1. Nearly three months later, she told a gathering in Washington of a working theory‘‘ of a poorly designed gusset plate and a heavy load of construction materials.

2. "They are usually in an X or V shape, and the gusset plate is where those members come together and are attached," Fuss said.

3. Each plate is individually designed, and someone could have miscalculated the load or weight–bearing capacity of an individual gusset plate, he said. In design there‘s always the chance for a blunder,‘‘ Corley said. One of the most common causes of collapse of any type of structure is the blunder.‘‘ Investigators are looking closely at the weight that was on the bridge when it fell.

4. Rosenker said there was little chance that bridge inspectors would have noticed undersized gusset plates. No one recognized that you could undersize a gusset plate,‘‘ Rosenker said. In the history of this organization, we have not seen anything like this before,‘‘ he said, adding that gusset plates are supposed to be stronger than the beams they connect. It was a shock, if you will, to the investigating team.‘‘ Dan Dorgan, the state bridge engineer in Minnesota, said that the assumption is that gussets wouldn‘t be the weakest point in the design. And, in fact, computer programs that generally model these bridges typically do not take gusset plates into consideration,‘‘ Dorgan said. They mainly look at the main members.‘‘ The Minneapolis bridge was deemed structurally deficient‘‘ by the federal government as far back as 1''0, and the state‘s maintenance of the structure has been questioned.