NationStates Jolt Archive

Last summer, my roommate and I built a little 20 ft. bridge across a creek in front of our apartment. We built it out of two ceiling rafters and some scrap wood. It lasted for about 6 months until it rained really hard one weekend and the whole creek flooded. The parking brick that we put on top of the bridge on one side of the bridge somehow eroded the creek bed and got swept about 40 ft. downstream. The bridge ended up in the Putnam river. :(

Here is a video of the bridge surviving one of the floods, but like I said, the last major flood completely destroyed it.
(http://www.youtube.com/watch?v=WqgRMBbm8ko)

To say the least, we are already planning a bigger bridge that will span the entire creek from bank to bank (about 45 feet). The head contractor at our apartment complex is actually giving us money and nice power tools to build this one so its gonna be good. :)

So what kind of bridge should I make? A larger truss bridge? A suspension bridge? An arc bridge? A rope bridge? Are their any other amateur engineers in NSG?

My two best ideas so far are:

1. A Wooden Truss Bridge. LINK1 (http://www.gov.mb.ca/chc/hrb/mun/m223.jpg) LINK2 (http://images.google.com/imgres?imgurl=http://www.past-inc.org/historic-bridges/glossary-truss.JPG&imgrefurl=http://www.past-inc.org/historic-bridges/Gloss-trussbridge.html&h=283&w=600&sz=44&hl=en&start=3&sig2=MoLcLy0f_FVrjZn_XuhElw&um=1&tbnid=AdcAlJmcIt27AM:&tbnh=64&tbnw=135&ei=jN_MR9iVL4OkeKfhtQY&prev=/images%3Fq%3Dtruss%2Bbridge%26um%3D1%26hl%3Den%26safe%3Doff%26client%3Dfirefox-a%26rls%3Dorg.mozilla:en-US:official%26sa%3DN) This would be pretty straight forward. Mostly 2x6 's bolted together with concrete footings buried in the ground and lots of metal joints. It would probably cost between $800-$1000, but we have a pretty good idea of how we would go about doing it.

2. A Rope Suspension Bridge. LINK1 (http://www.sxc.hu/pic/m/f/fo/fourtwo/192141_rope_bridge.jpg) LINK2 (http://www.blueforest.com/assets/large-page/picture_632.jpg) This design would be much cheaper and possible more fun. We have an old telephone pole that we would cut up into four pieces and bury in the ground on both sides of the creek. Then, steel cables and ropes would span the distance with wooden planks for footings. From what I understand, rope bridges are very strong and reliable if done right. The problem is that me and my roommate don't know very much about making things out of rope, and this bridge might end up being complicated and hard to complete.

So, any helpful suggestions or unhelpful jokes?

I would go with a Rope Suspension Bridge, it'd probably be easier to build and more fun to walk across. :)

Good luck on your project!

Go with the first one, a rope suspension would take too long to finish

Build an arc over the creek and use that to support your bridge deck. Add railings as necessary.

Truss bridges are much harder to design than you'd initially suspect. Rope bridges tend to become unsafe rather quickly.

Build a dam up creek. The use the water that comes through to power your house for free, when it floods. :p

Make a stone bridge with those rocks on the bank.

A stone bridge would take forever to build, you have to carve each indiviual stone and you have to make sure the water can get through, it's just too much trouble. Wooden bridges are much simpler.

Build a dam up creek. The use the water that comes through to power your house for free, when it floods. :p

What about the rest of the time, huh? :p

Make a stone bridge with those rocks on the bank.

What about the rest of the time, huh? :p

Well, I think its sunny down in Atlanta, so they wouldn't need the power those days :p

Truss. It's mostly a bunch of triangles and the only thing stronger than a triangle is a circle, which includes half circles (arches).

I would go with the rope suspension. Just make sure your ropes are very well attached, other than that it doesn't seem to hard. I find truss bridges ugly, a RS-bridge could be much more elegant, basically just the bridge deck and some ropes.

A good Bridge Example of Stone is Potter Heigham Bridge in Norfolk on The Norfolk Broads.

A good example of wooden Bridges are Brunel's Trestle Bridges in the South West of England.

Build an arc over the creek and use that to support your bridge deck. Add railings as necessary.

Truss bridges are much harder to design than you'd initially suspect. Rope bridges tend to become unsafe rather quickly.

I don't see how an arch is going to easier. How would you support the center of the bridge? The only way that I see would be cables. And I know that Arches push outward on their foundations, so I would have to use more concrete and dig much larger foundations. I don't see an easy way to do it.

I am probably gonna go with the truss bridge because I think it would be the safest and the easiest to build. I will only build the rope suspension if money is an issue I think.

or you could just not bother making a new bridge maybe?
Just a plank of wood attached to some rope to stop it floating away would probably do, so if it does flood again it's no major loss.
meh i'm better at making dams than bridges, they were ace fun.

make a monkey bridge. their easy, fun and cheap.

most scout manuals will give you the basics of making one.

Those are not safe, fun, but not safe. And the head contractor at our apartment complex would not pay us to make one of those.

make a monkey bridge. their easy, fun and cheap.

most scout manuals will give you the basics of making one.

Make one of each type at different parts of the creek

or you could just not bother making a new bridge maybe?
Just a plank of wood attached to some rope to stop it floating away would probably do, so if it does flood again it's no major loss.
meh i'm better at making dams than bridges, they were ace fun.

We made some stepping stones but you could only use them about half the time because of the water rising and alot of people didn't use the steps because you have to climb the sides of the creek. Plus I was drunk one time and I tripped and got my foot all wet. It sucked.

An Arch which cleared the main channel of the Waterway Is what I'd advise.

Though I'm more used to bridges boats have to sail under, than bridges that have to survive major floods.

What kind of foot traffic per day are we talking about here?

Also, I think you need to do a materials, cost, and labour analysis before deciding on which kind of bridge to build. If it's just you and your roommate working on the project, I would suggest the rope bridge. As for Posi's suggestion of arch bridge, Posi, GTFO. :p

Actually, I'm curious as to how deep this creek is. Because if it's relatively shallow, you can probably build a culvert crossing instead. I have some experience in culvert designing (and not as much in bridge designing), but I can probably find you some useful material for calculations if you need them.

you could try offering canoeing lessons to make up some money, then ram some stilts into the ground, which allow for ropes to be added too, then some stepping stones beneath, then a wooden bridge on top, secured by ropes, stones.
So if you will a sort of collage of lots of designs molded into one big unmovable one. This sounds kinda fun.

What kind of foot traffic per day are we talking about here?

Also, I think you need to do a materials, cost, and labour analysis before deciding on which kind of bridge to build. If it's just you and your roommate working on the project, I would suggest the rope bridge. As for Posi's suggestion of arch bridge, Posi, GTFO. :p

Actually, I'm curious as to how deep this creek is. Because if it's relatively shallow, you can probably build a culvert crossing instead. I have some experience in culvert designing (and not as much in bridge designing), but I can probably find you some useful material for calculations if you need them.

Probably about 100-150 people would cross it in a day. The water is normally a little over a foot deep but when it rains hard, it becomes about 8 feet higher. We want to make a bridge that goes from bank to bank (46 feet) so that it never touches the water when it floods, and we want to avoid putting supports in the creek bed because the sand is very loose and we don't know how to pour concrete around water.

We have drawn very detailed plans and done a budget for a simple truss bridge. It will cost $1000 (actually just $850 but we are asking for more than we need). Mostly it would be made from 2x6's bolted together.

The problem with a rope suspension bridge is that we don't really know how to make one of those. We have little experience with rope. Do you know of any good designs?

A culvert crossing would probably get flooded over like our old bridge. It would have to be very big but it might work, I dunno much about culvert crossings. What do you think?

One of the old bridges, from back when I was a kid (read: My parents still only had AOL) was in the woods near my house, it was a pair of telephone polls someone had laid across a creek a long time ago. Because of how long the creek had been around, and the constant rate of flow, the creek really didn't widen over the years, it just got deeper. Eventually, in the most absolutely torrential downpour I have ever experienced, the earth supporting one of the telephone polls collapsed, leaving us with a shockingly lopsided bridge, but it was still crossable.

Those woods, though, were awesome. It was an oversized playground, really, a highly contained physical area, but to us, it was bounded only by our imaginations. It came complete with lots of brambles and high grass, perfect for elementary school aged boys to have a rollicking good time. We created all sorts of myths about the woods, to make our sense of adventure greater. Some of our myths turned out to be more than slightly derogatory towards the woods adventure (the myth of the Satanists in the abandoned tree house, being one of the most prominent, that was only reinforced by the discovery of a dead squirrel in said abandoned tree house, when we actually managed to make the climb). It was a great time, and we spent far more time doing cool stuff out there (slingshots and old cans anybody? booyah!) than we did indoors playing Sega.

Always, I will fondly remember those woods, and can only hope that my own children will one day have such a wonderful resource.

Make a bridge out of witches!

Probably about 100-150 people would cross it in a day. The water is normally a little over a foot deep but when it rains hard, it becomes about 8 feet higher. We want to make a bridge that goes from bank to bank (46 feet) so that it never touches the water when it floods, and we want to avoid putting supports in the creek bed because the sand is very loose and we don't know how to pour concrete around water.

We have drawn very detailed plans and done a budget for a simple truss bridge. It will cost $1000 (actually just $850 but we are asking for more than we need). Mostly it would be made from 2x6's bolted together.

The problem with a rope suspension bridge is that we don't really know how to make one of those. We have little experience with rope. Do you know of any good designs?

A culvert crossing would probably get flooded over like our old bridge. It would have to be very big but it might work, I dunno much about culvert crossings. What do you think?
I think what you have now is probably pretty good. Like I said, I don't know that much about bridge design, so can't really help you in the design department. And the crossing is a little to deep/floody to make a culvert crossing. The cost you said seems reasonable, I guess the last thing to consider is how long it would take to build and how many people you would need. As long as you've got that figured out, I think you're pretty much ready to go. Of course, you don't want the bridge to fall/break under extreme windy conditions, etc, so I would foolproof my design just to make sure, even if it would mean more materials/more cost. (engineering ethics and all that jazz).

aaand...yeah. If you don't mind, can you send me your design? I'm really interested in seeing what you've got.

I think what you have now is probably pretty good. Like I said, I don't know that much about bridge design, so can't really help you in the design department. And the crossing is a little to deep/floody to make a culvert crossing. The cost you said seems reasonable, I guess the last thing to consider is how long it would take to build and how many people you would need. As long as you've got that figured out, I think you're pretty much ready to go. Of course, you don't want the bridge to fall/break under extreme windy conditions, etc, so I would foolproof my design just to make sure, even if it would mean more materials/more cost. (engineering ethics and all that jazz).

aaand...yeah. If you don't mind, can you send me your design? I'm really interested in seeing what you've got.

http://photos-331.ll.facebook.com/photos-ll-sf2p/v193/57/43/39804331/n39804331_32209844_3988.jpg

Alright, I don't have the designs with me right now so I just did a little doodle in power point. Its crude but it works. Figure B just shows the lengths and general design. The trusses are single 2x6's and the top and bottom are double 2x6's bolted together. Figure A is a closup of the inside of the the main bottom piece to show how the walkway will be installed so as to avoid contact with the trusses. Both ends will be set in concrete.

According to Wikipedia: (http://en.wikipedia.org/wiki/Truss_bridge)
its a Warren truss design.

Ok, I'm suprised this haven't been offered yet.

A Drawbridge! Think about it! You make a draw bridge that you're able to crank up when not in use (by a series of levers and pullies, and when you get a heavy rain storm, you can just pull the drawbridge up and you won't have to worry about losing it when it floods!

I think a simple one like the one in the picture below would do just fine.

http://webzoom.freewebs.com/superfoot/welcome%20drawbridge.JPG

Yeah, thats awesome. But I think a 46 ft draw bridge would be complicated. Plus people would get pissed if somebody drew up the bridge from the opposite side and no one could cross it.

That why instead of ropes, you could use screws underneath the bridge and have a crank at each end.

Ok, I'm suprised this haven't been offered yet.

A Drawbridge! Think about it! You make a draw bridge that you're able to crank up when not in use (by a series of levers and pullies, and when you get a heavy rain storm, you can just pull the drawbridge up and you won't have to worry about losing it when it floods!

I think a simple one like the one in the picture below would do just fine.

http://webzoom.freewebs.com/superfoot/welcome%20drawbridge.JPG

Yeah, thats awesome. But I think a 46 ft draw bridge would be complicated. Plus people would get pissed if somebody drew up the bridge from the opposite side and no one could cross it.

For that, a truss would probably be best.
A suspension bridge is overkill.
An arc is a lot more work than you need to do.
A rope bridge will be fun and make you feel adventurous.

Have fun though. I once bridged a 2ft deep ditch with a dead tree...

I don't see how an arch is going to easier. How would you support the center of the bridge? The only way that I see would be cables. And I know that Arches push outward on their foundations, so I would have to use more concrete and dig much larger foundations. I don't see an easy way to do it.

I am probably gonna go with the truss bridge because I think it would be the safest and the easiest to build. I will only build the rope suspension if money is an issue I think.The theory is that the arch is self supporting. The placement of the bridge deck depresses the arch and the arch in turn pushes the center of the bridge deck upward in an effort to return to its natural position.

Do you know how to make it so that the trusses do something to support the bridge rather than just add weight?

Also probably a good question, what are the materials you and your peeps are skilled at working with?

The theory is that the arch is self supporting. The placement of the bridge deck depresses the arch and the arch in turn pushes the center of the bridge deck upward in an effort to return to its natural position.

Do you know how to make it so that the trusses do something to support the bridge rather than just add weight?

Also probably a good question, what are the materials you and your peeps are skilled at working with?

An Arch!? Thats a stupid idea. You are stupid. No. The only arch design that doesn't push horizontally of its foundations is the "Tied Arch" bridge design. And how the hell would I make that out of wood? A hundred little 2x4 nailed together in a sweeping semi-circle. Despite being impossible for me to build, it would be expensive as hell considering all the wood AND cables that I would have to buy.

In the nonpolar warren truss design that I have adopted (copied), the trusses carry the weight of the bridge under tension. The top section takes all the compression forces so thats why I'm gonna make it double thick.

I was gonna make this bridge out of wood and wood bolts mostly. The longest section of 2x6 that our local lumber yard sells is 16 feet, so the longest section of my bridge is 16 feet.

Well, I'm no engineer, but I certainly applaud your efforts. Best of luck on the next bridge. And yes, in fact, I am Mardok, destroyer of bridges.

http://photos-331.ll.facebook.com/photos-ll-sf2p/v193/57/43/39804331/n39804331_32209844_3988.jpg

Alright, I don't have the designs with me right now so I just did a little doodle in power point. Its crude but it works. Figure B just shows the lengths and general design. The trusses are single 2x6's and the top and bottom are double 2x6's bolted together. Figure A is a closup of the inside of the the main bottom piece to show how the walkway will be installed so as to avoid contact with the trusses. Both ends will be set in concrete.

According to Wikipedia: (http://en.wikipedia.org/wiki/Truss_bridge)
its a Warren truss design.

Ok, so this design is completely wrong. I got the measurements wrong. We are redesigning the bridge now.

http://photos-331.ll.facebook.com/photos-ll-sf2p/v193/57/43/39804331/n39804331_32209844_3988.jpg

Alright, I don't have the designs with me right now so I just did a little doodle in power point. Its crude but it works. Figure B just shows the lengths and general design. The trusses are single 2x6's and the top and bottom are double 2x6's bolted together. Figure A is a closup of the inside of the the main bottom piece to show how the walkway will be installed so as to avoid contact with the trusses. Both ends will be set in concrete.

According to Wikipedia: (http://en.wikipedia.org/wiki/Truss_bridge)
its a Warren truss design.

Ok, so this design is completely wrong. I got the measurements wrong. We are redesigning the bridge now.