摘要:
柔性吊桥是指不设加劲梁或加劲梁高度很小的吊桥, 因其桥面系构造简单、耗钢量小、桥面架设和维护方便、桥型美观、造价低等特点, 适用于我国地形地势复杂的西南山区。柔性悬索桥中大部分荷载由缆索承担, 虽在设计时考虑了一定的安全系数, 但随着时间的推移, 车辆荷载作用下桥面将随悬索形状的改变而产生S形的变形, 不利于行车安全, 同时, 因超载、疲劳等不确定因素会导致吊杆破损, 给吊桥的安全运营带来威胁, 加上山区自然环境恶劣, 柔性吊桥疲劳寿命问题日益显现。近年来, 我国因吊杆断裂导致桥梁垮塌的事件频频发生。因此需要对柔性吊桥吊杆进行优化设计, 以保障桥梁的安全高效。以车里格桥为例, 研究吊杆的破损安全优化设计方案, 借助有限元软件计算原桥吊杆与基于应力差优化吊杆的内力, 对比分析其是否能够实现寿命差。主要内容包括: 1)通过理论分析和计算分析提出由内外部分组成的单吊杆优化方案代替传统的平行双吊杆, 并对其应力差及强度差的"破损安全吊杆系统"进行评估。2)介绍一种通过改变应力幅达到破损安全的设计方法, 并与普通单吊杆进行计算对比。3)用全动力模拟方法来模拟吊杆的骤断情况探究弹性块刚度对寿命差破损安全吊杆的破断影响。4)通过改变吊杆内外部分的面积比及弹性块的刚度探究了寿命差破损安全吊杆的优化效果。结果表明吊杆的破损安全优化设计方案并不能实现明显的寿命差, 在上述基础上提出在安全束下方添加橡胶垫块的方案, 通过调整应力幅差达到破损安全优化设计的目的, 并通过静、动力分析验证其优化效果; 最后通过调整截面参数和橡胶垫块刚度来探究破损安全吊杆的受力特点, 结果表明: 截面参数的调整对吊杆受力影响不大, 橡胶垫刚度的改变对吊杆应力幅的影响较为明显。
Abstract:
Flexible suspension bridge refers to a suspension bridge without stiffening beams or with a small stiffening beam height. Because of its simple bridge deck structure, low steel consumption, convenient bridge deck erection and maintenance, beautiful bridge shape, and low cost, it has the characteristics of being suitable for the complex topography of the southwest mountainous area in my country. Most of the load in the flexible suspension bridge is borne by the cables. Although a certain safety factor is considered in the design, with the passage of time, under the action of the vehicle load, the bridge deck will undergo S-shaped deformation as the shape of the suspension cable changes. It is not conducive to driving safety. At the same time, the boom will be damaged due to uncertain factors such as overload and fatigue, posing a threat to the safe operation of the suspension bridge. In addition, the harsh natural environment in the mountainous area causes the fatigue life of the flexible suspension bridge to become increasingly apparent. In recent years, there have been frequent incidents of bridge collapse due to suspender breaks in our country, and the consequences cannot be ignored. Therefore, it is necessary to optimize the design of the boom of the flexible suspension bridge to ensure the safety and efficiency of the bridge.Based on the engineering example of Chelige Bridge, the paper studied the optimization design plan of damage safety the boom, and calculated the internal force of the original bridge suspension rod and the optimized boom the based on the stress difference with the aid of finite element software, and analyzed whether it could achieve the life difference. The main contents include: 1)through theoretical analysis and calculation analysis, a single boom optimization plan composed of internal and external parts proposed to replace the traditional parallel double boom, and the "damaged safety boom system" of stress difference and strength difference was evaluated. 2)A design method to achieve damage safety by changing the stress amplitude was introduced, and compared with ordinary single boom. 3)Used the full dynamic simulation method to simulate the sudden breaking of the boom, and explored the influence of the stiffness of the elastic block on the breakage of the safety boom. 4)By changing the area ratio of the inner and outer parts of the boom and the stiffness of the elastic block, the optimization effect of the safety boom with poor service life was explored.The results showed that: The optimization design plan of damage safety of the boom could not achieve a significant difference in life. On the basis of the above, a plan to add rubber pads under the safety beam was proposed, the stress amplitude was adjusted to achieve the purpose of damage safety optimization design, and the optimization effect was verified through static and dynamic analysis; finally, the section parameters and the stiffness of the rubber pads were adjusted to explore the force characteristics of the damaged safety boom. It was found that the adjustment of the section parameters had smaller effect on the force of the boom, and the change of the stiffness of the rubber pad had a significant impact on the stress amplitude of the boom.
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