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.

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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.

Building a Wood-Framed Panelized Yurt: the book

We have a book! Actually, we have two books. Links to purchase them are below. Color printing costs were high on a 176 page book, so we also published a black and white version. The price is about 40% less than the color version, and the photos are clear enough to illustrate the task at hand.

Here are the links:

Building a Wood-Framed Panelized Yurt, in color

Building a Wood-Framed Panelized Yurt, black & white

Building a Wood-Framed Panelized Yurt, Pt. VII: The Book Proof!

We received the first proof of our book today! A random page opening revealed some of the details for the wall panel jig. There are 170+ pages of everything you’ll need to know to build and assemble a wood-framed panelized yurt.

There are a couple of drawings to finalize, and a few photos with explanations to add regarding final details, along with some additions and corrections to do. Then we’ll release the book to the world via Amazon.com.

Meanwhile, here are the Three Yaketeers, with Jeep the supervisor. “Another job, well done.” — Mr. Natural

 

 

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.

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.