Hi All

I am looking at the cooper bridge rating system and I am trying to learn more. The Bridge in question was built to an E 80 standard which seems to match the UP standards for industrial spurs. Given a steam locomotive's dynamic augment I am trying to figure out is the largest steam locomotive that can use such a bridge. Any direction to help my research would be a great help. Thanks in advance.


Robby Peartree

I don't remember too many details, but both the White Pass & Yukon, and the entire IRCA in Guatemala both used the Coopers E 27 raring for their bridges and the heaviest axle load that could roll across those were 27,000 lbs each, and those were originally steamers with 3-4 coupled axles and 40" - 44" driver diameter and driver spacings of 44" - 48". Both RR's used 40-45# rail when this rating was applied to the then new RR's.

I read about the Coopers ratings and took some notes on it, but ill have to locate them before I can help you much..

Your E 80 is limited to an 80,000 lb axle load, but that's all I know right now.

https://en.wikipedia.org/wiki/Theodore_Cooper

Two things-
One, is that this standard was developed with steam engines in mind.
Two, is that the wiki indicates that E80 is about one of the strongest bridges made. Based on the context of your question, it makes me think your E80 rating is wrong, the article is wrong, or you have one very, very strong bridge and don't realize it.

Below is the link I found.

Robby


http://www.up.com/cs/groups/public/@upr ... 710001.pdf

The Cooper loading, such as E-80, is just part of the picture. The other major consideration is impact factor, which is different for diesel versus steam locomotives. The latter use a larger factor on account of the "hammer blow" associated with the rotation of rods and counterweights. The impact factor also varies depending on the particular structural member under consideration. Notably, impact is only applied to portions of the bridge superstructure. The loadings on the substructure (i.e. concrete and masonry piers and abutments) do not have an impact factor applied. Note that the calculations for design shoring for below-track excavations (see the link provided by another respondent) do not include an impact factor for the same reason.

Chapter 8 of the AREMA "Manual for Railway Engineering" is the bible for this stuff. However, the following link has a good discussion of the complexities.

http://wisconsindot.gov/dtsdManuals/str ... e/ch38.pdf

Back during my brief tenure in the Bridge Office of the Reading Company's Engineering Department, we used a Cooper E-72 loading (with diesel impact) as the standard. However, just in case, every structural member was also checked against the loading of the Reading's 4-8-4 T1 locomotive with steam engine impact.

Most railroad bridges that are around the century mark in age were originally designed for something in the range of Cooper E-60 to E-65 with steam locomotive impact. Assuming the bridge has seen reasonable maintenance, a structural analysis typically reveals that they can accept any contemporary diesel locomotive loading. Your mileage may vary.

Caution: Unless you have extensive schooling in structural engineering, preferably in bridge design, detailed analysis of railroad bridges is absolutely not a do-it-yourself project. There are far too many complexities and nuances.

/s/ Larry
Lawrence G. Lovejoy, P.E.

Hi

Thank you for the response. I am not designing the bridge only looking at what is to be constructed and wondering what can actually go over it.
The bridge was designed with AREMA manual for railway engineering 2010. The live load is AREMA cooper E-80 and alternative live load with impact.
Bridge loadings and the difference conditions a steam locomotive introduces are interesting to me.
I wonder in this day and age of modern standards if the steam locomotive obsolescence does not hide an engineering surprise to the uninformed.

Robby Peartree

I've worked in the B&B ( bridge & building ) department CNW/UP in the field for 38 years. The worst vertical impact I've seen to a bridge is when an engine dips down into a depressed dump
( the Dump is at the immediate end of the steructure where the track ground contact ends and tends to get beat down and settle) then raise up out of it and slam down onto the bridge or trestle. 30 to 48 MPH is the best speed for the worst impact. On the stiffer trestle you get crushed caps ( caps are timbers that sit between the top of pilings or false bents and stringers)
The steel bridges seem to take it in stride but they definitely spring about. We weren't really concerned with short sharp impacts such as real bad flat spots on a loaded hopper. Now side loading a bridge is another animal all together. You can knock a trestle out of alinement with heavy slack action especially if the light cars are on the bridge.
The early Cooper ratings that I saw were designed for a number of 2-8-0's all the same weight being or running on a bridge at the same time. The higher the rating the more 2-8-0's. Our bridges spanned from 1880's to present. I hired out 1975 C&NW Chicago Terminal Division.

I recall seeing a particular issue of the publication of the organization for railroad track maintenance professionals. This one had an article about the problems of railroad bridges at the beginning of the age of articulated container cars.

A particular problem was noted with bridges of short spans (less than the truck-to-truck distance of these cars) The bridges would receive the loading and then it would be removed only to be loaded once again with the next truck. Longer spans would always have a loading; but, it would move across the bridge (that was always a problem).

The railroads found that the bridges built during the steam locomotive era were less subject to structural fatigue cased by these heavy loads. The new bridges that were built did not have the safety factors and over-design of the older bridges.

To carry the loads of the container cars railroads were modifying the new bridges built with two girders. The railroads were adding an additional girder beneath the center of the bridge.