Evaluation of necessary capacity and development of dynamic design method for unseting prevention cables of bridges with shock absorbing devices

对于带减震器的防脱拉索，目前还没有一种合理的设计方法。摘要本研究旨在探讨具减震器之防脱钢索之动态特性，并考虑其变形极限与非线性。研究结果表明，根据能量守恒定律设计减震器是可行的。然后，研究了连续梁桥防脱索的设计方法。一旦连续梁桥在一个桥墩处发生脱空，主梁很可能由于弯曲力或剪切力而倒塌。本研究以一连续梁桥为例，探讨防止主梁倒塌所需之防脱缆承载力，并进行静态与动态分析。静力分析结果表明，采用本文设计方法设计的防脱索具有足够的抗倾覆能力。动力分析表明，采用低刚度拉索作为防脱索时，由于弯矩过大，部分主梁产生屈服，进而估算了相邻桥梁碰撞时的相对速度，以估算碰撞力。采用二自由度模型进行了弹塑性响应分析。对输入运动类型、地面类别、阻尼比和碰撞弹簧的相对速度的影响进行了参数研究。与弹性响应相比，相对速度减少了大约一半，范围从0.3到2.5米/秒。最后，阐明了地基类别、自振周期微分比和碰撞弹簧对碰撞梁相对速度的影响。

A rational design method of an unseating prevention cable is not established yet especially for that with a shock absorber. This research aims to clarify a dynamic property of an unseating prevention cable with a shock absorber considering its deformation limit and nonlinearity. The results show that the shock absorber can be designed according to the law of conservation of energy.Then, the design method for the unseating prevention cable was studied for the continuous girder bridges. Once a continuous girder bridge becomes unseated at one pier, the girder is likely to collapse due to bending or shear forces. In this study, the necessary capacity of an unseating prevention cable to prevent the girder of a continuous girder bridge from collapsing was investigated using static and dynamic analysis. The static analysis verified that an unseating prevention cable designed using the present design procedure had sufficient capacity to resist the excessive bending moment and shear force caused by falling of the girder. The dynamic analysis showed that a part of the girder yields due to the large bending moment if a low stiffness cable is used as the unseating prevention cable.Further, the relative velocity during collision between the adjacent bridges was estimated in order to estimate the collision force. The elasto-plastic response analyses were carried out using 2-degree-of freedom model. The parametric study was conducted on the influence of the relative velocity of type of input motion, ground classifications, damping ratio and collision spring. As compared to elastic responses, the relative velocity was reduced in about half and it ranged from 0.3 to 2.5m/sec. Finally, it is clarified that the ground classifications, differential ratio of natural period and collision spring strongly affect on the relative velocity during pounding girders.