equation of structure system with MTMD is given and transformed from time domain into frequency domain. The transfer function in frequency domain is obtained. In the second method, the reaction of MTMD to structure and the earthquake load are taken as input of structure. The transfer function is deduced considering structural mode coupling. In the third method, the transfer function is obtained considering structural mode uncoupling. Inertia mass participation coefficient is presented which elucidates the action mechanism between MTMD and structure. They are illustrated, and compared with the dynamic time history analysis result. For control of multistory structures with MTMD, multi-mode control is superior to single-mode control. For analysis precision, considering modes coupling is superior to doing mode uncoupling. For shearing model, the result with uncoupling meets the engineering demand.
Abstract：
A mathematic model for eveluation of single-layer flat container stress under uniform internal pressure is established. The conformal mapping method is employed and an analytical formula is obtained. Good agreement with numerical solution is achieved in an example provided, validating the present solution. The present work is useful for developing new design theory and optimization method for flat containers.
A mathematic model for eveluation of single-layer flat container stress under uniform internal pressure is established. The conformal mapping method is employed and an analytical formula is obtained. Good agreement with numerical solution is achieved in an example provided, validating the present solution. The present work is useful for developing new design theory and optimization method for flat containers.
Abstract：
Based on the large deformation theory for the extensible elastic beams, the governing equations of post-buckling of a simply supported elastic beam subjected to a distributed tangential follower force along the central axis are established. They consist of a boundary value problem of ordinary differential equations with strong non-linearity, in which seven unknown functions are included and the arc length of the deformed axis is considered as the one of the basic unknown functions. By using shooting method and analytical continuation, the nonlinear boundary-value problem is numerically solved and the equilibrium paths as well as the post-buckling configurations of the deformed beam are obtained. The results show that the features of the equilibrium paths of the beam subjected to a non-conservative load are evidently different from those to a conservative one.
Based on the large deformation theory for the extensible elastic beams, the governing equations of post-buckling of a simply supported elastic beam subjected to a distributed tangential follower force along the central axis are established. They consist of a boundary value problem of ordinary differential equations with strong non-linearity, in which seven unknown functions are included and the arc length of the deformed axis is considered as the one of the basic unknown functions. By using shooting method and analytical continuation, the nonlinear boundary-value problem is numerically solved and the equilibrium paths as well as the post-buckling configurations of the deformed beam are obtained. The results show that the features of the equilibrium paths of the beam subjected to a non-conservative load are evidently different from those to a conservative one.
Abstract：
According to the curved beam theory of Love, the general nonlinear magnetoelastic coupled vibration equations of the end of circular collector ring on turbogenerator's stator are derived. Using Maxwell equations, Poisson equations of vector magnetic potential are solved by separation of variables. Magnetic density distribution of the circular collector ring is given. The magnetic forces sustained by end collector ring are deduced in analytical expression. Inherent vibration property of the end collector ring is analyzed, and the result is compared with those of the finite element method and experiments. Good agreement is reached, validating the analytical process presented in this paper. Meanwhile, it is believed that the method and the results given in the paper provide theoretical basis for design and vibration analysis of end collector ring of large turbogenerator's stator.
According to the curved beam theory of Love, the general nonlinear magnetoelastic coupled vibration equations of the end of circular collector ring on turbogenerator's stator are derived. Using Maxwell equations, Poisson equations of vector magnetic potential are solved by separation of variables. Magnetic density distribution of the circular collector ring is given. The magnetic forces sustained by end collector ring are deduced in analytical expression. Inherent vibration property of the end collector ring is analyzed, and the result is compared with those of the finite element method and experiments. Good agreement is reached, validating the analytical process presented in this paper. Meanwhile, it is believed that the method and the results given in the paper provide theoretical basis for design and vibration analysis of end collector ring of large turbogenerator's stator.
2003, 20(3): 104-107.
Abstract：
In order to calculate cable tension more precisely with the help of modern measuring technology, a new method is proposed in this paper based on cable segment's static analytical formula. After the coordinates of three points on a cable are measured, cable tension can be calculated by solving the corresponding non-linear equations. The precise laser measuring instruments can measure many cables from one site quickly, and therefore the effectiveness of this new method is guaranteed. Moreover, it overcomes the shortcomings of the comnonly used methods, whose results are affected by the end condition of cable. Numerical example indicates it is precise enough even if the cable's elasticity is neglected, and the cable tension error resulting from measurement and cable vibration is ignorable. The application to one cable-stayed bridge has verified the precision and practicability of the present method. It can be used during the construction and the service of cable-stayed bridge, suspension bridge, cable-suspended roof and other cable structures, whenever the cable is static or vibrating with small amplitude.
In order to calculate cable tension more precisely with the help of modern measuring technology, a new method is proposed in this paper based on cable segment's static analytical formula. After the coordinates of three points on a cable are measured, cable tension can be calculated by solving the corresponding non-linear equations. The precise laser measuring instruments can measure many cables from one site quickly, and therefore the effectiveness of this new method is guaranteed. Moreover, it overcomes the shortcomings of the comnonly used methods, whose results are affected by the end condition of cable. Numerical example indicates it is precise enough even if the cable's elasticity is neglected, and the cable tension error resulting from measurement and cable vibration is ignorable. The application to one cable-stayed bridge has verified the precision and practicability of the present method. It can be used during the construction and the service of cable-stayed bridge, suspension bridge, cable-suspended roof and other cable structures, whenever the cable is static or vibrating with small amplitude.
2003, 20(3): 108-114.
Abstract：
A damage detection procedure applied to mono-coupled periodic systems using a sensitivity-based method is presented in this paper. The first order approximation of the natural frequencies with respect to one single damage in different elements is obtained and then used to form the sensitivity matrix. Consequently, the stiffness changes due to damage can be identified by solving a set of underdetermined equations based on the sensitivity matrix. For complex structures, there are many possible damage locations, a means of improving the computational efficiency of damage detection while maintaining the accuracy for large periodic structures with limited available measured natural frequencies is introduced. The theoretical analysis and numerical results show that the sensitivity of natural frequencies to damage in different locations depends only on the mode number and the location of damage, and the proposed method can locate correctly single or multiple damages in a large periodic structure.
A damage detection procedure applied to mono-coupled periodic systems using a sensitivity-based method is presented in this paper. The first order approximation of the natural frequencies with respect to one single damage in different elements is obtained and then used to form the sensitivity matrix. Consequently, the stiffness changes due to damage can be identified by solving a set of underdetermined equations based on the sensitivity matrix. For complex structures, there are many possible damage locations, a means of improving the computational efficiency of damage detection while maintaining the accuracy for large periodic structures with limited available measured natural frequencies is introduced. The theoretical analysis and numerical results show that the sensitivity of natural frequencies to damage in different locations depends only on the mode number and the location of damage, and the proposed method can locate correctly single or multiple damages in a large periodic structure.
2003, 20(3): 115-119.
Abstract：
Magnetorheological (MR) damper is one of the more promising new devices for semi-active control of structures. External energy required by the adjustable fluid damper is minuscule while the damper can produce great force on the order of milliseconds. The characteristics of MR damper have been described by a set of nonlinear differential equations including three physical parameters such as displacement, voltage and force. When displacement and voltage are input into MR damper, the device can generate force. In this paper, the performance of MR damper is simulated based on system identification with optimal multi-layer perceptron neural networks and ARX model. The trained optimal networks can accurately predict force by a forward model and voltage by an inverse model. If the neural networks are used in a control system, the semi-active MR damper can be easily used for semi-active control of structures.
Magnetorheological (MR) damper is one of the more promising new devices for semi-active control of structures. External energy required by the adjustable fluid damper is minuscule while the damper can produce great force on the order of milliseconds. The characteristics of MR damper have been described by a set of nonlinear differential equations including three physical parameters such as displacement, voltage and force. When displacement and voltage are input into MR damper, the device can generate force. In this paper, the performance of MR damper is simulated based on system identification with optimal multi-layer perceptron neural networks and ARX model. The trained optimal networks can accurately predict force by a forward model and voltage by an inverse model. If the neural networks are used in a control system, the semi-active MR damper can be easily used for semi-active control of structures.
2003, 20(3): 120-124.
Abstract：
The seismic response of underground pipelines is usually calculated by the wave theory that assumes seismic wave as a traveling wave, which propagates along the axial direction or at some angle with the axial direction. This method can only solve the axial force and strain of pipeline due to the phase difference of ground motion. Some reference documents assumed the earthquake ground motion as a stationary random process distributed in space and time, and worked out the seismic response of pipelines using random vibration theory. But they neglected the effect of non-stationary ground motion, and especially the non-stationary ground motion in time domain that may be the most important factor giving rise to the axial force and the strain of the pipeline. In this paper, the ground motion time histories of each spot in the pipeline axis are generated based on the statistical model of ground motion, and the seismic responses of the pipeline are worked out by the series method. The results may better reflect the non-stationarity of ground motion in time domain and are closer to reality than those by wave theory and stationary random vibration theory.
The seismic response of underground pipelines is usually calculated by the wave theory that assumes seismic wave as a traveling wave, which propagates along the axial direction or at some angle with the axial direction. This method can only solve the axial force and strain of pipeline due to the phase difference of ground motion. Some reference documents assumed the earthquake ground motion as a stationary random process distributed in space and time, and worked out the seismic response of pipelines using random vibration theory. But they neglected the effect of non-stationary ground motion, and especially the non-stationary ground motion in time domain that may be the most important factor giving rise to the axial force and the strain of the pipeline. In this paper, the ground motion time histories of each spot in the pipeline axis are generated based on the statistical model of ground motion, and the seismic responses of the pipeline are worked out by the series method. The results may better reflect the non-stationarity of ground motion in time domain and are closer to reality than those by wave theory and stationary random vibration theory.
2003, 20(3): 125-128.
Abstract：
Small deformation problems of pre-stressed bar are studied in present paper. Regarding initial stresses as parameters, a variational principle of displacement is suggested. Numerical parameters are used to describe initial stress. Based on the variational principle, a mathematical system of equations to solve displacement components of the bar is established. Numerical parameters are contained in the obtained equations. The system of equations is suitable for dynamic analysis of stressed members including pre-stressed bars on that small deformations are superposed. Analyzing the mathematical system, it is observable that the stiffness, critical force, couple of elemental deformations and inherent frequencies are affected by the numerical parameters.
Small deformation problems of pre-stressed bar are studied in present paper. Regarding initial stresses as parameters, a variational principle of displacement is suggested. Numerical parameters are used to describe initial stress. Based on the variational principle, a mathematical system of equations to solve displacement components of the bar is established. Numerical parameters are contained in the obtained equations. The system of equations is suitable for dynamic analysis of stressed members including pre-stressed bars on that small deformations are superposed. Analyzing the mathematical system, it is observable that the stiffness, critical force, couple of elemental deformations and inherent frequencies are affected by the numerical parameters.
2003, 20(3): 129-133.
Abstract：
In this paper, non-probabilistic uncertainties in design of docking blocks are discussed. A mathematical model is proposed for optimization of docking blocks with uncertain ship girder loads and combined stiffnesses of docking blocks considered. Emphasis is placed on effects of non-probabilistic uncertainties in ship girder loads and combined stiffnesses of docking blocks on optimal solution. Numerical results show that uncertainties considered affect the optimization of docking blocks and lead to increase in weights of blocks. Increased weights are utilized to increase the resistance of the structure to variation of uncertain variables. The effect of uncertain combined stiffnesses of blocks on design is larger than that of ship girder loads with uncertainty.
In this paper, non-probabilistic uncertainties in design of docking blocks are discussed. A mathematical model is proposed for optimization of docking blocks with uncertain ship girder loads and combined stiffnesses of docking blocks considered. Emphasis is placed on effects of non-probabilistic uncertainties in ship girder loads and combined stiffnesses of docking blocks on optimal solution. Numerical results show that uncertainties considered affect the optimization of docking blocks and lead to increase in weights of blocks. Increased weights are utilized to increase the resistance of the structure to variation of uncertain variables. The effect of uncertain combined stiffnesses of blocks on design is larger than that of ship girder loads with uncertainty.
2003, 20(3): 134-141.
Abstract：
In this paper, an investigation on axial compression ratio of columns with T, L-shaped cross-sections is carried out by numerical method. The analytical results indicate that the axial compression ratio of columns with L,T-shaped cross-sections is related to section dimensions. In order to raise the axial compression ratio when the web is in compression, the favorable effects of changing the form of reinforcement and considering the confined concrete are discussed. The following results can be drawn through theoretical analysis: the axial compression ratio index reduces with the drop of the ratio of length to thickness of sections; the index will increase when the steels in the end of the web are enhanced; under certain diameter and spacing of stirrups, the axial compression ratio index is raised. At last, the axial compression ratio indexes considering the dimensions of columns with T, L-shaped cross-sections are given.
In this paper, an investigation on axial compression ratio of columns with T, L-shaped cross-sections is carried out by numerical method. The analytical results indicate that the axial compression ratio of columns with L,T-shaped cross-sections is related to section dimensions. In order to raise the axial compression ratio when the web is in compression, the favorable effects of changing the form of reinforcement and considering the confined concrete are discussed. The following results can be drawn through theoretical analysis: the axial compression ratio index reduces with the drop of the ratio of length to thickness of sections; the index will increase when the steels in the end of the web are enhanced; under certain diameter and spacing of stirrups, the axial compression ratio index is raised. At last, the axial compression ratio indexes considering the dimensions of columns with T, L-shaped cross-sections are given.
2003, 20(3): 142-149.
Abstract：
In studying the reinforcement of steel girder bridges in the project of raising train speeds of China抯 railway, a spatial dynamic analysis model for train-bridge systems under random excitations was established. The random excitations were analyzed and generated by the time series auto-regressive model from the experimentally measured wheel accelerations. The whole histories of the train running on bridges were simulated on computer. The responses of bridges were calculated and statistically studied. Based on the results, the reinforcement schemes for steel girders were designed and some of them were applied to real bridges. The field tests were carried out before and after the bridge reinforcement, which validated the effectiveness of the analytical method and the reasonability of the reinforcement schemes.
In studying the reinforcement of steel girder bridges in the project of raising train speeds of China抯 railway, a spatial dynamic analysis model for train-bridge systems under random excitations was established. The random excitations were analyzed and generated by the time series auto-regressive model from the experimentally measured wheel accelerations. The whole histories of the train running on bridges were simulated on computer. The responses of bridges were calculated and statistically studied. Based on the results, the reinforcement schemes for steel girders were designed and some of them were applied to real bridges. The field tests were carried out before and after the bridge reinforcement, which validated the effectiveness of the analytical method and the reasonability of the reinforcement schemes.
2003, 20(3): 150-154.
Abstract：
A computational model for triangular plate element under arbitrary excitation is established and a refined dynamic formulation taking in account the local effect is presented. With the present model, refined dynamic analysis of structures with complex boundaries can be performed. A cantilever plate is studied by conducting time-history analysis and modifying its local effect. The results are compared with those obtained using quadrangle plate element. It is shown that the local dynamic effect is directly proportional to the acceleration and the neglect of local effect results in significant differences of dynamic internal forces with their theorectical values. Thus, the local dynamic effect must be considered in the dynamic formulation for triangular plate element.
A computational model for triangular plate element under arbitrary excitation is established and a refined dynamic formulation taking in account the local effect is presented. With the present model, refined dynamic analysis of structures with complex boundaries can be performed. A cantilever plate is studied by conducting time-history analysis and modifying its local effect. The results are compared with those obtained using quadrangle plate element. It is shown that the local dynamic effect is directly proportional to the acceleration and the neglect of local effect results in significant differences of dynamic internal forces with their theorectical values. Thus, the local dynamic effect must be considered in the dynamic formulation for triangular plate element.
2003, 20(3): 155-160.
Abstract：
The energy absorption elements made of composites are often applied in impact protective engineering structures. The energy absorption ability of composite structures is a special mechanic behavior which differs from the strength and the stiffness of the structures. The objectives and methodologies for the energy absorption behavior of composite tube structures have their own characteristics. Over the recent years, the investigation on the energy absorption behavior of composite structures has been an attractive research topic in impacting protection applications. In this paper, we review the progress of the studies on energy absorption behavior of composite structures and propose some outstanding issues that require further studies.
The energy absorption elements made of composites are often applied in impact protective engineering structures. The energy absorption ability of composite structures is a special mechanic behavior which differs from the strength and the stiffness of the structures. The objectives and methodologies for the energy absorption behavior of composite tube structures have their own characteristics. Over the recent years, the investigation on the energy absorption behavior of composite structures has been an attractive research topic in impacting protection applications. In this paper, we review the progress of the studies on energy absorption behavior of composite structures and propose some outstanding issues that require further studies.
2003, 20(3): 161-166.
Abstract：
A prestressed steel girder is regarded as composite structure of girder and tendons, and the interactions between them are fully considered. The geometrical nonlinear finite element formulations for both girder and tendon are proposed based on the present girder element. The formulations are simple and straightforward. The experimental results of deflections at the mid-span and quarter span, bottom plate strain of the steel girder, and the tension increment of tendons are in good agreement with the theoretical calculations. This confirms the validity of the present formulation.
A prestressed steel girder is regarded as composite structure of girder and tendons, and the interactions between them are fully considered. The geometrical nonlinear finite element formulations for both girder and tendon are proposed based on the present girder element. The formulations are simple and straightforward. The experimental results of deflections at the mid-span and quarter span, bottom plate strain of the steel girder, and the tension increment of tendons are in good agreement with the theoretical calculations. This confirms the validity of the present formulation.
2003, 20(3): 167-170.
Abstract：
The space-time distribution of FAE detonation overpressure field is simulated by means of Object-MMIC, a dynamic program, in this paper. The changing pattern of damage radius and area of shock wave with effectivity are analyzed. It is found that the overpressure field can be divided into three subareas, namely, the direct action area of cloud detonation, the united action area of the detonation outcome and the shock wave, the shock wave action area. The damage area of cloud detonation shock wave increases linearly with the total energy of cloud detonation.
The space-time distribution of FAE detonation overpressure field is simulated by means of Object-MMIC, a dynamic program, in this paper. The changing pattern of damage radius and area of shock wave with effectivity are analyzed. It is found that the overpressure field can be divided into three subareas, namely, the direct action area of cloud detonation, the united action area of the detonation outcome and the shock wave, the shock wave action area. The damage area of cloud detonation shock wave increases linearly with the total energy of cloud detonation.
