I think that if I were the engineer operating those 3 locomotives at nearly 200 tons each, I’d have a whole lot of pucker going on crossing this bridge… Seems a might bit spindly for that amount of weight. I’m sure UP’s crack engineering team has tested it “six ways til sunday” but still, it just looks light for all of that weight.
I liked this bridge at Cutbank when I was aboard the Empire Builder.
http://railpictures.net/viewphoto.php?id=229779&nseq=0
I get the same feeling going over the High Bridge just west of Boone Ive been over it a couple hundred times but the bottom line is I dont like high places at all and by the way there was a conductor with the engineer in the cab of that locomotive Larry
Another one that could go to a museum ! Classic pin-connected deck truss, 7-panel single span, statically determinate externally & internally.
So the loads on each member are very predictable in magnitude and direction, and are all axial = along the member’s length. As a result, they don’t have to be beefed-up to carry loads that would be across or transverse to them (shears and bending moments, rarely torsion).
Can’t tell for sure from this far away, but all the tension members look like either rods or eyebars, and the compression members - the thicker or “heavier” ones, which makes them stiffer so they don’t buckle under load - look like they’re built-up with cross-laced pieces.
Built way back in the day when materials were expensive and labor was cheap - probably not a pound of surplus steel in it, each member was sized to carry the load it had to, and no more. So the bridge can carry the load it was designed to, and no more (except maybe for modern adjustments - “re-rating” - that may demonstrate that the materials can actually take more stress than was thought back when it was designed, and also the lack of steam locomotive “hammer” loads, etc.)
Note the symmetry of the 7 panels, and how the bracing is different in the middle 3 - more cross-bracing, which is the most in the center panel. That’s to handle the stress reversals that happen there when the loads are mostly
I have tremendous respect for people who can sit down and design something like this. Not to mention that this was designed and built well before the computer age, so the math and other engineering was done the old fashioned way.
Yup, never underestimate the power of a good slipstick and some powerful reduction methods.
Don’t forget that in many cases, structures such as this were actually over engineered, since the designers didn’t know what we know today about structural strength. As mentioned, they were also designed for the live load imparted by steam locomotives, something that is generally not a factor today.
Showing your age there, Chuck. The current generation of button pushers have no clue what you just said or the meaning behind it. Let 'em walk around dazed and confused for a while.[(-D][(-D][swg]
Somebody might be interested:
There is a contest for students to design a bridge using criteria like this
bridge satisfies.
Anybody can download a little program and try to design the least
expensive bridge that will pass a simulated load test.
http://bridgecontest.usma.edu/
"U.S. students age 13 through grade 12 are eligible to compete for
national recognition. Anyone else may enter our Open Competition.
“There are no prizes for the national contest this year. Nonetheless,
all contestants will experience the existential pleasures of
engineering …”
Created by the US Military Academy, to whom I have no connection save
that of a grateful citizen.
John
I haven’t heard the term “slipstick” since I was still required to use one (in college). This was about five years before Reader’s Digest had an article on buying the best calculator for your money.
CNW has a lot of bridges that look positively ancient, but still see heavy mainline traffic. Most of them are, I believe, Whipple trusses. Pretty distinctive! (Can’t post a photo, but Mike Yuhas’ winning photo a couple of contests ago featured one.)
Yes, I hadn’t heard the term since I don’t know when. One of my college friends had a 20" slipstick which, in its box, looked something like a short sword. It may have been possible to read it to four places. Everybody else who had one had a 10". There was a 30" one, made of tongue and groove boards, in the math classroom which was used to demonstrate its use to the poor students who had never had or seen one. It had only the A and B scales.
I wonder how many of the button pushers would know anything of logarithms. I used them in quantitative chemical analysis.
Johnny
And you would probably remember that the integral from 1 to cabin of dx over x would of course be log cabin, wouldn’t you?
A little bad engineering humor. I’ll go back to my corner now.
I was in an AF tech school when pocket calculators first hit the market. Add, subtract, multiply, divide. Nothing more.
In one of the modules of the course I was in, we had call to do some calculations - wavelength, I think. We had folks with slide rules (I can use one, just not well), calculators, and pencil and paper. The pencil and paper folks usually got the answer first…
On bridge strength - a common “test” at science fairs is building toothpick bridges and testing them with weights until they fail. Given the material, I think they do pretty well. I also recall such projects using corrugated plastic (like cardboard boxes, but plastic) to build chairs, again testing them for ultimate capacity.
Seeing what spindly bridges like the one that started this thread can handle makes one wonder what some of the heavy duty truss bridges the railroads built are capable of.
And you would probably remember that the integral from 1 to cabin of dx over x would of course be log cabin, wouldn’t you?
“And you would probably remember that the integral from 1 to cabin of dx over x would of course be log cabin, wouldn’t you?”
Chuck, you may come out of your corner.
I had not thought of that one. Don’t you need to add + C?
It’s been over fifty years since I thought much about calculus, except to remember that the first derivative of the equation that expresses your position with respect to time is your velocity and the second derivative is your acceleration. Of course, I have never worked such an equation out. I tried using calculus in my introductory physics course, and my professor told me not to, since the other students (but one who was a bio-chemistry major and one who was a history major) were still taking their required course in calculus (I started the calculus course the summer after my freshman year, working with it at night since I was working on the college building and ground crew from seven to six Monday through Friday and from seven to noon on Saturday; I finished it, with a special dispensation from the dean of students, after the cutoff time for finishing uncompleted work, in the fall)
Johnny
Calculus was my downfall in college. But logarithms were fascinating in high school.
Anyone else ever see a slipstick in the form of a disc?
Yes, I had one at one time. I do not remember if it is still around or not.
As a chemistry major, I had to have calculus, and I was pleased with the two C’s that I got (I won’t say that I earned). I also took a course that was called “differential equations.” Soon after we started the semester, the professor (my third math professor) decided that we should study the LaPlace Transform. I don’t remember anything about it except that it was useful for something, and all you had to do was plug numbers into a formula and calculate the answer–and the final was simply that; take numbers from the problem, plug them into the equation and calculate the answer. This was one of the easiest finals I ever had. I think all three of us in the course came out with the same grade.
Wasn’t that Scotsman, Napier, something? And the englisman, Briggs, was even better because he worked out a table of common logarithms. Did you work with natural logarithms or only common logarithms? I never used natural logarithms.
With logarithms, of course, you have to be careful that you write them down exactly else you go where you did not want to go. Also, all users of logarithms and slide rules know that your answer can be no more precise as to significant figures than the least precise number used in your calculation. It is easy, when using a calculator, to present more significant figures in the answer than the original numbers permit.
Johnny
Slide rules? I manufactured various parts for the Pickett Corporation. Oh that WAS a long time ago.
I’m currently looking at my Pickett Model N902-ES, which I keep in my desk drawer at work for sentimental value. I last used it back during tech school in 1972-73.
Being an unreformed EE, I had to use natural (base e) and unnatural (base 2 and base 10) logarithms both from time to time. I do recall the circular slide rules, but I never had one. I guess you could avoid the folded scales on that one, maybe.
With respect to significant figures, I always loved the answers students would put on lab reports with five significant digits when they had two percent instruments making the measurements. After a quarter of being smacked for doing that, a few of them finally got the point. Later on, of course, I would see “real” engineers doing the same thing. I had to smack a few of them for writing requirements unnecessarily tight that couldn’t be verified with normal test equipment. I guess some never grasp the concept.