Welcome to Building a Suspension Rig. The article itself will be relatively SFW, but will touch on one of the ahh, more salacious hobbies for which I am known.
Shibari, or alternately Kinbaku, is a Japanese influenced style of rope bondage. An important aspect of which is suspension; or using ropes to both bind and lift a model into the air while she is bound.
Rope suspensions are a big draw. Seeing one is often what gets people interested. It’s what caught my eye years ago when I first started learning. I thought, “Shit, tying chicks up in the air looks fun. I need to learn how to do that.” Little did I know this would lead to learning about (rudimentary) structural engineering, working load limits, and other such arcane and perverse arts.
If you read the Movin’ On Out article you may recall a throw-away mention of using one of the rooms in the house as a dedicated rope room. In order to do that, I needed a hard point from which to do suspensions. Which sounds easy enough.
A hardpoint is an attachment point connected to a structure that will (hopefully) support the weight and dyna
mic forces of a body being suspended and put in motion in the air. This can be as simple as throwing a climbing strap over a large branch of a tree, and using various equipment stolen from rock climbing and wilderness rescue to create a place to suspend from. Other outside applications include using wooden swing-set kits with 4×6 lumber for the beam and 4×4 lumber for the legs. Indoors, most applications involve tying into rafters/beams in one fashion or another. Partly depending on if one has access to the attic space above a ceiling. Either way, the goal is to distribute the weight and force so that the person being suspended doesn’t fall on her head or shoulder because the hardpoint comes out of the ceiling.
Most folks only want a single point. Usually this involves a 4×6 beam spanning at least 3 rafters, with a forged, shouldered eyebolt through the center of it. The eyebolt is then below the ceiling. Often folks will put an empty light fixture box in place so that the eyebolt is inside it. A blank cover with a magnet glued in the middle can then be used to disguise the eyebolt. However, if you either can’t get into the attic above the ceiling or want more than one point, folks will often to with unistrut (or superstrut). Unistrut is 12 gauge (at least for this application) steel or aluminium product generally used in commercial construction for hanging race ways, ducting, wiring, etc. It’s easy to bolt to things, and so the common approach is to get a 10′ length and bolt it to the ceiling joists through the drywall. Then use forged eyebolts with shoulders as the hardpoint. This is one of the simplest ways to do things; most forged eyebolts are rated specifically for rigging and have easy to determine WLL (working load limits.)
A digression, Working Load Limit is really important with this. WLL is determined by taking the Minimum Breaking Load and dividing it by a Safety Factor. Because we are dealing with humans and the risk of catastrophic injury or death is there, the normal WLL for rope suspension is MBL * .10. In other words, a 10 to 1 factor. Concientious riggers then add in an additional safety factor as many suspensions are dynamic (IE: the person being suspended doesn’t go straight up and down, they may be moved about in multiple directions). Generally the thinking goes, if you’re tying someone that weighs up to 200lbs you want to have a WLL of at least 1000lbs or greater. Unistrut bolted to 6-8 joists/rafters are going to meet that requirement. An eyebolt rated at 2000lbs+ WLL is less than $10, so over-engineering is easy to accomplish.
What if you can’t bolt to the ceiling joists? Either because you are in a rental, or because you have plaster & lathe ceilings, or (as I discovered) your home has wooden ibeams for joists? Well, you can build a free-standing structure. There are tons of designs for these out there where you buy some lumber and bolt together a stable structure. The aforementioned swingset sets can also be adapted. And there are some various “portable” hardpoints made for people who do silks, or for cleaning deer, or any number of other applications. None of these are that great. You have a really limited working area where the structure is stable. Or you can only tie in one place.
I like to do a style of suspenion that involves using lengths of architectural grade bamboo. By having multiple lengths, you can move the person being suspended in multiple dimensions. You can manipulate pitch, yaw, and roll as well. As mentioned though, my original plan of buying $100 worth of unistrut was out the window. You can’t bolt anything to the bottom of I-Joists. This sent me on an odyssey. I spent months measuring, designing, reviewing documentation for Simpson’s StrongTie products, measuring again, re-designing, and etc.
The rope room is on the lower floor. The back wall is a foundational wall, the floors are concrete, and the ceiling is just over 8′ and has dimensions of 17.5′ x 14′. I settled on a design that is 14’x16′ using wood and various Simpson Strong-Tie connectors. If you’ve any interest in building structural shit, I highly encourage you to take a look at their catalogue. They make some cool hardware.
The design itself went through a half-dozen revisions, changing as I learned more about how to calculate WLL and about the products I wanted to use. Once I had the final version it was time to buy materials and start the physical labor.
The lumber I purchased is as follows. I had to sell like 3 orphans to afford it. Normally this would be less than an orphan.
The hardware connectors weren’t much cheaper. The following Simpson Strong-Tie connectors were purchased:
Corner Caps: 4
Mid Point Caps: 6
4×6 Joist Hangers: 2
Post Bases: 9
2×6 Joist hangers: 16
With materials purchased the next step was preperation.
I thoroughly sanded each of the beams and posts and joists. I rounded the corners and edges slightly on all of it. Went from rough to fine grit in three stages to make everything smooth. Then stained all 27 pieces of wood. All of the hardware was spray-painted a mat black and given two coats. I left the fasteners the default stainless.
Installing it required a little help from my friends. We used the post caps to bolt the beams to the tops of the beams for the north side, then attached the post bases, raised things into position, and bolted the bases to the concrete floor. We did the same for the south side. Then put in the middle row of posts and the east, west, and central beams. And finally added in the middle joists using joist hangers. To finish it off and to keep it square I then custom cut some wedges to get in the corners.
Lastly, I needed to hang the bamboo. I still need a few more lengths of it, and I’ve taken to learning to flame treat them. I also added smart lights so I can control the color and intensity of the lighting. A few other bits of furniture and some jute rugs to complete the look and it is ready for rope shenanigans
All in all, it took about 8 hours to assemble it. And I probably put in a good 20-40 hours cutting, sanding, and staining.
But here is the end result: