Hoisting a Suspension Bridge to its New Post

This was the next part of the repair process. Once the post was installed, gravel was shoveled in and tamped. The official tamper tool was too big at first so a 2×4 worked. Next they hooked up the cable to the dead-man and tightened the turnbuckle, which will be adjusted again later. Then it was time for a beer! The hard part was over.

Now it was time to hoist the bridge. They used the come-along again, which worked okay but seemed like it needed help. It took a bit of regrouping, but finally they added a cable winch so there were two devices working instead of one. It took time, but the 80′ bridge was eventually hoisted! All pictured here happened in about 5 hours, including beer breaks.

BridgeUp

BridgeUp2She’s a little beat up and broken, but at least she’s up!

CheeseThe obligatory cheesy grin, photo compliments of the amazing Keith Grossman!

KeithIsFirstWe cleaned off the leaves and the boys crossed the bridge, Keith first. The decking is pretty badly damaged but it was okay for now. Nice not to have to walk across that creek again this winter, assuming the bridge stays out of trouble. Here’s to hope!

Next, Marvin will be straightening things out and making it a little safer for crossing. We’ll replace all the decking as time and weather allows.

Thanks for stopping by. Check out the movie on our Facebook page! And, be sure to check out our book about building this strong bridge. Here is the link:

Building a Small Cable Suspension Bridge with the Cable Locking System

Images, diagrams, and text copyright 2013-2019 by Marvin Denmark unless otherwise noted. Please do not copy and post my content anywhere without my permission. Thank you.

Replacing the Post on a Small Cable Suspension Bridge

P1020059

As you might remember, February 25, 2019 was a bad day for our 80′ suspension bridge that we built in 2005. Part of a large maple tree weighted down from heavy snow decided to break and fall directly on one of the support posts on the other side of the creek, bringing lots of other trees with it. Once it thawed and we could get someone over to clean up the mess, we assessed the damage. We had to replace the post, which involved many steps, and most of the decking. Also, we had to raise the bridge again.

We lined up a contractor and a crew to do the work with Marvin’s supervision, but they were busy and having a hard time fitting us in. Summer came and went, and when the rains started this fall, we decided we could do it ourselves with help from our neighbor (and plenty of beer!). We are not as young as we were when we built this bridge, but we still have the same determination to get the job done. To note, since the damage is on the other side of the creek, everything had to be done by human power and ingenuity. And did I mention plenty of beer? I think I did.

Beers

dig it

 

DigItTools

One of the first tasks was to dig up the old post. All went well until we realized it was buried 4′ deep, not 3′. We should have read our book! The last foot or so needed a special tool since there was no room for a shovel. The cut cake pan worked the best. Cut the pan and then screw the two halves together and we had a quick and easy gravel scoop!

CutNewPostCarvePostEnd

We used a power pole again, though this one is pretty substantial. The end was carved for the metal collar that connects to the bridge cable and to the cable to the dead man. Holes were drilled and the raw end was treated with preservative.

BangingCollar

Marvin had to chisel the collar off the old post, then he replaced both eye bolts, which were bent when the trees hit the post. The eye bolt for the bridge cable is 3/4″ and the one for the dead man cable is 5/8″.

The above collection of photos shows some of the post-wrangling. The two guys used a pee-vee, cables, chains, and a handy little tractor on the opposite side to get the post across the 40 foot wide creek with steep banks on both sides. There’s a movie of some of this on our Facebook page, link below. If you wonder why a lot of cable is wrapped up on the tractor bucket, that’s because we had to reel it in as the post headed across the creek.

PostReadyAndTripodTripodPulley

Next, the boys built a tripod using 20′ 2x4s and installed a pulley at the top. At first they had rope to pull up the post, but it was soon replaced with cable because the post was heavier than estimated.

They used a come-along which worked to get the post raised so much, then the post had to be secured, the rope loosened, and the come-along reset. It took several resets before the post finally drifted above the hole.

InPost

 

TargetAim

The last trick was to center the post on the pin in the concrete pad as it was lowered into the 4′ deep hole.

PostIn

The new post is in place!

BridgeSpanWithNewPostIt was cool to see the new post up and almost ready for the bridge deck. Next, we back-fill with gravel (by hand of course) and tamp it in. Stay tuned, and be sure to watch for exciting movies on our Facebook Page here!

Thanks for stopping by. Be sure to check out our book about building this bridge. Here is the link:

Building a Small Cable Suspension Bridge with the Cable Locking System

Images, diagrams, and text copyright 2013-2019 by Marvin Denmark unless otherwise noted. Please do not copy and post my content anywhere without my permission. Thank you.

Suspension Bridge VS Big Tree: Bridge Wins!

February 25, 2019 was not a good day for our suspension bridge. A snowstorm hit that weekend with 8-12 inches of wet, heavy snow, and trees started falling everywhere. Power was out all over the state, including here (which isn’t that unusual given our rural location). But alas, one big alder tree snapped and landed on one of the bridge posts, breaking it in half. Here’s what we were faced with when we cleared out the mess on the our side:

BridgeNorth

The cable-locking system held up as did all the stringers. We can’t see the other end of the main cable but assume it is also okay. Just nothing there to hold it up anymore!

BridgeDamage1

Since the creek is still too high/freezing cold to cross, we can’t easily assess all the damage. But the bridge is “hanging in there” until help can arrive. Hopefully our spring won’t need any maintenance in the meantime.

Once we cut away the mess, we’ll need to dig out the old post (three feet), get another post across the creek and in place, tamped in with gravel, and then all the hardware re-attached. The decking will have to be removed so the structure can be lifted up more easily. As for the dead man, we’ll have to find out how it fared the blow.

BridgeDamage2

You can see the tree that did the deed just uphill from the bridge. Nice aim, tree!

BridgeDamage3

Ah well, it was time to replace the decking anyway. We’re looking for metal paneling of some kind (that we can afford). I’ll post photos of the fix later in the spring! Onward. P.S.: We’re getting too old for this sh*t.

Book-inspired Suspension Bridge in Virginia

We were delighted to finally receive photos of a suspension bridge that was inspired by our book, Building a Small Cable Suspension Bridge With the Cable Locking System.

1-7

According to the builder, Mo Goldman, the bridge is just under 40′ feet in length and 4′ wide (basically half the length of our bridge) and is located in Virginia just outside of Charlottesville.

1-5

The posts are aluminum, 13′ in length, 6″ round with 1/4″ thick side walls, easy for two guys to carry. The post holes are 3′ deep and about 2′ around; the posts are placed on a concrete footer prior to pouring around them. Everything was hand-dug and poured because they were limited to access with a Polaris on one side.

It was fun to see that Mo set up a temporary cable to move materials across. That’s how we moved our gravel for the opposite side, one bucket at a time. But Mo took it further and carried the posts, other materials, plus wheelbarrow and even himself across their “zip line.”

SetUpStringers

Mo also followed the idea of setting up the catenary curve between two trees/structures located away from the creek to plan and build the cables and stringers on dry ground.

MoGoldman

Mo didn’t use our cable-locking system, but instead used a system often used for this type bridge – an appropriate length “eye” bolt placed in a drilled hole in the beam. The suspenders were then connected with a chain connecting link, which uses a threaded portion mating to a free spinning nut to open or close it.

He wrote to us about the bounce in his bridge which was more than he expected, though not a big deal. I noticed that he paid attention to harmonic resonance in the arrangement of the stringers so they were assumed off the “nodes,” so wondered if the decking material he used could be partly responsible (a suspension bridge is going to bounce, that’s a given). He used a material called Trex, which is a deck material made from recycled plastic and wood fiber. Trex tends to flex more than standard lumber does. We concluded that he needed to stiffen the deck, so now he is working on some ideas.

1-8

Mo even put up a sign on his bridge similar to ours and inspired us to remake our sign so that it names the creek, too. We hope others who build a bridge based on what we did will also send us photos and notes about their building experience.

Meanwhile our book is available in paperback and as an ebook via Amazon.com.

 

Cable Locking System (CLS) Dimensions Explained

Off and on we receive requests for the cable locking system (CLS); either the parts or for dimensions. As we have stated before, we could not produce/have manufactured, store and handle/ship the parts at a reasonable cost to the buyer, so we do not provide them for sale. While all of this information is in the book or in previous blogs, we thought we would try to break down the method for sizing of the CLS so interested bridge builders could use the information to have their parts manufactured close to home.

Refer to the drawing below to picture the description that follows.

IMG_2305

The main body of the CLS was made from a section of rectangular steel tube of 4″ X 5″ outside diameter, the section being 1-3/4″ wide. The wall thickness was .17 of 1 inch, which is very close to 3/16″. The interior was therefore close to 3-5/8″ by 4-5/8″, which fits nicely with a 4X4 (nominal) piece of lumber. So that defines the main body of the device. [After my project, I now would recommend using a 4″ X 6″ tube for the extra room for maneuvering the cable during assembly.] There is a locking plate that fits inside of the main body. It is also .17 of an inch (3/16″) and is sized to fit just inside, at 3-9/16″.

The location of the keyhole is placed in this method: the keyhole is composed of a large hole with a smaller slot. If you picture the end of that slot as a hole of the dimension of the suspending cable, that hole would be placed in the exact center of one of the 4″ ends of the rectangular tube, the remaining keyhole would point towards one of the tube’s edges. The locking plate is treated similarly.

The dimensions for the keyhole are determined by making them slightly larger than the materials passing through. Since the suspending cable is 3/16″ the hole was enlarged by 1/32″, thus the hole was drilled at 7/32″. For the large end of the keyhole the dimension of the stop was the guiding size. The aluminum cable stops once crimped on measured 1/2″, which is enlarged by 1/16″ to allow for easy passage of the stop through both plates of metal. So that hole is drilled at 9/16″. There is nothing imperative about these drilled dimensions. If you use different materials than you adjust the holes accordingly.

For the inverse CLS, [picture in your mind] you simply need to cut off the bottom half of the 4X5 steel tube section. You now have essentially a section of steel C channel of 4″ width, with 2 1/2″ flanges. Now mirror-image this remaining half. You should have it placed beneath the 4X4 beam, cradling it. This changes the CLS from a tension device to a compression device, but the plates function in the same manner as before. All sizing remains the same. What does change is that you have to drill a 5/8″ hole (insert an anti-corrosion vinyl tube in hole) in the 4X4 beam so the suspending cable can pass through to access the inverse CLS.

As we have said before, you may freely use this information to build your own bridge or your friend’s bridge. But if you want to mass produce these parts please contact us regarding licensing.

Thanks for stopping by! Be sure to check out our bridge book if you’re thinking about building (or just reading about building) a DIY cable suspension bridge. Here is the link: Building a Small Cable Suspension Bridge with the Cable Locking System

Images, diagrams, and text copyright 2018 by Marvin Denmark unless otherwise noted. Please do not copy and post my content anywhere without my permission. Thank you.

How to Build a Small Cable Suspension Bridge

INSTRUCTABLE-BRIDGE-LOGOWildcatMarvin

As mentioned, we built this bridge and wrote a “how we did it” book about the process a few years ago. Recently, I thought it would be fun to share the basics of this design as an Instructable for people who have enough skill to be able to take the information and work with it. And as we do in our book, we recommend having your specific design approved by an engineer just to be on the safe side.

Here is the link: Building a Small Cable Suspension Bridge – the Basics Plus a Video Demo

I entered their “Outdoor” contest and you can kindly vote if you like by clicking the little vote button at the top of the instructable page. Thanks! I need a t-shirt.

UPDATE: Thank you for your votes – were a winner! We won a t-shirt and a waycool  Campstove 2 from BioLite Energy!

BridgeWin

Adjusting a Suspension Bridge Deck

One of the hazards of building a bridge in the woods is that there are trees in the woods. And trees sometimes fall. It was only a couple of weeks after my bridge was completed that a tree fell on it. It bounced off without causing damage other than a dent in a deck board.

A couple of years ago during a flood, a tree next to the bridge came down, and while not actually falling on the bridge, parts leaned heavily on the suspension cable. I cut off the branches that were in our way and let the rest stay for now since I was busy with other projects. This spring I finally cut the rest of the tree that was affecting the bridge cable. I knew that the deck had sagged a bit and would need to be adjusted at some point.

TreeBridge

That’s why I have turnbuckles installed on all the deadman-to-post cable connections as shown in my book, Building a Small Cable Suspension Bridge. I could just turn them to pull the posts back and level out the deck again.

bridgeturnbuckle2

I used  what was handy to provide a resistance (something to work against) to turning the turnbuckle – in this case a big stick and a metal pipe.

bridgeturnbuckle3

WD40 oil worked to loosen up the connections. They weren’t rusty having been protected under the cover of those white tubes all these years, but they didn’t want to break loose easily.

bridgeturnbuckle4

I used a small bar for turning, but a longer one could have made things easier.

bridgeturnbuckle5

I used a pencil mark to verify if I was tightening or loosening.

bridgeturnbuckle6

Once they broke loose, each turnbuckle turned easily.

bridgeturnbuckle7

Jeep seemed amused that one side was now lower than the other. But that’s just part of the process!

bridgeturnbuckle8

I worked on all four turnbuckles, using line of sight to achieve the results I wanted.

bridgeturnbuckle9

All done, until the next tree takes a dive into the creek and the bridge is in its way.

This all only took about 30 minutes. Here’s a movie of the process if you’ve never seen a turnbuckle in action.

Thanks for stopping by! Be sure to check out our suspension bridge book. Here is the link:

Building a Small Cable Suspension Bridge with the Cable Locking System

Images, diagrams, and text copyright 2013-2017 by Marvin Denmark unless otherwise noted. Please do not copy and post my content anywhere without my permission. Thank you.