独柱墩梁桥倾覆临界状态分析及规范法的适用性

为了对独柱墩梁桥的倾覆机理与安全性评价进行研究，以哈尔滨阳明滩大桥已发生倾覆事故的独柱墩梁桥为例，进行精细化三维有限元建模，将支座视为橡胶单元，并记入几何、材料双重非线性，在多种基准验算荷载作用下进行结构极限破坏状态的全过程分析；同时提出4个依次发生的临界倾覆状态，连续描述整个倾覆过程中不同阶段的受力临界行为，利用抗倾覆安全系数的概念针对不同临界状态定量确定独柱墩梁桥的抗倾覆性能，并结合实际倾覆事故进行合理性验证。将规范法、仿真分析的结果与实际情况进行了对比，研究结果表明：基于理想支承刚体转动的规范方法会明显高估其抗倾覆性能，运营阶段不仅应避免支座脱空现象，还应进一步控制上部结构梁体扭转角不超限；建议采用弹性体空间计算模型，计算支座恒载反力与活载最大竖向负反力的比值，作为针对第1临界倾覆状态（支座脱空）的抗倾覆安全系数；当55 t车辆或公路-I级作为验算荷载时，该系数应分别大于1.3或2.0，并计入橡胶支座与主梁底面之间的相互作用。

Critical Condition Analysis of Overturned Bridges with Single-column-piers and Applicability of Design Standards

In order to investigate the mechanics of overturn and safety assessment of single-column-piers, a fine 3D finite element modeling, taken a certain single-column-pier bridge where the overturning accident has taken place as an example, was built by simulating the bearings with rubber elements and considering the geometric and material nonlinearities. Besides, a full-range analysis for the ultimate failure state of the overturned bridge under several types of unbalanced vehicle loading (checking loading) was conducted. Four critical overturn conditions which continuously occur were proposed to describe different mechanical behaviors during the entire overturn process. The safety factor of anti-overturn was used to quantitatively determine the anti-overturn performance of bridges with single-column-piers corresponding to different critical conditions. The rationality was verified by the overturning accidents of the bridge. Results of design standards, simulated analysis and real conditions, were compared. The results show that the design standards will highly overestimate the anti-overturn behavior based on the rigid body rotation of the bridge model with ideal supports. During the entire operation stage, the bearing disengagement needs to be avoided and the torsion angle of superstructures also needs to be limited. The ratio of dead load counter force and the maximum live load negative reaction force is calculated by dint of space calculation model of the elastomer. The calculated ratio is regarded as the safety factor of anti-overturn for the first critical overturn condition. The values of such safety factor are suggested to be more than 1.3 and 2.0, when 55 t car beam and highway-I are taken as checking loadings. All the analyses for the overturn behavior of bridges with single-column-piers need to consider the interaction between rubber bearings and bottom surface of girders.