3

Please help. I made a swing for my kids and now am wondering how safe it is. The swing beam is pressure treated yellow pine 4x6 and 16 feet long. The swing hangers are attached to the 4 inch side of the wood. At one end it sits in a deck bracket on top of a 4x4 attached to a fort. The other end sits on a horizontal beam of an A frame attached with brackets and lag screws.This A frame is placed 12 feet from the fort portion so that the other 4 ft of beam extends past the A frame. There are 3 swing stations and then a trapeze on the far end past the A frame.

My concern is that when my 60lb kid uses the swings I notice "bounce" of the beam. The center of the beam visibly moves though the attached points at fort and a frame do not seem to move at all. Is this safe? Thanks so much.

Deborah
  • 31
  • 1
  • 1
  • 2

1 Answers1

3

The usual disclaimers apply. I'm not a licensed structural engineer, I'm not providing engineering advice, I'm just reporting what standard load calculations in the literature say, etc....

Assuming no major defects, and using #2 graded southern yellow pine in wet service (the least optomistic numbers), with an actual size of 3.5" x 5.5" (typical of planed "4x6") a 415 lb load at the middle of (aka point loading) the 12 foot span should be safe.

Some deflection is normal. The above load should have a bit less than 1/2" deflection.

http://www.forestryforum.com/members/donp/beamclc_ctrpointload.htm

Uniformly loaded (not really applicable, but "the other extreme" as you interpolate 3 swing positions) 825 lbs, with a deflection a bit more than 1/2" (considered OK for a roof, too much for a floor.)

http://www.forestryforum.com/members/donp/beamclcNDS2.htm

There are some slight complications (about a 20% reduction in loading, IIRC) induced by the cantilever overhang, but none should really be of great concern for normal-szed children. On the third hand, if you wanted to bolt/screw/glue/nail a pair of 2x10 or 2x12, one to either side of the swing beam, that should stiffen it up quite a bit.

Ecnerwal
  • 235,314
  • 11
  • 293
  • 637