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Heavy swing gates support posts


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Hello my name is Heath 

im going to be building a large heavy swing gate for a customer . And i would like other fabricators advice on posts . Each gate section is 11’ long and 5’6”high . The total calculated steel weight per ft comes to 786 lbs per gate half . there will also be a 3” x 12” x 5.5’ timber cnc cut at an arch that will be , and im guessing here approximately 150-200 lbs . So approximately 1000 lbs per gate . Its heavy and rubust . The ball bearing hinges i have selected are rated for 3000 lbs a pair. I personally will be adding 3 hinges per side as it eases my mind . The posts themselves i have chosen will either be 6”x6”x.500 wall square tube or 8”x8”x.500 wall and probably the latter  the post bottom will have 1.250 plate welded to it and 1.250 holes cut in for 1.250 studs.

the customer has a large selection of un used steel screw piles 4” and we are thinking of using them to mount the posts of the gate onto .

we would utilize 4 screw piles per side and screwed in 9’ and then a mating flange/plate 1 1/4” to join all 4 screw piles then the post plate bolted to the screw pile plate w 6 or 8  1 1/4” b7 studs . Im a fan of overkill than not . Gentlemen whats your opinions 

oh and i was thinking of slushing the 8x8x1/2” tubes with concrete 

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Add the weight of the neighborhood children (and drunk adults) to the weight of the gate when calculating the leverage factor.  Be sure and have adjustable hinges so you can make adjustments for any differences between the gate  and post support.  You do know to make the gate out of square to take into account the droop factor when it is mounted. That way it droops INTO square.

What ever you figure for support posts, double the strength calculated and then double it again.  That is a lot of lever arm being applied to the support post. Make the gate and supports strong enough to take a full force hit by a vehicle. It will happen at some point.

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You only need two hinges. Actually 3 hinges makes adjustment in this plane more complex. The bottom bearing holds the vertical weight. You can get these adjustable in and out and sideways as well.

The top hinge handles the horizontal pull or drop. It too should be adjustable.

If you set your post in concrete, the amount of concrete below ground keeps it from falling over. Basically the weight of the crete matches the weight of the gate. It is a ratio and I don't remember what it is.

A structural engineer is your friend here, if you don't have the experience.

 

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I would suggest substantial under ground work  If your vertical post  is solidly attached to a + normal to the axis of the post it will help deal with stresses as the gate swings.  For gates not nearly so wide I would suggest a solid connection that goes underground from one gate post to the other with a good gusset at each post |__| with side pieces to deal with side forces  T   .

With an 11' gate Sag will be an issue. Designing it to "sag into straight" is impressive as it's difficult. Designing the gate to resist sag may be easier. You will note that many fabbed gates end up with turnbuckles.  (Remember triangles are your friends when designing things to resist sag.)

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Simple spaced vertical bars or something a bit more Tijou-ish?

Does anyone remember if this is addressed in the COSIRA book(s)?

Thanks John I will try to pound that value into my brain for future use!

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Thanks, John. This is for traditional joinery even if you use scrolls for gussets.

All the mortise/tenon's, collars etc lock together when it sags.

You still need a turnbuckle or adjustable nut from the top hinge thru the vertical post to adjust the whole gate to parallel. And this is why a middle hinge is not needed.

Been a while, but it's like riding a bicycle.

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The design the customer wants is big and chunky. The main frame on each gate is 6”x3”x.375 wall and the pickets are 2”x4” x.188 wall . In the first 5’ section the 2x4 vertical pickets are seperated to accomidate a cnc curved cut timber that starts by the hinge bottom portion of the inside frame and  curves slightly to meet the top inside frame . I figured a heavier wall material for the outside frame to eliminate as much sag as possible. 
 

the picture provided was just one of the few i have done . This gave the general idea . But in reality there are 13 pickets per gate half 

1E0EEFE9-9595-4450-B514-EAD7C63ACE55.jpeg

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On 9/10/2020 at 10:37 PM, ThomasPowers said:

Does anyone remember if this is addressed in the COSIRA book(s)?

Hi Thomas, sorry for any confusion but,

Upon checking, apparently so, but this conflicts with what an original CoSIRA instructor told me, and it worked well for me on the larger gates

The reference for the PDF format is Wrought Ironwork, Part 6  page 86 Lesson 30, Item D, and the recommendation is 1/16" per foot.

See what works best for you

 

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I got this from a Whitaker gate workshop at Russ Swiders shop, Rowe, N.M.

I believe he said 1/8" per foot. However that was a long time ago, and my notes are not available. He could have said 1/16". Sorry for the confusion

I've done one pair of 12' gates and set them to 1/8". Worked for me.

 

 

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I think a better term is rack, not sag. 

I think of sag as to what happens between the post you hang the gate on and the gate itself. Sag can increase for a number of reasons and can be corrected by how you build the top hinge.

Rack should only happen once if you have a good gate design. No matter how good your heel bars, collars, rivits and tenon's, there is always a little play. You may not be able to get movement by hand, but when you hang a 12' by 800# gate on a single point, things will move. They should mechanically lock into place and then it's a done deal. 

Concerning 1/8" vs 1/16" per foot rack, I must say with my large gates I mentioned above, my skill level wasn't what it became later on, especially being my  first set of gates. It could very well be that it's a good thing I used 1/8" because my joinery may have been a bit sloppy. If I'd used 1/16', perhaps it would not have racked square. 

 

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The 1/8" worked well for me too,

Although the CoSIRA books are a good/excellent reference source, they are not definitve, merely a very convenient guide

They are now readily available as softback reprints for anyone interested, and can't find them as a PDF download.

 

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On 9/15/2020 at 4:30 PM, John B said:

They are now readily available as softback reprints for anyone interested, and can't find them as a PDF download.

Just ordered the reprints of "The Blacksmith's Craft", "Wrought Ironwork", and "Decorative Ironwork". I'd downloaded the PDFs, but I prefer an actual book.

8 minutes ago, ThomasPowers said:

I even have memorized what CoSIRA stands for!

Council for Small Industries In Rural Areas!

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