Whats the name of this bridge??
- Thread starter WCL
- Start date
mezzoprezzo
Content appreciator
Looks like two Pratt's then.
And not just the bridge, but also the apparent trespassers on the line between each section.
And not just the bridge, but also the apparent trespassers on the line between each section.
But not quite true Pratts. The trusses aren't tall enough to allow beams from side to side or any top X bracing. Still considered a Pratt though. The advantage is they allow a bit more clearance underneath between the bottom of the span and the water then a deck plate or through plate girder span.
Ben
Ben
Yea, I think those are what you'd Call "Half-Height Pratts". Thats also probably why they're so short for Pratts..... The strength (Or amount of wieght the bridge can hold over the length of its span) of a Pratt is going to be proportionate to how tall it is. With no top Bracing, I'd imagine there would be a further notable loss of strength, though negligable compared to what was lost with the given half height. Still, they're serving their purpose by keeping trains outta the drink!
And I would think Ben here has created comparable bridges, or something that can be fudged as a stand in at least if there isn't anything exact (IDK, his Bridge Library would make most Librarians pause for a second....).
Falcus
And I would think Ben here has created comparable bridges, or something that can be fudged as a stand in at least if there isn't anything exact (IDK, his Bridge Library would make most Librarians pause for a second....).
Falcus
And if you can't find something suitable I can always modify one or make a new one for you.
There is an engineering "rule of thumb" that says the length of a truss should not be longer then 9 times the height of a truss panel. This isn't official but if you look at bridges on the DLS you will see all of us have pretty much adhered to this "unofficial" rule.
Material doesn't matter be it wood or steel - the rule of thumb applies.
Ben
There is an engineering "rule of thumb" that says the length of a truss should not be longer then 9 times the height of a truss panel. This isn't official but if you look at bridges on the DLS you will see all of us have pretty much adhered to this "unofficial" rule.
Material doesn't matter be it wood or steel - the rule of thumb applies.
Ben
lmao. Long Live Bubba!
I easily believe that.
If I remember rightly, theres a series of geometric equations that govern the operational strength based on length, height, and bracing. The geometric patters weren't done just because engineers 100 years ago didn't think there were enough squares or triangles in the world.....
Falcus
Well Ben, do me a favor, if you ever get a hold of them, send em my way, and I'll do the same in opposite. As I recall there used to be a book of standards that was published annually or bi-annually around the turn of the last century that would have had these in it. Regardless, I'm currently taking Graphical Engineering at a local college and would love to do a Pratt Truss in Solidworks if the opportunity presented itself, lol. I'd have to imagine it wouldn't be too difficult either, all lines and angles, nary an Arc to be found..... At least Ogee curves are easy to do on the computer (Don't get me started on Drafting those suckers, whole class spent days on a tool with one, and the professor stood up at the end and drew it out in 15 minutes..... you could hear a pin drop in a class of 22+ people). Still, I have to wonder if anyone's paid to put a Pratt into a modern (I barely count auto-cad as modern anymore *shudders*) 3d Drafting program....
Falcus
Falcus
I'm not an engineer so wouldn't have a clue where to look for info like that and probably wouldn't recognize it if I did find it but if I ever see it and recognize it for what is you got it. Hint - I wouldn't put the champagne in the fridge just yet, lol.
At a guess I'd think collage courses like strength of materials, modulus of stress etc. would turn up some of it in the text books. A Pratt Truss might be one of the simpler examples.
I have seen a few diagrams over the years showing which of the various structural members were in tension and which in compression but no math shown to go with them. More of a general illustration then anything serious. Most of these designs were calculated out well over 100 years ago. Materials may have improved but the basic calculations are still valid.
Finally - as I understand it some of the fancier designs were made to get around someone else's design patent.
Ben
At a guess I'd think collage courses like strength of materials, modulus of stress etc. would turn up some of it in the text books. A Pratt Truss might be one of the simpler examples.
I have seen a few diagrams over the years showing which of the various structural members were in tension and which in compression but no math shown to go with them. More of a general illustration then anything serious. Most of these designs were calculated out well over 100 years ago. Materials may have improved but the basic calculations are still valid.
Finally - as I understand it some of the fancier designs were made to get around someone else's design patent.
Ben
You'd be looking for a Book printed in the first 50 years of the 20th century labeled something along the lines of "Book of Engineering/Railroading/Civil Standards, XXX Edition". You wouldn't find too many Blueprint type Design drawings (Probably what would be there would be shrunk down and referenced as an example), but alot more text, and some math in places. Its the Math that will be the pertinent part. Expect Algebraic looking equations. Things like Y=Wx/D*3.14 (Non-working guessed example).
As I understand it, what went on is that Bridge design got so refined after doing it for 2000 years, people figured out that if you made two bridges of the same material, in same quantaties, there are certain design features that will allow a bridge to extend farther, or carry more weight, then other designs. These features were often, again as I understand it, boiled down to the mathematical equations I'm discussing as their final proof's of superiority over other designs (The scientific approach of peer review being "Find a bridge design that can reliably produce better numbers").
The Plans I have a sneaky suspicion you're looking at/using to build your bridges are probably builder's bluprints. These would have all the scaling and dimensioning, but rarely any of the Designer's/Engineer's notes or Math on it. These kinds of plans are what the Construction foremen would be handed, because you wanted him to get the muscle to put Brick A here and Beam B there, and math might confuse him, so were just gonna draw a big simple picture with numbers for distances and hope he got past 3rd Grade (This being the mentality of alot of engineers and "White collar" folk back in the first half of the last century, if you ever read some of these peoples opinions about things and other people, it really is interesting to see how prevalent prejudice was back then).
As far as Materials science is concerned, I don't think too much has changed in the last 70 years or so.... Concrete is now cheaper then Steel I would imagine, so it might make more sense economically to drop 100 tons of concrete then 80 of Steel, but the design precepts for steel bridges haven't changed any....
And yes, I hadn't thought about that before, but I have heard of copyright shenanigans before in other areas, so that doesn't really surprise me much.
Falcus
As I understand it, what went on is that Bridge design got so refined after doing it for 2000 years, people figured out that if you made two bridges of the same material, in same quantaties, there are certain design features that will allow a bridge to extend farther, or carry more weight, then other designs. These features were often, again as I understand it, boiled down to the mathematical equations I'm discussing as their final proof's of superiority over other designs (The scientific approach of peer review being "Find a bridge design that can reliably produce better numbers").
The Plans I have a sneaky suspicion you're looking at/using to build your bridges are probably builder's bluprints. These would have all the scaling and dimensioning, but rarely any of the Designer's/Engineer's notes or Math on it. These kinds of plans are what the Construction foremen would be handed, because you wanted him to get the muscle to put Brick A here and Beam B there, and math might confuse him, so were just gonna draw a big simple picture with numbers for distances and hope he got past 3rd Grade (This being the mentality of alot of engineers and "White collar" folk back in the first half of the last century, if you ever read some of these peoples opinions about things and other people, it really is interesting to see how prevalent prejudice was back then).
As far as Materials science is concerned, I don't think too much has changed in the last 70 years or so.... Concrete is now cheaper then Steel I would imagine, so it might make more sense economically to drop 100 tons of concrete then 80 of Steel, but the design precepts for steel bridges haven't changed any....
And yes, I hadn't thought about that before, but I have heard of copyright shenanigans before in other areas, so that doesn't really surprise me much.
Falcus
I've read the American bridge design was generated to get around the patent for the Bascule bridge design. They are in most respects the same - just the way the counter-weight is done is different. Slightly more complex to my way of thinking.
Ah well - back to making a passenger station inside a snow shed. Should give you a hint as to how much it snowed there, lol.
Ben
Ah well - back to making a passenger station inside a snow shed. Should give you a hint as to how much it snowed there, lol.
Ben