Written by: Jared Spaniol, Application Engineer
I have been wanting to add a free-standing hammock hanger to my backyard to enjoy the nice fall weather and now that the fall season is here, I decided to start researching options. I have an ENO DoubleNest Hammock that is approximately 10 feet in length. When I saw some of the prices of the ones available online that would fit my hammock I thought they were a bit expensive, or at least more than I was willing to spend. The moderately priced ones I saw were designed more for those rope style hammocks, not the lightweight Nylon parachute material ENO uses because the attachment points are slightly different. I probably could have modified my hammock to fit, but they weren’t meeting my footprint constraints anyway. I wanted something with a very small footprint since I have a small area to work with and didn’t want to have to step over a large fixture frequently. I also wanted the hammock to be very easy to install and remove from the hanger since I wasn’t planning to leave it up continually to avoid weather and sun damage.
After some online research of the products on the market, and options to build one, I decided to build my own. I put together a quick constraints summary to make sure the design would meet my needs.
The easiest and most readily available material to use for this project was some SCH 40 galvanized steel pipe that can be bought at the local Home Depot. The design was simple and straightforward, basically just two t-shaped pipes connected by a straight pipe (Figure 1). The model assumes this is all one piece for simulation purposes, but there are “T”, straight, and 90° connectors in the system.
How could I optimize this design to better meet my constraints? Remember, I want it to be lightweight and still hold up to 400 lbs., while reducing cost. Should I just go with the 1” pipe, which I know will hold the weight but is probably overdesigned, or would a 3/4” pipe work? That is the main concern.
This is a common problem a lot of companies face. They know they can overdesign and meet the constraints, but with SOLIDWORKS Simulation the design can be optimized. All the forums and tutorials I read recommended using a 1” or even 1-¼” SCH 40 steel pipe. Some comments said I could get away with the 3/4″ pipe, but had no testing or justification to back that up. Since I know how trustworthy the internet is – and didn’t want to land on my back on the concrete – I needed to know for sure. If I can use the 3/4’” pipe it will save some cost and weight. I have SOLIDWORKS Simulation so this is something I can get a reassuring answer for in a few quick steps.
This is a very simple model and only took a few minutes to setup. A custom weldment profile was used to create weldment profiles for the SCH 40 pipe in two sizes, 1” and 3/4″, based on the SCH 40 sizings which aren’t exactly made to those sizes. I used a configuration to control the two sizes so a simulation could be analyzed within the same file for an easy comparison of results.
The simulation setup was relatively straightforward. The forces were setup at a 45-degree angle based on how a hammock would sit in the hanger. A force of 200 lbf was applied to each top bend of the hanger along that 45° angle totaling a 400 lbf. Based on the results, it was decided that any further simulation wasn’t needed in this case, but the side to side forces from the hammock swinging with a person in it could have been analyzed for further assurance of the designs’ capability.
The results show that the pipe is far from yielding or failing with either size configuration so that wasn’t a concern. The displacement is also very small on both sizes of pipe, so the concern for any significant bending was minimal. Therefore, it was decided to go with the lighter, cheaper option, the 3/4” option.
Figure 2 shows the results summary and comparison between stress and displacement for each pipe size.
The question I leave you with is… could the hammock hanger have used 1/2” pipe and still been safe? It likely would have been a good idea to analyze the opposing axis forces to account for swinging back and forth for that configuration as there is some flexing of the pipe when swinging in it. Figure 3 shows an initial test setup and Figure 4 shows the completed project in use for full relaxation value.