Research and Optimization of Steel Caisson Positioning and Lowering Process for Cross-Sea Bridges under Complex Marine Conditions
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摘要:
跨海桥梁大型预制钢沉井的定位下放施工面临着海洋复杂环境中极端波浪和水流的巨大威胁，深入研究波流作用下钢沉井定位下放过程中的动力特性对钢沉井的定位准确性、下放稳定性及施工安全性具有重要意义. 基于LS-DYNA有限元程序构建波流作用下三维全尺寸钢沉井流固耦合模型，通过与Stokes二阶波浪解析解和已有水槽耦合实验结果进行对比，验证该三维流固耦合模型的准确性；使用已验证模型探究波浪参数、水流参数、锚缆布置形式以及结构下放位置等对钢沉井定位下放过程中所受的波流荷载和动力特性影响规律. 研究结果表明：所提出的锚缆布置形式可以有效降低钢沉井结构在不同波流作用下的位移和倾角，其最大倾角不超过2°；相较于水流单独作用，波流共同作用对钢沉井造成的最大水平力、水平位移和倾角至少分别增加了约86.34%、25.15%和112.96%；随着钢沉井淹没深度的增加，钢沉井所受最大水平力和水平位移分别增大了约41.90%和50.62%，钢沉井的最大倾角却减小了约31.06%；在钢沉井定位下放研究中，应充分考虑结构在不同下放深度时所受的波流荷载和位移等的影响，为分析钢沉井下放过程中的稳定性提供可靠的理论基础.
Abstract:The positioning and lowering construction of large prefabricated steel caissons for cross-sea bridges is facing significant threats from the complex marine environment, including extreme waves and currents. In-depth research on the dynamic characteristics of the steel caisson during the positioning and lowering process under wave and current effects is of great importance for the positioning accuracy, lowering stability, and construction safety of steel caissons. Based on the LS-DYNA finite element program, a three-dimensional full-scale steel caisson fluid-structure coupling model under the action of wave and current is established in this paper. By comparing with the second-order Stokes wave analytical solution and the experimental results of the existing flume coupling experiment, the accuracy of the three-dimensional fluid-structure coupling model is verified. Subsequently, the validated model is used to investigate the influence of wave parameters, flow parameters, anchor cable arrangement, and structure lowering position on the wave-current loads and dynamic characteristics during the positioning and lowering process of the steel caisson. The research results indicate that: the arrangement 3 of anchor cables can effectively reduce the displacement and inclination of the steel caisson structure under different wave and current conditions, with a maximum inclination angle of no more than 2°. Compared to the individual effect of currents, the maximum horizontal force, horizontal displacement, and inclination angle of the steel caisson caused by the combined effect of waves and currents increased by at least about 86.34%, 25.15% and 112.96%, respectively. As the submergence depth of the steel caisson increases, the maximum horizontal force and horizontal displacement experienced by the steel caisson increase by approximately 41.90% and 50.62%, respectively, while the maximum inclination angle of the steel caisson decreases by approximately 31.06%. In the study of positioning and lowering process of the steel caisson, the influence of wave and current loads and displacements on the structure at different lowering depths should be fully considered, so as to provide a reliable theoretical basis for analyzing the stability of the steel caisson in the process of positioning and lowering.
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图 7 不同锚缆布置形式下结构位移对比
Figure 7. Comparison of peak displacements of the structure with different anchor cable arrangements
图 8 钢沉井触底示意（V=5 m/s）
Figure 8. Schematic diagram of a steel caisson in contact with the seabed (V=5 m/s)
图 10 钢沉井位移时程对比
Figure 10. Comparison of the time histories of displacements on steel caisson
图 11 不同工况下钢沉井所受水平力和位移峰值对比
Figure 11. Comparison of peak horizontal force and displacement of steel caisson under different conditions
图 12 不同下放深度钢沉井所受水平力和位移峰值对比
Figure 12. Comparison of peak horizontal force and displacement of steel caisson under different lowering depths
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