sistering joists

[Steve Barker]

some time ago i inquired about fastening some steel plate to the sides
of some 100+ year old, full dimension, rough cut oak floor joists to
stiffen them up. I've decided to sister them with like sized (2x8) wood
instead. These are the second story floor joists and they are 2x8 and
span 15.5 feet. I've got the ceiling out on the lower level and want to
stiffen them up before i go back with new ceiling. My question is, what
is the best way (and frequency) to attach them? Screws, nut and bolt,
nail, glue, etc?? It's a balloon style house and i'll be able to set
the new sisters up on the ledger board like the originals. My main
concern is pulling them together in such a fashion as to best create a
"oneness" .

thanks!

--
Steve Barker
remove the "not" from my address to email

[Ed Pawlowski]

If possible to have enough open time, I'd use some adhesive too. A
bead of construction adhesive along the length, then nail in place.
Give the wood is rough cut and old, adhesive may not do all that well
though.

I've seen a few methods. Driving a pair of 16d nails every 12",
alternatively, a pair of screws about the same distance, and bolts
through. Good reason to buy a nail gun that will fit in the space
between joists.

I'd take a look here too
http://www.finehomebuilding.com/PDF/Free/021184090.pdf

[Sonny]

I would think the joists are 2' apart. I suppose you know to put the
crown, of the sisters, up. Lift the old joists, a bit, by jacking,
before attaching the sisters, if the lifting doesn't interfer with
anything. X bracing between the joists would hurt, either, if
convenient.

In order of my preference, with construction adhesive: 1) nut and
bolt, 2) lag bolts, 3) nails... staggered top and bottom every
12"-16".

Sonny

[Steve Barker]

Thanks Ed, for the reply and the link. Open time won't be a problem.
It's been open for 6 years now. another few days or weeks won't make a
difference.

[Steve Barker]

Thanks for the reply. they are somewheres in the 16" range oddly
enough. (my wall studs range from 12" to 20". LOL! ) Working with this
old house (1871) has certainly been enlightening.....

I was wondering about the nut and bolt thing. If drilling all those
holes would weaken more than helping. I do have a right angle drill and
can do that.

[DD_BobK]

A couple comments & questions......

What are the actual dimensions of the original oak joists?

If they are 1-7/8 x 7-7/8 (or are they larger?) and the dimensions of
the sistering joists are 1.5" x 7.25",
the sistering process will only add 62% to the floor stiffness.

The old oak will probably not be very accepting of nails. :(
This is unfortunate since nailing is a great way to a create a "no
slip" connection.

Bolts are a less than optimum way to sister joists....too much slop in
the holes.

To get the sister joists to accept some of the dead load & to preload
load them,
I would suggest jacking up each old joist slightly and holding that
position while attaching the sisters.

My preferred method of sistering the joists is to use Simpson 1/4" x
3" SDS Drive Screws
http://www.strongtie.com/products/connectors/SDS.asp
A single row of screws at 12" o/c should be adequate since each screw
is good for ~200lbs+.
Double rows staggered at 12" o/c would be great but over kill.

I suggest match drilling both joists at 3/16", see how that works for
oak joists to avoid splitting.
These screws should pull the joists together nicely.

cheers
Bob

[Steve Barker]

On 1/23/2012 12:15 AM, DD_BobK wrote:
>
> A couple comments& questions......

>
> What are the actual dimensions of the original oak joists?
>
> If they are 1-7/8 x 7-7/8 (or are they larger?) and the dimensions of
> the sistering joists are 1.5" x 7.25",
> the sistering process will only add 62% to the floor stiffness.

They are about 1 3/4 x 7 5/8 i'm a thinking. (i'm not where they are
right now.

>
> The old oak will probably not be very accepting of nails. :(
> This is unfortunate since nailing is a great way to a create a "no
> slip" connection.
>
> Bolts are a less than optimum way to sister joists....too much slop in
> the holes.
>

> To get the sister joists to accept some of the dead load& to preload

> load them,
> I would suggest jacking up each old joist slightly and holding that
> position while attaching the sisters.

I had already planned to do this. I think they will jack up a half inch
or better without too much effort.

>
> My preferred method of sistering the joists is to use Simpson 1/4" x
> 3" SDS Drive Screws
> http://www.strongtie.com/products/connectors/SDS.asp

I think this is the product that was suggested when i was contemplating
putting on steel plate.

> A single row of screws at 12" o/c should be adequate since each screw
> is good for ~200lbs+.
> Double rows staggered at 12" o/c would be great but over kill.
>
> I suggest match drilling both joists at 3/16", see how that works for
> oak joists to avoid splitting.
> These screws should pull the joists together nicely.

Do they need washers, and

Would you still apply construction adhesive with this fastener program?


>
> cheers
> Bob

Thanks for the help, Bob. I think the fastener idea is great and will
plan to use them.

[DD_BobK]

As long as you keep the bolts in the middle third of the joist depth,
the holes won't matter.
If you decide to use double rows of the SDS 1/4" screws keep them at
least 2" from the top & bottom of the joist.

cheers
Bob

[Steve Barker]

> least 2" from the top& bottom of the joist.
>
> cheers
> Bob

:)

[HeyBub]

Steve Barker wrote:
>
> Would you still apply construction adhesive with this fastener
> program?
>

Yes. As much adhesive as you can possibly apply.
a) Adhesive and its application is cheap,
b) It can't hurt, and
c) A massive layer of adhesive can spread the shear force over a huge
area.

[DanG]

Steve, Simpson has a line of screws meant for what you are doing. If
those joists are as old as you say, they may be too hard for this and
might require predrilling. I would use at least a 400 grade
construction adhesive. You will need a system of strings or laser(s) to
monitor what is going on. I would think you want to get to "in plane"
and then actually crown each joist a like amount, perhaps 3/4 to 1".

http://www.strongtie.com/products/connectors/SDS.asp


___________________________________

Keep the whole world singing . . .
Dan G
remove the seven

[tra...@optonline.net]

Construction adhesive and nails work for me,
as long as the joists are straight and come together.
Simple and I'd say about as effective as anything
else for the application. The point to joining them
together is to prevent them from bowing laterally
and you don't have major force in that direction.

[Steve Barker]

thanks Dan!

[Steve Barker]

thanks!

[Steve Barker]

Thanks for the reply!

[bob haller]

when this old house sisters beams they always use a single bead in a
continious lazy S fashion.

using a massive amount of adhesive may not help.

they showed a previosly sistered beam that someone used circle
adhesive.

it didnt adhere, the circles trapped air and prevented adhesion.

in any case use carriage bolts to hold it alltogether..... if its a
bad issue add a steel plate between the sisters for extra stability

[EXT]

"DD_BobK" <rkaz...@gmail.com> wrote in message
news:01cfa853-1f6b-404c...@f1g2000yqi.googlegroups.com...

> On Jan 22, 8:02 pm, Steve Barker <ichasetra...@notgmail.com> wrote:
>> some time ago i inquired about fastening some steel plate to the sides
>> of some 100+ year old, full dimension, rough cut oak floor joists to
>> stiffen them up. I've decided to sister them with like sized (2x8) wood
>> instead. These are the second story floor joists and they are 2x8 and
>> span 15.5 feet. I've got the ceiling out on the lower level and want to
>> stiffen them up before i go back with new ceiling. My question is, what
>> is the best way (and frequency) to attach them? Screws, nut and bolt,
>> nail, glue, etc?? It's a balloon style house and i'll be able to set
>> the new sisters up on the ledger board like the originals. My main
>> concern is pulling them together in such a fashion as to best create a
>> "oneness" .
>>
>> thanks!
>>
>> --
>> Steve Barker
>> remove the "not" from my address to email
>
> A couple comments & questions......
>
> What are the actual dimensions of the original oak joists?
>
> If they are 1-7/8 x 7-7/8 (or are they larger?) and the dimensions of
> the sistering joists are 1.5" x 7.25",
> the sistering process will only add 62% to the floor stiffness.
>
> The old oak will probably not be very accepting of nails. :(
> This is unfortunate since nailing is a great way to a create a "no
> slip" connection.

A good nail gun should be able to handle it, but it would need to be tested.
I have seen shipping pallets made of some incredibly hard lumber and nailed
together. The nails will break rather than pull out.

[harry]

If you decide to use nuts and bolts, you can put timber connectors
btween the old and new wood. (big spikey washers).
You might need g-clamps the press the timbers together and large
heavy duty washers on the bolts. Depends how hard the timber is.

Timber connectors treble or quadruple the strength of the job without
them.

http://shop1.actinicexpress.co.uk/shops/Jandsfasteners/index.php?cat=Timber_Conectors

[Joe]

>snip<

Working on a similar situation I used 3/4" plywood 8" nominal width
and sistered both sides of the old joists. Opted for a slow cure epoxy
for the adhesive, as only a few of the joists suffered from old
plumbing cut outs. The cut outs were filled with new wood as needed
and the whole clamped until final cure, no other fasteners used as
they would only be for show.
Since you are dealing with old oak, this might be your best option.
Also, rough cut lumber is best secured with epoxies for maximum
adhesion as the resin tolerates considerable unevenness with no loss
of adhesion.

Joe

[Sonny]

>  X bracing between the joists would hurt, either, if
> convenient.
>

That was supposed to be ... wouldn't hurt, ....

Sonny

[HeyBub]

EXT wrote:
>
> A good nail gun should be able to handle it, but it would need to be
> tested. I have seen shipping pallets made of some incredibly hard
> lumber and nailed together. The nails will break rather than pull out.

Given your average sweet-gum tree, about all you CAN make of it are pallets
and shoring material for deep trenches.

[JIMMIE]

If you have oak up there I would be thinking about a way to display it
and not put up a ceiling . I cant imagine the oak beams you described
not being strong enough for the job. They have worked for 100 years
they will be doing the job in 100 more. Don't even think about nails.

Jimmie

[Steve Barker]

lol. oh they do the job, they're just bouncy. too much span for 7-1/2"
of wood. And after 6 years, we're tired of looking at them.

thanks for the reply.

[cl...@snyder.on.ca]

I built my shed using mixed hardwood 2X4 rough lumber from
sheet-metal skids - and I had to drill for virtually EVERY SPIKE.

[gregz]

15.5 feet. That's crazy.

I did some beefing up. I first jack each joist, then add stiffening. I hand
nailed, and bolted, and screwed. Did not PL Premium. Good thing to do. My
first floor joists are 2x10 12 foot long. I found stiffening works with
only a 5/8 inch sheathing cut from 4x8 sheet. I was not really worried
about stiffening, mostly trying to get rid of the sag. Best done over a
long time period with the jacks. I didn't need to go from end to end on the
joists, just middle.

When I hand nailed, I first drilled holes. Also with bolts. I had to try
and pull together warped boards. Nailing is otherwise sufficient, but add
glue. Check above joists. You may need some shims.

Greg

[Oren]

On Mon, 23 Jan 2012 05:44:35 -0800 (PST), "tra...@optonline.net"
<tra...@optonline.net> wrote:

>Construction adhesive

I would use urethane caulk adhesive. They build cars, buses and trains
with the stuff. It "will stick to a ball of lard!"

Get some on your fingers or on your clothes -- chew is off with your
teeth and throw the clothes in the trash.

[Red Green]

DD_BobK <rkaz...@gmail.com> wrote in
news:01cfa853-1f6b-404c...@f1g2000yqi.googlegroups.com:

SPF lumber? SYP and surely LVL would bump that up.

[Colbyt]

"Steve Barker" <ichase...@notgmail.com> wrote in message
news:vImdnQIgWt9oRoHS...@giganews.com...

> some time ago i inquired about fastening some steel plate to the sides of
> some 100+ year old, full dimension, rough cut oak floor joists to stiffen
> them up. I've decided to sister them with like sized (2x8) wood instead.
> These are the second story floor joists and they are 2x8 and span 15.5

> feet. I've got the ceiling out on the lower level and want to stiffen

> them up before i go back with new ceiling. My question is, what is the
> best way (and frequency) to attach them? Screws, nut and bolt, nail,

> glue, etc?? It's a balloon style house and i'll be able to set the new

> sisters up on the ledger board like the originals. My main concern is
> pulling them together in such a fashion as to best create a "oneness" .
>
> thanks!
>
> --
> Steve Barker

When I paid a structural engineer to confirm what I already suspected was
true, he advised, 16D CC nails 16" OC, 3 in a vertical row and 2 in the
middle of the OC repeated on the other side in an alternating pattern. This
was BNG (before nail guns) and I drove every one of those suckers by hand.
In oak I would pre-drill with a 1/8" bit because of splitting hazard.



--
Colbyt
Please come visit http://www.househomerepair.com

[DD_BobK]

Adhesive is great, lots of contact area to spread the load.
But adhesive can be really messy and two rows of SDS screws is plenty
of shear transfer.

[DD_BobK]

On Jan 23, 5:44 am, "trad...@optonline.net" <trad...@optonline.net>
wrote:

t4-

Nails are very good for shear transfer (no slop in holes like bolts)
but that 100 year old oak may not accept them readily.

Depending on the sister joist geometry, the SDS screws may or may not
need to take much shear load.
It all depends on the load path. If the sister joists bear up against
the floor sheathing and the sister joists bear against the ledger
(with or without blocks), then the screws will carry very little
shear.

If the sister joists only bear on the ledger & not against the floor
sheathing, the SDS screws will wind up taking load out of the original
joist and into the sister joist.

Getting the sister joist to bear cleanly & continuously against the
floor sheathing will be difficult.
The SDS screws (or adhesive) will do the important job of getting the
old & new joist to work as two springs in parallel.

Lateral support of the new joist is a secondary task for the screws,
composite action is the primary.

cheers
Bob

cheers
Bob

[DD_BobK]

Bolts require a hole tat least as large as the bolt shank, this makes
a sloppy fit.
Lags (SDS) screws need a pilot hole (screw root diameter or smaller),
makes for excellent shear transfer..... no slop.

cheers
Bob

[DD_BobK]

Joe's suggested fix is a very good one.

I "top" sistered my living room ceiling / attic floor joists,
orignally full sized 2x4's that I "glued into" 2x8's using a slow cure
epoxy paste (Sikadur 35?).
I just mushed them together and let them cure, no clamping. I tested
a trial sample and the "glued up" 2x8 failed at a bottom chord knot
before the glue budged.

The Sikadur 35 is a heavy paste that allows a bond line as thick as
1/8".

cheers
Bob

[DD_BobK]

On Jan 23, 9:25 am, "EXT" <noem...@reply.in.this.group> wrote:
> "DD_BobK" <rkaza...@gmail.com> wrote in message

I doubt even a "good" nail gun (NR83) will do the job but a palm
nailer will.

[DD_BobK]

Steve's situation is an issue of stiffness not strength.
Too much bounce means he needs to add stiffness and that relates
mostly to joist depth.

Per the joist calculator mentioned recently in another thread, a 15'
span needs a 2x10 of decent timber or a 2x12 of lesser material.

If my calcs are correct, Steve's original joists sistered with new
2x8's will be stiffer than a 2x10 by 13% but t only be 55% as stiff as
a 2x12.

cheers
Bob

[DD_BobK]

On Jan 23, 5:21 pm, Red Green <postmas...@127.0.0.1> wrote:

Engineered timber is a possibility depending on what Steve wants to
do.

The bottom line is, 2x8's are not deep enough...... 2x10's would be
better.

cheers
Bob

[DD_BobK]

Steve-

"too much span for 7-1/2" of wood"

totally true.......

Depending on how much bounce you want to remove, you might consider
using an engineered wood product.

http://woodbywy.com/literature/LB-4010.pdf

[Vic Smith]

On Mon, 23 Jan 2012 21:22:36 -0800 (PST), DD_BobK <rkaz...@gmail.com>
wrote:

>
>If my calcs are correct, Steve's original joists sistered with new
>2x8's will be stiffer than a 2x10 by 13% but t only be 55% as stiff as
>a 2x12.
>

How can you measure stiffness without testing the plank?
Do you use an accepted norm?
This stuff is beyond me, except I can see how glue would work well
with sisters.
I always clamp glue, but never used epoxy.

I use a lot of drywall screws and lag bolts to slap stuff together.
My brother was a general and I listen to him for some things.
He told me once that 2 nails can be better than 6 screws for resisting
shear in some circumstances.
Don't remember what we were talking about, maybe roof hurricane
tie-downs.

--Vic

[DD_BobK]

On Jan 23, 10:03 pm, Vic Smith <thismailautodele...@comcast.net>
wrote:
> On Mon, 23 Jan 2012 21:22:36 -0800 (PST), DD_BobK <rkaza...@gmail.com>

Of course stiffness can be determined by testing but stiffness can
also be calc's based on the joist geometry & material.
Especially in Steve's situation where he's interested in boosting
stiffness.

An idea of the existing stiffness can be calc'd as well as for the
proposed sister. Added 50% might help, adding 100% or more would be
better.
WIthout an idea of where his floor is compared to "idea" he might be
over killing or way under shooting.

Take a look at this joist calculator. You can "play" with the joist
size, timber species & timber grade and see how the allowable span
changes.

http://www.awc.org/calculators/span/calc/timbercalcstyle.asp?species=Eastern+Hemlock-Balsam+Fir&size=2x6&grade=No.+2&member=Ceiling+Joists&deflectionlimit=L%2F240&spacing=12&wet=No&incised=No&liveload=20&snowload=-1&deadload=10&submit=Calculate+Maximum+Horizontal+Span#answer

Drywall screws should only be used for drywall and temporary, rather
than permanent loads.

" He told me once that 2 nails can be better than 6 screws for
resisting shear in some circumstances."

that's a pretty general statement, I know for a fact that a single
1/4" SDS will take the place of a handful of nails.
His statement tends to be more correct for small screws but IMO screws
(SS) are better in a lot of locations (exterior exposure & esp open
patio covers) since over time they will not rust and encourage rot or
lose strength. Galvanized timber connector nails will last a long
time, SS ones even longer but #10 SS screws in the same application
will last a long time plus provide better withdrawl resistance.

I know nails are shear fasteners and better than screws in shear but
over the years I've seen those shorty connector nails rust out / rot
out in patio covers to the point that I changed my tune.....

what good is a screw that's rust away & help rot out the wood?
IMO better to drill out the hanger nail hole and use a larger dia SS
screw (larger root diameter) than stick with nails that I know will
cause the failure of the entire system.


I always clamp (or screw) when using traditional glues.
When I top sistered my ceiling joists there was no easy way to clamp
so I used epoxy paste that was forgiving of joint gaps.
I pretested a sample made with rough timber, dirty just brushed off.
The sample failed at 175 psi shear when a knot in the bottom member
failed.

Based on my crappy sample, I knew that my sistered joists would
perform better since I wire brushed both faces of the glue joint and
none of the bottom chord members had large flaws. Plus, based on my
calcs, my shear demand was WAY lower than 175 psi more like less than
50 psi

cheers
Bob

[Vic Smith]

On Tue, 24 Jan 2012 09:48:00 -0800 (PST), DD_BobK <rkaz...@gmail.com>
wrote:


>

>Take a look at this joist calculator. You can "play" with the joist
>size, timber species & timber grade and see how the allowable span
>changes.
>
>http://www.awc.org/calculators/span/calc/timbercalcstyle.asp?species=Eastern+Hemlock-Balsam+Fir&size=2x6&grade=No.+2&member=Ceiling+Joists&deflectionlimit=L%2F240&spacing=12&wet=No&incised=No&liveload=20&snowload=-1&deadload=10&submit=Calculate+Maximum+Horizontal+Span#answer
>

That's handy.
Reason I asked is I put 2 extra ceiling joists in my garage when I
bought this place.
How it was built didn't seem right. 6' centers in some places.
Probably built in 1959.
Those joists are 21' 2x6 and from what I can figure basically just tie
the top sills together and square.
Good place to hang lights and the door opener too.

Anyway, I've seen too many garages fall out of square.
Besides that I wanted to put plywood up there as a storage platform.
When I ordered the joists from HD I said pine, because I thought
that's what the old ones were.
They said they only had Douglas fir that long, so that's what I got.
Precut the angles, jigsawed a hole in the fascia, and slid them onto
the plates. Nailed them in. Patched the fascia hole.
A couple years later I put up alum gutters, soffit/fascia.

Put a few 4x8 x1/2 plywood up there and started storing stuff, nothing
real heavy.
Boxes of Christmas decorations and the like.
Garden tools in the winter, snow shovels in the summer, etc.
Then I told my kid to get rid of the 4 tires he was keeping in there
because the alloy rims were "special," or put them up on the platform.
I was tired of them getting in my way.
He did that. 2 stacks of 2, alongside each other.
A couple years later I was chatting with my 80-year-old neighbor in
the garage and he pointed out one of my new joists was sagging.
He's retired building trades and has the eye for it, but when he
pointed it out I saw it.
Tires came down and it sprung back up.
6" won't take much load over 21'.
I learned that quick.
But I'm still tripping over or moving those tires.

>Drywall screws should only be used for drywall and temporary, rather
>than permanent loads.
>

I started using them to put together 8' workbenches at least 30 years
and they're good for that. You can knock them down if you have to,
though I never did any of 6 or so I built.
No real load on the screws. Solid as the day they were built,

>" He told me once that 2 nails can be better than 6 screws for
>resisting shear in some circumstances."
>
>that's a pretty general statement, I know for a fact that a single
>1/4" SDS will take the place of a handful of nails.
>His statement tends to be more correct for small screws but IMO screws
>(SS) are better in a lot of locations (exterior exposure & esp open
>patio covers) since over time they will not rust and encourage rot or
>lose strength. Galvanized timber connector nails will last a long
>time, SS ones even longer but #10 SS screws in the same application
>will last a long time plus provide better withdrawl resistance.
>
>I know nails are shear fasteners and better than screws in shear but
>over the years I've seen those shorty connector nails rust out / rot
>out in patio covers to the point that I changed my tune.....
>
>what good is a screw that's rust away & help rot out the wood?
>IMO better to drill out the hanger nail hole and use a larger dia SS
>screw (larger root diameter) than stick with nails that I know will
>cause the failure of the entire system.
>

Fasteners are a science in themselves. I wouldn't do anything
structural without expert advice on fasteners.

>I always clamp (or screw) when using traditional glues.
>When I top sistered my ceiling joists there was no easy way to clamp
>so I used epoxy paste that was forgiving of joint gaps.
>I pretested a sample made with rough timber, dirty just brushed off.
>The sample failed at 175 psi shear when a knot in the bottom member
>failed.
>
>Based on my crappy sample, I knew that my sistered joists would
>perform better since I wire brushed both faces of the glue joint and
>none of the bottom chord members had large flaws. Plus, based on my
>calcs, my shear demand was WAY lower than 175 psi more like less than
>50 psi
>

You did your homework.

--Vic

[JIMMIE]

Bob, just wondering your if your calcs take into account the existing
wood is 100+ year old oak.Usually these timbers were made from
heartwood. It is surprising to me it is not rigid enough already. I
would look to see if it is in fact the joist that are giving when he
walks on them and how they are giving. The problem could be that the
flooring is not strong enough to properly distribute the weight from
joist to joist. Lack of a proper subfloor could cause this which is a
common condition in old homes. Just something else to think about.

Jimmie

[Steve Barker]

oh, believe me, when you walk across the west one third of the room and
the china hutch on the east wall jingles, it's the joists moving. <G>
And no 7.5" of wood of any vintage or species is good for a 15.5' span.
I redid the lower level with 2x10's and put a support beam down the
center of THAT span. Of course it wasn't a problem to do, since the
joists are only 8" off the dirt!

[DD_BobK]

On Jan 24, 2:11 pm, Vic Smith <thismailautodele...@comcast.net> wrote:
> On Tue, 24 Jan 2012 09:48:00 -0800 (PST), DD_BobK <rkaza...@gmail.com>

> wrote:
>
>
>
> >Take a look at this joist calculator.  You can "play" with the joist
> >size, timber species & timber grade and see how the allowable span
> >changes.
>

> >http://www.awc.org/calculators/span/calc/timbercalcstyle.asp?species=...

Vic, those "joists" you describe from the 1959 garage are not
joists.
They were not designed or installed to resist bending loads.
They are "tension ties" to resist the spreading force generated by the
roof.
To span 21' as a joist you would need at least a 2x10.

I stand by my comments on drywall screws. They are easily the most
mis-used fastener in America.
They are not the appropriate fastener for anything other than
drywall. Hacks use them to hang kitchen cabinets.

cheers
Bob

[DD_BobK]

Jimmie-

The wood is not the problem. The joist depth & span are the issues.
Steve made no mention of the subfloor construction and, yes,
the subfloor construction can influence overall floor behavior but
it's pretty much a secondary effect.

Steve could "box out" his wimpy joists with a lots of blocking, lots
of glue and a structural skin on the bottom surface of the joists to
create composite action floor. This would increase the floor stiff
and get adjacent joists to share load. It would be a LOT of work and
still probably not work as well as sistering especially if Steve used
deeper sisters.

A number of year ago I worked on a floor vibration problem. It
involved a kitchen and living space over a 25' garage. Unfortunately,
the joists were spec'd as 12" floor trusses. They skimped on the depth
to stay within a city overall building height limitation. The condos
were three story.

The 12" floor trusses were too flexible, should have been at least
14". A real PITA to fix.

cheers
Bob

[Steve Barker]

> The wood is not the problem. The joist depth& span are the issues.

> Steve made no mention of the subfloor construction and, yes,
> the subfloor construction can influence overall floor behavior but
> it's pretty much a secondary effect.
>
> Steve could "box out" his wimpy joists with a lots of blocking, lots
> of glue and a structural skin on the bottom surface of the joists to
> create composite action floor. This would increase the floor stiff
> and get adjacent joists to share load. It would be a LOT of work and
> still probably not work as well as sistering especially if Steve used
> deeper sisters.
>
> A number of year ago I worked on a floor vibration problem. It
> involved a kitchen and living space over a 25' garage. Unfortunately,
> the joists were spec'd as 12" floor trusses. They skimped on the depth
> to stay within a city overall building height limitation. The condos
> were three story.
>
> The 12" floor trusses were too flexible, should have been at least
> 14". A real PITA to fix.
>
> cheers
> Bob

just for informational purposes, the flooring upstairs is 1x6 yellow
pine T&G 90 degrees to the joists. Same age as. The ceiling downstairs
will be 1x4 pine T&G (painted) so i won't get any benefit from that
either. I'm mainly just not wanting the china cabinet upstairs to sound
off (as bad, i know i won't eliminate it entirely) every time we walk
across the bedroom or sewing area.

[DD_BobK]

Steve-

I found an email I wrote back in 2005 to another engineer about a
floor he was designing
but the most important thing I found was this link to a Canadian
report

http://www.nrc-cnrc.gc.ca/eng/ibp/irc/cbd/building-digest-173.html

The section about Vibrations from Walking is most applicable,
particularly the last two paragraphs.

If you really want to reduce that vibration "go big" on the sister
joists...... like ~ 2x12 engineered timber.
But you'll lose ~5" of room height. :(



Robert Kazanjy
4/5/05
to seaint
Dave-

Ralph's comments are right on target, I cannot emphasize too strongly
that this could generate problem that dwarfs your design fee.

Talk to the customer (end user ideally).

This really could be a problem downstream depending on the room usage
& their perception of the floor performance.

I highly suggest reading
Canadian Building Digest
CBD-173. Floor Vibration

http://www.nrc-cnrc.gc.ca/eng/ibp/irc/cbd/building-digest-173.html

I've done a fair amount of dynamic floor vibration testing & once
people get sensitized to it, it can be a real problem making them
happy.

I suggest forgetting about span/360 or span/whatever

deflection less than 1/16" under a 220 lb load is a good check. Also
joists at 12 o/c are much better than 16" o/c. Blocking is generally
not effective in achieving load sharing for vibration loading.

I'm not exactly clear on your floor system layout

You've also got to consider the dynamic response of the steel beams in
conjunction with the timber; the floor system as a whole. If the
customer is involved, has informed consent & is aware of possible
consequences of the "cheaper" solutions you're much better off.

To prevent vibration you need stiffness or mass; your choice.

cheers
Bob

[Steve Barker]

> I've done a fair amount of dynamic floor vibration testing& once

> people get sensitized to it, it can be a real problem making them
> happy.
>
> I suggest forgetting about span/360 or span/whatever
>
> deflection less than 1/16" under a 220 lb load is a good check. Also
> joists at 12 o/c are much better than 16" o/c. Blocking is generally
> not effective in achieving load sharing for vibration loading.
>
> I'm not exactly clear on your floor system layout
>
> You've also got to consider the dynamic response of the steel beams in
> conjunction with the timber; the floor system as a whole. If the

> customer is involved, has informed consent& is aware of possible

> consequences of the "cheaper" solutions you're much better off.
>
> To prevent vibration you need stiffness or mass; your choice.
>
> cheers
> Bob

Bob, thanks for all the info you've put up. I could afford to lose a
little ceiling height, (it's 8'4" now). But it's not all that GREAT big
of a deal. Also, my hvac and electrical is all finished, and i have a
great big sun pipe coming down through there, so I can't sister EVERY
joist. If it were before all this, I probably could have gone to a 10
or even 12" sister. It's just the two of us living here and the one
room above is our bedroom and the other side of the upstairs (no
partition) is her sewing room. There'll be no dances going on up there
or kids running around.. LOL!

[Tony Miklos]

If you can loose a little ceiling height, how about a small beam
perpendicular to the joists right down the middle, maybe a post in the
middle could make it a very small beam? That would make things really
solid and oh so much less work.

[Steve Barker]

I really did consider that option, but there's really not that much
UNDER the floor (and no access) to hold the posts. PLUS, one of them
would be dead center of a window.

[bob haller]

> remove the "not" from my address to email- Hide quoted text -
>
> - Show quoted text -

i would sister to a steel plate...........

[Steve Barker]

On 1/26/2012 10:01 AM, bob haller wrote:

>
> i would sister to a steel plate...........

that was my first plan over a year ago, but not worth the expense and
hassle of procuring (and drilling) the the plate(s) for no more than i'm
trying to gain. Thanks for the suggestion.