中文摘要：

变分原理通常应用于箱形截面梁剪力滞效应弹性分析，本文基于换算截面法，运用变分原理推导了预应力混凝土简支箱梁均布荷载作用、钢筋混凝土简支箱梁集中荷载作用的剪力滞系数计算公式，考虑了混凝土开裂对箱梁剪力滞效应的影响，并与试验结果和规范方法进行了对比分析。变分原理分析开裂混凝土箱梁剪力滞效应方法力学概念明确，是其弹性分析适用范围的拓展，亦可推广应用到混凝土连续箱梁开裂后的剪力滞效应分析，具有广阔的应用前景。

英文摘要：

Variational principle usually applied in shear lag effect analysis of box girder. In the paper,base on transformed-section method, adopting variational principle, it deducing shear lag coefficient formulation of simply supported prestressed concrete box girder under uniform load and simply supported reinforced concrete box girder under concentrated load, concrete cracking is considered in shear lag effect, and compared with experimental result and design code. It is clear in mechanical concept to analyze shear lag effect of cracked concrete box girder by variational principle, it is the extension of elastic analysis, and it can also be applied in shear lag effect analysis of cracked concrete continuous box girder, it has wide application prospect.