Does anyone know how much can generally be notched from the bottom
corner of a joist when it is sat in
a joist hanger, in order to adjust the height for variations in the
brick coursing ?
Joists are 225 x 75mm.
Simon.

K5 factor. Modify the calculated max shear stress by beam depth after
notching/beam depth.

On Mon, 17 Aug 2009 11:49:31 -0700 (PDT), a certain chimpanzee,
sm_jamieson randomly hit the keyboard and
produced:

Does anyone know how much can generally be notched from the bottom
corner of a joist when it is sat in
a joist hanger, in order to adjust the height for variations in the
brick coursing ?

Rafters can be birdsmouthed, and up to one third is a rule of thumb,
so I assume joists are the same. I know I've had floor joists & steel
beams which have been chamfered to ridiculously small depths and still
passed calculations. I'm no engineer, but AFAIK, longish lengths fail
in deflection or bending long before they would fail in shear.
--
Hugo Nebula
"If no-one on the internet wants a piece of this,
just how far from the pack have you strayed?"

Hugo Nebula wrote:
On Mon, 17 Aug 2009 11:49:31 -0700 (PDT), a certain chimpanzee,
sm_jamieson randomly hit the keyboard and
produced:

Does anyone know how much can generally be notched from the bottom
corner of a joist when it is sat in
a joist hanger, in order to adjust the height for variations in the
brick coursing ?

Rafters can be birdsmouthed, and up to one third is a rule of thumb,
so I assume joists are the same.

Don't assume. Rafters are largely in compression. Joists are pure
bending moment.

However having said that joist are way too STRONG in order to meet
deflection/loading targets.

So you can probably notch massively,.


I know I've had floor joists & steel
beams which have been chamfered to ridiculously small depths and still
passed calculations. I'm no engineer, but AFAIK, longish lengths fail
in deflection or bending long before they would fail in shear.

Yes.

On Mon, 17 Aug 2009 21:52:42 +0100, The Natural Philosopher wrote:

Hugo Nebula wrote:
On Mon, 17 Aug 2009 11:49:31 -0700 (PDT), a certain chimpanzee,
sm_jamieson randomly hit the keyboard and
produced:

Does anyone know how much can generally be notched from the bottom
corner of a joist when it is sat in
a joist hanger, in order to adjust the height for variations in the
brick coursing ?

Rafters can be birdsmouthed, and up to one third is a rule of thumb,
so I assume joists are the same.

Don't assume. Rafters are largely in compression. Joists are pure
bending moment.

Definitely worth checking. All the out-buildings around here (barn aside)
have the rafters cut to about half their depth where they meet the walls,
and it doesn't seem to cause any issues - but then maybe that's due to
the way they're anchored (and anything toward the outer edges beyond the
cut doesn't exactly have to support a lot). As you say, joists probably
have quite different loading characteristics, particularly at the ends.

However having said that joist are way too STRONG in order to meet
deflection/loading targets.

So you can probably notch massively

Probably, assuming they're not all like that. My gut feeling* - and
that's all it is - is that I wouldn't want to take more than about 20%
of the total height though, if I could help it. But then surely more than
that suggests a brick structure below which has some major issues of its
own? :-)

* I tend to massively over-engineer stuff - and if it's around long after
I'm gone, well that's generally no bad thing...

cheers

Jules

Jules wrote:
On Mon, 17 Aug 2009 21:52:42 +0100, The Natural Philosopher wrote:

Hugo Nebula wrote:
On Mon, 17 Aug 2009 11:49:31 -0700 (PDT), a certain chimpanzee,
sm_jamieson randomly hit the keyboard and
produced:

Does anyone know how much can generally be notched from the bottom
corner of a joist when it is sat in
a joist hanger, in order to adjust the height for variations in the
brick coursing ?
Rafters can be birdsmouthed, and up to one third is a rule of thumb,
so I assume joists are the same.
Don't assume. Rafters are largely in compression. Joists are pure
bending moment.

Definitely worth checking. All the out-buildings around here (barn aside)
have the rafters cut to about half their depth where they meet the walls,
and it doesn't seem to cause any issues - but then maybe that's due to
the way they're anchored (and anything toward the outer edges beyond the
cut doesn't exactly have to support a lot). As you say, joists probably
have quite different loading characteristics, particularly at the ends.

However having said that joist are way too STRONG in order to meet
deflection/loading targets.

So you can probably notch massively

Probably, assuming they're not all like that. My gut feeling* - and
that's all it is - is that I wouldn't want to take more than about 20%
of the total height though, if I could help it. But then surely more than
that suggests a brick structure below which has some major issues of its
own? :-)

* I tend to massively over-engineer stuff - and if it's around long after
I'm gone, well that's generally no bad thing...

cheers

Jules

Think Sydnney harbour bridge, upside down. That's the shape where there
stresses are on a joist. The ends are pretty irrelevant. Its not shear
that will get you: its actual wood splitting..

On 17 Aug, 22:38, Jules
wrote:
On Mon, 17 Aug 2009 21:52:42 +0100, The Natural Philosopher wrote:
Hugo Nebula wrote:
On Mon, 17 Aug 2009 11:49:31 -0700 (PDT), a certain chimpanzee,
sm_jamieson randomly hit the keyboard and
produced:

Does anyone know how much can generally be notched from the bottom
corner of a joist when it is sat in
a joist hanger, in order to adjust the height for variations in the
brick coursing ?

Rafters can be birdsmouthed, and up to one third is a rule of thumb,
so I assume joists are the same.

Don't assume. Rafters are largely in compression. Joists are pure
bending moment.

Definitely worth checking. All the out-buildings around here (barn aside)
have the rafters cut to about half their depth where they meet the walls,
and it doesn't seem to cause any issues - but then maybe that's due to
the way they're anchored (and anything toward the outer edges beyond the
cut doesn't exactly have to support a lot). As you say, joists probably
have quite different loading characteristics, particularly at the ends.

However having said that joist are way too STRONG in order to meet
deflection/loading targets.

So you can probably notch massively

Probably, assuming they're not all like that. My gut feeling* - and
that's all it is - is that I wouldn't want to take more than about 20%
of the total height though, if I could help it. But then surely more than
that suggests a brick structure below which has some major issues of its
own? :-)

* I tend to massively over-engineer stuff - and if it's around long after
I'm gone, well that's generally no bad thing...

cheers

Jules

I wouldn't need to notch anywhere near 20%, so no issues then.
Cheers,
Simon.

On 17 Aug, 19:49, sm_jamieson wrote:
Does anyone know how much can generally be notched from the bottom
corner of a joist when it is sat in
a joist hanger, in order to adjust the height for variations in the
brick coursing ?
Joists are 225 x 75mm.
Simon.

Simon
The rough rule of thumb is 1/8th the depth.
The joist is in tension at this point.
if you want to be purist drill a hole at the requisite point and cut
to the hole so as not to cause a stress point
That having been said I have seen plenty of joists cut deep and they
fail or not depending entirely on the span and load
Failure mode is splitting along the middle (near the neutral axis) by
the top of the cut
Chris

On 18 Aug, 08:41, "Why?" wrote:
On 17 Aug, 19:49, sm_jamieson wrote:

Does anyone know how much can generally be notched from the bottom
corner of a joist when it is sat in
a joist hanger, in order to adjust the height for variations in the
brick coursing ?
Joists are 225 x 75mm.
Simon.

Simon
The rough rule of thumb is 1/8th the depth.
The joist is in tension at this point.
if you want to be purist drill a hole at the requisite point and cut
to the hole so as not to cause a stress point
That having been said I have seen plenty of joists cut deep and they
fail or not depending entirely on the span and load
Failure mode is splitting along the middle (near the neutral axis) by
the top of the cut
Chris

OK thanks, I'll drill a hole for the "corner" of the notch. I only
need to
notch a small amount.
Simon.

"The Natural Philosopher" wrote in message
...


Don't assume. Rafters are largely in compression.

If rafters are in compression what keeps the walls from spreading out?

"dennis@home" wrote in message
...


"The Natural Philosopher" wrote in message
...


Don't assume. Rafters are largely in compression.

If rafters are in compression what keeps the walls from spreading out?

Usually the ceiling joists to which the rafters are fixed or collar ties.
Except for an old barn I have responsibility for, where there are no ceiling
joists and the collar ties are not substantial enough. The walls are
spreading out.


--
Bob Mannix
(anti-spam is as easy as 1-2-3 - not)

On Aug 18, 1:34*pm, "dennis@home"
wrote:
"The Natural Philosopher" wrote in ...

Don't assume. Rafters are largely in compression.

If rafters are in compression what keeps the walls from spreading out?

Mostly it's down to the fact that the walls are thick enough and heavy
enough that the thrust line doesn't go outside the walls. The tension
in the joists can help, or you can add flying buttresses, or the walls
can fall over after a while.

.... but rafters /are/ in compression.

dennis@home wrote:


"The Natural Philosopher" wrote in message
...


Don't assume. Rafters are largely in compression.

If rafters are in compression what keeps the walls from spreading out?




Joists?

Perhpas one of us is using the wrong term..the joists are horiozontal
tension members and the rafters are the slopey bits?

"Bob Mannix" wrote in message
...

"dennis@home" wrote in message
...


"The Natural Philosopher" wrote in message
...


Don't assume. Rafters are largely in compression.

If rafters are in compression what keeps the walls from spreading out?

Usually the ceiling joists to which the rafters are fixed or collar ties.
Except for an old barn I have responsibility for, where there are no
ceiling joists and the collar ties are not substantial enough. The walls
are spreading out.

6 mm stainless wire stretched across is incredibly strong.

"The Natural Philosopher" wrote in message
...
dennis@home wrote:


"The Natural Philosopher" wrote in message
...


Don't assume. Rafters are largely in compression.

If rafters are in compression what keeps the walls from spreading out?




Joists?

Perhpas one of us is using the wrong term..the joists are horiozontal
tension members and the rafters are the slopey bits?

Probably.
I have only had dealings with trussed rafters..
In those all the peripheral members are in tension on one side and
compression on the other.
The inside bits tend to be in compression AIUI.

On 18 Aug, 14:05, The Natural Philosopher
wrote:
dennis@home wrote:

"The Natural Philosopher" wrote in message
...

Don't assume. Rafters are largely in compression.

If rafters are in compression what keeps the walls from spreading out?

Joists?

Perhpas one of us is using the wrong term..the joists are horiozontal
tension members and the rafters are the slopey bits?



Tie beams! (aka ceiling joists often - which is why if there is a
joint in the middle over a partition it needs nailing or strapping and
why it is important to tie into the wall plate_
chris

dennis@home wrote:


"The Natural Philosopher" wrote in message
...
dennis@home wrote:


"The Natural Philosopher" wrote in message
...


Don't assume. Rafters are largely in compression.

If rafters are in compression what keeps the walls from spreading out?




Joists?

Perhpas one of us is using the wrong term..the joists are horiozontal
tension members and the rafters are the slopey bits?

Probably.
I have only had dealings with trussed rafters..
In those all the peripheral members are in tension on one side and
compression on the other.
The inside bits tend to be in compression AIUI.

Yup. Thats why a truss is a truss. No (few, low) bending stresses anywhere.

Why? wrote:
On 18 Aug, 14:05, The Natural Philosopher
wrote:
dennis@home wrote:

"The Natural Philosopher" wrote in message
...
Don't assume. Rafters are largely in compression.
If rafters are in compression what keeps the walls from spreading out?
Joists?

Perhpas one of us is using the wrong term..the joists are horiozontal
tension members and the rafters are the slopey bits?



Tie beams! (aka ceiling joists often - which is why if there is a
joint in the middle over a partition it needs nailing or strapping and
why it is important to tie into the wall plate_
chris
Ok. ill settle for tie beams!

On Tue, 18 Aug 2009 14:29:21 +0100, dennis@home wrote:
If rafters are in compression what keeps the walls from spreading out?

Usually the ceiling joists to which the rafters are fixed or collar ties.
Except for an old barn I have responsibility for, where there are no
ceiling joists and the collar ties are not substantial enough. The walls
are spreading out.

6 mm stainless wire stretched across is incredibly strong.

That's been done to our garage... badly :-)

Evidently the walls started spreading at some point, so they just punched
holes in either side wall at the top halfway down the length, and ran 3/8"
cable across.

It's a really sloppy job, but the cable must be under a hell of a lot of
tension (and I don't know how weak the walls would be without it) - so I'm
not inclined to try and tidy it up. I just put "rebuild garage" on the
to-do list instead as that's a much more interesting DIY project

cheers

Jules