Re: Chama bridge part 2 - caution model content *PIC*

Hi Dave,
I like the detail shot of the Chama River Bridge abutment support. My attached photo is of the first pier from the Chama end of the bridge. This is the other end of the span you have the the photo of on your web site. Notice that the second span (to the right in my photo) has the same type of footing to the pier. The left footing in my photo is dissimilar. Steel bridges always have one end of the bridge fully restrained (like the left-hand footing in my photo). The other end is always allowed to move in the direction of the track or roadway. It shows up much better in your next to last photo than in my photo that the partially restrained footing does not allow left and right movement keeping the bridge aligned with the track. However the longitudinal direction can expand and contract. Since this is a pinned truss bridge and the partially restrained footing does not restrain vertical displacement, you might actually cut the rails and lift one end of the bridge up pivoting on the pin on the pier in the river. I'd definately NOT advise trying this, but it might help understand the structure and what you are seeing.
I'd also like to mention that this type of sliding joint was sometimes required periodic maintenance to have greese or other lubricant around the sliding areas to prevent rusting of the bearing plate surface. More modern structures used a pizza slice type wedge that would allow the wedge to roll over the surface. It requires less maintenence - just making sure junk (like logs or rocks) get in the way of the movement.
Doug