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.

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

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

We 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

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.

 

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!

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.

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.

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.

 

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

The new post is in place!

It 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.

Scaling Up the Size of the Yurt – the Beams

Let’s consider the beams for the 20 foot yurt. For the book I used a 4.5/12 slope and for practical reasons I would use it for your project. I’ve walked on many different sloped roofs and on some that couldn’t be walked on without ropes. I can say that you can comfortably walk or work on a roof that is a 4.5/12 slope.

One thing that you may not immediately notice is that I assign the slope to the beam and not the roof plane. Why do that? If you use the roof plane you subsequently have to calculate the “hip” (that joint that joins the adjacent abutting planes) of the roof structure; i.e. directly over where the beams run. Why make things more complicated? Because the beam’s lengths are determined using a slope calculation, it simplifies your calculations. So now to that calculation.

When you solve for the hypotenuse of your 4.5/12 slope (triangle) you have a 4.5” leg perpendicular to a 12” base leg (level). Both squared (20.25+ 144) gives you 164.25 and the square root of that is 12.816 (your hypotenuse). How does all of this relate to the beam? Two things: first for every foot on the level that the beam travels the beam rises by 4 1/2 inches (so for a theoretical beam of 10 feet the “up” end is 45 inches higher) and second, for every foot traveled horizontally (on the level) the beam’s length increases by X 1.068 (so in our 10 feet run the beam grows to (10 X 1.068) or 10.68’ which is just over 10’-8”.

So to complete the beam length calculations you have to subtract the skylight ring assembly and add the overhang you want (here beams are assumed to go all the way to the center of the yurt). Both of these are accomplished in the same manner as above.

For the skylight, take the diagonal of the framing of the skylight ring (a level measurement from one corner to the opposite corner) and then halve that. That is then taken from the beam overall length, after calculating the “sloping” length.

The overhang is a bit different. To make it simple just consider the overhang equal to whatever you extend the beam tail (whatever is hanging past the walls). So, if you wanted a two foot overhang, just extend the beam out two feet (using the slope calculation, of course). This will be close enough for a two foot overhang.

Otherwise, if you want a more precise dimension for your overhang you will need to do some more calculations. This requires a bit of trigonometry. It goes like this: Say you want a two foot overhang. This is a two foot projection that is horizontal (level) from the wall and parallel to the wall. Since we know the number of sides we have, we get the number of divisions in the 360 degree circle. That gives us the peak angle for our triangle. We will use 1/2 of that angle (see drawing below). Our long side of the triangle is 2’ (our overhang). So solving for the hypotenuse: recalling our trig formulas: CAH — cosine of the angle = adjacent side divided by the hypotenuse. Solving for H we divided through by A to get H=C/A. Now do the “rise” calculation from above to get the actual beam overhang length. This sounds like a lot of work, but honestly, it’s easier than reading this entire article!

Be sure to get a copy of the book which explains the rest of building a wood-framed panelized yurt. It’s available on Amazon in color paperback, color ebook, and b&w paperback. And hey, if you build a yurt after reading our book, please send photos to share, thanks!

Here are the links to purchase the book:

Building a Wood-Framed Panelized Yurt, in color

Building a Wood-Framed Panelized Yurt, black & white

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:

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!

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.

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

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.

Scaling Up the Size of the Yurt

I want to talk about scaling up the size of the yurt. We had considered adding this in the book but decided against it. So I will take you through the process now. The size or diameter of the yurt in the book was 16 feet. Considering the next reasonable size up one might think of a 20-foot diameter. Let’s follow the steps to creating it. The parts that get affected are the foundation, floor panels, wall panels (though not height), beam length, roof panels, and possibly the skylight (size). If you follow this process you can create a yurt of any size (within reason, as loads on the beams become a factor). We begin with the floor plan, which in turn informs us of what the foundation will be.

With a diameter of 20 feet we are looking for the circumference. That is found with the formula C = d X pi (circumference = diameter X 3.1416). C = 62.83185. With this information we can find the number and width of the wall panels. First, for the number of walls, we divide the circumference by 4. Four feet is the “ideal” working dimension for our walls. When we divide we get 15.7. An uneven number or decimal number doesn’t work well for wall layout. We want an even number of walls, so we round up to 16. Now we divide the circumference by 16 to get walls of approximately 3.927 feet or 3 ft – 11 1/8 in. That’s a good workable number.

Let’s step back a second. When we divide the circumference of a circle by assigning a number of sides to it not only do we get our floor panel angles at the peak and the base (more on that shortly) but we also get a dimension that makes for an approximate length for the base of the triangle, which will be our wall length. But this dimension is not the true base of the triangle. To get that you would have to use the chord length formula. There are variations on that formula depending on the conditions known. For us it is the simple one: 2 r sin (angle)/2. We have a radius of 10 feet and an angle of 22.5 degrees. 2 (10) sin 11.25 degrees = 3.9018′, or 3 feet – 10-13/16 inches. This is our most correct length for the base of our triangle and the width of our walls.

The next step is to find the angles involved in making the various panels. We now have 16 sides around this yurt. In recalling our math classes we know there are 360 degrees in a circle. Dividing 360 by 16 will give us 22 1/2 degrees for the peak angle. The sum of the interior angles of a triangle is 180 degrees so that leaves us 157.5 degrees for the base angles. Since the sides are equal, than the angles are equal at 78.75 degrees. Remember, the peak angle for our yurt in the book had 12 sides and thus (360 divided by 12) 30 degrees with base angles of 75 degrees each. Some people may not like dealing with partial angles, seeking more simplicity in their work. So let’s look at this yurt with more sides, but same diameter, say 18. That would give us angles at the peak of 20 degrees and at the base 80 degrees. Using the chord formula above the wall length will be around 3.49 feet long. That will waste about 6 inches of siding plywood for each wall but is still a workable width.

With the information above we can layout the foundation, and we could finalize the math to build the floor panels. We can build the walls also. If we follow the process in the book you will see that not much changes except for the length of floor joists and later the roof framing members. Walls will stay the same height so just a width adjustment is necessary. I should say at this point that you could make the walls taller to any height chosen, which will only effect a later calculation for the placement for the skylight ring and it’s tower height. So feel free to experiment!

Following this information and combining it with what is in the book you should be able to design your own yurt of practically any size. Just remember the larger you go the more need for paying attention to the loads placed on various members.

Next time I will talk about the beams, tower and skylight, and roof panels for a larger yurt.

Here are the links to purchase the book:

Building a Wood-Framed Panelized Yurt, in color

Building a Wood-Framed Panelized Yurt, black & white

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.

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.

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.”

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.

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.

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.

 

Building a Wood-Framed Panelized Yurt: the movie

Robin put together a movie called “How to Build a Yurt in About Five Minutes.” You can view it by clicking here!

If you’re intrigued yet need more information, you can also buy the book in either color or black and white. It’s 176 pages of step-by-step instructions with lots of photos and drawings, and also includes a materials list for a 16-foot yurt:

Here’s the link to the color version of the book.

Here’s the link to the black and white version of the book.