Gate tech -- engineer/math help

[kaiser715]

I got a 16' farm gate on my driveway. Put it up when we first bought the place. Used an 6x6 post about 3.5' in the ground. Had to adjust/straighten the post a couple of times as the weight of the gate pulled it out of kilter.

I got some drops of 8" steel square tube, about 6' each. What I am thinking to do is to pour a concrete footing, with anchor bolts to bolt down the post (I'll weld it square to a piece of 1/4 plate). Shims or bottom-side nuts to level.

The gate weights 151 pounds. Two questions about the concrete base: 1) how much weight should I plan for in concrete; and 2) square and deep (3') or larger surface area and 1' or less deep?

It will need to support the gate in 2 positions, open and closed (90* to each other)

 

[awheelterd]

I got a 16' farm gate on my driveway. Put it up when we first bought the place. Used an 6x6 post about 3.5' in the ground. Had to adjust/straighten the post a couple of times as the weight of the gate pulled it out of kilter.

I got some drops of 8" steel square tube, about 6' each. What I am thinking to do is to pour a concrete footing, with anchor bolts to bolt down the post (I'll weld it square to a piece of 1/4 plate). Shims or bottom-side nuts to level.

The gate weights 151 pounds. Two questions about the concrete base: 1) how much weight should I plan for in concrete; and 2) square and deep (3') or larger surface area and 1' or less deep?

It will need to support the gate in 2 positions, open and closed (90* to each other)

Preface *I'm no engineer*

I would imagine you would need a shit ton of concrete to make for certain it never starts to sag while holding all the weight. Does the gate stay open or closed most of the time? If closed, I would do a guy wire from the top back to the bottom of a second post with a solid bar spanning the tops, like a high tension electric fence corner. Or just get one of those wheels on a spring to take some of the weight off

 

[83oldyoda4x4]

You need to put in a 2nd post to brace the first. We always did something like this when building fence corners or gate openings. Typically with 2 telephone poles or 6x6 posts. The diagonal wire or cable can be adjusted as needed.

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[Futbalfantic]

Needs more triangulation.

 

[jeepinmatt]

Deeper is better. A 150lb gate doesn't seem that heavy. Was the original post in concrete or just dirt?

 

[rockcity]

Your weak point is going to be the 1/4” baseplate.

and make sure you put plenty of rebar in the concrete or it’s going to crack and be useless.

 

[shawn]

Your weak point is going to be the 1/4” baseplate.

and make sure you put plenty of rebar in the concrete or it’s going to crack and be useless.

Base plate should be 1/2".... Or use a continuous pipe and put it 2-3ft down.

 

[Fabrik8]

If you really want to weld stuff, make a post with a flange, and do whatever you want for a footing to bolt the post down. Doesn't matter.
Then weld two horizontal legs close to the bottom of the post, 90 degrees apart.
Then make a footing for the end of each leg, with concrete weight to match the gate weight.
Your 150lb gate at 8 ft center is 150*8=1200 lbf*ft of moment about the hinge post.
So if your legs are say 3 feet long, you would need 1200/3=400lb of concrete (minimum) at the end of each leg to balance the gate in each direction. Or 200lb with a 6ft leg, etc.
The weight of the legs would subtract from that as well, at half the leg length.
You're really just making counterweights in the form of a footing. I'm just having fun with alternative ideas.

You can do the same thing with braced posts, but have more options.

If you just do a single post with a deep concrete footing, the concrete weight doesn't matter too much because the concrete weight is so close to the post. With the footing depth, most of what the concrete is doing is just bearing on the soil to resist the gate torque (the bearing ability is probably a lot greater than the concrete weight).
If you do a single post with a shallow footing, you need a lot of concrete area to get the weight away from the post, and to change the distance of the post to the edge of the bearing (like a floor lamp with a big diameter base).

 

[powerstrokin04]

Preface *I'm no engineer*

I would imagine you would need a shit ton of concrete to make for certain it never starts to sag while holding all the weight. Does the gate stay open or closed most of the time? If closed, I would do a guy wire from the top back to the bottom of a second post with a solid bar spanning the tops, like a high tension electric fence corner. Or just get one of those wheels on a spring to take some of the weight off [emoji38]

Like said as an option, the training wheel method works well. We used the support wheel on 10+ gates over the years. From the cheap tube gates to heavy steel gates. It's the fastest and cheapest route. Both google examples.

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