考虑车桥耦合振动的钢梁桥腹板间隙的疲劳分析

发布时间：2019-02-27 15:53

【摘要】：钢桥平面外变形是钢桥抗疲劳设计的一大难点,钢桥腹板间隙微小的平面外变形可以产生很大的弯曲应力,导致腹板间隙疲劳裂纹的萌发和扩展,萌生于主梁腹板上的疲劳裂纹严重威胁了桥梁的设计使用寿命。许多学者通过静力分析或者在静力分析的基础上叠加一个动力冲击系数来考虑车辆荷载的动力效应对腹板间隙应力的影响。然而,在桥面不平整度较差的情况下,规范中的疲劳动力冲击系数可能低估了车辆动力冲击效应,往往导致腹板间隙的实际疲劳寿命低于设计寿命。为了更准确的研究桥面不平整度退化过程中车辆荷载动力效应对腹板间隙疲劳寿命的影响,本文的研究内容和主要结果如下:(1)根据AASHTO桥梁设计规范建立了 4座不同跨径的I型简支钢梁桥的有限元模型和疲劳车的三维模型;通过疲劳车移动加载分析了腹板间隙的应力分布规律,并研究了桥梁跨径和腹板间隙长度对腹板间隙应力的影响程度。结果表明腹板间隙长度对腹板间隙应力的影响较小,桥梁跨径是影响腹板间隙应力的主要因素。(2)在假定的交通量和环境条件下,研究了桥面不平整度的退化过程,得到桥面不平整度从一个等级退化到另一个等级过程中所需的时间和通过车辆的数量,以及桥面不平整度处于不同等级所占的时间比例。(3)根据桥梁和车辆接触点的作用力和位移关系建立三维车桥耦合振动模型,采用模态叠加技术和四阶伦格库塔法求解,通过数值分析获得不同桥面不平整度等级下腹板间隙的应力和应力幅水平,和不平整度退化过程中车辆荷载动力效应对I型简支钢梁桥腹板间隙的应力和应力幅冲击系数。结果表明:基于腹板间隙应力幅计算的冲击系数大于传统基于应力的冲击系数;AASHTO规范中采用的疲劳冲击系数0.15在不平整度较差时低估了车辆荷载动力效应对腹板间隙疲劳寿命的影响,基于此本文提出用于腹板间隙疲劳寿命评估的应力幅冲击系数建议值。(4)本文采用基于MATLAB编写的雨流计数程序统计疲劳车通过时腹板间隙产生的应力幅,基于S-N曲线并结合Palmgren-Miner线性累积损伤准则对钢桥腹板间隙进行疲劳寿命评估。研究结果表明:定期进行桥面维护可以有效减小腹板间隙的疲劳损伤并延长腹板间隙的疲劳寿命。本文建议的腹板间隙应力幅冲击系数和路面养护时间对评估和延长腹板间隙的疲劳寿命具有重要意义。
[Abstract]:The out-of-plane deformation of steel bridge is a difficult point in anti-fatigue design of steel bridge. The small out-of-plane deformation of web gap of steel bridge can produce great bending stress, which leads to the sprouting and propagation of fatigue crack in web gap. The fatigue cracks on the web of the main beam seriously threaten the design life of the bridge. Many scholars consider the influence of dynamic effect of vehicle load on web clearance stress by static analysis or superposition of a dynamic impact coefficient on the basis of static analysis. However, in the case of poor deck irregularity, the fatigue dynamic impact coefficient in the code may underestimate the vehicle dynamic impact effect, which often results in the actual fatigue life of the web gap being shorter than the design life. In order to study more accurately the influence of vehicle load dynamic effect on the fatigue life of web clearance in the process of deck irregularity degradation, The research contents and main results are as follows: (1) according to the design code of AASHTO bridge, the finite element models of four simple-supported steel beam bridges with different spans and the three-dimensional models of fatigue vehicles are established. The stress distribution law of web clearance is analyzed by moving load of fatigue vehicle, and the influence degree of bridge span and web gap length on web gap stress is studied. The results show that the web gap length has little effect on the web gap stress, and the bridge span is the main factor affecting the web gap stress. (2) under the assumed traffic volume and environmental conditions, the degradation process of the unevenness of the bridge deck is studied. To get the time and the number of vehicles needed to reduce the unevenness of the bridge deck from one grade to another, (3) the three-dimensional vehicle-bridge coupled vibration model is established according to the force and displacement relationship between the bridge and vehicle contact points, and the modal superposition technique and the fourth-order Ranger-Kutta method are used to solve the model, and the three-dimensional vehicle-bridge coupling vibration model is solved by the modal superposition technique and the fourth-order Ranger-Kutta method. By means of numerical analysis, the stress and stress amplitude levels of web clearance under different deck irregularity grades, and the stress and stress amplitude impact coefficient of vehicle load dynamic effect on web clearance of I type simply supported steel beam bridge during the process of irregularity degradation are obtained. The results show that the impact coefficient calculated based on the web gap stress amplitude is larger than the traditional stress-based impact coefficient. The fatigue impact coefficient 0.15 adopted in the AASHTO Code underestimates the influence of the dynamic effect of vehicle load on the fatigue life of web clearance when the irregularity is poor. Based on this, this paper puts forward the recommended value of stress amplitude impact coefficient for fatigue life assessment of web clearance. (4) in this paper, the rain flow counting program based on MATLAB is used to calculate the stress amplitude produced by webs clearance when fatigue car passes through. The fatigue life of steel bridge web gap is evaluated based on S-N curve and Palmgren-Miner linear cumulative damage criterion. The results show that the fatigue damage of web gap can be effectively reduced and the fatigue life of web space can be prolonged by regular maintenance of bridge deck. The stress amplitude impact coefficient and pavement maintenance time suggested in this paper are of great significance for evaluating and prolonging fatigue life of web clearance.
【学位授予单位】：湖南大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：U441

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