Study On The Beam-Shell FSI Dynamic Model And Its Engineering Applications Of Large Aqueduct

In this paper, structural FSI dynamic analysis method and its engineering applications, as well as seismic dynamic response of large aqueduct were studied and analyzed detailedly. The main work and conclusions show as follows:1. Based on structural dynamic analysis theory and FSI analysis theory, the beam-shell FSI dynamic analysis model of large aqueduct structure has been put forward creatively, by the method combining plane problem with space problem. Using the beam-shell model, the difficulties solving 3D two-way FSI problems can be effectively solved by means of simplifying 3D FSI problem to 2D FSI model, and the computational efficiency of FSI can be greatly enhanced, and the 3D effect of FSI can be reflect. Also, the beam-shell model can be used for FSI calculation under longitudinal seismic excitation, and can be used for the aqueduct structure with a aqueduct body stiffened structure. By contrast with simulation results, the new model can not only well simulate responses of displacement, internal force and the hydrodynamic pressure of the aqueduct body and the support structure under longitudinal and horizontal seismic excitation, and can reflect the 3D effects of FSI, and can enhance simulation accuracy to meet the requirements, but also maintain a very high computational efficiency, can significantly reduce the computer time to facilitate large-scale FSI analysis and calculation of multi-span construction. Thus, it can be used as a safe, efficient and practical simplified 3D dynamic analysis model of large aqueduct.2. Under longitudinal seismic excitation, FSI effects were studied, as well as the simulation results of existing aqueduct FSI calculation model were evaluated. The results show that FSI have damping effect, which the responses of water aqueduct are significantly less than waterless aqueduct, thus the waterless seismic responses can be used as a control of the longitudinal seismic work situation in the design of aqueduct. In addition, the simulation results the existing additive all water mass method used for longitudinal FSI dynamic analysis of aqueduct have large error.3. The torsion of aqueduct body was studied by joint multi-span FSI calculation and analysis on the horizontal seismic excitation, using the beam-shell model. The results show that, under the horizontal seismic action, the greater difference between the stiffness of supports of each span, the torsion angle displacement difference between both ends of aqueduct body will be greater. But the torsion angle displacements at both ends of aqueduct body are not large that have little effect on the safety of aqueduct body. The difference between the stiffness of supports of each span has little effect on the torsion moment of aqueduct body, but the torque at both ends cross-section of the aqueduct body can not be ignored; For the simply-supported aqueduct body whose seismic safety can be meet requirements, if mid section bending internal force as a control condition to design the whole aqueduct body, when the bending-torsion coupling effect is small. Otherwise, it might be difficult to meet the seismic requirements between the mid section and the end section of aqueduct body.4. Dynamic effects of water sealed belt of large aqueduct were studied deeply. Using the beam-shell model, by joint multi-span FSI calculation and analysis on the horizontal and longitudinal seismic excitation, longitudinal opening displacement and lateral disturbed displacement were analyzed, and the influences of FSI on dynamic responses were analyzed by comparison of the FSI results and the waterless results. The results show that: under lateral seismic action, longitudinal opening displacement and lateral disturbed displacement of the water sealed belts both are very small so that the water sealed belts are safe, because of the bigger lateral stiffness of aqueduct; Under longitudinal seismic action, the longitudinal stiffness of pier under the water sealed belt has an important influence on longitudinal opening displacement of the water sealed belt, the longitudinal stiffness of lower support smaller, the longitudinal opening displacement bigger; When the aqueduct suffered adverse longitudinal seismic action, the longitudinal opening displacement of waterless condition is much larger than that on water condition, therefore, water sealed belt will be tension failure, and then lost the usage function; Different seismic excitation, often cause the longitudinal opening displacement value of the water sealed belt quite different, therefore, we must fully take into account the nature of the impact of incentive loads in longitudinal opening displacement longitudinal seismic design of water sealed belt.5. The influences of fluid velocity on lateral and vertical FSI effects of aqueduct were studied. The characteristics of FSI effects of aqueduct with fluid velocity and the influence level of fluid velocity can be identified by research, which provide the basis for aqueduct structure analysis, various simplified models available, and model test under fluid velocity condition. The results show that the influence level of fluid velocity on static and dynamic FSI responses of aqueduct is very limited within the design velocity range of 1.0-2.5m/s. So, for the aqueduct structural analysis, the influence of longitudinal flow can be negligible.