nhrand TESTING A BRIDGE The topic is facinating. I'm reminded of a photo I have of a new bridge on the Central Vermont at Hartford, VT, being tested in 1887 by stretching 12 locomotives over the four deck-type truss spans totalling 650 feet. The 9 4-4-0's and 3 2-6-0 locomotives weighed 845 tons. I wonder, was this an appropriate test or just a publicity event ?
TESTING A BRIDGE
The topic is facinating. I'm reminded of a photo I have of a new bridge on the Central Vermont at Hartford, VT, being tested in 1887 by stretching 12 locomotives over the four deck-type truss spans totalling 650 feet. The 9 4-4-0's and 3 2-6-0 locomotives weighed 845 tons. I wonder, was this an appropriate test or just a publicity event ?
Thanks to Chris / CopCarSS for my avatar.
Real life bridge test
https://www.youtube.com/watch?v=HZ7FKYU-cwE
Never too old to have a happy childhood!
Sorry, but your statement about highway bridges is about 90% inaccurate. There is no "handbook" where you just magically pick out highway bridges. Bridges are designed considering economics (steel vs. concrete vs....), construction methods, subsurface conditions and the resulting foundations, schedule, traffic, construction phasing, and environmental impacts. There are standard beam sections, mainly in concrete bridges, but each highway bridge has its own unique features that makes it pretty much one of a kind, just like a railroad bridge.
D&HRetireeIMPACT!
Can't forget dynamic augment - that vertical impact that even a well-balanced steam locomotive imparts to roadbed, or bridge in this instance. As I recall, this was one of the considerations for the Cooper ratings.
It thus follows that the raw ratings of a bridge may well have been overkill based on first generation power and cars. Today's heavier locomotives and cars might tax that.
Larry Resident Microferroequinologist (at least at my house) Everyone goes home; Safety begins with you My Opinion. Standard Disclaimers Apply. No Expiration Date Come ride the rails with me! There's one thing about humility - the moment you think you've got it, you've lost it...
Middleton was an R.P.I. graduate and a member of the Rensselaer Model Railroad Club way back about three iterations ago. When I first joined the Club I was told that Middleton had built the deck truss bridge that dominated the layout.
Anyway, railroads may use different "E" loading design ratings for different lines. Branch line bridges may be designed to a lesser standard than main line bridges. Although many branch line bridges will be hand-me-downs from main line bridge repklacments.
IMPACT! An additional weight "felt" by the bridge when the train comes onto the bridge. Impact varies with speed, type of engine, length of bridge span, open vs. ballast deck and other factors. Impact under a steam engine with recipracating drive rods is considerably greater than impact under a diesel engine with smoothly applid power. It was often necessary to limit the speed of a heavy car over a bridge in order to reduce the impact loading and hence total loading on the bridge. This is one way in which the diesel has extended the life of many older bridges.
Having been prematurely retired in 1996, I may be a bit "rusty." As I recall the maximum moment developed by a movable load crossing a span occors when one of the heavy loads is the same distance from one end of the span as the center of gravity of the loads applied to the bridge member is from the opposite end of the span. While Cooper loadings were designed for steam locomotives by the time diesels arrived the operating supervision had some concept of cooper loadings developed by various classes of engines so the Engineers used equivalent cooper loadings for the new diesels. The arrival of computers made this SO much easier. Back when I was clearing heavy loads over our railroad, the major on-line shipper of these loads was able to provide me with a print-out of the equivqlent Cooper loadings the combination of load and car would develop on various lengths of spans. Can you imagine trying to do this manually for a sixteen-axle car with a million pound load? Our railroad adopted the E-80 design standard back in the 1930's. As far as estimating dead load, whenever we completed design of a bridge, the weights of various components were entered in a file and plotted as a guide for estimating dead loads for future designs.
BaltACDI have always been led to believe that the Cooper Bridge rating. while having an axle weight component, had that component 'magnified' by the pounding action of the steam engines that operated over the bridges.
Keep in mind that there are other factors in design, including longitudinal braking, taken as ~15% of the live load expressed 6'-8' above TOR, and acceleration, which WAS a nominal 25% of rated adhesive weight at 3' above TOR before corrections for AC and better adhesion were made (I don't know what they are now but MC will).
M636C blue streak 1 What about bridge loading for a train of all iron ore cars load density is very close. In fact I was just scanning some slides from 1977 and 1978 of an iron ore car which had been instrumented to measure track forces... One thing that hasn't been discussed is that the Cooper loadings are influenced by both axle load (of course) and axle spacing. Because iron ore can be very dense, the cars are usually small, but the shortest axle spacing is between cars under the coupler. This was easily seen on strain gauge output from test sections of rail. During my University holidays in 1970-71 I worked assembling English Electric locomotives. They had built two types of locomotives, one weighing 62 long tons and one weighing 89 long tons, both with six axles. These were 3'6" gauge for operation on light rail. I later worked for Queensland Railways and I had to go out one night to a derailed pineapple train on the Yepoon branch. One of the 62 ton locomotives had broken the rail (30 lb per yard, Carnegie Ironworks 1885). The track engineer admitted the locomotive was not at fault... But the two locomotives had the same truck design, but to meet the Cooper bridge loadings, the axle spacing of the closer axles had to be increased by 4-1/2 inches on the 89 ton locomotives. The wooden moulds for the frames had an extension piece inserted and the "seams" were visible on the castings. The axle loads were 15 long tons = 33600 lbs so I guess the bridges were built to Cooper E30.... Peter
blue streak 1 What about bridge loading for a train of all iron ore cars load density is very close.
What about bridge loading for a train of all iron ore cars load density is very close.
In fact I was just scanning some slides from 1977 and 1978 of an iron ore car which had been instrumented to measure track forces...
One thing that hasn't been discussed is that the Cooper loadings are influenced by both axle load (of course) and axle spacing. Because iron ore can be very dense, the cars are usually small, but the shortest axle spacing is between cars under the coupler. This was easily seen on strain gauge output from test sections of rail.
During my University holidays in 1970-71 I worked assembling English Electric locomotives. They had built two types of locomotives, one weighing 62 long tons and one weighing 89 long tons, both with six axles. These were 3'6" gauge for operation on light rail. I later worked for Queensland Railways and I had to go out one night to a derailed pineapple train on the Yepoon branch. One of the 62 ton locomotives had broken the rail (30 lb per yard, Carnegie Ironworks 1885). The track engineer admitted the locomotive was not at fault...
But the two locomotives had the same truck design, but to meet the Cooper bridge loadings, the axle spacing of the closer axles had to be increased by 4-1/2 inches on the 89 ton locomotives. The wooden moulds for the frames had an extension piece inserted and the "seams" were visible on the castings.
The axle loads were 15 long tons = 33600 lbs so I guess the bridges were built to Cooper E30....
Peter
I am not an Engineer and most recently stayed at a Sleep Inn.
I have always been led to believe that the Cooper Bridge rating. while having an axle weight component, had that component 'magnified' by the pounding action of the steam engines that operated over the bridges.
CivilTom,
Welcome to the forum, will interested to see more of your posts.
- Erik
P.S. Some very familiar names from 13 years ago in this thread.
Thirteen years later responding to your post...my wife and I recently visited Age of Steam Roundhouse in Sugarcreek, Ohio. It is a very worthwhile museum with an operating engine roundhouse, workshops for the restorers, etc. Among many steam engines on display was a Baldwin Locomotive, Engine #33, a 2-8-0 that ran on the Lake Superior and Ishpeming Marquette & Southern. It hauled heavy ores, coke, etc.
Of interest to me is that the tour guide, a civil engineer, told us that the 2-8-0 engine was used as the Theodore Cooper Standard E10 loading for trestle/truss design which is still in use today by engineers using an 8-times factor or E80. The standard specifies the use (for design of a bridge) of two of these engines in tandem, or double header as my Dad used to call them followed by an "infinite" number of rail cars with uniform loading per foot of rail. The Wikapedia describes the Cooper E10 rating standard and mentions the E72 for concrete bridges and E80 for steel. They don't provide explanation as to the lesser value for concrete. In doubt, I would use the E80 for both as policy.
Part of my interest in this is that I'm a retired engineer from the Babcock & Wilcox Company where I performed Mechanical engineering tasks and computer programming for 43 years on high pressure boilers, mostly utility.
Back in my school days a Akron U. we were introduced to loadings that matched the E10 as an example problem for analyzing what the author called "influence diagrams". It is a method to estimate the most severe loads created in a particular (or several) components of a bridge while an object (locomotive, tender and cars) passes across the bridge. Back then (circa 1972) such a task was extremely tedious and the text book we used explained how to reasonably estimate the position of the engines and tenders on the bridge that generated the highest loading for an element of the bridge being designed.
Most beam and bridge designs concentrate on dead load of the structure itself which is static and stays in place for analysis. Often, live loads are applied as uniform loading and can be proportionally added to dead load, but only if the structure we are sizing is considered to carry live loading that doesn't act like a concentrated load or at least doesn't move around.
Moving or dynamic loads (not vibrations in this discussion) must be analyzed by literally running many, many static loadings by allowing the steam engines to incrementally cross the bridge, in we'll say, 1 foot increments and in effect take an analysis "snap shot" of the trains in that position and seeing what loads are generated. The trains are allowed to creep forward and stopped after an increment and another loading case is analyzed. This is repeated until the engineer has been assured that all worst case loading configurations have been tested. With today's computers, the task is automated and much quicker. Back in the day, we had methods of reducing the manual trial load positions of the train, trying just a few likely highest load scenarios.
I think the highway bridge designers have a similar loading pattern or template that consists of various types of truck cabs and loaded semi-trailors. They also assume certain "standard" loads per axle acting along the bridge length. I would be curious if today's engineer has programs available to allow the truck to "creep" across the bridge so that the point of highest loading is realized. The problem is complicated on short span bridges because you cannot generally place the truck centered on the span, some of the wheels will hit one or more approaches on either side of the span, hence the need to incrementally allow the truck to take on multiple positions.
Murphy Siding wrote: dldance wrote: Murphy Siding wrote: My book goes on to say "One of the heaviest loading standards ever adopted was used for the Burlington's bridge accross the Ohio River at Metropolis, Illinois, which was designed for a live loading of two Cooper's E90 locomotives.......(and) ...7500# per lft of trailing loading following." This bridge was built in 1917. Why would it have been built to standards higher than today's bridges?Isn't that a double track bridge? If so - then that loading assumption sounds correct.dd There you go. That would explain why they designed it for two E90 loads. Any thought about why E90 in 1917, versus E80 today? Were they expecting steam engines to get a lot heavier than an average 1917 unit?
dldance wrote: Murphy Siding wrote: My book goes on to say "One of the heaviest loading standards ever adopted was used for the Burlington's bridge accross the Ohio River at Metropolis, Illinois, which was designed for a live loading of two Cooper's E90 locomotives.......(and) ...7500# per lft of trailing loading following." This bridge was built in 1917. Why would it have been built to standards higher than today's bridges?Isn't that a double track bridge? If so - then that loading assumption sounds correct.dd
Murphy Siding wrote: My book goes on to say "One of the heaviest loading standards ever adopted was used for the Burlington's bridge accross the Ohio River at Metropolis, Illinois, which was designed for a live loading of two Cooper's E90 locomotives.......(and) ...7500# per lft of trailing loading following." This bridge was built in 1917. Why would it have been built to standards higher than today's bridges?
Isn't that a double track bridge? If so - then that loading assumption sounds correct.
dd
Not only were they expecting steam engines to get larger - engines did. But larger engines were also longer - spreading that load over more spans of a trestle so E80 was and is sufficient for shorter spans. But a large bridge -like the Ohio bridge has long spans. Thus, larger engines still appear as a concentrated load on a long span. Long bridges may also have considerable approach grades - such as the Huey Long bridge across the Mississippi. These approach grades could require additional helper engines. Mid-train or pusher helpers to spread bridge loading adds operational complexities.
....Kevin:
Don't forget the dozen's and dozen's of passenger trains that had to find their way along that 4-track main in it's hay day too.....A very busy ROW.
Quentin
1435mm wrote: mudchicken wrote:It's not the AC part of the locomotives that adds on the extra safety factor to Cooper's System, it's the "high adhesion tration motors & wheelsets" ...You ought to see what happens on some old timber trestles when there is a predominant direction of tonnage and the stringers start walking off the bents & pile caps!True enough but no one seemed to get excited about it until A.C. locomotives appeared.I've seen some of those timber bridges. Exciting!S. Hadid
mudchicken wrote:It's not the AC part of the locomotives that adds on the extra safety factor to Cooper's System, it's the "high adhesion tration motors & wheelsets" ...You ought to see what happens on some old timber trestles when there is a predominant direction of tonnage and the stringers start walking off the bents & pile caps!
True enough but no one seemed to get excited about it until A.C. locomotives appeared.
I've seen some of those timber bridges. Exciting!
S. Hadid
I was once a passenger in a car that crossed an old, poorly maintained and partially rotten wooden road bridge, at way too high a speed. That bridge squirmed like a belly dancer lying in a hot skillet. Exciting wasn't the word for it - VERY high pucker factor.
D. B. Steinman must be David Barnard Steinman, a brilliant bridge engineer of the 1920-1950 period, best known for his long-span suspension bridges, most notably the Mackinac Bridge between Michigan's upper and lower peninsulas. Steinman was not a major railroad bridge engineer as he came onto the scene a little too late to garner any of the big commissions such as his predecessors Lindenthal and Modjeski.
I had no idea Steinman had proposed an alternate to the Cooper system. New to me.
In fairness to your old CE text there wasn't much railroad bridge work happening back then, nor much expected to happen.
Murphy Siding wrote: dldance wrote: "Cooper's loadings do not accurately picture today's trains. [Remember this is 1967 text.] but they are still in general use despite the availability of several more modern and more realistic loadings such as Dr. D. B. Steinman's M-60 loading."What is M-60, and how does it compare to the Cooper loading? I tried to google it, but to no avail. I now know how to load an M-60 machine gun, and learned a little about M-60 tanks though.
dldance wrote: "Cooper's loadings do not accurately picture today's trains. [Remember this is 1967 text.] but they are still in general use despite the availability of several more modern and more realistic loadings such as Dr. D. B. Steinman's M-60 loading."
"Cooper's loadings do not accurately picture today's trains. [Remember this is 1967 text.] but they are still in general use despite the availability of several more modern and more realistic loadings such as Dr. D. B. Steinman's M-60 loading."
Other than this text - I have never heard of it either. The text references Transactions of the American Society of Civil Engineers, vol, 86.
This most interesting thread finally caused me to dust of a text from my 1972 structural analysis class (copyright 1967). Cooper was not even mentioned in the index - but the book introduces the chapter on moving loads with the AASHO H-loadings for highway trucks - which were clearly modeled on Coopers E-loadings. The 489 page text devotes exactly 3 paragraphs to live loads for railway bridges, including a concise description the Cooper's E-loading system. The bias towards highway and structural analysis is implicit in the following quote:
The text also points out that Cooper loadings are proportional -- an E-75 loading is 75/40 of an E-40 loading.
Why did I keep the book? It has a wonderful section illustrating many types of trusses.
The Cooper Rating system applied to timber bridges as well as iron and steel. (It's just a method for estimating live load.)
Many railroad timber bridges, particularly trestles, were engineered informally, based on experience and standard drawings and details. If a Cooper Rating was ever applied it was only after the fact when someone wondered if the bridge would support a heavier locomotive.
S, Hadid
...Mr. Hadid:
Yes, understand the photos and comments of failures of the Quebec episode, etc....I had read of the effort to build said bridge some time in the past and all the failures that occured, etc....What a mess that was until they finally got a bridge...{complete bridge}, in place. Wonder who stood the extra cost to finally get it up and operational.
This whole thread catches my interest on a narrower and historic scale. I am presently working on a history of the Union Lumber Company of Fort Bragg, CA and its two railroads - one being the well-known California Western (CWR). I have yet to gain access to CWR's records, and have not yet seen anything specific in Union Lumber's surviving archived papers relative to the timber trestle and timber or steel bridge designs the company used between 1885 and 1970.
Initially, CWR and its immediate forebear (Fort Bragg Railroad) used redwood A-frame (or modified King) through bridges of a single span with longer trestled approaches to cross creek and river gulches where spring freshet floods might do the most damage. Two particularly bad Noyo River crossings (before 1926) required Howe deck trusses with trestled approaches. By the 1920s as heavier steam power and train loadings became the norm, the railroad began to abandon the use of A-frame bridges ad settled into using steel plate deck bridges on reinforced concrete piers, often with redwood timber trestled approaches. Still, through the late 1940s, steam power had to be separated (mid-train helpers) over most of the CWR since double-headed locomotives exceeded the A-frame bridge loading restrictions. I think the last A-frame bridge was removed and replaced with a steel deck bridge about 1964.
I haven't yet been able to determine if the ULCo/CWR used the Cooper standard in planning its timber bridges and trestles, or whether Cooper was or is used for anything other than steel bridges on steel or concrete/masonry piers.
~Kevin
PRR - "The Standard Railroad of the World" - I always thought this promotional phrase the company employed was just self-aggrandizement, and surely it was, but I have to guess it came semi-deservedly in that the Pennsy had to tote a great deal of weight in its many daily freight trains of coke, coals, steel and iron along with a host of general merchandise. But that's grist for other topic threads...
It figures that the PRR would use its own standard. Note that the YV 2-6-0s have an axle loading on drivers of 40,000 lbs -- or E40.
Quentin -- the photos inserted above show the SECOND Quebec bridge, which was vastly heavier than the first (failed) bridge. As noted by Paul, the center suspended truss section fell while it was being lifted off barges to its final position due to a construction error. Also, the narrative at the linked site is an account of the collapse of the first bridge (even though it pictures the second), which isn't very helpful.
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