back in the mid 60's, what style of bridges were being built for a heavy traffic mainlines?? i am planning on building one on a radius. there will be 2 main lines running on it. thanks...
At that time, if the under-track clearances allowed, the preferred design would have been a steel deck girder with a solid, ballasted deck. For situations where the railroad had to bridge streets or highways the girders would be extended above the deck and the under-rail section would have been reduced to the thickness of the floor structure.
Through trusses were going out of use (too restrictive to high, wide loads;) and closed, ballasted decks were preferred for new construction since they didn't require special ties or track-building techniques and were easier to maintain. They had the added advantage of protecting the deck structure from the weather, and the world under the bridge from dirty drips and falling objects.
Of course, a lot of the bridges in use in the 1960s had been built decades before, to earlier designs and standards. There are bridges in use today that date from the early 20th century and before.
The one design to avoid (model press and practices notwithstanding) is the timber trestle. Most of the earliest ones were converted to embankments before Teddy Roosevelt made a name for himself. More recent ones are either on temporary track scheduled for use and removal (one near Humboldt, AZ, provided access to a mine - when the mine played out, tracks and trestle vanished) or scheduled for replacement with fill material. Either way, they were very unlikely to be found on main track as late as 1960.
Chuck (modeling Central Japan in September, 1964 - with lots of deck girder bridges)
Just as a matter of interest, I recently travelled on ViaRail from Toronto to Vancouver and at Parry Sound we crossed a bridge which appeared to be of wooden construction. If it is this must be one of the last timber mainline bridges still in use.
Perhaps a Canadian member has more information.
Dave.
Edit: After Googling "Parry Sound Trestle" I found an article about this bridge, It is a steel trestle built in 1908 but from above when viewed from the train only the upper wooden track structure can be seen
My understanding is that the CPR converted all of its timber trestles in the Rockies to steel construction or fills with culverts within about 40 years of the original placement. I don't know about other small ones here and there, but I would be surprised. On the other hand, didn't the failure to properly maintain a short wooden trestle result in the rather bad accident at Hinton, AB, just a few years ago? That was on CN's lines if I recall.
-Crandell
Edit - It was Edson, and it was a girder bridge.
does anyone have any pics of a deck girder bridge on a radius?? i have been searching on google with not much luck... thanks ...
I would imagine the Keddie Wye bridges are deck girders on radii.
http://www.flickr.com/photos/79924635@N00/92416597
The Spanish Fork Bridge (Keddie Wye's official name) is an older, open-deck design incorporating both deck girders and deck trusses in its design. I'm sure that if it ever needs serious rehab a ballasted deck modification will be considered.
The girders themselves are straight, but of sightly different lengths in the same span, and meet end to end at an angle. In an open frame design the object is to keep steel directly beneath the rail. Ballasted decks, with their more forgiving structure, allow some slight deviation. If the deviation becomes great, the lengths of the individual spans will have to be shortened, or a third support girder will have to be placed under the deck. Five girders under two tracks on a ballasted deck bridge are not uncommon.
That, incidentally, is another advantage of a ballasted deck. It can handle more curvature per span than an open deck.
Chuck (modeling Central Japan in September, 1964)
The Southern Pacific (now UP) main line crossing the Yolo Bypass (west of Sacramento) was still on timber trestles in the 1960's. The components are mostly, perhaps all concrete now (replacing the wood in kind). Replacement with concrete was done a little at a time over many years. I don't remember when the first concrete appeared on the structure, but believe it wasn't until the 1990's.
The wooden bents on a trestle in Marysville CA (on the Shasta Route) have been wraped and covered with a layer of concrete or stucco.
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