Gate Design

[BarbaraT]

I building some big gates... 8m Span - 2.5m High
I have about 600kg of oak.

So there going to be big and heavy with Electric openers.

A few concerns / questions..

Being a engineer I wanted to double check where the loads are.. the design doesn't seem to have many diagnals and as expected the bulk of the load it through the centre panelling..
This is shown in the FEA below, The forces in the centre panelling should be fine as it's also solid oak and 1 inch thick,

Stress in the joints also looks realitivly low, Hopefully I won't snap the oak pegs holding the gates together....

My plan was to tongue and groove the centre planks and slot them in a groove, as it shrinks and dries is this okay?
Don't nail or glue them?

I worry slightly about the stress in the gate posts but there really big and heavy.. 200mm x 200mm x 3m long..
If I cast a great big concrete block .. 800 x 800 x 800 with the post in the centre I'm guessing it won't go anywhere.. but the gates are going to be really heavy...

Forces wise it would be ideal to link the two end posts together, with the final post bolted to the house. add a 45 degree post supporting the other end..
I'm just not convinced it's required.

 

[Inspector]

I'm not a gate builder but two things stand out to me.

If you make a groove for the boards to sit in there must be a way for the water to get out or it will rot. Better is to find away to make it without any grooves or pockets.

Similar to above is the post encased in concrete. The water runs down between the wood and concrete. You set it up to rot unless the post is placed on or in some gravel under the concrete to let the water drain out.

Pete

 

[Tris]

Personally I'd want more than 500mm in the ground. We usually have 750 to hang a 12ft farm gate from. Keep the hole as small as you can, it rocks less. If you can't get a longer post (3.6m would be good) then drive 5ft lengths of rebar or heavy angle iron into the base of the hole before concreting the post in. Ensure the concrete is trowelled off so it slopes away from the post, there's nothing that'll rot it quicker than water held around the base.

Is it possible to use wheels on the gates to take some of the load off the frame? A bit like Victorian cast iron gates used to have

 

[Yojevol]

I would investigate Gate Support Rollers:-
https://www.amazon.co.uk/Caster-Bra...hvtargid=pla-2347648811897&psc=1&gad_source=1

 

[Fitzroy]

As per inspector the groove will be a rot pocket, not immediately in oak but it will lessen the life span. Groove for the top of the boards and then just centre nail/fix each one to the bottom rail with expansion gaps around.

Never seen an FEA for a gate before! I'm not sure the boards would act in that way in an actual gate, being 'loose' in the rebates they could only take load if the frame dropped and trapped them top and bottom. I'd be tempted to take them out the design and rerun it, possibly adding their equivalent weight on the bottom rail.

Fitz

 

[BarbaraT]

I'm not a gate builder but two things stand out to me.

If you make a groove for the boards to sit in there must be a way for the water to get out or it will rot. Better is to find away to make it without any grooves or pockets.

Similar to above is the post encased in concrete. The water runs down between the wood and concrete. You set it up to rot unless the post is placed on or in some gravel under the concrete to let the water drain out.

The posts are easy enough, I've bought some post savers, the soil is quite sandy so drains well.

I could possibly run a thinner lower bar, but I don't love the idea of putting any force on nails.. Would look something like this.

The Advantage with the groove in the top and bottom is It's acting like a big wooden I beam

I might look at mounting them flush, Guessing you have them sat in a L shape section

This one looks like a bit of quadrant.. to seal the groove.

Without the central wood taking the load it starts to sag, and this is without any play in the joints, you then add your diagnals to stop it drooping.

being 'loose' in the rebates they could only take load if the frame dropped and trapped them top and bottom

I'm guessing this is exaclly what it will do.. As all the planks won't perfect some will take more load than others as the gate starts to sag.

We usually have 750 to hang a 12ft farm gate from. Keep the hole as small as you can, it rocks less. If you can't get a longer post (3.6m would be good) then drive 5ft lengths of rebar or heavy angle iron

There the biggest I could get hold of in width.They weigh 96kg each so there not light..

I'm happy to dig a hole 1.2m deep hole fill it with big bits of angle iron..(100mm from the surface) Cast the bottom half leaving a hole 500mm deep before dropping the post in between the steel angle irons and filling the top half in.

should give me a 3.7m pole with the bottom 0.7m made from concrete and steel..

I would investigate Gate Support Rollers:-

I don't think the ground is flat enough, It's also all been block paved with a slope on so I don't really want to touch it.

 

[Inspector]

You could use a pair of boards across the bottom on either side of the slats. Water drains and it you go a little nautical, copper nails and roves will hold it together, looking better than nails or bolts. They are a proven method of holding boats together so a gate should be fine.

Pete

 

[toolsntat]

Look at large heavy gauge box section or RSJ, both cladded in oak for the posts.
Both giving durability and strength.
Galvanising wouldn't go a miss.
Cheers, Andy

 

[spanner48]

First thoughts:

1: The gate leaf design itself is weak. The angled bracing against gravity is too shallow. Better would be the classic 'Curved Hanging Stile' design for each leaf:

Alternative would be to have curved slam stiles, and angled compression struts from the bottom of the hanging stile. Same difference.

2: 500mm ground depth is quite inadequate. Last time I installed a 3 metre gate, the manufacturers offered either 750mm, or a deeper, 1 metre underground, hanging post. I chose the 1 metre and haven't regretted it – looking at all the gates with hanging posts that have keeled over under gravity over time.

3: Rot in the centre panels: make the lower mortices for the panel strakes. Fill each one with rot-proofing [CCA Copper-Chrom-Arsenate is best, if you can get it]. Leave the bottom ends of the strakes in a bath of it at the same time. Wait for it to soak in. THEN drill an angled drainage hole from the outside into the bottom of each mortice.

4: Rot in the hanging posts: leave the below-ground portions dipped in rot-proofing for a couple of weeks before installing.

Or use galvanised RHS

 

[BarbaraT]

I already have the wood so the gate posts are going to have to be extened with concrete and steel
happy to go down a meter

This is very boring.. I'm not keeping in sheep, I also want to reduce the wind blowing down the drive.
I also can't cut curved timbers as I don't have a big band saw.. I cut My first ball with a router and it was painful enough.

The first design had a curved top, but i decided it was too hard to cut.

3: Rot in the centre panels: make the lower mortices for the panel strakes. Fill each one with rot-proofing [CCA Copper-Chrom-Arsenate is best, if you can get it]. Leave the bottom ends of the strakes in a bath of it at the same time. Wait for it to soak in. THEN drill an angled drainage hole from the outside into the bottom of each mortice

I watched a video on similar and the general consensus was that the rot proofing was a bit of a wate of time.


I'm hoping the post savers will reduce most of the rot in the uprights.

Happy to varnish it every couple of years.