This paper describes a study on improving redundancy in a 240 m span steel Pratt truss bridge. Redundancy was evaluated from two perspectives. The first perspective was how many members would induce bridge collapse owing to their own damage, and the second perspective was how many members would be damaged owing to another member’s damage. Members corresponding to these two perspectives were widely present throughout the subject truss bridge. As a measure to improve redundancy of the subject truss bridge, the method of installing alternative load paths by retrofitting additional braces was studied. Three proposals with different geometry of the additional braces were compared, and "X bracing", which equipped X-shaped braces by adding braces in the opposite direction to the existing diagonal member, demonstrated excellent performance. In addition, the effect of the method retrofitting the cable along the member was also studied. Next, the placement patterns of "X bracing" on 18 truss panels of the subject truss bridge were examined using an optimization technique. It was clarified that examination of the placement for the additional braces was important for the efficient improvement of redundancy, and that the optimum placement of X bracing was in the alternating areas. Finally, the buckling gusset plate of the I-35 W bridge was also in the alternating area, suggesting that reinforcement of the alternating area might be important for redundancy of truss bridges.

本文描述了一项关于提高 240 m 跨度钢普拉特桁架桥冗余度的研究。从两个角度对冗余进行了评估。第一个角度是有多少构件会因自身损坏而导致桥梁倒塌，第二个角度是有多少构件因其他构件损坏而损坏。与这两种观点相对应的成员广泛存在于整个主题桁架桥中。作为提高主体桁架桥冗余度的措施，研究了通过改造附加支撑来安装替代载荷路径的方法。比较了具有不同几何形状的附加支撑的三种方案，通过在现有对角线构件的相反方向上添加支撑来配备 X 形支撑的“X 支撑”展示了出色的性能。此外，还研究了沿构件改造电缆的方法的效果。接下来，使用优化技术检查了主题桁架桥的 18 个桁架面板上的“X 支撑”的放置模式。澄清了检查附加支架的放置对于有效改善冗余很重要，并且 X 支架的最佳放置在交替区域。最后，I-35 W 桥的屈曲角撑板也在交替区域，这表明交替区域的加固可能对桁架桥的冗余很重要。使用优化技术对主题桁架桥的 18 个桁架面板进行了检查。澄清了检查附加支架的放置对于有效改善冗余很重要，并且 X 支架的最佳放置在交替区域。最后，I-35 W 桥的屈曲角撑板也在交替区域，这表明交替区域的加固可能对桁架桥的冗余很重要。使用优化技术对主题桁架桥的 18 个桁架面板进行了检查。澄清了检查附加支架的放置对于有效改善冗余很重要，并且 X 支架的最佳放置在交替区域。最后，I-35 W 桥的屈曲角撑板也在交替区域，这表明交替区域的加固可能对桁架桥的冗余很重要。