Advice wanted regarding footings for heavy iron swing gates .

[Dutchclogger]

A local charity has asked my advice about new footings for a heavy iron swing gate on their depot that needs repaired.
Due to a very sandy terrain (no rock or clay bed in the Netherlands) I am undecided whether a spread footing (reinforced slab and small upstand ) or two reinforced footing's joined together with a Grade Beam would be best .
If a go for the Grade beam can I place it on top of the existing piles by building a new pile cap and would this transfer the forces into the pile.
Would a 1m x 1m x 400mm Spread footing do the same job or would this sink in to the sandy ground in a few years ?
Its a simple enough little re bar and concrete job but want thoughts on which method would be the best.

 

[John D v2.0]

I like the beam idea, also if the gates are tending to lean together another option is a strut at the top oi you don't need the clearance for tall vehicles

 

[^woody^]

There is nothing wrong with sandy ground unless the sand gets washed away. So a 1m pad foundation may well be OK, but its hard to tell from 400 miles away.

If there is a nearby pile which can be used at reasonable cost, then that would be the best - but it would seem to require a certain amount of engineering.

 

[bernardgreen]

The weight of the gate creates two horizontal forces on the post. Towards the post at the bottom hinge and away from the post at the top hinge. These two forces create a moment of rotation on the post that tries to topple the post.

An equal and opposing moment of rotation must be created by the ground acting against the post under ground otherwise the post will topple over.

Gate posts in sandy soil need to be deep enough to reach a point where the sand can oppose the rotation with only a small horizontal force. Vibration from the gate opening and closing will "soften" the sand in contact with the post.

 

[Dutchclogger]

Piles are used everywhere in the Netherlands due to the sand the country is built on.
I am hoping when we dig down (easy digging in sand ) we will find some piles that are at a suitable distance apart and alignment for the pads to sit on.
We work with pile caps all the time,its just a matter of cutting the concrete away to the required depth and fixing the rebar pad over the pile with the piles rebar extending into the pad to form a bind by some bob bars.
The charity seem to think a Grade Beam would be the better choice ,myself I think it is extra work and cost and the advice here seems to back this up.
John D its a entrance for a truck so a strut is not suitable.
Couple of rough sketches showing the "first plan" ...
I think this is more than enough but even though I have 40 years in the game advice is still appriciated guys.

 

[Dutchclogger]

The weight of the gate creates two horizontal forces on the post. Towards the post at the bottom hinge and away from the post at the top hinge. These two forces create a moment of rotation on the post that tries to topple the post.

An equal and opposing moment of rotation must be created by the ground acting against the post under ground otherwise the post will topple over.

Gate posts in sandy soil need to be deep enough to reach a point where the sand can oppose the rotation with only a small horizontal force. Vibration from the gate opening and closing will "soften" the sand in contact with the post.

Hmm bernardgreen....now you have me wondering if the pad and beam construction is sufficient, even though I have looked online and checked this with some gate constructions.The example below is a reinforce pillar going into the footings but these gate post's I have been asked to loom at are bolted onto the pads. Thoughts on the sketches would be much appriciated.The thing is its not a money job but a favour to some mates so I need to get it right or I wont get no beer #

 

[bernardgreen]

Remember there are two directions of topple, one when the gates are closed and the other at 90 degrees when the gates are open.

The beam across the driveway will oppose the toppling forces created when the gates are closed but may just roll when the gates are open. Extensions to prevent roll may be necessary

 

[Dutchclogger]

ok in the direction of the gate opening....that sounds logical.