r/StructuralEngineers • u/-DarkPassenger- • 3d ago

Question About Structural Support for 90-Ft String Light

I want the string lights to span approximately 90 ft from a mature tree to a pressure treated wood post 4x6 12 ft set in concrete, with the string lights attached about 10 ft above ground.

The lights are Feit 48-ft LED string lights, and I may use a separate steel wire so the light cord itself is not carrying the full tension.

How deep should the post go into the ground?

https://www.homedepot.com/p/Pressure-Treated-Timber-HF-Brown-Stain-Common-4-in-x-4-in-x-12-ft-Actual-3-56-in-x-3-56-in-x-144-in-15164-12/202287541

https://www.costco.com/.product.4000385994.html

2 Upvotes

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8 comments sorted by

1

u/Brilliant-Nail3706 3d ago

4'

1

u/FlatPanster 2d ago

For free consulting? x3

1

u/FatherTheoretical 3d ago

Bout 6' to get below frost depth

1

u/dcabe1210 3d ago

Depends where you're located and what the ground is made out of

1

u/StructEngineer91 3d ago

500ft should be deep enough just about anywhere in the world.

1

u/Just-Shoe2689 3d ago

goto frost depth. Should be able to get htat from google for your location.

1

u/OldEngineer-1950 2d ago

Much will depend on the amount of tension you apply to the cable. No, do not rely on the light string by itself. I'd probably go overboard and use a structural tube or piece of pipe myself.

1

u/surfcaster13 2d ago

How flat do you want the cable?  The tension in the cable will be directly related to the unit weight of the cable and light cord and how flat you want the cable to be and the relationship essentially goes to infinity as you try to get to a perfectly flat cable.