http://s845.photobucket.com/albums/ab14/Silversensitive/?action=view¤t=DSCF2247.jpg
(Sorry, unable to establish a link)
The work is well under way on a vertical lift span replacing an over century old swing span.
Fixed.
New photos added. Construction continues.
Another interesting bridge project is the moving of the Houma, LA lift bridge on the UP( former SP) to Freeport , TX to replace a badly deteriorated swing span. The Houma bridge was fairly new (built 1980’s) but was on a now abandoned line. The Freeport bridge was built in 1914 and was deteriorating in the salt air from the Gulf of Mexico.
http://s845.photobucket.com/home/Silversensitive/index
I doubt if at Houma they had to fight ice. Late December in the north makes working outside no fun. Worst of all, over water.
Interesting photos - thanks for sharing and posting the link.
Yes, I understand the old bridge will be scrapped. A question about that was asked during a presentation by a BNSF official that I posted a link to about a month ago, and that was the answer. Aside from its raw age and the questions about its integrity that raises, the design - note the multiple thin parallel ‘eyebars’ for cross-bracing in some of the panels - has been obsolete for many years now.
The BNSF presentation - be forewarned, it’s 136 sleides = 108 MB in size, so it will take awhile to download - and my index and comments on it are here:
Railroad Engineering - BNSF Abo Canyon, Memphis IT, & Burlington Bridge
http://cs.trains.com/TRCCS/forums/p/182911/2001900.aspx#2001900
The segment of the presentation on this bridge are slides 89 - 129 inclusive.
- Paul North.
What was the reasoning behind all the cross bracing and bolted eyes? Was welding not used 120 years ago to attach individuals pieces of a structure? It worked for over a century.
Very short history of structural steel design and fabrication:
Welding was not widely used until the 1950’s or so for buildings, and the 1960’s or so for highway bridges - 1970’s for railroad bridges. 120 years ago almost all connections were hot-riveted or held together with large - like 6+" diam. round metal pins. Starting after World War II or so bolted connections were used, and still are.
The cross-bracing is part of the truss design - a series of interconnected triangles, which are very stiff and strong against motion and loads. Without it the bridge would be a series of rectangles, and much easier to flex and deflect under load into a parallelogram/ diamond/ rhomboid shape, unless the corners were made really massive and stiff.
The bolted eye-bars - which might be ‘pinned’ instead/ also - are members that are either:
-
Always in tension under load, so they don’t have to be thick to resist buckling under compression loads because they are never exposed to those kinds of loads. This is determined by the selection of the design or style of the truss, and the sizing of the panels and where the members are in it; or,
-
is subject to reversals from tension to compression and back again as a train proceeds across the bridge. That too is determined by the same factors. In some instances the designer chooses to prevent that member from carrying much compression; in other cases, the member can’t be allowed to carry much compression load, because where it will transer that load to is not easily accepted by the structure. So those members are made as thin eyebars - that way, when any compression load is placed on them, they will flex a little bit and refuse to carry that load. As a result, the load has to find another ‘path’ instead, one that the designer or the bridge style prefers.
For more on this, look for a book on old steel bridges.
Turn buckles on rods are visible on this old bridge. What was the logic behind their use? Were they adjusted at regular intervals? When did this go out of favor?
Obsolete technology is usually so much easier to comprehend.
PDN’s explanation of eye bolts is very revealing. Remember last summer (?) the Oakland Bay bridge authority found several eye bolts cracked and had to close the bridge until replacement bolts were shiiped in from out of state.
PDN’s explanation of eye bolts is very revealing. Remember last summer (?) the Oakland Bay bridge authority found several eye bolts cracked and had to close the bridge until replacement bolts were shipped in from out of state.