Oklahoma Suspension Bridge
6 Steps
This is a 76' suspension bridge across an arm of the pond on my property. It is built from treated dimensional lumber and galvanized wire rope with a small amount of plated 3/16" proof coil chain. Oh, and lots of bolts and screws!

I needed the bridge to more directly connect the meadow below my house with my picnic grounds  - which were on the other side of the sometimes-arm-of -the-pond, sometimes-nearly-impassable-ravine.

This is the best resource I found online for building this bridge:

http://www.trailstobuild.com/Articles/PochuckBridgeEngineeringArticle/Pochuck%20Quagmire%20Bridge.htm

The bridge cost about \$4000 to build and took several hundred hours of labor and thought.

Not that the thought wasn't labor, too!

I want to thank all of you that voted for me in the Woodworking Contest. I ended up 6th in the voting! Now for the judging!

Jake

Update - runner up in the Woodworking contest. I got a t-shirt - I'm happy! :)
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Step 1: The Math!

First step in any bridge project is to measure the approximate span for the bridge - both ends of which should be at approximately the same elevation - and then decide what exactly you want to be able to cross the bridge. Those two facts set all the other dimensions. Our bridge was 76 ft across and needed to accommodate a garden tractor or a golf cart and perhaps 20 people at a time - not coincident with the garden tractor or the golf cart. A golf cart with 4 people is about 1500 lbs, 20 people are as much as 4000 lbs, while a garden tractor is only about 500 pounds. The garden tractor and the golf cart required a 5 ft wide deck.

An then there is the math in a suspension bridge. This is actually a fairly easy part once you use a spreadsheet and this formula:

y=(lbm/ft)/2T * x^2

which gives the sag ("y") in the catenary cable (which is not a catenary but rather a parabola) at any point along the deck ("x") as a function of the suspended weight and the tension ("t") at mid span. For my purposes, t is an input, along with the weight per linear foot of bridge (actually, half the linear weight as there are 2 cables) and the sag is what I aim for. Given the limitations of the equipment and dimensional lumber -I could not readily have raised anything longer than the 16 ft laminated posts (4 2x8x16 glued and bolted) with which I constructed the 2 towers- and minimal bury (approximately 2 ft) that meant I had at most 13.5 ft of max sag to work with. I aimed 12.75 ft of sag to allow for about 6 in of arch in the deck plus a really short suspender at mid span.

Taking all that into account, the suspended weight of the bridge is about 4000 lbs, almost all of which is the weight of the dimensional lumber used in constructing the deck. I used 2 in board for everything - 2x4x16 and 2x8x16.

With that weight, span and sag, I calculated a tension with 2000 lbs of load and treated lumber at 40 lbs/cu ft (which may be heavy, as it is more than the average weight of the pieces I weighed) at 2500 lbs. I used 2200 lbs in my calculations. From that all other loads, such as anchors, eye bolts, turnbuckles, were set. All the main load carrying material (wire rope, etc) were rated 3500 lbs or greater working load. I used 1/2 " galvanized wire rope (about 5500 lbs working load) for the catenary cable and 3/16 in galvanized aircraft cable (850 lb working load) for the suspenders. There are 37 2x8 joists on 2 ft spacing with 37 suspenders from each cable.
handydave937 says: Oct 31, 2011. 9:57 AM
That is some project. I'm sure there are several special words used to get it all together.
eugeneb4 says: May 26, 2011. 8:00 PM
That's freaking awesome!!
Ghost Wolf says: Jan 31, 2011. 11:05 PM
How big is this pond/river of yours?
Jakebutnottheone (author) says: Feb 24, 2011. 6:40 AM
The pond is about 3.5 acres when full. It is only full after a stiff rain, and then only for a few weeks. Most of the year there is no water below the bridge. It's not exactly dry, either. :)
Ghost Wolf says: Feb 24, 2011. 7:35 AM
Oh cool I bet you get lots of mosquitos
Jakebutnottheone (author) says: Mar 3, 2011. 6:36 AM
Not that many mosquitoes. LOTS of frogs and dragon flies, not to mention lots of fish in the pond! :)

Now gnats, that's a different story!
Ghost Wolf says: Apr 15, 2011. 2:06 PM
some people eat flys for protien
rprough says: Oct 3, 2010. 2:15 AM
Do you think creosoting the anchors before inserting into the ground would be a good idea?
Jakebutnottheone (author) says: Oct 3, 2010. 12:13 PM
Any treatment of the anchors is a good idea, but I personally am not comfortable with the idea of creosote. There are other ground line treatments available, and I may use one of those. In the long run, I will probably replace the anchors with steel screw anchors. Greater, and more certain, uplift resistance as well as a far longer life.
rprough says: Oct 3, 2010. 3:23 PM
Forgot about the steel screw type. What comes to mind is the tiedown anchors used for a mobile to secure it. Good amount of uplift resistance.
Jakebutnottheone (author) says: Feb 24, 2011. 6:46 AM
The manufactured home tie downs are also often screw anchors. Using those anchors I could double up each anchor and provide the uplift I desire. I haven't yet decided how I shall do it.
hifatpeople says: Oct 24, 2010. 10:39 AM
what high school class teaches this? i took an "introduction to engineerig and design" class on accident and thay had nothing but BS. what class would this be? it looks like it would be really helpful in the future.
mg0930mg says: Feb 9, 2011. 7:10 PM
I took a class called pre-engineering and it showed us our model bridges and we took an equation to see how much pressure it could take my 1 ft long bridge could withstand about 250 lb.
hifatpeople says: Feb 9, 2011. 9:34 PM
care to summarise all u learned in that class?
Jakebutnottheone (author) says: Oct 27, 2010. 11:55 AM
No high school class I know of teaches this. As for me, I thought it up, read it up, put it up.

More or less. :)
g.petinati says: Feb 2, 2011. 1:40 AM
This is awesome!

I'm an architect and I can say that this bridge really brought something special to the property.

Bravo!
drewgrey says: Nov 25, 2010. 10:16 PM
Wow, great job.
captain Jack says: Oct 29, 2010. 11:48 AM
Magnificent. Congratulations!
nfarrow says: Oct 12, 2010. 8:09 AM
Really cool. Do you have anymore images of the bridge?
Jakebutnottheone (author) says: Oct 13, 2010. 7:46 AM
One more, which I have added to this step as the last pic in the series.
chapa-de-frente says: Oct 7, 2010. 10:30 PM
*bows to greatness*
VadimS says: Oct 5, 2010. 1:24 AM
Voted
rimar2000 says: Oct 4, 2010. 5:40 PM
VOTED!
Jakebutnottheone (author) says: Oct 4, 2010. 5:43 PM
Thanks! There are so many great projects! I voted for several!
Ricardo Furioso says: Sep 26, 2010. 6:32 AM
Astonishing.
Inspiring.
Intimidating.
Have you any photos of the critically important anchors and more info on how the cables attach to them?
Also, can you describe more about the spikes.
Thank you for an outstanding Instructable.
Jakebutnottheone (author) says: Sep 27, 2010. 8:08 AM
I added two additional pics to Step 2 and 1 pic to Step 6.
Ricardo Furioso says: Sep 27, 2010. 11:55 PM
Did you install plates front and back of the laminated anchor?
What kind of glue did you use to laminate the anchor?
Wow.
Jakebutnottheone (author) says: Sep 28, 2010. 4:27 AM
Big washers on the other side of all 3 bolts. And I used construction adhesive to laminate the anchors (all the posts, really).

It is very difficult to line up plates on both sides of the posts. I had to do it on the towers, but it was no simple task to bore holes in the posts that aligned with the plates on both sides so that the holes pre-bored in the plates would work out.. Next time, I drill one side, bore the holes, mark the plate for the other side and then drill those holes!
Jakebutnottheone (author) says: Sep 26, 2010. 2:14 PM
I will take additional pics and add them to the instructable. The spikes are 10 in (I think) long and similar to a really, really big nail. They are pounded in about 40%. They are what the concrete bears upon, whether in up lift (anchors) or in down force (tower legs). There are 6, as I recall, in each anchor, alone with two bolt ends.
rpb says: Sep 14, 2010. 2:46 AM
Fascinating - many thanks for writing that up. An amazing project!
CrLz says: Sep 13, 2010. 5:12 PM
Amazing project- thanks for sharing the process!
RAF2 says: Sep 13, 2010. 6:54 AM

Very nice!

That is a lot of work, but the feeling of getting the job (well) done is priceless.

Greetings,
Jakebutnottheone (author) says: Sep 13, 2010. 7:33 AM
So priceless that two months later I am still kind of stunned!
x2percentmilk says: Sep 13, 2010. 5:54 AM
Excellent excellent job, and good write up. This is the kind of stuff you cant find elsewhere no the internet :)
Jakebutnottheone (author) says: Sep 13, 2010. 6:28 AM
Well, I couldn't find it anywhere else, excepting the Pochuck bridge reference I give in the intro.
cescu says: Sep 13, 2010. 5:48 AM
Great job! very very nice; at university im studing bridges! are you an engineer?
Jakebutnottheone (author) says: Sep 13, 2010. 5:51 AM
Yes, I am an electrical engineer. I don't think that translates too well into bridge design.

Were I starting engineering school now, however, I might choose to study bridges, too!
symesy says: Sep 12, 2010. 4:14 PM
A little bit of grease goes a long way on thoes turnbuckles. Also if you used gal ones they can be a bit harder to work because of the galvanising on the threads, stainless ones might be more expensive but would make it a lot easier.
Jakebutnottheone (author) says: Sep 12, 2010. 5:33 PM
Both those things are true - but I wanted them to stay put once they were adjusted, so I put no grease on them, and they were expensive enough that for one adjustment, or very few over the life of the bridge, I was okay with the galvanized.
symesy says: Sep 12, 2010. 7:37 PM
Fair enough. Just thought id say. Great build anyways, its really good to see people building. Good on ya.
janettetsmith says: Sep 12, 2010. 6:46 PM
Well, step one eliminates me.  This is awesome.
Jakebutnottheone (author) says: Sep 12, 2010. 7:20 PM
Well, I'd be more than willing to do the spreadsheet part to whatever suspension bridge you think you might want to build. :)
Sep 12, 2010. 4:09 PM
(removed by author or community request)
Jakebutnottheone (author) says: Sep 12, 2010. 5:33 PM
At least part of the time that is true. The rest of the time...
bowmaster says: Sep 12, 2010. 4:52 PM
Dang, this is cool. I wish I had a stream in my yard!!!
ARJOON says: Sep 12, 2010. 11:27 AM
so nice. but i have doubts on the main columns are they enough deep as they are pretty close to the river if erosion persists it might falls. Just a point by the way super great bridge
Jakebutnottheone (author) says: Sep 12, 2010. 1:54 PM
Erosion is a concern over the long haul. I have a plan in mind should that eventuality come about. The plan involves a lot more concrete as well as steel to support the base of the towers, which will no longer be embedded.
deetip2003 says: Sep 12, 2010. 11:32 AM
I am so beyond impressed. Would love to have one but participating in building one would surfice..lol. Great Job Jake.
Jakebutnottheone (author) says: Sep 12, 2010. 1:53 PM
So, get a neighbor or friend hooked on the idea and we can make it happen together. :)
arkie says: Sep 12, 2010. 12:04 PM
THAT's a nice piece of work! Good design: not only does it do what it's supposed to, but it looks awesome, too! And, it is very comforting to see another 'not-so-young' feller doing some some fine construction.

Congratulations on a super build.
Jakebutnottheone (author) says: Sep 12, 2010. 1:52 PM
Thanks! I loved your bridge, and I doubt I would have posted here if I hadn't had your bridge posting to encourage me.
leemck says: Sep 12, 2010. 12:07 PM
I enjoyed the Tacoma Narrows bridge link. The story of the struggle to understand the failure problem as it was observed and partly fixed (but the understanding wasn't developed fast enough to beat the disaster) is much better than the usual 3 minute physics class film. Looking at your bridge, I have been trying to understand what happens when the bridge twists? Thinking about a single suspension wire, where it attaches to the roadway, bridge twist applies several forces in several directions. The next question about bridge twist is suppose the lawn tractor is on the middle of the span and it moves sideways six inches. Does the bridge get into a positive feedback situation where the twist of the bridge increases due to the change in the center of gravity of the tractor? How about, attach a fiberglass tape underneath the bridge, connect it to a \$30 digital vernier caliper and you can have a deflection safety instrument to warn you when maintenance is needed. Wait, I have a simpler scheme. Measure bridge twist with a laser pointer and a target. When a limit on allowable twist is reached, back off. Your bridge is simply beautiful, your accomplishment delightful. Thanks for publishing.
Jakebutnottheone (author) says: Sep 12, 2010. 1:51 PM
I have so much truss with respect to the length of the bridge, as well as the width of the bridge itself, that I will never have to worry about twist due to wind loading. Typical designs for suspension bridges is to aim a 1 foot of width for every 150 foot of span. I have 1 foot of width for every 15 foot of span! As for loads on the bridge, they can't contribute to twist but they can contribute to sideways movement. I have a little too much sag for conventional suspension bridges, leading to relatively more sideways motion, but if you think about it, each time the deck moves sideways it also moves up on the side to which if moves, leading to a natural movement back to the middle. So, with the dampening from all the connections in the bridge, as soon as there is no energy input, motion stops. We have had high winds already and the bridge didn't move at all.
Warren.Sensei says: Sep 12, 2010. 12:34 PM
This was a difficult set of pictures to understand, mostly due to the orientation of the workpiece. I did not understand which direction was which (for instance, where the suspender was going to go in its final orientation in the bridge). I am usually quite good with spatial relationships, but I couldn't figure out how this was going to work structurally until I saw the pictures in the second-to-last step.

After-the-fact picture taking is not possible, but you might add a picture with a couple of arrows or lines drawn indicating how the forces and cables will go.
Jakebutnottheone (author) says: Sep 12, 2010. 1:45 PM
That is a good suggestion. I don't know how to make it more clear, but I will think on it.
t.rohner says: Sep 12, 2010. 12:36 PM
Wow!!!
Jakebutnottheone (author) says: Sep 12, 2010. 1:44 PM
I feel the same way. :)
Anthony Cervantes says: Sep 12, 2010. 12:43 PM
Thank you for sharing this!

Jakebutnottheone (author) says: Sep 12, 2010. 1:44 PM
Thanks!
ktkeith says: Sep 12, 2010. 1:16 PM
Fantastic project! Congratulations!

Just to be clear, though: there is no tension-adjusting mechanism on the vertical stays? You calculated the length of each stay assembly at each joist, built them to that length, and installed them that way without any further fine-tuning possible, is that right?

It obviously worked great, but what would happen if one of the assemblies was slightly off-length? And how do you deal with creep (stretch) in the suspension cables and vertical stays?

Jakebutnottheone (author) says: Sep 12, 2010. 1:44 PM
The tension adjusting mechanism is the clips on the lower end of the suspenders. If the are loosened the cable can be adjusted in length, effecting a change in the tension of that particular suspender. If I had been THAT confident of my calcs and measurements, I would have used swaged attachments at both ends!
BigAl67 says: Sep 12, 2010. 6:54 AM
I had felt pretty good about carving that walnut into a neckerchief slide, but after seeing what you've done, well that is just too impressive. I saw something similar done in Cambodia years ago but they had dozens of people working on it. Very nice Cheers!
Jakebutnottheone (author) says: Sep 12, 2010. 7:00 AM
You've caught me reading online this morning! LOL!

I have been thinking about all the projects on this site, and all the things people do to make things, and I think that, large or small, it is the making, the creating, that is important.

I had an opportunity, and need even, the requisite skills and enough help and money to make it happen. There are many projects here for which I entirely lack the skills to make happen, and to attempt those projects would be beyond me.

It also helps, in a long project like this, that I am at my best with a deadline and when I obsess, both of which were true.
casperdub says: Sep 12, 2010. 11:11 AM
Inspirational work...
there are so many cool projects on this site & this is one is one of those that keeps yah seeing & doing more...
I have a blog http://casperdub.blogspot.com (scrapbook) of my work which you might find interesting (the folding, sideways sliding kids-scale chairs video begins automatically part way down the blog)
perhaps I should enter something here...
this is my first time ever commenting on this site...
thanks for sharing the process.
ubiquitoussmokey says: Sep 12, 2010. 10:49 AM
very cool! thanks for sharing it with us! :)
crustyasp says: Sep 9, 2010. 9:23 AM
Just a few comments, WOW, Fantastic, Open mouthed awe. Amazing project. I may build one of these for my mud puddle in the front yard, overkill, but it sure would impress the neighbors!
Jakebutnottheone (author) says: Sep 10, 2010. 12:36 PM
Also - should you decide you want to grace your mudpuddle with a suspension bridge, I would love to help in whatever way I can - thinking and the spreadsheet for sure!
crustyasp says: Sep 11, 2010. 2:38 PM
I think I'll put the mud puddle bridge on hold for a bit, until I win a lottery up here in Canada. That way my neighbors will call me eccentric, not crazy. I'll hold you to the thinking and spreadshheet part,and I'll also supply the beer and hammock for you. lol
Jakebutnottheone (author) says: Sep 11, 2010. 6:30 PM
Really, a mud puddle bridge would cost next to nothing at all! :)
Jakebutnottheone (author) says: Sep 9, 2010. 9:43 AM
thanks! I get that a lot, actually, when people come to the house. it's almost embarrassing because other than being big, it just didn't take that much talent or skill.

But don't let me stop you. Keep those superlatives coming! :)
carlo\$ says: Sep 11, 2010. 6:19 PM
Awesome!!! How long will the footing last? Is it submerged in the water?
Jakebutnottheone (author) says: Sep 11, 2010. 6:30 PM
The footings are about a foot or two above the high water line, as well as back several feet from the water's edge. So, barring erosion (which has been minuscule in the last 15 years) they should last a very long time. If they don't, for whatever reason, I have a plan to replace them. The plan involves steel and much more concrete. :)
Dennis.x.i says: Sep 10, 2010. 9:11 AM
Nicely done, I love this project. But the suspension cable isn't secured to the pillars on real suspension bridges they hang over them and are secured to the ground behind the pillars to allow them to move so that the pillars aren't being pulled front to back(if I'm not mistaking). Although it probable doesn't make a difference on a bridge of this size , I thought I'd share it. :)
forgive me my English I'm from Belgium.
Jakebutnottheone (author) says: Sep 10, 2010. 10:51 AM
yes, it different. I chose this configuration because of installation issues - I needed the towers to be anchored before I pulled in the catenary cables. So, I beg to differ - this IS a real suspension bridge, it is just not a continuous cable suspension bridge. :)

If I had pulled in the catenary cables without any other structure attached, it would not have been an issue and I could have used a continuous cable. The problem is that installing the deck from the in-air cable would have been all but impossible.

I could have used the same process of floating the bridge to the site and then taking the catenary cables over a saddle to each anchor and then raising the substructure, but then the towers would have had to have a greater "bury" and that would have reduced the max sag, which would have increased tensions and loading everywhere else in the bridge, or would have required longer tower legs, and they were as long as I could comfortably handle as it was!
Dennis.x.i says: Sep 10, 2010. 3:57 PM
I didn't mean to call the bridge not a real suspension bridge, I was just wondering.
grts
Jakebutnottheone (author) says: Sep 10, 2010. 4:43 PM
I know. Just teasing you. :)
ourmoneypit says: Sep 10, 2010. 10:15 AM
Awesome job, both on the bridge and the instructable. I, too, have always been curious about suspension bridges, and found this fascinating. We have a small stream to span -- I'd need no more than 30' end to end -- so we can easily do it without a suspension bridge, but I gotta say you make it verrry tempting. :-)
Jakebutnottheone (author) says: Sep 10, 2010. 10:52 AM
So, say you wanted to make it a suspension bridge, I'd be ecstatic to help you with it! LOL! It's like I have this whole new hobby interest and no way to express it!
ourmoneypit says: Sep 10, 2010. 3:52 PM
I may just take you up on that, you know. Let me spend some more serious time with this 'ible and I'll let you know.
Jakebutnottheone (author) says: Sep 10, 2010. 4:42 PM
It was a serious offer. I already have a spot in mind for a second bridge on MY place. There is something very satisfying about bridges. For one thing, they require no finish work - you put the last screw in the deck and you are DONE!
uberwald says: Sep 10, 2010. 2:18 PM
Are you worried about the pressure treated wood leaking toxins into your water when it rains? Have you considered sealing it or painting to minimize that?
Jakebutnottheone (author) says: Sep 10, 2010. 2:59 PM
I have... considered the effects of the pressure treated wood. I plan to seal the wood in the near future.

In any case I am not exactly worried. The wood is not treated to the highest level, and sealing it will do a lot to preserve not only the environment but also the wood itself. We use very few pesticides or herbicides on the property, or even chemical fertilizer, and the total environmental load of bad stuff is very, very low.
cpotoso says: Sep 10, 2010. 11:30 AM
Fantastic instructable and absolutely amazing bridge!
Foxtrot70 says: Sep 10, 2010. 7:06 AM
Excellent project! Reminds me of when I was in Boy Scouts 40 yrs ago. I was completing Pioneering Merit Badge. I had construced a swinging rope bridge on the ground. The raising occured when I pulled on the two hand rail lines and the main walking rope and the two towers rose! To test th bridge I was the first to cross it.
Jakebutnottheone (author) says: Sep 10, 2010. 7:21 AM
Functionally, the only difference are the trusses that stiffen a suspension bridge. It's always fun when it works, no? :)
Rmal says: Sep 10, 2010. 5:15 AM
really cool!
buirv says: Sep 9, 2010. 2:36 PM
Awesome - Great math work!!!
Jakebutnottheone (author) says: Sep 9, 2010. 2:52 PM
Thanks! An engineering education comes in handy every once in a while!
Tazo says: Sep 9, 2010. 2:34 PM
Very nice job. I have only one question, besides your son-in-law, who else helped you, how many peole worked on this project?
Jakebutnottheone (author) says: Sep 9, 2010. 2:52 PM
I did most of the work (more than 75%), and beyond that, the list of helpers in order of contribution is as follows: my son, my brother-in-law and his two sons, a friend, my daughter and son-in-law, coworkers 1, 2 and 3, my cousin, and my wife. Frankly, it would have been very hard to finish the work in the two months I allowed myself were it not for the help I received.
cncarlton says: Sep 9, 2010. 12:33 PM
Love it!!!!!!!!!!!!!!!!!!!! Awesome instructable, thanks for posting. I even read most of the math :-)
Jakebutnottheone (author) says: Sep 9, 2010. 1:45 PM
The math isn't too bad, particularly when you cheat the way I did and just make the bridge be lots of short, short, SHORT straight lines. Dividing the bridge into 2000 increments means that each increment is only about 1/2 in in length - more than accurate enough for this project! In fact, only 3 of the suspenders needed any adjustment after raising. I count that as a near miracle. :)
omnibot says: Sep 9, 2010. 1:07 PM
Well, an instructable on how to build a bridge. Now I HAVE seen everything.
Jakebutnottheone (author) says: Sep 9, 2010. 1:41 PM
There are two other bridges on the site, but this is the only Suspension Bridge. And I have to tell you, there isn't much out there ANYWHERE. That's why the Pochuck Bridge article I link to in the Intro was so valuable to me.

But it is a lot of fun to be the only one here. :)
seamster says: Sep 8, 2010. 9:42 PM
Thank you for taking the time to post this. I really enjoyed it.

I particularly like instructables like this--large but do-able projects that encourage the rest of us to just go for it. Very nice addition to the site.
Jakebutnottheone (author) says: Sep 9, 2010. 4:23 AM
You have hit upon what has been one of my greatest pleasures. As friends have seen and used the bridge, suddenly, they are tackling their own big projects, willing to be patient, to make mistakes and to just keep persevering. They tell me the bridge inspired them.

Rewards come in many forms, and this, to my mind, is one of the best.
seamster says: Sep 9, 2010. 10:30 AM
I agree.

People in general are much more capable than they think. For anyone who's taken on a challenge and over come it, they realize that patience and determination are the biggest factors. It reminds me of that quote about perspiration and inspiration.

(Who said that anyway?)
Jakebutnottheone (author) says: Sep 9, 2010. 10:48 AM
it is attributed to Einstein, but I think he borrowed it himself.
mikeasaurus says: Sep 8, 2010. 4:45 PM
Nice build, the results speak for themselves.

I like how you addressed the Tacoma Narrows bridge, too. Way to think about some of the outcomes.
Jakebutnottheone (author) says: Sep 8, 2010. 5:08 PM
The outcome I fear is the anchors pulling out of the ground! If I get to do this again, I will use screw anchors, professionally installed. I could readily get 10k lbs of uplift with a screw anchor. I also would know just how much uplift resistance I had, and that is pure guess right now, excepting that I know I put a boatload of concrete in the ground for each anchor - and it was hard, hot work.
mikeasaurus says: Sep 8, 2010. 9:38 PM
Based on what I see from your designs, the weakest point could be the concrete foundations. Would love to see some detail of the footing connection, and with the support post connections.

Really, when you you consider potential load, soil erosion, and external loads there's always room for more counterweight. However, it's nothing you can't fix with a nice concrete bridge-entryway later on.

Really, the bridge looks great. I wish my neighbour had one these instead when I was growing up instead of the planks-on-rocks method. Though it's better than we had (nothing!).
Jakebutnottheone (author) says: Sep 9, 2010. 4:18 AM
I have 10 in spikes on all sides of both the tower legs and the anchors, plus vertical rebar in the anchor concrete. The footing for the tower legs is approximately 2 square ft. Given the soil at the bridge site, I have something around 4000 lbs of load bearing in each footing. So far it has been enough.

But I have contingency plans if either the tower footings or the anchors, or both, prove inadequate. At least, I have plans if the inadequacy is not demonstrated by catastrophic failure. :)
bobby sissom says: Sep 8, 2010. 7:17 PM
you are the backyard bridge building god and i kneel whilst saying we're not worthy,we're not worthy
Jakebutnottheone (author) says: Sep 9, 2010. 4:13 AM
LOL! This project is really nothing more than a little math, a lot of small projects and a boatload of time.

But when it was done...
pantalone says: Sep 8, 2010. 7:06 PM
Thank you for this. Suspension bridges have always been a mystery to me, and it's fascinating to see one get built from start to finish. Well done!
Jakebutnottheone (author) says: Sep 9, 2010. 4:12 AM
It was fascinating to me as well. All kinds of small work, but when added all together - whoa! How cool it became. Totally unanticipated. :)
thomped says: Sep 8, 2010. 5:19 PM
Nice Project, Well done.
Next time id suggest you use a chain block to hoist up the lines, you can normally hire them cheaply. using turnbuckles works but you don't want to overheat the steal because you may be effecting the rating on them.

Again well done.
Jakebutnottheone (author) says: Sep 8, 2010. 5:28 PM
Turnbuckles were only for final adjustment. Come-alongs did the raising. Even so, and using 9/16ths turnbuckles, it was still hard, hard work getting those last few inches of sag pulled up.

A rented chain block would have been far easier than the come-alongs. If I do it again, I will likely consider using them.
kelseymh says: Sep 8, 2010. 4:56 PM
Unbelievable! That's a tremendous job, and very nicely documented. Thank you for putting this together for the rest of us to admire and wish about...
Jakebutnottheone (author) says: Sep 8, 2010. 5:11 PM
Truthfully, if the project had required anything more than your basic deck building skills, you could just write FAIL on it and call it done. As it was, a little math, some sticks of lumber, a few screws, lots of wire rope and VOILA! BRIDGE!

Thank you for the documentation comment. There is no way to document everything that goes into a bridge like this without writing a book. Maybe a small book, but a book nonetheless.
Kaelessin says: Sep 8, 2010. 2:31 PM
You sir are one ambitious bloke! Great job!
Jakebutnottheone (author) says: Sep 8, 2010. 2:53 PM
I needed a bridge, and couldn't, or wouldn't, afford to have one like a park might have (approx \$30k for the bridge alone, and who knows how much for installation?). So there was little choice except to build one. I decided upon a suspension bridge because all the parts are manageable by hand or with minimal mechanical assistance.

It all worked out way better than I imagined. :)
nachosyumm says: Sep 8, 2010. 2:26 PM
=O Wow, this is amazing. While I'm sure most people don't have a need for a 76' suspension bridge, I'm sure most of us are dreaming that we had one too.

One question though. I'm guessing it is a river or something, what about boats and other aquatic vessels
Jakebutnottheone (author) says: Sep 8, 2010. 2:51 PM
No river, just an arm of a runoff pond in central Oklahoma. Sometimes it is dry under the bridge, sometimes the water is within 3 ft of the bridge. The water is about 10 ft deep at max water elevation, so that gives you an idea of how much the pond goes up and down with rainfall. It takes a lot of rain to fill!