Reinforcing of Cylindrical Footings for Fence Posts

[mlzahn]

Is reinforcing needed in cylindrical footings used for fence posts? Posts are 12 high, spaced at 8 feet.

Is there an allowance for not using reinforcing?

Thank you.

 

[racookpe1978]

I've never seen any used. Never used any in any fence posts I've installed.

Fence failure is usually from a slump in the land (the dirt moves, dragging the fence with it) or a failure of the concrete to hold the load (the fence forces the post and its concrete to move through the dirt because the post and concrete were too shallow and too small a weight/too narrow a diameter to withstand the sideways pressure of the load.

I assume somewhere rebar has been used, but I've never seen it. (Think about cover depth for the rebar needed to avoid rust underground, and compare that to the diameter of the concrete around the average post. How are you going to get cover depth plus rebar plus rebar-to-post distance to develop the rebar strength? Wouldn't you see the "post" working directly as a "over-sized" rebar member to prevent the concrete from cracking under its bending moment?

 

[TLHS]

If your post is embedded full depth and is strong enough to hold the full moment, I would basically assume that the concrete is just working in bearing to transfer the load across a larger area of soil. Even if the concrete failed as a structural unit, would anything happen?

I guess you could design it as a composite section, though. Or if the moments were small you could try to see if you could design it as mass concrete.

 

[BAretired]

Fenceposts have footings?

BA

 

[msquared48]

BA:

I commonly set mine in a dry mix of concrete and let it hydrate with time. Mine have been in the ground as such in the northwest environment here over 30 years with no probs. PT 4x4's in post hole dug holes.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[msquared48]

For a 12 foot high fence, you probably will need a pole type foundation unless you embed larger members, depending what your wind load requirements are.

You mprobably will ned a permit too due to the 12 foot height, depending on your jurisdiction.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com