基于线性规划的连续刚构桥合龙段顶推力研究

Research on closure jacking force of continuous rigid frame bridge based on linear programming method

为了确定多跨连续刚构桥合龙顶推力的最优解,以1座多跨混凝土连续刚构桥为工程背景,取各合龙段顶推力为设计变量,以各墩顶和墩底截面应力为目标函数,以顶推过程中桥墩截面应力为约束条件,基于多目标线性规划方法对合龙段顶推力进行求解。计算时忽略顶推力对主梁混凝土徐变的影响,考虑其对桥墩混凝土徐变的影响,通过线性迭代计算获得非线性最优解,同时对比2种顶推方案(方案1为3个顶推力;方案2为2个顶推力)的优劣。研究结果表明:采用提出的方法经过4次迭代即可收敛,计算方便快捷;考虑合龙顶推力产生的徐变效应时,主梁应力变化幅度相对较小,而桥墩应力变化幅度很大;合龙前施加顶推力对主梁内力影响相对较小,且可以有效调整桥墩受力,使得桥墩在成桥状态荷载组合作用下截面上下缘应力分布均匀;当实际合龙温度与设计合龙温度存在差异时,也可以通过调整顶推力使桥墩受力达到理想状态;采用方案2顶推时结构形成3个独立的框架结构,具有较大的整体刚度,便于保持顶推过程中的稳定性,虽然其增大了顶推力,但减少了顶推次数,总体而言优于方案1。

In order to determine the optimal solution of closure jacking forces of multi-span continuous rigid frame bridges, a multi-objective linear programming was used to calculate the jacking force by selecting a multi-span continuous rigid frame bridge as the engineering background, the jacking force of each closure as design variables, the section stress at the top and bottom of piers as the objective function and the section stress of piers during the process of jacking as constraint conditions. The influence of jacking forces on creep of concrete of the main girder was neglected and on creep of concrete of the pier was considered. And the nonlinear optimal solution was obtained by linear iterative calculation. The advantages and disadvantages of the two jacking plans （the number of jacking forces were three and two in the first and the second plan, respectively） were compared in the end. The results show that the calculation converges after four iterations and the procedure is proved to be quick and convenient for design, while considering the creep effect of closure jacking force, stress variation of the main girder is relatively small, while stress variation of the pier varies greatly. The jacking force applied before closure has relatively little influence on internal force of the main girder, and can also efficiently adjust stress of the pier, so that distribution of stress at the upper and lower edges of the section is uniform under load effects of completed bridge state. When the actual closure temperature is different from the designed closure temperature, stress of the pier can be reached to an ideal state by adjusting jacking forces. While adopting the second plan, three independent frame structures are formed, which have the larger integral rigidity and are easy to maintain stability during the jacking process. Although the jacking force is increased, the jacking times are reduced. Overall, the second plan is better than the first one. 3 tabs, 4 figs, 24 refs.