Message #150678

[Christian Kielbasa]

Low redundancy, high strength
The eyebars in the Silver Bridge were not redundant, as links were composed of only two bars each, of high strength steel (more than twice as strong as common mild steel), rather than a thick stack of thinner bars of modest material strength "combed" together as is usual for redundancy. With only two bars, the failure of one could impose excessive loading on the second, causing total failure—unlikely if more bars are used. While a low-redundancy chain can be engineered to the design requirements, the safety is completely dependent upon correct, high quality manufacturing and assembly.

In comparison, the Brooklyn Bridge, with wire cable suspension, was designed with an excess strength factor of six, which proved fortunate owing to a contractor's substitution of wire weaker than that specified. (This was discovered before completion and additional strands were placed in the bundles.)