Bridges, Trestles, and ballsting

[Herc Driver]

I've tried to find the answer to this, and haven't been too successful...so allow me to ask...

I've noticed on some metal structures, the ballast continues from the track onto the bridge (or trestle), while in other places I've seen no ballast at all. Is that railroad policy specific or based on elevation or length of the trestle or bridge?

The reason I'm asking is, I placed a low-lying trestle on my layout and can't decide if I'm supposed to continue the ballast across the span or not. Locally, I've seen it both ways on the Norfolk Southern rails (which I think are actually owned by CSX), but can't discern why sometimes the ballast continues across, and other times it does not.

Thanks guys.

[nachoman]

Google "ballasted deck bridge" - plenty of links to browse. Specifically I found a thread on another forum (I will use proper etiquette and not link to that forum).

[Herc Driver]

Thanks for the tip! I'll check that out on google right away...I just wasn't finding the right links I guess, and couldn't find it in any books I have either. Thanks.

[doctorwayne]

If I recall correctly, there was an article on this in a recent issue of RMC. Evidently, the track geometry is easier to maintain on a ballasted bridge than it is on one with no ballast. Where bridge ratings are sufficient to accommodate the extra weight, many are being converted to ballasted decks.

Wayne

[nachoman]

Thanks for the tip! I'll check that out on google right away...I just wasn't finding the right links I guess, and couldn't find it in any books I have either. Thanks.

Boy I know how that goes. Sometimes you need the right key word or combinations of. BTW, if you put a (-) sign in front of a word in a google search, it will eliminate results that use that word. Sometimes that is handy when your keyword brings up results from another subject. Let's say you want to search for "southern pacific gp38-2 photos", and when you type that into google, most of the results relate to an atlas gp38-2 that they just released. To clean up the search a bit, you can type "southern pacific gp38-2 photos -atlas" and get more of what you are looking for.

It reminds me of an argument I had with my parents as a kid. I would ask them how to spell something, and they would say "look it up". I would then reply "how can I look it up if I don't know how to spell it?" Sometimes the most frustrating part of internet searches is just figuring out what something is called in order to search for it. Kinda hard to search for a "carburetor do-hickey"

[doctorwayne]

Kevin, third post down: Carburettor doo-hickey.

I guess that you just gotta use the proper spelling.

Wayne

[P5se Camelback]

MY GOD, MAN!!!

Where did you find that? (Yeah, yeah, I know, right where is was when I went to it using the link! ) But did you actually Google "Carburetor doo-hickey?"

I have to go put on a fresh pair of knickers now ... been laughing too hard! Sorry ... I'm easily amused!!!

[doctorwayne]

....But did you actually Google "Carburetor doo-hickey?"

Not quite: I spelled it "do-hickey".

Wayne

[Herc Driver]

Aw great...now you're saying I've got to ballast my carburetor doo hickey?!? Wait...I'm confused.

Good tip about the minus (-) sign on google...I didn't know that one!

[Fluesheet]

Herc,

A ballasted deck will allow the right of way over the bridge to be maintained with the same equipment used to maintain non-bridged right of way, and I suspect it spreads the load over the bridge better than a non-ballasted bridge. And as Doctor Wayne commented, alignment is more flexible than rail-on-bridge-tie. The latter also complicates the maintenance of the right of way approaching the bridge as it must meet the bridge height - adding too much ballast to the approaches, for example, would cause a problem when you get to the bridge. Ballasted decks don't have that problem (I've seen some with a LOT of ballast on them!)

As to why they do it in some cases, and not in others, I don't know. I would suspect expense, expected bridge load and when the bridge was designed are a couple factors. For example, the ballasted decks around here are generally shorter spans, more recently built (maybe 1930 on) and on heavy main lines. Recent grade crossing elimination projects in my area have all been ballasted deck.

Matt

[Herc Driver]

Matt, thanks for the great information.

I've seen bridges and trestles ballasted and some not, without stopping to think why there's a difference. I guess, to make sure I have no labor problems from my LPP's, I'll ballast the trestle on my layout, but with a better understanding as to why it should be.

Thanks guys!

[BR60103]

I suspected that it might have to do with drainage -- bridges over streets seem to be ballasted with a solid bottom while those over streams are just have the ties screwed to the girders.

[nachoman]

I suspected that it might have to do with drainage -- bridges over streets seem to be ballasted with a solid bottom while those over streams are just have the ties screwed to the girders.

Perhaps to keep stuff from falling onto people's cars Remember direct dump toilets?

[Fluesheet]

Good comments above regarding drainage and falling stuff. It occurred to me that reading my 1929 Railway Engineering and Maintenance Cyclopedia might help!

Here's a couple of relevant sections:

"The choice between these two types is governed largely by local conditions. The open deck is obviously the cheaper form, but permits the dropping of coal, water and other substances from the bridge and is thus likely to become a source of complaint [on bridges crossing streets]"

"... While treatment undoubtedly prolongs the life of the timber in a material degree, it is to be remembered that generally ties in a bridge deck are favorably situated to offer maximum resistance to the influences of decay..." (a very long way to say that they don't hold water!)

" A solid floor on a steel or concrete bridge permanently and effectually precludes the dropping of material from a bridge to the passageway below, and is for this reason the most desirable form at crossings spanning city streets or heavily traveled thoroughfares. The ballast deck further provides somewhat better riding surface over the bridge than an open wooden deck, since on a ballast deck bridge the track structure itself is practically identaical in character with that on an ordinary roadbed, and the track is maintained in line and surface by the ordinary section gangs."

Goes on to say that concrete floors effectively permanently protects the metal structure of the bridge and maintenance costs on such bridges are much lower than open deck, making them "a source of ultimate maintenance economy".

"...where open tie deck is used, the elevation of the rail is, in a measure, permanently established, The work of section gangs on the track , performing the ordinary maintenance tasks of lining, surfacing, tamping, cleaning, ballast, etc.,invariably tends to raise the track [and the open deck bridge will eventually be in a depression]..."

On the other hand:

"...[on solid deck bridges] cases have been known where a bridge which was originally built with 18 inches of ballast aquired in the course of twenty years over 4 ft. of ballast." (!)

So open - cheaper, drain very easily, possibly leading to longer tie life
Solid - Smoother, cheaper to maintain, longer lived, protects streets below, easier to maintain the roadbed

Good book!

Matt

[Herc Driver]

WHOA! Now that's some kind of information! Thanks Matt!!!