Why do some plate girder bridges have ballast? That must add a lot of weight to it.
It's all figured in, during the design of the bridge. If it has ballast, it is a deck-type plate girder bridge. The track is laid in the ballast as it would be on grade.
Some plate girder bridges, the ties act as the deck. Some use timbers, and some have a reinforced concrete deck that is supported by the plate girders.
Not sure of the advantage or the circumstances for one type over the other, I guess it's all in the design of what the bridge is crossing and the span required.
Maybe a resident civil engineer will chime in.
Mike.
My You Tube
Dissusion here
http://forums.railfan.net/forums.cgi?board=Infrastructure;action=display;num=1111672974
I tried to sell my two cents worth, but no one would give me a plug nickel for it.
I don't have a leg to stand on.
mbinsewi If it has ballast, it is a deck-type plate girder bridge.
If it has ballast, it is a deck-type plate girder bridge.
This has ballast. It is NOT a deck-type plate girder bridge:
Ed
Any more pictures of that bridge Ed? I would like to see the substructure.
Mike
Yes, Ed's example is a Through Plate Girder bridge. Some newer truss bridges also have ballasted decks. (Many older trusses cannot accommodate the extra dead load.) In other words, any type of bridge could have a ballasted deck if the design is robust enough.
An open deck is cheaper, often a consideration, but a ballasted deck means the track structure is more uniform, easier to maintain, and the fire hazard is greatly reduced. The deck pan may be concrete or steel. Some wood pile trestles have a deck pan made of wood rather than precast concrete.
John
mbinsewi Any more pictures of that bridge Ed? I would like to see the substructure. Mike
Nope, especially not of the substructure.
Through-girder bridges are usually used to maximize clearance underneath. When they're ballasted, they TEND to use floor beams to connect the girders, cover those with steel plate (if necessary) to keep the ballast from falling, and then ballast and track. Sometimes the design of the floor beams is such that they obviate the need for the steel plate.
Here's another:
http://www.bridgeofweek.com/2015/12/plumas-county-california-bridges-union.html
7j43kThrough-girder bridges are usually used to maximize clearance underneath. When they're ballasted, they TEND to use floor beams to connect the girders, cover those with steel plate (if necessary) to keep the ballast from falling, and then ballast and track. Sometimes the design of the floor beams is such that they obviate the need for the steel plate.
OK, so now I know. Just thinking that something is holding the ballast there. I hope the OP's question is answered !
7j43khttp://www.bridgeofweek.com/2015/12/plumas-county-california-bridges-union.html
Scroll down to the second picture. Neat dint in the first gusset on the right! Something whacked it hard enough to bend the gusset out of place and pop some rivets.
Dave
I'm just a dude with a bad back having a lot of fun with model trains, and finally building a layout!
That gusset is often called a "knee brace". It's very typical (but not bent) of Through Plate Girder bridges. Occasionally they will be outside the main girder rather than on the inside. Pony trusses will often have them too. I have also seen photos of wood pony trusses with outside knee braces.
In Charlotte, NC, at the intersection of Interstate 85 and Graham, there is a span of ballasted plate girder bridges that have always been a curiosity to me. This is at the exit for my NC offices, so I see these bridges fairly often.
.
I don't have a picture of the street level view of the bridges, so I Google-Earthed it.
The rails through the bridges are off-center, which I do not understand. The bridges are not wide enough for them to have been double tracked once, and it looks like the tracks are off center by only a couple of feet.
I have never seen another single track railroad bridge where the tracks were off center, except in the case where it was originally double tracked and one line was removed.
Any ideas? Is this a regular practice? What is the reason?
-Kevin
Living the dream.
Kevin, The track is probably off center to allow room for maintenance vehicles. Most railroads have a maintenance road which runs next to the track.Answer to OP is that bridges with ballast are easier to build and maintain because the ties and rails are not part of the structure. They are just regular track and the bridge just holds the ballast.
Kevin,
As far as I can see, the track is centered on the main part of the bridge--over the roadway. I measured it from the aerial photo. The shadow may give an offset impression.
On the two approach bridges, the track is offset with relationship to the ballast and the "ballast trough". But it DOES appear to be centered over the girders underneath. For some reason, the trough is not symmetrical over the bridge girders. It doesn't have to be. But the track is centered on the REAL part of the bridge.
Track doesn't HAVE to be centered on a bridge. But it always is, in the "best design", because it is cheaper. And if you ask the people who are paying for the bridge, they will think that is of great significance.
7j43kAs far as I can see, the track is centered on the main part of the bridge--over the roadway. I measured it from the aerial photo. The shadow may give an offset impression.
Yeah, if I had known this topic would come up in discussion I would have gotten out of the car and snapped a picture. The tracks are definitely off center, by a visible amount.
I will be back in Charlotte in March. I will get a goodf picture at street level then.
I just spent more time looking at pictures of that bridge, both from overhead and from underneath. Every time I found something that suggested an offset like you're describing, I always found that it was due to the camera angle. That even applies to my earlier statement about the short approach bridges. I now DO NOT think the concrete deck is offset on the supporting girders. The view I was looking at is not DIRECTLY overhead, and I can see how the elements visually offset at that angle.
I'm NOT saying you're wrong. Just that it is not evident in the pictures. I suspect the only way you can KNOW that it is offset is by standing on the tracks, and taking some photos down them. Even better, while you're up there, measure the distance from the girder to the track rail. If they're different, you've GOT IT. You can even say how big the offset is.
I do wonder why you say there's an offset. What are you looking at that says that to you?
Google Earth uses some rendering algorithms that can make for some goofy-looking images:
CN bridge by Edmund, on Flickr
WLE bridge3 by Edmund, on Flickr
EDIT
So I jumped into street view and looked down the track:
Charlotte by Edmund, on Flickr
Yes, the track looks to be a foot or two off the center line. Aesthetically, it will bug you, like a picture frame that's crooked on the wall. When they poured the abutments and set the bridge in place the track may have been re-aligned ever so-slightly.
I80Ngraham by Edmund, on Flickr
From an engineering standpoint, NBD. Heck, in Cleveland the super engineers located a new bridge pier a whole two-feet-nine inches off! That's what you get for $300 million these days.
http://www.cleveland.com/metro/index.ssf/2012/07/pier_for_the_new_inner_belt_br.html
Regards, Ed
Kevin has a winner, here, folks.
(other) Ed's photo shows a clear offset.
Scaling off the photo, it looks like the "left side" is wider than the "right side" by about 40".
A person could (and does) wonder why.
It looks like the load on the right hand girder has been increased by 15% beyond design (assuming they didn't actually design to have the offset).
I SURELY do wonder about this one.
Kevin, I have this assignment for you..........
Lone Wolf suggests the offset is to allow space for maintenance equipment. This might make sense, but there doesn't seem to be a lot of space there, so I don't know how practical it would be.
It seems more likely that a nearby curve was realigned, and the approaches don't match up exactly the way they did before the realignment. But that's just speculation.
Tom
ACY TomLone Wolf suggests the offset is to allow space for maintenance equipment. This might make sense, but there doesn't seem to be a lot of space there, so I don't know how practical it would be.
Consider, too, that there is a grade crossing with easy vehicle access at one end of the bridge and a nearby highway and another crossing at the other.
No real need to drive a maintenance vehicle alongside the track with easy access like that. Many of the maintenance trucks today have pretty beefy hi-rail attachments anyway so an access road isn't always necessary.
Thank You, Ed
gmpullmanHeck, in Cleveland the super engineers located a new bridge pier a whole two-feet-nine inches off! That's what you get for 300 million these days.
That's a good one Ed. Walsh is currently building the Zoo Interchange project in Milwaukee. I know a few cement finishers from our local that work for them.
What till I run into them again.
ACY Tom Lone Wolf suggests the offset is to allow space for maintenance equipment. This might make sense, but there doesn't seem to be a lot of space there, so I don't know how practical it would be.
When I was checking out the underneath of the bridges, it appeared to me the bridges were centered on their piers. Which has me believing the track is offset from the overall center.
As opposed to the bridge being offset from the piers and track.
I expect the railroad predates the current bridge. In that case, a temporary bridge was probably built to the side. And the track had a "joggle" (technical term) over from its permanent alignment. And then the track was put back where it had previously been.
My guess is that the guys building the bridge arrived after the temp bridge and joggle were built. And they never sighted down the track to check their bridge placement. Likely, for placement, they had some survey done from an existing landmark. Which was not the track. And they never thought to reconcile their survey with the reason they were there (the track)(over the roadway).
So, based on the survey, the bridge was placed properly. I believe. It's just that their monument (survey term) was "off". Or, yikes, their surveyor was incompetent. Perhaps both.
The closest curve looks to be about half a mile away. And not exactly a hairpin, either.
As promised... I am in Charlotte, North Carolina, and I took a picture of the bridge in question and measured the offset. We do not need to rely on Google images for this discussion any more.
The rail is about 5 feet from the girder on the right, and a bit less than 8 feet from the girder on the left. It is off center by about 17 inches.
Any ideas for why it is like this? I really have none, and I have never seen another bridge like this.
Kevin
I don't know if easement is the word I am looking for, but I'll bet the State didn't want a railroad bridge any closer to the highway so they can work on that (road) bridge The wider side of the RR bridge is probably the usual clearance to the track. .
Henry
COB Potomac & Northern
Shenandoah Valley
SeeYou190Any ideas for why it is like this?
The B&B gang (Bridge & Building) had a different set of prints than the M-of-W track laying gang.
Whichever one you ask, it was the "other" gang that was off!
Sometimes when I see big projects involving tunnels, skyscrapers or huge bridges it amazes me that anything lines-up.
BigDaddyI don't know if easement is the word I am looking for,
Easement (as in real estate ownership) may be the exact term we're looking at here. The R-of-W for the highway may indeed butt right up against the railroad "easment" or property line. Without filing all sorts of variance documents the RR simply placed the "new" bridge as close to the highway as possible without "crossing the [property] line".
The railroad certainly didn't want to, or have to, keep the track centered between the girders to keep the tangent to avoid having unnecessary curves, so the off-set was an acceptable compromise.
Perhaps?
Cheers! Ed
what is the build date on the rr bridge if its older than the highway ? is there a historical society in the area if so ask them , they might know the anwser.
Agreeing with Ed. So, whats the problem? Is this a big deal that needs investigation? Does the track on every bridge have to be exactly down the center? Who knows.
I'm sure it's an easment type situation, and the builders did what would work.
If you truly need to know whats up with this, contact the state DOT, find out who the job superintendent was, and dig further.
mbinsewiSo, whats the problem? Is this a big deal that needs investigation? Does the track on every bridge have to be exactly down the center? Who knows.
No problem and no big deal. It is just an interesting anomoly. As we all know, there is a prototype for everything if you look hard enough.
I have looked at thousands of railroad bridges and photographed hundreds, and this is the first one I have ever found where the track is obviously so far off center.
To me, it is no more than just an interesting curiosity for discussion, theories, and amusement. On my model railroad all the bridges will have centered track. I prefer to model what is normal. My nonsense just looks better that way.
SeeYou190On my model railroad all the bridges will have centered track.
I often see and sometimes photograph, real-life views of things that would not translate well to a model railroad.
Stuff like crooked utility poles, oddly painted structures or, as you point out, track not centered between the girders, unless of course, it was former double track that had been "downsized".
IMG_2710 by Edmund, on Flickr