悬索桥主缆的次应力分析

Secondary Stress Analysis of the Main Cable of Suspension Bridges

针对在主缆的设计中,采用高的安全系数避免对细部次应力分析而使主缆的承载能力没有充分发挥的现状,尝试对悬索桥的次应力进行较为详细的分析.对悬索桥的主缆由于丝股长度差异、钢丝弹性模量差异以及钢丝弯曲等原因产生的次应力进行分析,并给出了相应的经验计算公式;对缆索角度变化产生的次应力,对以往的计算方法进行了分析,并针对更一般的情况进行了理论分析和公式推导,给出了计算算法;对于由于缆索形状的变化而产生次应力,分解为空隙率差异、截面特性差异、截面形状差异三部分进行分析.分析了悬索桥主缆出主鞍近六边形截面到第一个索夹处圆形截面引起的次应力.最后,结合国内某大跨度悬索桥主缆次应力计算的实例,对次应力的发生部位以及次应力对结构安全的影响进行了分析,并按照英国、日本和丹麦大跨度悬索桥主缆安全系数的计算方法对实例的安全系数进行了分析,认为其安全性能够得到保证.

In the designs of main cables of the suspension bridges in China, the capacities of the cables have always been undervalued without calculating the secondary stresses. This paper will present the detailed analysis of the secondary stresses. Some experiential formulas are given to consider the uneven stress caused by the different lengths and elastic modulus of tensile compression and the bending stress while passing curved plane. The calculation method of the stress caused by the deflection angle of the cable is presented after the formulas derivation. The stress is analyzed specifically due to the transforming of the cable section from square to circle and from hexagon located in the outlet of the cable from the main saddle to circle at the first cable band from the tower. At last, the secondary stresses of the cables of a large span suspension bridge in China are calculated while the location of the stress is also presented in a table. The influence of the secondary stresses on the safety of the suspension bridge is also analyzed. The safety factor is analyzed according to the calculation methods that are used in the UK, Japan and Denmark. It can be deduced from the results that the safety of cable can be guaranteed.