How to calculate moment, shear and floor with equivelent cooper E loadings for a GE C40-8 locomotive. I need to build a table for bridge spans up to 100 feet.
The specs for C40s are well documented online.
I cannot find my AREMA books with the practical formulae, its been years since I've even thought about this stuff.
Randy
Perhaps Private Mail to Overmod. I will ask our Physics /Math guy tomorrow see what he says. He is a P. Eng
Would be like trying to teach surgery on-line - needs a least 1, possibly 2 semesters of 3-credit courses in Statics and Simple Structures.
Moreover, those loads depend on the length of each span- i.e., is a 80' span a single span or 2 of 40'? - and if a truss, the configuration/geometry of each of the triangles of that truss. That kind of information is necessary to calculate the "influence line" for those loads in each member. Without that info, there are so many combinations that it's not practical to do so. Even with it, there will be a different E-rating for each member - all will have to be checked, because the lowest rating will control. Note too that these loads are just the 'external' ones for each memeber, and don't take into account the 'internal' loads and stresses which depend on the shape and materials of each member as well.
Nevertheless, here are a few links froma quick Google search that may be useful. Note the scheme of the Cooper's loading, and that a rough approximation may be obtained by comparing the axle loads and spacings of the E-10 loading with the axle loads and spacings of the C40-8. Also note how the frame and truck centers of the C40 act as kind of a superimposed bridge across several of the Cooper's axles.
https://www.trainorders.com/discussion/read.php?1,706188
https://en.wikipedia.org/wiki/Theodore_Cooper#Coopers_Loading_System
http://www.dot.ca.gov/des/techpubs/manuals/bridge-memo-to-designer/page/section-17/17-130.pdf
https://www.arema.org/files/library/2001_Conference_Proceedings/00040.pdf
Note the 2nd sentence in the Introduction of the above reference (emphasis added):
"While it is possible and permissible to compute ratings for specific equipment, such practice is uncommon, and the Cooper’s E loading is the common standard."
Also, in the Fatigue Criteria Effect table on page 4, note how there are many different ratings for the many parts of the same structure, even the 88' Thru Girder at the bottom (since the others are longer than the 100' in the Original Post).
- PDN.
Don't look to those that built the pedestrian bridge at FIU for advice.
Never too old to have a happy childhood!
Suspicion is that it is material supplier/buyer that will have 'splainin to do. Forensic engineering on this one will be interesting to see if design vs. construction vs. materials can be separated in the final analysis. (Something went terribly wrong in the post tensioning process)
Wise counsel from PDN. Something still missing.
I have not looked at the 'accelerated' construction methodology carefully, but I immediately thought of the lesson taught by the flying-buttress failure at Beauvais Cathedral. This bridge was, I understand, intended to be cable-stayed. But before even starting to erect the pylon, let alone string and tension the cables that will suspend the beam of the deck with gravitational stabilization ... they start cranking up the longitudinal tension in that long, slender deck, not stopping when cracking and then spalling is observed? With traffic passing below?
Eerie similarity with that answering-machine business to Theodore Cooper's letter about the Quebec Bridge signs of failure in 1907, perhaps a similar case of improperly-diagnosed massive overstrain out of expected planes.
mudchickenSuspicion is that it is material supplier/buyer that will have 'splainin to do. Forensic engineering on this one will be interesting to see if design vs. construction vs. materials can be separated in the final analysis. (Something went terribly wrong in the post tensioning process)
Interesting dashcam video of the collapse showing what appears to be a buckling about 30-40 feet south of the north support of the span, which wouldn't have been my guess originally. The forensics on this one will be interesting.
I downloaded the NBS report on the 1981 walkway collapse in Kansas City and the investigative findings, beyond the obvious engineering errors (designing something that was unreasonably difficult to implement then approving a design change without realizing that the load on critical elements was doubled by the change) into more subtle errors of design and construction.
This all goes back to a wonderful quote by a high-rise structural engineer who opined that the difference between conservative engineering and rabid paranoia was barely detectable. That's not limited to structural engineering, by the way.
ChuckCobleigh This all goes back to a wonderful quote by a high-rise structural engineer who opined that the difference between conservative engineering and rabid paranoia was barely detectable. That's not limited to structural engineering, by the way.
I've run across several oopsie's in my career as an EE which I attributed as being due to "insufficient paranoia", i.e. not taking some time into thinkng what could go wrong. This is even more important when an oopsie could lead to serious injury or loss of life (which can happen with electronic equipment).
I'd also am interested in seeing a forensics report on the FIU bridge collapse.
I'd also second MC's comment about Paul's post. I know enough about structural engineering to know that I don't have a clue about to properly due a Cooper's E-loading rating.
erikemI've run across several oopsie's in my career as an EE which I attributed as being due to "insufficient paranoia", i.e. not taking some time into thinkng what could go wrong. This is even more important when an oopsie could lead to serious injury or loss of life (which can happen with electronic equipment).
I think maybe all of us who have some serious work in EE or other fields have seen that. I always loved the phrase "mission critical" as defining the level of concern required. I worked with a software engineer who epitomized my paranoia statement, in that any time he made even a one-line correction would spend some time agonizing over how the change could bite us. When he came up empty, he would release the change for testing. We were rarely bitten by anything he did.
I know enough about structures from statics and solids to appreciate the complexity of the problems involved and I guess I'm glad that I went the EE path with its own complexity problems. An appreciation of Professor Rube Goldberg is nonetheless a good thing to have.
OvermodI have not looked at the 'accelerated' construction methodology carefully, but I immediately thought of the lesson taught by the flying-buttress failure at Beauvais Cathedral.
In this case the accelerated bridge construction means the concrete bridges was built on a nearby site. When finished it was transported like a pre-cast concrete element into its final position. Video: http://abcnews.go.com/US/explaining-accelerated-bridge-construction-technique-collapsed-miami-bridge/story?id=53777995
OvermodThis bridge was, I understand, intended to be cable-stayed.
Yes, the bridge looks like a cable stayed bridge: http://www.mcm-us.com/sites/default/files/styles/project/public/slider/east_view.jpg?itok=h0vYI120
But I found a US Today online report that states that the bridge was a truss bridge. They pylon and the stays were just for show: https://www.usatoday.com/story/news/2018/03/16/miami-bridge-collapse-suspension-cables-support-tower/431418002/
Here are two quotes from the linked report: Cheryl Stopnick, an outside spokeswoman for FIGG Bridge Engineers, which designed the bridge, said the structure was “truss bridge with above-deck truss elements.”
Robert Accetta, the National Transportation Safety Board investigator in charge, said diagonal elements between the bridge’s canopy and deck worked like a truss bridge. But the cables designed to fan out from the column weren’t needed to support the bridge deck, he said. “As I understand it, these were cosmetic,” Accetta said. “They were not structural members.”
I don't know if this is correct but it would explain the otherwise odd building sequence.
I have problems with the post tensioning process too. I would have aspected it was already done on the building site before final positioning. The location of the intermediate supports for the transport might have prevented the full tensioning though. Then I would have expected to keep the intermediate transport supports in place until the post tensioning is finalized.
Or it was post-tensioned for its own weight on the building site and that worked for the transport too. So post-tensioning after final erection might have been added for the additional dead loads and live loads only.
But that is monday morning quarterbacking. Will see what NTSB will find out.Regards, Volker
VOLKER LANDWEHRBut I found a US Today online report that states that the bridge was a truss bridge. They pylon and the stays were just for show: https://www.usatoday.com/story/news/2018/03/16/miami-bridge-collapse-suspension-cables-support-tower/431418002/
Now that is really stunning. Have any other bridges been built with large elements appearing to be standard functional structural components, but actually being just for syle and appearance?
Plenty of stuff out there with zero members and dead load. (usually at an architect's insistance for aesthetics or weather protection purposes)...no big deal normally.
[quote user="mudchicken"]
[/quote] At the risk of flingin' a polecat in the middle of the family choir practice; and someone who was almost victimized/mashed, by another engineering mistake , some years back. Paranoia, in the practice of engineering, can be a good thing at times. [ My close call was almost caused by six floors of 'double-tee's' {precast/prestressed concrete beams} that were caused to fall,when a supporting point, sheared off, and caused the cascade of the entire six floors of parking garage,stair -well to collapse, above the point where we were eating lunch. ] Which, I guess is why, Engineering, like Medecine, is only 'practiced' by those IN the professions; done well by some, not so much by others.
mudchicken Plenty of stuff out there with zero members and dead load. (usually at an architect's insistance for aesthetics or weather protection purposes)...no big deal normally.
I am just surprised that a truss bridge would be built to look like a suspension bridge complete with a tower that looks to be 50-70 feet tall and array of suspension cables fanning out from the tower and connecting to the bridge trusses; -----when the tower and cables are not actully performing any support function, but are just there to make the bridge appear to be a suspension bridge.
Overall, there is just something about this bridge project that makes it seem like so much more than just a bridge.
samfp1943Paranoia, in the practice of engineering, can be a good thing at times.
I wouldn't go so far. But respect for the task ahead and self-reflection are desirable.
With experience you learn were you have to do a double take. Some construction elements have internal reserves others like brackets don't.Regards, Volker
For us viewers of this thread that have almost no idea of bridge construction we have some questions. Forensics has much to follow thru . Suspect that this short list is only a sampling of problems that may have occured ?
1. Design -- Not enough steel as one possible item
2. Materials not up to specification
3. continous pour or separate ?
4. Concrete used stale
5. placing finished bridge on transporter
6. placing on columns
7. Any pretensioning
8. What caused crack and location top or bottom maybe indicating compression or tension crack
9. Did failure of bridge start at crack
10. Did post tensioning close crack and cause failure
.
I have a question on a bridge with a flat floor (concrete), a vertical center truss above the floor and little arch to the floor. How does the tension to the floor address (handle) the vertical forces on the structure? At first look, the bending moments on that long span are asking for fracture. I would love to see the calculations. The stays had to be there to transfer the vertical loads from the span to the pylon. Also, how was the center truss connected to the floor? That could be a stress point leading to cracking.
I have a question on a bridge with a flat floor (concrete), a vertical center truss above the floor and little arch to the floor. How does the tension to the floor address (handle) the vertical forces on the structure? At first look, the bending moments on that long span are asking for fracture. I would love to see the calculations. The stays had to be there to transfer the vertical loads from the span to the pylon. Also, how was the center truss connected to the floor? That could be a stress point leading to cracking. I hope they have test cylinders of the concrete to prove it had the speciied strength.
2018...two thousand and eighteen.
Advanced computers and technology.
The Romans could have built this thing and it would still be there.
Electroliner 1935 I have a question on a bridge with a flat floor (concrete), a vertical center truss above the floor and little arch to the floor. How does the tension to the floor address (handle) the vertical forces on the structure? At first look, the bending moments on that long span are asking for fracture. I would love to see the calculations. The stays had to be there to transfer the vertical loads from the span to the pylon. Also, how was the center truss connected to the floor? That could be a stress point leading to cracking. I hope they have test cylinders of the concrete to prove it had the speciied strength.
The truss consists of the bottom deck, the diagonal struts, and the top deck. The vertical load tends to sag the truss between its two end supports. The sagging force puts the lower deck into horizontal tension which is resisted by the tension cables embedded in the concrete of the lower deck.
Electroliner 1935I have a question on a bridge with a flat floor (concrete), a vertical center truss above the floor and little arch to the floor. How does the tension to the floor address (handle) the vertical forces on the structure?
The bottom plate is the bottom chord of the truss, the roof plate the top chord. The top chord gets compressive stress, the bottom chord tensile stress.
Concrete is not well suited for tensile stress. Its tensile strength is less predictable than compressive strength. Therefore in dimensioning is said (at least here in Germany) that all of the tensile stress has to be carried by reinforcement steel.
But you can replace normal reinforcement with post-tensioning. As long as the compressive stress from post-tensioning is higher than the load tensile strength the bottom chord reacts as if concrete would be able to carry tensile stress like compressive strength.
What I described is full post-tensioning. Partial tensioning is possible too but would go too far here.
The post-tensioning reduces the deflection compared to standard reinforcement.
Electroliner 1935The stays had to be there to transfer the vertical loads from the span to the pylon.
The stays are not necessary if the truss is designed and analysed properly
Electroliner 1935Also, how was the center truss connected to the floor? That could be a stress point leading to cracking.
That is something that we don't know. The joints would be included in structural analysis and would be shown in the reinforcement drawings. They are critical points but doable.Regards, Volker
MiningmanAdvanced computers and technology.
Both have a drawback. One gets ever closer to the limits andone doesn't realize it as the software does most of the work.
When I started my career computers were in their infancy and I was able to control the results. Today different safety factors for different load cases and different material safety factors for different load cases make checks almost impossible. You overlook a wrong input on don't realize the wrong result
Nowadays you are walking on a fine line sometimes.
MiningmanThe Romans could have built this thing and it would still be there.
Yes if they could, but the bridge would have been ten times heavier. And no they were not able to build a bridge with 175' single span, multiple arcs yes.Regars, Volker
I am NOT an Engineer, though I thought I wanted to be a ME when I went to Purdue over 50 years ago.
As an outsider, what I see of Engineering in the late 20th and early 21st Centuries has been the aim to minimize costs of a project as opposed to insuring the safety of a project. With the access to the higher level mathmatics and other design facilities - the stresses of both materials and the designs are being calculated to the Nth degree - as opposed to engineering those projects to exceed that designed degree by a factor of 2 or more.
Yes it would cost more and to this layman it would also do more to insure safety.
In the recent history of engineering failures - THERE HAVE BEEN TOO MANY FAILURES!
I speculate that this was not a design flaw, but rather an error in the design of the method of construction or a failure to follow a correct method. The most specific information that I have heard reported is that they were tightening the tension cables in the first diagonal web member at the north end of the truss when the truss collapsed. I draw no definite conclusions from that other than it was underway at the time of the collapse.
Much has been explained about the adjusting of the tensioning cables, and what a critical procedure it is. Some reports say that the cables were found to be too loose. It remains to be seen whether this cable adjusting was part of the plan or something decided in response to some contingency.
Then there is the matter of the cracks that had been discovered and reported a few days earlier. They were dismissed as not being a structural concern. And yet they have offered no explanation for them.
One scenario that I can see that might fit uneplained cracking and unexplained cable looseness is that the truss was mishandled and damaged during the installation process using the big mobile jacking tables.
Miningman 2018...two thousand and eighteen. Advanced computers and technology. The Romans could have built this thing and it would still be there.
You're tellin' us!
Certainly, bigger, heavier, maybe not as pretty, but the fact remains it would still be there!
I'm not an engineer, not by any means, and when the engineers speak I usually shut up and listen, but running through the back of my mind right now is what an old Medieval cathedral builder might have said...
"Forsooth brethren, if thou art not sure, build it stronger!"
blue streak 1For us viewers of this thread that have almost no idea of bridge construction we have some questions. Forensics has much to follow thru . Suspect that this short list is only a sampling of problems that may have occured ? 1. Design -- Not enough steel as one possible item . . .
. . .
It will be interesting to see if that's what happened in the FIU bridge, or something else which is equally plausible at this point (my guess is a botched post-tensioning jacking procedure).
Offhand, I can't think of any US freight railroad structures that are cable-stayed or use post-tensioned concrete - might be some, but not very many. In contrast, there are several in use for light-rail systems.
BaltACDAs an outsider, what I see of Engineering in the late 20th and early 21st Centuries has been the aim to minimize costs of a project as opposed to insuring the safety of a project.
You are right, it isall about cost. We know more about material properties so we can allow higher stresses. There are new materials e.g high performance concrete which is much less fault-tolerant than standard concrete.
I'm not sure if the next is true for the USA too. The nominal safety factor has been the same in Germany over all the years. But in reality it always has been higher. This margin has been reduced to almost zero with better analysis methods (software) and using the better knowledge of material properties.
Here Germany the safety factor is between 1.75 and 2.1 depending on mode of failure. There are very few failures here. We have something here called two-person integrity. We analyze and design and an indipendent engineer checks or work and only with his approval we can go forward. It adds about 1% to the costs.Regards, Volker
EuclidI speculate that this was not a design flaw, but rather an error in the design of the method of construction or a failure to follow a correct method.
It can be anything from faulty structural analysis to wrong drawings to missed indermediate states of construction to bad workmanship. Except a few cases it is usually a combination.
EuclidThen there is the matter of the cracks that had been discovered and reported a few days earlier. They were dismissed as not being a structural concern. And yet they have offered no explanation for them.
Cracks in concrete are not pe se a problem. Cracks up to a width of 0.01 inch in tensioned concrete. Concrete is a crack prone building technique because of the low tensile strength and brittleness.Regards, Volker
Firelock76"Forsooth brethren, if thou art not sure, build it stronger!"
The problem is, we civil engineers are sure now. In medieval the masters of their time knew little. All was try and error.Regards, Volker
VOLKER LANDWEHR Euclid I speculate that this was not a design flaw, but rather an error in the design of the method of construction or a failure to follow a correct method. It can be anything from faulty structural analysis to wrong drawings to missed indermediate states of construction to bad workmanship. Except a few cases it is usually a combination. Euclid Then there is the matter of the cracks that had been discovered and reported a few days earlier. They were dismissed as not being a structural concern. And yet they have offered no explanation for them. Cracks in concrete are not pe se a problem. Cracks up to a width of 0.01 inch in tensioned concrete. Concrete is a crack prone building technique because of the low tensile strength and brittleness.Regards, Volker
Euclid I speculate that this was not a design flaw, but rather an error in the design of the method of construction or a failure to follow a correct method.
Euclid Then there is the matter of the cracks that had been discovered and reported a few days earlier. They were dismissed as not being a structural concern. And yet they have offered no explanation for them.
Yes, it could be a very large number of possibilities for the cause, and the investigation will be gigantic in scope. I followed the search for cause of the 35W bridge collapse in Minneapolis, and it was complex. In this case, I am only considering what I have heard and looking for ways the pieces might fit together.
I know that cracks in concrete are normal and acceptable within limits. And they have not offered any photographs, sketches, or descriptions of the cracks that would allow someone to judge them. However, the cracks were discovered and deemed to be a concern by people involved with the project who would probably be familiar with what type of cracking is normal and acceptable. So this cracking seems to have raised an eyebrow. Then at that point, the official conclusion that the cracks were not associated with a structural problem seems to be presented rather tentatively, rather than as a firm assertion. There were also reports of bystanders hearing loud, whip-cracking-like pops shortly before the bridge collapsed.
In some of the news, one expert was quoted as saying that any cable tensioning should not be performed with the road open for traffic to pass below. How is the tensioning performed? I am guessing that they use a very sophisticated hydraulic puller that shows the exact amount of pulling force applied to each cable. If so, how is the cable secured to hold that exact tensile load after the procedure has finished? How can they reduce tensioning on the cable if necessary?
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