中文摘要：

系杆拱桥是拱肋、吊杆、系杆等组合共同受力的，针对这一受力特性，由能量变分原理推导出系杆拱拱肋的弯矩增大系数实用计算公式，以工程实例将所推公式与现行桥规中偏心距增大系数的简化公式计算结果进行对比。结果表明，推导出的实用计算公式的计算结果与现行桥规按照裸拱简化为当量长度的直杆的计算结果相差12．9％～24．3％，所推公式在简化前后计算结果相差在1％左右，显示出简化后的计算公式有一定的经济实用性。所推公式中，系杆拱桥拱肋的弯矩增大系数随轴力增大而略显增大，且与约束条件及荷载形式相关，拱式结构中拱肋的偏心距增大系数与偏心受压直杆的偏心距增大系数有较大差别。

英文摘要：

The arch ribs, hanger rods and tie rods of tied-arch bridge are commonly forced. According to this characteristic, the calculation formula of moment amplification factor of tied-arch rib is derived based on energy variational principle. The results of the project examples calculated by the derived formula and the simplified formula of eccentricity amplification factor in current bridge specification are compared. It shows that （ 1 ） the difference of calculation results between derived practical formulas and naked arch simplified equivalent straight bar under the existing bridge specification is 12.9% - 24. 3% ; （ 2 ） before and after simplification of the structure, the calculation results by derived formula is deviated about 1%, which means the derived formula is comparatively economic and practicable ; （3） the moment amplification factor increases with the increase of axial force, and it is related to the constraint and load form; （4） the eccentricity amplification factors of eccentric compressed bar and arch rib in arch structure has great difference.