Jun Dong

Studies on geometric control mechanism of constructional process of cantilever casting for large-span continuous box-girder bridge

Considering the general background of engineering project of Wuzhong Yellow River Highway Bridge, which belongs to large-span continuous girder bridge, some investigations of geometric control in the process of actual cantilever construction are discussed in this paper. Based on different theories of geometric control, the method of self-adaptive control has been adopted, by which such main influences as pre-cambers, elevations and deformation of guyed travelers on the structure of pre-stress large-span continuous girder bridge are analyzed and the formulae of initialize heights of girders are deduced. Then, according to the demands of design and construction for the bridge, a geometrical FEM model with spatial nonlinearity is established and its construction process has been simulated so that some key parameters of geometric control would have been determined. For examples, the initial curves of pre-camber for different span are obtained, and pre-elevations are done in which a long-term course of shrinkage and creep influence of concrete on the structure and other faults in other large-span bridges are considered. Finally, the objective curves are obtained on the basis of pre-camber curves. The measured data from three stages of every segment of construction are all processed, in which the data of elevations of No. 10 pier including theoretical simulation and measurement in site while their pre-stress tension is finished are compared with each other and very good agreement is given between them. The results demonstrate the theoretical simulation and related program are reliable. All these investigations not only provide a basis for the bridge of linear control, but also a reference about geometric control for construction of the other similar large-span bridge.

Dynamic Response Analysis of Lining Structure with Primary Defects for Tunnel under Moving Train Loading

Considering the background of vibration engineering of lining structure of subway tunnel with primary defects under moving train loading, and according to the measured information of a dynamic loading spectrum of subway in Beijing, dynamic response of the lining structure with differently primary defects caused by neighboring tunnel construction has been investigated for different cases including one-way and two-way trains in this paper. The results show that the curves of dynamic time history analysis are similar with each other for displacement and stress under different cases with differently primary defects. The peak value of displacement and stress under the case of two-way train is much larger than that under the case of one-way train, and the structure primarily depends on tensile strength of concrete in safety. Under the case of one-way train with primary defects would there be no defect by vibration loads.

Mechanical Mechanism Analysis of Longitudinal Cracks Appeared in a Large Cable-Stayed Bridge Cable Tower

The cable-stayed bridge which has been found longitudinal cracks in tower is taken as the background, combining with the original design information and the results of bridge inspection. The numerical simulation on temperature effect of cable tower has been done with MIDAS/Civil, and the results have the same trend with observed in bridge inspection, indicating that the cracks in tower probably are caused by temperature effect. Then, some suggestions are raised in the end of this paper about how to deal with these cracks. This work could be a valuable reference for similar large cable-stayed bridge. And the temperature stress should be paid more attention in design process to avoid appearance of temperature cracks which affect beauty and durability of structure.

Studies on Aseismatic Performance of a Typical Subway Tunnel with Initial Defects Caused by Construction of New Down-Through Tunnels

For the engineering background of subway tunnel with initial defects caused by the construction of new down-through tunnels, the aseismatic performance of the existed tunnel is studied so as to reveal the mechanism of seismic dynamic response by using finite difference method. Numerical simulation shows that the tunnel is deforming in its entirety since such physical variables as velocity, displacement and stress in its all key weak points have same dynamic tendency under influence of approaching construction of tunnels, and these variables are much larger than those without any influence. After down-through construction, much influences of aseismatic performance are mainly taking place at both the side wall and the upper arch, and the shearing damage are mainly doing in surrounding soil mass. Due to widely shearing damage after down-through construction, it is suggested that grouting reinforcing should be applied so as to make them much stiffness as a whole.

Investigation of Numerical Modeling for Concrete Corroded by Chloride Ion Diffusion

For concrete structure lack of enough durability due to corrosion by chloride ion under chlorine salt environment, and based on the Fick’s Diffusion Law, a mathematical model for concrete corroded by chloride ion diffusion is established and studied. Based on Galerkin FEM with weighted residuals, numerically discrete analysis of the models and final finite-difference-discrete format about time are obtained. Comparisons of PDE models between traditional heat conduction and chloride ion diffusion have been done. According to different parameters and APDL in ANSYS, a program for transformation of parameters including initial and boundary conditions is designed, so as to solve modeling by resolving module of heat conduction in ANSYS. A two-dimensional example from references, namely a concrete plate corroded by chloride ion under chlorine salt environment, is analyzed. All the results show the investigation is reliable and feasible for the research of durability of concrete structure under corrosion environment.

Investigation of Dynamic Load Test of an Existed Reinforced Concrete Rigid-Frame Arch Bridge

For an existed reinforced concrete rigid-frame arch bridge in reconstruction project, reinforcement effects of the bridge are studied and discussed while the original load grades are maintaining and it is based on dynamic load test including scheme, execution and FEM analysis in this paper. In our investigations, such characteristics as dynamic flexibility, impact coefficient, natural vibrations and dynamic responses are analyzed. All the investigations show that the bridge meets the original-designed-loading requirement, which behaves well in dynamic characteristics after being strengthened and whose stiffness also satisfies requirement.

Investigation of Temperature Effects of Box-Girder Bridge in Typical Winter Weather of QINGHAI-TIBET Plateau

Based on the engineering background as which a box-girder bridge under construction in typical winter weather of Qinghai-Tibet plateau is chosen, a diffusion equation of temperature of the structure has been established, whose choices of initial and boundary conditions are discussed according to the field monitoring data and local weather information including solar radiation and air convection. Secondly, some tests of numerical simulation have been done by FEM software, and related parameters of the model are obtained. Finally, based on the determinate parameters, the temperature fields of another box-girder bridge are simulated, which agree with the measured data in the field. All these show that the investigation is not only providing basic parameters for temperature loading in the control of construction process of the bridge, but also providing significant reference for the design and construction of the same kind of bridges in typical winter weather of Qinghai-Tibet plateau.

Analysis of Seismic Response for an Extradosed Cable-Stayed Curved Bridge Based on Different Design Parameters

Based on the characteristics of low tower and few cables in extradosed Cable-Stayed bridges, simulation models are established for investigations of structural dynamic characteristics under different design parameters, which is related to the practical engineering of Longjing Bridge. As the design radius and pier beam connection form are chosen for the variable, the paper is focus on the influence of dynamic characteristics under the two parameters in extradosed cable-stayed curved bridges. Since the earthquake response spectrum data from National seismic code in 2008 and with the CQC vibration mode combination method, the diversified models are built by Midas/civil so as to explore the earthquake response mechanism under different design parameters. The result show that these two design parameters have some great impacts on dynamic characteristics of extradosed cable-stayed curved bridges, which has direct effect on the bridge seismic performance. The conclusion is the important reference for practical engineering and providing basis for seismic design parameters, but also for seismic design and construction in extradosed cable-stayed curved bridges.

Studies on Dynamic Response of Subway Tunnels with Initial Defect under Long-Term Train Loads

Based on the background of a subway construction project, deterioration characteristics of the existed subway tunnels under long-term train loads is studied by using the method of stiffness discount which could reflect fatigue damage of the structure. Firstly, dynamic response of the tunnel with initial defects caused by approaching construction under long-term train loads is analyzed according numerical simulation, and some results under different degrees of fatigue are obtained. Then, numerical results of acceleration responses at such different points as the upper vault, the side wall and the bottom of tunnels in two directions, are compared with each other while the train loads are applied at the left tunnel, especially under three different stiffness. Our investigation shows local structural damage in the position with initial cracks will be caused by a high cycle stress although there are fewer influences of stiffness changes on dynamic response of tunnels.

Studies on dynamic behavior of the Subway Station influenced by down-through tunnel during strong seismic

The project of the south-to-north water transfer whose tunnel down-through Wukesong Subway Station is taken as a background in this paper. Firstly, some 3D dynamic model are established while considering the soil-structure interaction, adopting D-P model and selecting Rayleigh damping and viscous-elastic artificially boundary conditions. Then, such contents as internal forces, deformations and their time-history changes at the points in the existed metro station are studied in detail under strong earthquake. The final results show that maximum displacement of the monitor point is smaller than the size of the station structure during strong seismic, and the peak of internal force is markedly. The value of the maximum displacement and internal force of monitor node and occurrence time is largely related with the peak acceleration of seismic wave input, whose part of the time-history internal force exceed the allowed capacity of the structure, the column bias damage as bend and force, the station roof and floor easy happening bend destructive. Section changes place happening easily shear failure as stress concentration. The relative displacement value of structure component on both ends is the main factors affecting the structure of normal use that cannot to be ignored. Research results can be used for reference for design, construction and safety assessment for similar structure.