基于改进挠度理论的双缆多跨悬索桥刚度特征研究

Multi-span suspension bridge has a great spanning capacity and a broad application prospect in crossing-sea engineering. However, the too large flexibility of the multi-span suspension bridge limits its development, and multi-span suspension bridges have been built through the regulation of the tower stiffness to solve this problem. This project intends to study a new type of multi-span suspension bridge cable, which set two main cables with different sags in the same cable plane, to improve multi-span suspension bridge stiffness through changing cable system. The basic principles of deflection theory is introduced into the study of double-cable multi-span suspension bridges, expend the research subject form "main cable - stiffening girder" to "top cable – bottom cable – stiffening girder", mechanical equilibrium equation of double-cable system is established and the analytic formulas about deformation and force of the structure are deduced, so basic working principle of double-cable multi-span suspension bridge is revealed. On this basis, parametric study and local model test are performed to study contribution of main structural members such as tower, stiffening girder and cables to the structural rigidity, the results are verified with theoretical results. The appropriate parameters value is proposed. Influences of structural member restraint to mechanical performance are studied based on FEM to clarify proper structural system. The implementation of the project expands the application of deflection theory and provide theory basis for construction of double-cable multi-span suspension bridge.

多跨悬索桥跨越能力大，应用前景广阔，然而，柔度过大的弊端制约了多跨悬索桥的发展，已建成的多跨悬索桥均通过调节中塔刚度来解决这一难题。本项目拟研究一种新型双缆多跨悬索桥结构，在同一索面设置垂度不同的两根主缆，通过改变缆索体系来提高多跨悬索桥刚度。项目将挠度理论的基本原理引入双缆多跨悬索桥的研究中，研究对象由 “主缆—加劲梁”拓展到双缆体系中的“上缆—下缆—加劲梁”，构建双缆体系平衡微分方程，推导结构变形与受力的理论解析公式，揭示双缆多跨悬索桥的基本工作原理；在此基础上，通过数值分析及局部模型试验研究塔、梁、缆等主要构件对于结构刚度的贡献，并与解析结果相互验证，提出双缆多跨悬索桥的参数取值区间；基于有限元法研究构件约束方式对力学性能的影响，明确双缆多跨悬索桥的适宜结构体系。本项目的实施拓展了挠度理论的适用范围，为双缆多跨悬索桥的建造提供了理论依据。

多跨悬索桥跨越能力大，应用前景广阔，结构刚度不足是建造多跨悬索桥面临的关键技术难题，采用刚度较大的桥塔又会使主缆在中塔鞍座的抗滑安全性降低。本项目研究了一种新型缆索体系的双缆多跨悬索桥，通过提高缆索体系的约束刚度来解决多跨悬索桥刚度不足的难题。项目提出了用于结构变形及主缆抗滑计算的双缆多跨悬索桥简化力学模型，推导了塔、梁变形的解析计算公式；进一步发展双缆体系，提出了“上缆变下缆”的主缆布置方式，提高了主缆在中塔鞍座的抗滑稳定性；基于这一主缆布置形式，以恒载作用下桥塔两侧主缆内力相等为条件，推导了荷载在上、下缆分配比例及主缆抗滑安全系数解析计算公式，阐明了恒活载比值、主缆垂跨比对主缆抗滑安全性的影响；以主缆抗滑安全系数及加劲梁挠跨比为控制指标，推导了双缆多跨悬索桥中塔刚度上、下限取值的解析计算公式；研究不了同结构体系的汽车、温度荷载效应，推荐双缆多塔悬索桥采用全漂浮+中塔设置纵向弹性索体系；分析了主缆垂跨比与结构刚度及主缆抗滑的影响，推荐了适宜的主缆垂跨比。