Can you give me the load limit on a 4x6 pine board 18' long used for a swing set? Thank you
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1Hi, Joan, and welcome to Stack Exchange. Are you asking about the weight of the board, or the load capacity of the board?– Daniel GriscomOct 23, 2017 at 16:04
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Also, will the beam span 18 feet, or is it like a typical swingset where part of it cantilevers?– isherwoodOct 23, 2017 at 16:05
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Is it supported at the ends (18 foot span) or somewhere else? i.e. legs 12 feet apart with 3 feet sticking out at the ends, or 3 sets of legs 9 feet apart, or two sets of legs 18 feet apart? Beam calculators are not too hard to find, but for a swing set you might want to increase the safety factor (amount by which you exceed the expected load when calculating.) Grade of the lumber also matters.– EcnerwalOct 23, 2017 at 16:07
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...I'm betting there's a 90+ percent chance OP is asking how much weight can hang from the 4"x6"x18' pine beam. +1 so she can upload a helpful drawing or picture or something.– elrobisOct 23, 2017 at 16:53
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The beam is 18' long supported on each end, no support in middle. Not sure of the grade of lumber. I just need to know worst case how much weight can the swings support. Sorry I don't have a picture or more info. Thanks for any help.– JoanOct 24, 2017 at 15:05
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2 Answers
Assuming it’s “Lodgepole Pine” (Idaho Pine and Ponderosa Pine is slightly less) and it’s grade is a No. 2 and better (no loose or missing knotholes), then a 4x6 spanning 18’ will support about 105 lbs. loaded at the mid-span (slightly higher if it’s loaded at third points or further from the center point).
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Is there any resource that lists maximal admissible workload of various beam/planks? In case I want to check a similar-yet different configuration.– ebosiAug 21, 2018 at 15:54
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2@ebo I’ve seen structural tables on the internet. Maybe Google “Structural beam tables”.– Lee SamAug 21, 2018 at 16:21
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Better idea instead of the 4x6 use 2 2x8 boards bolted of nailed together. Ive done this on a 18 foot span and it holds 3 large adults (over 200 lbs each) on swings without any flex or bowing. Outdoors i would use a good grade of treated lumber to prevent decay from the elements and longer life.
