基于联合静动力修正的混凝土斜拉桥主梁挠度变化规律研究

Deflection Variation Rule of Main Girder for a Concrete Cable‑Stayed Bridge Based on Combined Static and Dynamic Modification

针对混凝土斜拉桥服役期间主梁不断下挠的问题,该文基于修正模型分析大跨度混凝土斜拉桥服役期间主梁挠度变化规律。采用联合静动力的有限元模型修正方法,构造双目标优化问题,基于非支配排序遗传算法(NSGA-Ⅱ)求解,得到Pareto最优解集,从Pareto最优解集中找到协调最优解,从而实现有限元模型修正。模型修正后的静力位移和自振频率计算值与实测值吻合较好,能更好地反映结构的实际工作状态。在此基础上,结合主梁线形历年监测数据,分析不同徐变模式及拉索松弛效应等时变因素对主梁线形的影响,分析结果表明:采用CEB-FIP 2010徐变模式计算的挠度与实测挠度更加接近。中跨跨中下挠量最大,服役20年下挠量约为270 mm;主梁跨中挠度前5年平均增长率达33 mm/年,前5年挠度约占前40年的50%,后期主梁下挠趋于平缓。

In order to solve the problem of continuous downward deflection of the main girder for a concrete cable-stayed bridge during its service life,the deflection variation of the main girder for a long-span concrete cable-stayed bridge during its service was analyzed based on the modified model.A dual-objective optimization problem was constructed by using the combined static and dynamic finite element model modification method and was solved by the non-dominated sorting genetic algorithm(NSGA-Ⅱ).The Pareto optimal solution set was obtained,and the coordinated optimal solution was found in the Pareto optimal solution set,so as to modify the finite element model.The calculated values of static displacement and natural frequency of vibration were in good agreement with the measured values after model modification,which can appropriately reflect the actual working state of the structure.On this basis,the influence of time-varying factors such as creep mode and cable relaxation effect on main girder alignment was analyzed by referring to the monitoring data over the years.The results show that the deflection calculated by CEB-FIP 2010 creep mode is closer to the actual deflection.The largest downward deflection is located in the middle span of the bridge,which is about 270 mm after 20 years of service.In the first five years,the average growth rate of the mid-span deflection of the main girder is 33 mm per year,and the total deflection in the first five years accounts for about 50%of that in the first 40 years.The downward deflection of the main girder tends to be gentle in the later period.