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.

 

[HOJ]

I look at things from a simplistic perspective, an 8m gate opening is huge, would it be an option to reduce the width of the main gates and add infills/pedestrian gates to the either side, in the same design to balance the look.

Out of curiosity, in your evaluation software does it work out the strength in the type of joints employed in the construction.

I wouldn't be taking a lot of notice of a video using carp softwood jammed in the ground, why would you even think to use it directly buried in the ground my Oak gate posts has been in the ground since 1989 with a 4m 5 bar gate swinging off one and a 1m one on the other.

 

[davethebb]

BarbarT, The stresses the FEA calculates are low for wood. However, for the joints (pegged tenons), you are likely to have issues later in life where the joint is in tension. The lower diagonal would be better if it went down to the lower hinge. This way, this is in compression and is taking most of the load in compression, and thus, you remove a lot of the issues of the high loads on the pegged joint.

The second thing to consider is the section of the gate post. This will be subject to a bending force, and over time, any wood will slowly bend (I have used 200 mm oak with a std. 3mt gate, and this has distorted slightly over 10 years). Multiple hinges will help. For stability, you should consider a metal box or an I-beam section clad in wood. This will withstand the opening and closing forces better. Remember, most of the time, the end of the gate is supported when closed but unsupported when open.

If you go with wooden oak posts, soak them in creosote (original if you can get it - normally from farm suppliers) for a minimum of a week. Let them dry and then use "post saver" or Blackjack tape, but ensure all the posts in the ground are covered; otherwise, they will rot from below.

 

[Amplidyne]

Three definites for me. Posts to go in as deep as possible. Diagonals to go to lower hinge. Boards not to sit in any sort of groove no matter how treated. I've used a single board across with lighter gates with the boards nailed on with non rusting nails. As inspector suggests, a pair of boards in this case perhaps.

 

[BarbaraT]

Sorry Amplidyne but what a load of Rubbish..

Posts to go in as deep as possible.

Should I hire a boring machine then and go down 100m, Anything deeper than 1.5m is a complete waste of time and effort.

Diagonals to go to lower hinge.

Diagonals to go to lower hinge. - If you want to make a gate as cheap and as light as possible then yes. Is this gate the designed to be cheap.. No
Are there 100's of other ways to do this.. yes

I've used a single board across with lighter gates with the boards nailed on with non rusting nails.

Your gate wasn't made from 124kg of oak that's going to shrink and move.. If you made if from balsa you could proabaly glue it together with PVA.
I fully agree that a conventional gate like this is going to be lighter

Boards not to sit in any sort of groove no matter how treated.

Should glass also not sit in grooves, how about the gate or fence below.. Its not ideal, but far from a rule

Stress wise the forces are very low, with 2000kg hanging off the end of the gate I only saw 4mpa, failure is at 5.5Mpa
Total weight of the large gates is 124kg each..


What about cutting a tenon on the length of the boards, and adding a chamfer to the top of the beam along the bottom. I also wondered about gluing it with gorilla glue, that will foam up and fill any gaps.

Add a thick layer of varnish every couple of years, I'm undecided about vent holes in the bottom..

BarbarT, The stresses the FEA calculates are low for wood. However, for the joints (pegged tenons), you are likely to have issues later in life where the joint is in tension. The lower diagonal would be better if it went down to the lower hinge. This way, this is in compression and is taking most of the load in compression, and thus, you remove a lot of the issues of the high loads on the pegged joint.

The second thing to consider is the section of the gate post. This will be subject to a bending force, and over time, any wood will slowly bend (I have used 200 mm oak with a std. 3mt gate, and this has distorted slightly over 10 years). Multiple hinges will help. For stability, you should consider a metal box or an I-beam section clad in wood. This will withstand the opening and closing forces better. Remember, most of the time, the end of the gate is supported when closed but unsupported when open.

If you go with wooden oak posts, soak them in creosote (original if you can get it - normally from farm suppliers) for a minimum of a week. Let them dry and then use "post saver" or Blackjack tape, but ensure all the posts in the ground are covered; otherwise, they will rot from below.

I could brace the back of the gate like below...

I like the idea of having a stainless steel skid plate, possibly in the open and closed postion..

Ideally I wanted stone posts till i got a price.. I've also already got the oak posts. I thought about wood cladding, but it doesn't seem to age well. I'm not convinced all my corner joints wouldn't open up.

I've bought a 5m roll of the postsave stuff and have some of the good old stinky creosote..

3 big gate hinges should also help, especially if the hinges are as long as the ones below.

I look at things from a simplistic perspective, an 8m gate opening is huge, would it be an option to reduce the width of the main gates and add infills/pedestrian gates to the either side, in the same design to balance the look.

Out of curiosity, in your evaluation software does it work out the strength in the type of joints employed in the construction.

I wouldn't be taking a lot of notice of a video using carp softwood jammed in the ground, why would you even think to use it directly buried in the ground my Oak gate posts has been in the ground since 1989 with a 4m 5 bar gate swinging off one and a 1m one on the other.

There is a narrow lane your pulling off so your turning 90 degrees as well as pulling in. I've also added a pedestrian gate one side.
It could be made less, but it's surprising how often I want to reverse a luton van in or have hired a skip.

The software is solidworks premium, It's just modelled as one big lump. I could set the model up with all the joints, pins, friction, add the oak properties so it takes into account grain direction..etc etc etc
Then I could model the airflow over the gate.. work out when it will resonate.. I could be optomising it for the next 3 months, maybe shave 40kg off the weight...

But I would rather be in the workshop making the gate....

If my oak gate lasts 36 years I will be amazed, I'll be happy with 10

 

[Inspector]

An alternative for the bottom board and vertical boards. If the verticals are thick enough, say 1 1/4", you could groove the bottoms of each of them. The bottom board would have a raised centre that the verticals sit on. That would let them all drain without entrapping anything. Wouldn't add much if any strength. I still feel the best and strongest approach is the two bottom boards on either side of the verticals that I mentioned in post #7. You'll figure out something that satisfies your needs. Best of luck.

Pete

 

[toolsntat]

Have you decided on what electronic opener/closer system you are using at this stage and allowed for that in you're design ?
Cheers, Andy