`King Street Bridge failure`

Classic case of a doubler plate welded all around its tip, creating a fatigue crack initiation site at the change in stress concentration. Used to motivate the AISC fatigue-class restrictions on wrap-around welds.

In fact this type of detail right here, where they weld the end of the doubler plate they put on to stiffen up the beam — that's the reason for the King Street Bridge failure in Australia, which is sort of a famous weld failure. I don't think anybody got killed, but it was sort of a major bridge in Sydney or somewhere. It just cracked. They had a doubler plate and they had welded all around the tip. And people learned, oh, that's not a good design detail, because you'll start a fatigue crack right there at the change in stress concentration.

Cruciform fillet weld detail with full wrap-around at a doubler plate; hydrogen crack at the high-restraint location grew in fatigue on the tension side until the bridge collapsed. Used as the case for why modern codes prohibit wrapping welds around the ends.

I had mentioned the King Street Bridge failure in Melbourne, Australia, and I was looking through a book on design of weldments for this course and came across the design that caused the failure. Here's the girder which is holding up the bridge — a very big girder; they didn't give me the dimensions. You had a plate and another plate, and they put fillet welds along here. On one side you have a fillet weld, and on the other side they had what they call a doubler plate. You need a little more stiffness on the flange, so they put a doubler plate on. I had mentioned to you they had welded all the way around.