[Attention Surplus Disorder]

One assumes it was thoroughly engineered; however, in that picture, to my eye, the vertical steel supports directly over the concrete pylons appear...skinny....as they are no thicker than the members forming the trangles within the truss structure(s). My implication being: The members within and forming the triangles within truss structures are either overspec'ed or the verticals directly over the concrete pylons are underspec'ed because the triangles are pretty much just in compression whereas the verticals are not only in similar compression, but have to support the weight of the whole thing. Disclosure: I'm not a structural engineer.

[meyer]

One assumes it was thoroughly engineered; however, in that picture, to my eye, the vertical steel supports directly over the concrete pylons appear...skinny....as they are no thicker than the members forming the trangles within the truss structure(s). My implication being: The members within and forming the triangles within truss structures are either overspec'ed or the verticals directly over the concrete pylons are underspec'ed because the triangles are pretty much just in compression whereas the verticals are not only in similar compression, but have to support the weight of the whole thing. Disclosure: I'm not a structural engineer.

I think it's a rigid structure from one end of the girder'ed section to the other, with the little pylons in the middle just to hold up the weight. The tangental support would be primarly at each end of the girder structure.

But, being a rigid structure, and being a bit aged and probably having a great deal of rusted fasteners, the structure was prime for a cascading failure as a result of a single failure.

My guess is that some important piece or brace broke - but it was something that wouldn't have caused a collapse back in 1967 when the bridge was new. However, considering that there are many old bolts or rivets, stress cracks, and other weaknesses, a simple failure and shifting load might have been all it took to cause the total collapse of the structure.

[Gideon7]

In that picture, to my eye, the vertical steel supports directly over the concrete pylons appear...skinny....as they are no thicker than the members forming the trangles within the truss structure(s).