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Home > Archive > Building and Construction > July 2006 > Re: Can you place anchors in a concrete slab at a later date?
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Re: Can you place anchors in a concrete slab at a later date?
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| Chris Lewis 2006-07-14, 1:25 pm |
| According to Keith Boeheim <kboheim@rochester.rr.com>:
> We are having a concrete driveway put in next week and we want to put up
> a 16x16 out building next year. I am having the pad for the building
> done at the same time as the driveway. For safety reasons I don't want
> the contractor putting in the threaded anchors for the walls during the
> pour. How can I install these anchors next year when we are ready to put
> up the building?
I can appreciate the concerns that you have about protruding bolts
being a hazard, but a properly concreted-in J bolt is so superior to
just about everything else, that for a 16x16 outbuilding I'd strongly
recommend installing them now anyway.
Put cinder blocks or flower pots (why not with flowers?! ;-) over/around
them or something like that to eliminate the safety/tripping hazard.
If you do choose to install later, research concrete anchoring
systems on the net, and follow the instructions of the one you
choose _to_the_letter_.
Remember, this isn't a lifting load (w.r.t. the big dig accident
a few days ago), so that's not going to happen. But strong
winds are perfectly capable of moving structures like this,
and just picking up lag screws and anchors out of a hardware
store bin _can_ be a mistake if you don't install them properly.
Apropos this, I just repaired a deck railing mounting support
that was less than 3 _months_ old, because the alleged
"professional handyman" who previously owned the house didn't know
that the lag screw is supposed to thread _into_ the anchor, not
just push the anchor farther back into the ridiculously
deep hole in the masonry.
Seriously.
The hole was so deep that the the lag screw pushed the anchor 4"
behind the face of the masonry and didn't engage the anchor _at all_.
He was expecting this nonsense to pass inspection.
Without washers under the lags.
Fixing the anchors involved pulling the lags out (they were loose.
Pulled straight out), fishing out the anchors with wire, threading the
anchors on just enough to bind in the hole, and then winching up the
lags.
Not to mention the 4' long cleated together 2x12 (! what was
he holding up? The Queen Mary?) deck support "beam" he was
supporting both ends on some pieces of rotting wood lying
horizontally on the dirt, when a perfectly adequate masonry
post was 6" away from one end, and butted up against masonry
on the other. So I did 2 2x6s supported on the post and
a 2x4 sleeve-anchored to the wall for the other end, and
inspection passed.
What an airhead.
We assume that he sold the house and left town because the
work he was being paid to do for others was so obviously
and completely half-assed.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.
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| El Barto 2006-07-14, 8:25 pm |
| clewis@nortelnetworks.com (Chris Lewis) wrote:
>Remember, this isn't a lifting load (w.r.t. the big dig accident
>a few days ago), so that's not going to happen. But strong
>winds are perfectly capable of moving structures like this,
>and just picking up lag screws and anchors out of a hardware
>store bin _can_ be a mistake if you don't install them properly.
Actually, it's the lifting forces imparted by high winds that the
anchors need to handle.
If the structure is tied together (e.g., with hurricane clips,) then
high winds going over the roof will create suction and uplift forces.
These must be withstood by the anchors, or the scructure will lift off
its foundations. (If the scructure isn't tied together, then the roof
will just fly off.)
The other thing that happens is that lateral wind forces on one side
of the scructure will tend to push that wall inward, rotating it
around the sill plate. This will create a lot of upward force on the
anchors, as the wall is essentially a large lever. This can be
mitigated somewhat by using sheathing (OSB, plywood, etc.) around the
outside of the structure, or at least at the corners, to counteract
the racking forces.
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| ameijers 2006-07-14, 8:25 pm |
|
"Chris Lewis" <clewis@nortelnetworks.com> wrote in message
news:12bfd4tabteqh2e@corp.supernews.com...
> According to Keith Boeheim <kboheim@rochester.rr.com>:
>
> I can appreciate the concerns that you have about protruding bolts
> being a hazard, but a properly concreted-in J bolt is so superior to
> just about everything else, that for a 16x16 outbuilding I'd strongly
> recommend installing them now anyway.
>
> Put cinder blocks or flower pots (why not with flowers?! ;-) over/around
> them or something like that to eliminate the safety/tripping hazard.
>
> If you do choose to install later, research concrete anchoring
> systems on the net, and follow the instructions of the one you
> choose _to_the_letter_.
>
Unless this shed OP is putting in next year is metal, he should lay up or
pour a proper foundation stub wall. Even a PT sill plate sitting at slab
level is asking for trouble. Yeah, an 8 or 12 inch wall sticking up for a
year is a PITA, but less hazardous than J bolts sticking up from a flat
slab.
aem sends....
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| Chris Lewis 2006-07-14, 8:25 pm |
| According to El Barto <hatespam@hatespam.com>:
> clewis@nortelnetworks.com (Chris Lewis) wrote:
[color=darkred]
> Actually, it's the lifting forces imparted by high winds that the
> anchors need to handle.
Sorry, should have been clearer. Yes, I've seen the calculations
showing many 100's of pounds of uplift per rafter under hurricane
situations with relatively "normal" size roofs. I meant that they're
not under continuous stress 24x7, holding up tons of concrete - where
the slightest imperfections in installation/bad concrete/vibration
_may_ work some anchors loose.
That said, I like the other idea, forming a 12" stub wall with
anchors (perhaps female thread slugs, not threaded rod) in _that_.
The OP would be far happier with the resulting structure.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.
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| Robert Gammon 2006-07-15, 9:25 am |
| El Barto wrote:
> clewis@nortelnetworks.com (Chris Lewis) wrote:
>
>
>
> Actually, it's the lifting forces imparted by high winds that the
> anchors need to handle.
>
> If the structure is tied together (e.g., with hurricane clips,) then
> high winds going over the roof will create suction and uplift forces.
> These must be withstood by the anchors, or the scructure will lift off
> its foundations. (If the scructure isn't tied together, then the roof
> will just fly off.)
>
> The other thing that happens is that lateral wind forces on one side
> of the scructure will tend to push that wall inward, rotating it
> around the sill plate. This will create a lot of upward force on the
> anchors, as the wall is essentially a large lever. This can be
> mitigated somewhat by using sheathing (OSB, plywood, etc.) around the
> outside of the structure, or at least at the corners, to counteract
> the racking forces.
>
I will note that Steel Frame houses use chemically anchored bolts to
attach the steel to the slab. These bolts are installed AFTER the slab
has cured. see www.tri-steel.com
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