Non-engineer here, I'm trying to adapt a typical "A-frame swingset design" (like this https://www.instructables.com/id/Free-standing-A-Frame-Swing-Set/) to be a small set of traveling rings for the kids (inspired by these: https://travelingrings.org/).
To that end, I'd like to make an A-frame swingset that is relatively high (10 or 11 feet to the bottom of the swing beam, as opposed to the usual 7-8 feet), and relatively long (16 feet swing beam without a supporting A-frame in the middle). The reason why the lack of middle support is important is because of the large amount of clearance that traveling rings require.
This readily available swingset bracket (https://www.amazon.com/Frame-Brackets-Complete-Mounting-Hardware/dp/B01M28VV0N/ ) supports a 4x6 beam , and I've seen comments from people successful supporting 12 foot spans with this type of bracket, even though the manufacturer recommends a 10 foot span.
My question is three fold:
- Would a 4x6 beam safely support a 16 foot span for this type of application? (assuming standard treated lumber like redwood or pine, not glulam or lvl) This question was somewhat addressed here: Is this swing beam safe? And my conclusion is that a 4x6 is iffy.
My primary question, assuming the that a 4x6 is a risk, is the following:
- If not, would a 4x8 beam which was notched at both ends to fit the 4x6 bracket support a 16 foot span? (with the same assumption around non-engineered lumber)
- If no to both #1 and #2, would a 4x8 beam on a different type of bracket be able to support this span?
My main concern is deflection & buckling from force applied in the center. The largest kid currently weighs 70lbs, and there could be as many as three kids on the set at a time, swinging vigorously and possibly in sync.
Final followup question:
- In the A-frame design from instructables that I linked to above, the a-frames are supported by a cross beam. Would it compromise the integrity of the design if the cross beam were moved lower to the ground? I'd like to keep the center of the A-frames open if possible, in case the kids swing through them. My intuition is that it actually strengthens the design if the cross beams are lowered, but just wanted to get a sanity check on that.
Thank you in advance for any help you can offer to vet the safety of this design.