Hi. I am having a set of metal driveway gates
delivered later today, two gates 3' high 4'
wide, not elaborate and not vastly heavy. Will
the existing wooden fence post put in about a
year ago be substantial enough to hold one of
the gates? It's 70mm x 75mm and held to the
ground by a Metapost bracket which is bolted to
the concrete drive using 4 bolts. The other
gate will be off the concrete area and probably
held by a similar post using a drive-in
Metapost. Wouls this be OK or do I need to
re-inforce the post in some way?
TIA for your advice.
I don't see how it will be possible for anyone to say without more
details - such as how thick the concrete is, the length of the bolts, etc.
The weight of the gate is important - but how it it (mis)used is a big
factor. People climibing on and over the gate can exert a huge force.
The gate manufacturer should have given details of the post requirements.
My suspicion is that neither post will be up to the job - especially the
drive-in one. A couple of kids swinging on a gate produces a great deal
The concrete is about 5" thick and the 4
"multimonti" bolts holding the Metapost are 10mm
X 70mm with a max loading of 2.8 Kn per bolt (?).
No kids to worry about and when the gates are
closed they will be padlocked. Due to the shape
of the ground where the two gates meet in the
closed position they will be virtually touching
the ground. The gates may have info with them
but they haven't arrived yet.
Thanks for the reply.
As far as the gate is concerned if an individual gate is heavier than 40kg,
it would be enough to snap the 2.8kN bolts. I wont go into the calcs, it's
simple enough but that's what I come up with using a factor of safety of 2.
HOWEVER. I think the bolts are more likely to let go of the concrete before
they actually snap, or possibly the metpost base may bend slightly..
As a Civil Engineer, (not chartered yet, must get around to it one day...) I
often quote the old addage, "If it looks wrong, it probably is wrong.
Whilst a fence will flex somewhat, and absorb windload, particularly gusts,
so reducing the load on the metpost foundation, if the gate flexes it is a
disaster as it won't close properly.
With gates you need good solid posts in good solid foundations, the thing
you should be worrying about is deflection of the post, not failure of the
post. By the time the post fixings fail, the deflection will have rendered
the gates inoperable.
I would suggest a minimum post size of 100mm square, but in reality, if they
were my gates I'd want 125mm square. In addition I'd want deeper founded
posts. The height of the actual fixing area of a metpost fixing is around
100-150mm yes? Thats simply not enough. You need to dig holes and put in
proper posts as stated above, I'd suggest a 600mm (2 foot) depth of post.
Failing this, if you cant dig, and you have to go with the metpost fittings,
you need a further support point near the top of the post. To demonstrate,
pick up a chair with one hand by holding only the botm of one
leg...hard/impossible isn't it?!? Now repeat the excercise but use your
previously free hand to hold the top of the same leg and lift, easy peasy
Whats either side of the post? If its brickwork/blockwork you could bore
through a post and bolt it to the wall at a higher level. If it's fence,
I'm sorry but you're stuffed!
Sorry if I'm telling you things you don't want to know. Feel free to email
me. I don't hide behind antispam email addresses, I just use a yahoo
account and clear it out occasionally.
I don't like the idea of a 4 inch post holding these gates, especially one
held in place by a Metapost. If you put your hand on the top of the post can
you move it - either by bending it or having it slop in the Metapost? If you
can then you need to do things differently. If you can't, then maybe it will
work, but some of this will depend on how well such a slim post puts up with
the constant one-way pull of the gate. When Metaposts are used for fencing,
the loading is intermittent, when the wind blows. Are the posts softwood, or
oak? I bet they are soft.
Thanks for the feedback, very informative. I do
see what you mean by the posts not being strong
enough for gates. Problem is we don't have
anywhere else to fix them. Could I reinforce
the posts with metal bars running the length of
them? The one that's in the metapost fixed to
the concrete is near the edge of the drive and I
could bolt a metal bar to the post and the
concrete. Where the other one has to go there
is possibly just enough room to dig a hole and
put the post into concrete directly.
How about a gate support castor to take the hinged weight of the gate. Save
the hassle and may cost less than reinforcing the posts.
I have no knowledge of the company in the link so it is not a
recommendation - just an example.
Shock horror! You mean 20,000 fence installers can be wrong?
(I'm fed up with digging rotten wood out of concrete, breaking the
concrete out, putting in a spur, then coach-screwing the original post
onto the spur - still, done most of them now!)
Yes, they are! But then most of these posts will have been put in by people
who are charging per hour and their customers would ahve a fit if they
charged for the time spent ramming the posts - as they should be done. So
they all get done incorrectly. The day of reckoning is yet to come. But you
and I who are not chrging for our time can do it properly.
There you go. My point exactly. In addition the posts that are set in
concrete tend to rot more quickly and, because there is no flexibility in
the concrete, break off at ground level more easily when the wind blows.
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