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Sorry in advance if this question is excessively noobish or seems lazy. I have no engineering background and am unsure where to get started tackling this problem. Links to resources that could put me on the right path would be very much appreciated. I'm not looking for others to do my work for me; I just want to know what sorts of calculations I need to do.

I'm looking to build a cube-shaped structure, roughly 10 ft cubed, for suspending a series of seats (swings, sort of) for people to sit on. I'd planned on building the structure out of 12" aluminum trusses or buying one pre-made. Here's an example of what I might buy or try to build, for visualization.

I'd then loop rope around the horizontal trusses, using the rope to hang "benches"/"swings" from the structure. I'd attach the trusses to plates and use rebar to affix the plates (and the structure) to the underlying ground.

So the question is -- How do I test whether this structure would be sturdy/safe?

  • If I'm planning on hanging, let's say, five seats from each horizontal segment, how can I calculate if the trusses would support that sort of vertical force?

  • How about the horizontal force caused by someone potentially swinging on one of the seats?

  • Horizontal forces caused by wind hitting any tarp (solid or perforated) I use to cover the structure?

If this calculation is too complex/multivariate for an amateur like myself to reliably tackle, is there somewhere I could turn for an engineer's feedback?

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  • $\begingroup$ This is quite an involved process. If this is a temporary structure (to be moved around from place to place), then you have a greater issue with the foundations, since they'll need to be designed for multiple soil types. Find yourself a licensed engineer to do these calculations for you (preferably one with experience with this sort of structure). $\endgroup$ – Wasabi♦ Mar 20 '16 at 22:45
  • $\begingroup$ It sounds like you may be working on an entertainment project - ANSI E1.43 - 2016 which is freely available from PLASA/ESTA may apply or at least be close. It describes the appropriate steps which will involve including someone who has appropriate engineering knowledge and applying extra safety factors to recognize that most equipment is not designed to support humans.. $\endgroup$ – Ethan48 Mar 21 '16 at 14:28
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There is not a single safety calculation for a structure. Something built-up like this has multiple failure points, and each requires a separate calculation.

For example, each fastener may shear, bend or get stripped. Each would be a different calculations (for each fastener). To totally inspect if the structure performs as expected you need a) a lot of calculations from an experienced engineer or b) a good FEA model from an professional engineer.

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In the first link you give there is a link to a PDF document which gives loading values for the trusses in various different load setups. For the sort of cubic structure you describe these should be perfectly valid as long as they are assembled as designed and this should give you a good starting point for an initial estimate for the load capacity of the structure.

You will also need to incorporate some sort of safety factor: a number you multiply your expected load by to get the required capacity of the structure. For example, if you have a known load of 100 kg a safety factor of 3 would give you a required capacity of 300 kg.

This safety factor reflects your uncertainty about your analysis and gives some margin for unexpected circumstances, especially where the structure has safety implications.

As you are looking at prefabricated struts I would suggest that you find a reputable supplier and talk to them about your application. These things are designed to be versatile and general-purpose, so if you can describe your application in detail they should be able to give you specific advice.

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