Chain link post strength

[Cooler]

My lally columns are concrete filled.  I've been told that is mainly to prevent rust from the inside.  I'm not sure I believe that.  I do think it is good for axial compressive strength (pressing straight down).  

A narrow column of concrete will probably snap like a pretzel, even when encased in a steel post.  It sounds like a lot of work for little return.  

How did you calculate the required strength for the posts in the first place?

[Mr_Mike]

That was all about lost password, and inability to retrieve. Set up other account, and one of our administrators saw it and helped me reset my orig password.  They did a great job. I wasn't getting emails on resetting password, etc.
The "Guest" post was first under my other name, that was deleted. It was great of the administrator to leave the post, with "Guest" name. The Administrator contacted me thru the new screen name, and that account is closed, so I can't look to see who the Admin. was.
All is well now
Hope this clears up the mystery.

Yes, it was a mystery.

[Lynden]

You would get some added strength by filling the posts with concrete.

The added strength comes because in order to be bent or pushed over the posts must get squashed or the sides must split. The concrete prevents squashing and the steel post itself is highly resistant to splitting. You can also add a length of 3/8" rebar for additional strength.

[EightFingers]

How long would it take for the concrete to dry?

[Mr_Mike]

How long would it take for the concrete to dry?

Concrete doesn't dry, it cures. 28 days is the norm. However, I contend it is really not worth it. Given my cost is reduced by doing the work myself, I'll buy the thicker posts.

Lyndon: Yes, it adds strength due to reducing buckling. However, does it add strength commensurate with the effort involved vs the cost of thicker posts. I contend it does not. Rebar down the center will do essentially nothing.

[daddo]

That kind of narrows down your location and soil type. 80 mph winds; Within 150 miles of the coast, in Tornado alley, California's trade winds or anywhere in between getting a viscous blue northern.  


 If the soil gets saturated a lot or is loose during these winds, you might consider additional post bracing or go deeper- perhaps a bigger concrete area as well.  The sched 40 posts would be better assurance and insurance. 

[TDKPE]

If you define 'failed' as being bent enough to not look plumb enough, then local wall crippling of the tube is still a long way off. Unless it's really thin walled. But in general, the tube will bend unacceptably before actual buckling or crippling occurs on the inside of the bend, and a concrete core won't stop that initial plastic deformation.

And as Mike said, a length of rebar in the center won't do anything. If you need greater bending resistance for a given fence height, use a thicker wall, or a larger diameter, or both.

JMO

[Lynden]

I contend it is really not worth it.  Given my cost is reduced by doing the work myself, I'll buy the thicker posts.  

Lynden:  Yes, it adds strength due to reducing buckling.  However, does it add strength commensurate with the effort involved vs the cost of thicker posts.  I contend it does not.  Rebar down the center will do essentially nothing.

I totally agree. In areas with high wind-loads, use heavier-gauge posts. When repair time and costs are considered, it's probably better to use heavier-gauge posts.  However, I'm curious about how much strength is gained by adding concrete to a lighter-gauge post.  Here's a video which compares various gauges of fence posts. Too bad they didn't include a couple of posts filled with concrete.

https://www.youtube.com/watch?v=USdXosoSOf8

I agree that adding a length of rebar down the center of a concrete-filled post wouldn't add much strength.

[daddo]

Concrete is brittle and only serves well in compression loads. If you could pressurize the concrete in the post somehow I could see an advantage. But if the concrete has anywhere to go even slightly, it will crack, break or give away to an extent the post will still bend or kink unacceptably.

[EricU]

Even if there were a few cracks in the concrete, it would still help the pipe resist buckling.  At least until it turned back into powder.  I'm assuming fence posts fail in buckling, is that wrong?