Based on Hamilton principle,the governing differential equations and the corresponding boundary conditions of steel-concrete composite box girder with consideration of the shear lag effect meeting self equilibrated st...Based on Hamilton principle,the governing differential equations and the corresponding boundary conditions of steel-concrete composite box girder with consideration of the shear lag effect meeting self equilibrated stress,shear deformation,slip,as well as rotational inertia were induced.Therefore,natural frequency equations were obtained for the boundary types,such as simple support,cantilever,continuous girder and fixed support at two ends.The ANSYS finite element solutions were compared with the analytical solutions by calculation examples and the validity of the proposed approach was verified,which also shows the correctness of longitudinal warping displacement functions.Some meaningful conclusions for engineering design were obtained.The decrease extent of each order natural frequency of the steel-concrete composite box-girder is great under action of the shear lag effect.The shear-lag effect of steel-concrete composite box girder increases when frequency order rises,and increases while span-width ratio decreases.The proposed approach provides theoretical basis for further research of free vibration characteristics of steel-concrete composite box-girder.展开更多
The dynamic finite element model （FEM） of a prestressed concrete continuous box-girder bridge, called the Tongyang Canal Bridge, is built and updated based on the results of ambient vibration testing （AVT） using a...The dynamic finite element model （FEM） of a prestressed concrete continuous box-girder bridge, called the Tongyang Canal Bridge, is built and updated based on the results of ambient vibration testing （AVT） using a real-coded accelerating genetic algorithm （RAGA）. The objective functions are defined based on natural frequency and modal assurance criterion （MAC） metrics to evaluate the updated FEM. Two objective functions are defined to fully account for the relative errors and standard deviations of the natural frequencies and MAC between the AVT results and the updated FEM predictions. The dynamically updated FEM of the bridge can better represent its structural dynamics and serve as a baseline in long-term health monitoring, condition assessment and damage identification over the service life of the bridge .展开更多
The free vibration analysis of simply supported box-girder bridges is carried out using the finite element method.The fundamental frequency is determined in straight,skew,curved and skew-curved box-girder bridges.It i...The free vibration analysis of simply supported box-girder bridges is carried out using the finite element method.The fundamental frequency is determined in straight,skew,curved and skew-curved box-girder bridges.It is important to analyse the combined effect of skewness and curvature because skew-curved box-girder bridge behaviour cannot be predicted by simply adding the individual effects of skewness and curvature.At first,an existing model is considered to validate the present approach.A convergence study is carried out to decide the mesh size in the finite element method.An exhaustive parametric study is conducted to determine the fundamental frequency of box-girder bridges with varying skew angle,curve angle,span,span-depth ratio and cell number.The skew angle is varied from 0°to 60°,curve angle is varied from 0°to 60°,span is changed from 25 to 50 m,span-depth ratio is varied from 10 to 16,and single cell&double cell are used in the present study.A total of 420 bridge models are used for parametric study in the investigation.Mode shapes of the skew-curved bridge are also presented.The fundamental frequency of the skew-curved box-girder bridge is found to be more than the straight bridge,so,the skew-curved box-girder bridge is preferable.The present study may be useful in the design of box-girder bridges.展开更多
Temperature field and its variation with time are necessary for analyzing the thermo-mechanical performance of mass concrete structures at their early ages. This paper carries out a temperature field simulation analys...Temperature field and its variation with time are necessary for analyzing the thermo-mechanical performance of mass concrete structures at their early ages. This paper carries out a temperature field simulation analysis for an original segment of a real box girder bridge with the finite element software ANSYS. Two representative exothermic rate models are used to describe the heat- releasing process caused by the cement hydration in concrete. The exothermic rate model that conforms to reality more closely is recognized by comparing the simulation results with the data gathered from the optical fiber temperature sensors pre-embedded in the original segment. The air temperature and wind velocity that constitute thermal boundary conditions are determined in the light of the local meteorological department and correlative research achievements of recent years. Moreover, the consideration for the steel formwork acting as a barrier to heat loss is also proved to be beneficial to improve the simulation effect.展开更多
In this article, the current railway box girder bridge erecting machines at home and abroad are briefly introduced and analyzed, the research & design situation of class 900t railway box girder bridge erecting mac...In this article, the current railway box girder bridge erecting machines at home and abroad are briefly introduced and analyzed, the research & design situation of class 900t railway box girder bridge erecting machines is described, and also the principle for determining the overall plan and a series of issues much concerning the design of key components of class 900t railway box girder bridge erecting machines are described.展开更多
A field test was conducted to investigate the distribution of temperature field and the variation of thermal stress for a prestressed concrete(PC)box-girder bridge.The change of hydration heat temperature consists of ...A field test was conducted to investigate the distribution of temperature field and the variation of thermal stress for a prestressed concrete(PC)box-girder bridge.The change of hydration heat temperature consists of four periods:temperature rising period,constant temperature period,rapid temperature fall period and stow temperature fall period.The peak value of hydration heat temperature increases with the increasing casting temperature of concrete;the relation between them is approximately linear.According to field tests,the thermal stress incurred by hydration heat may induce temperature cracks on the PC box-girder.Furthermore,the nonlinear distribution of temperature gradient and the fluctuation of thermal stress induced by exposure to sunlight were also obtained based on continuous in-situ monitoring.Such results show that the prevailing Chinese Code(2004)is insufficient since it does not take into account the temperature gradient of the bottom slab.Finally,some preventive measures against temperature cracks were proposed based on related studies.The conclusions can provide valuable reference for the design and construction of PC box-girder bridges.展开更多
基金Projects(51078355,50938008)supported by the National Natural Science Foundation of ChinaProject(094801020)supported by the Academic Scholarship for Doctoral Candidates of the Ministry of Education,China+1 种基金Project(CX2011B093)supported by the Doctoral Candidate Research Innovation Project of Hunan Province,ChinaProject(20117Q008)supported by the Central University Basic Scientific Research Business Expenses Special Fund of China
文摘Based on Hamilton principle,the governing differential equations and the corresponding boundary conditions of steel-concrete composite box girder with consideration of the shear lag effect meeting self equilibrated stress,shear deformation,slip,as well as rotational inertia were induced.Therefore,natural frequency equations were obtained for the boundary types,such as simple support,cantilever,continuous girder and fixed support at two ends.The ANSYS finite element solutions were compared with the analytical solutions by calculation examples and the validity of the proposed approach was verified,which also shows the correctness of longitudinal warping displacement functions.Some meaningful conclusions for engineering design were obtained.The decrease extent of each order natural frequency of the steel-concrete composite box-girder is great under action of the shear lag effect.The shear-lag effect of steel-concrete composite box girder increases when frequency order rises,and increases while span-width ratio decreases.The proposed approach provides theoretical basis for further research of free vibration characteristics of steel-concrete composite box-girder.
基金National Natural Science Foundation of China Under Grant No.50575101Transportation Science Research Item of Jiangsu Province Under Grant No.06Y20
文摘The dynamic finite element model （FEM） of a prestressed concrete continuous box-girder bridge, called the Tongyang Canal Bridge, is built and updated based on the results of ambient vibration testing （AVT） using a real-coded accelerating genetic algorithm （RAGA）. The objective functions are defined based on natural frequency and modal assurance criterion （MAC） metrics to evaluate the updated FEM. Two objective functions are defined to fully account for the relative errors and standard deviations of the natural frequencies and MAC between the AVT results and the updated FEM predictions. The dynamically updated FEM of the bridge can better represent its structural dynamics and serve as a baseline in long-term health monitoring, condition assessment and damage identification over the service life of the bridge .
文摘The free vibration analysis of simply supported box-girder bridges is carried out using the finite element method.The fundamental frequency is determined in straight,skew,curved and skew-curved box-girder bridges.It is important to analyse the combined effect of skewness and curvature because skew-curved box-girder bridge behaviour cannot be predicted by simply adding the individual effects of skewness and curvature.At first,an existing model is considered to validate the present approach.A convergence study is carried out to decide the mesh size in the finite element method.An exhaustive parametric study is conducted to determine the fundamental frequency of box-girder bridges with varying skew angle,curve angle,span,span-depth ratio and cell number.The skew angle is varied from 0°to 60°,curve angle is varied from 0°to 60°,span is changed from 25 to 50 m,span-depth ratio is varied from 10 to 16,and single cell&double cell are used in the present study.A total of 420 bridge models are used for parametric study in the investigation.Mode shapes of the skew-curved bridge are also presented.The fundamental frequency of the skew-curved box-girder bridge is found to be more than the straight bridge,so,the skew-curved box-girder bridge is preferable.The present study may be useful in the design of box-girder bridges.
基金The Soft Science Foundation of Ministry of Construction of China (No.06-k3-14)
文摘Temperature field and its variation with time are necessary for analyzing the thermo-mechanical performance of mass concrete structures at their early ages. This paper carries out a temperature field simulation analysis for an original segment of a real box girder bridge with the finite element software ANSYS. Two representative exothermic rate models are used to describe the heat- releasing process caused by the cement hydration in concrete. The exothermic rate model that conforms to reality more closely is recognized by comparing the simulation results with the data gathered from the optical fiber temperature sensors pre-embedded in the original segment. The air temperature and wind velocity that constitute thermal boundary conditions are determined in the light of the local meteorological department and correlative research achievements of recent years. Moreover, the consideration for the steel formwork acting as a barrier to heat loss is also proved to be beneficial to improve the simulation effect.
文摘In this article, the current railway box girder bridge erecting machines at home and abroad are briefly introduced and analyzed, the research & design situation of class 900t railway box girder bridge erecting machines is described, and also the principle for determining the overall plan and a series of issues much concerning the design of key components of class 900t railway box girder bridge erecting machines are described.
文摘A field test was conducted to investigate the distribution of temperature field and the variation of thermal stress for a prestressed concrete(PC)box-girder bridge.The change of hydration heat temperature consists of four periods:temperature rising period,constant temperature period,rapid temperature fall period and stow temperature fall period.The peak value of hydration heat temperature increases with the increasing casting temperature of concrete;the relation between them is approximately linear.According to field tests,the thermal stress incurred by hydration heat may induce temperature cracks on the PC box-girder.Furthermore,the nonlinear distribution of temperature gradient and the fluctuation of thermal stress induced by exposure to sunlight were also obtained based on continuous in-situ monitoring.Such results show that the prevailing Chinese Code(2004)is insufficient since it does not take into account the temperature gradient of the bottom slab.Finally,some preventive measures against temperature cracks were proposed based on related studies.The conclusions can provide valuable reference for the design and construction of PC box-girder bridges.
